Hampton's hump , also called  Hampton hump , is a  radiologic sign  which consists of a shallow wedge-shaped opacity in the periphery of the  lung  with its base against the pleural surface. It is named after  Aubrey Otis Hampton , who first described it in 1940. [ 1 ]  Hampton's hump along with  Westermark sign  may aid in the diagnosis of  pulmonary embolism , although they are rare and their sensitivities and interoperator reliabilities are low. If the sign is present in an image, there is a high chance that the person has a pulmonary embolism, but when the sign is absent a pulmonary embolism is not ruled out.


Hampton's line  is a thin,  radiolucent  line seen across the neck of a  gastric ulcer  filled with  barium sulphate  during a  barium meal . It is a sign of  mucosal   edema . [ citation needed ]


It is named after  Aubrey Otis Hampton . [ 1 ]


High attenuation crescent sign  or  hyperdense crescent sign  is a radiologic sign indicating impending aortic rupture. [ 1 ] [ 2 ]  It is seen as a curvilinear area paralleling the vessel wall of the aorta. [ 3 ]  The hyperdense area is due to intramural or mural thrombus haemorrhage. The blood that dissects through mural thrombosis or wall of the aneurysm causes weakening of the wall. [ 4 ]  This is of relatively high density compared to the psoas muscle in contrast-enhanced CT and greater than the aorta in non-contrast CT imaging. [ 5 ]


The  hilum overlay sign  is an imaging appearance on  chest radiographs  in which the outline of the  hilum  can be seen at the level of a mass or collection in the mid chest. [ 1 ]  It implies that the mass is not in the middle  mediastinum , and  is either from anterior or posterior mediastinum(most of the masses arise from the anterior mediastinum). [ 2 ]


The  holly leaf sign  is a  radiologic sign  observed on  chest radiographs  that has been used to describe the appearance of  pleural plaques  typically resulting from  asbestos  exposure. The irregular margins of a calcified pleural plaque are known to resemble the spikey edges of a holly leaf. [ 1 ]


The "Honda sign" ( H-pattern [ 1 ] ) is a radiologic sign seen in case of sacral insufficiency fracture in bilateral sacral insufficiency fractures on a radioisotope bone scan. [ 2 ]  It gets its name because the shape observed resembles the logo of the  Honda  motor company, resembling the alphabet "H".


This sign is typically associated with bilateral fractures of the superior and inferior pubic rami. In simpler terms, it indicates a specific pattern of pelvic fractures where both the upper and lower parts of the pubic bones are fractured on both sides. [ 2 ]


While Honda sign is diagnostic of sacral insufficiency fracture, it is visible in only up to 40% of the cases. [ 3 ]


The  hot nose sign  refers to increased  perfusion  in the nasal region on nuclear medicine cerebral perfusion studies in the setting of  brain death . The absent or reduced flow in the  internal carotid arteries  is thought to lead to increased flow within the  external carotid arteries  and subsequent increased perfusion in the nasal region. [ 1 ]


A  hot quadrate sign  is an imaging appearance of increased enhancement in CT scans or MRI, or radiotracer accumulation in  nuclear medicine , in which there is enhancement of the  quadrate lobe  of the  liver . The appearance is an indirect reflection of the collateralized flow of  SVC syndrome , in which occlusion of the  superior vena cava  leads to preferential flow to the quadrate. [ 1 ]


The sign is similar in mechanism but distinct in significance from the  hot caudate sign , in which the  caudate lobe  of the liver shows preferential enhancement or radiotracer accumulation with  hepatic vein  occlusion in  Budd Chiari syndrome . In the latter, the caudate shows preferential flow because its direct drainage into the  inferior vena cava  remains unobstructed, as opposed to the remnant liver which drains into the hepatic vein. [ 2 ]


The  hotcross bun sign  is a  radiologic sign  observed on transverse T2-weighted  magnetic resonance  (MR) images of the brain, describing a cross-shaped (or cruciform) hyperintensity within the  pons . This sign is most commonly associated with the cerebellar subtype of  multiple system atrophy  (MSA-c). [ 1 ]  It is also associated with  spinocerebellar ataxia ,  progressive multifocal leukoencephalopathy ,  paraneoplastic cerebellar degeneration , and  Creutzfeldt-Jakob disease . [ 2 ]


The  insular ribbon sign  ("loss of the insular ribbon") is a  radiologic sign  observed on  computed tomography of the brain  following acute  middle cerebral artery strokes . This sign describes the loss of definition between gray and white matter in the brain along the lateral margins of the  insular cortex . [ 1 ]  Loss of the insular ribbon occurs when  edema  forms in the cerebral tissue of the  ischemic  area following  cerebrovascular occlusion , [ 2 ]  obscuring the gray-white interface.


The  J-shaped sella sign  is a  radiologic sign  observed on lateral views of skull  radiographs  as the forward elongation of the  sella turcica , and its extension below the  anterior clinoid process . [ 1 ]  This abnormality causes the sella turcica to resemble the letter J. This sign is a normal variant in 5% of children, [ 1 ]  but it is also associated with  optic nerve glioma ,  hydrocephalus ,  mucopolysaccharidoses , and  achondroplasia . [ 2 ]


Jackstone calculus  is a type of urinary tract stone characterized by its unique appearance with stippled and spiculated contour, resembling a  toy jack . [ 1 ] [ 2 ]  Jackstone calculi are composed of calcium oxalate dihydrate, which gives them their irregular shape. [ 3 ]  They are often detected in radiological investigations or cystoscopy. [ 4 ]


Juxtaphrenic peak sign  is a radiographic sign seen in lobar collapse or after  lobectomy  of the lung. [ 1 ] [ 2 ]  This sign was first described by Katten and colleagues in 1980, and therefore, it is also called Katten's sign. [ 3 ]  The juxtaphrenic peak is most commonly caused due to the traction from the inferior accessory fissure. [ 2 ] [ 4 ]  The prevalence of the juxtaphrenic peak sign increases gradually during the weeks after lobectomy of the lung. [ 5 ]


Kerley lines  are a  sign  seen on  chest radiographs  with interstitial  pulmonary edema . They are thin linear pulmonary opacities caused by fluid or cellular infiltration into the  interstitium of the lungs . They are named after Irish neurologist and radiologist  Peter Kerley . [ 1 ] [ 2 ]


They are suggestive for the diagnosis of  congestive heart failure , but are also seen in various non-cardiac conditions such as  pulmonary fibrosis , interstitial deposition of  heavy metal  particles or  carcinomatosis  of the lung.  Chronic Kerley B lines may be caused by fibrosis or  hemosiderin  deposition caused by recurrent  pulmonary edema .


These are longer (at least 2cm and up to 6cm) unbranching lines coursing diagonally from the  hila  out to the periphery of the lungs. They are caused by distension of anastomotic channels between peripheral and central lymphatics of the lungs. Kerley A lines are less commonly seen than Kerley B lines. Kerley A lines are never seen without Kerley B or C lines.


These are short parallel lines at the lung periphery. These lines represent interlobular septa, which are usually less than 1 cm in length and parallel to one another at right angles to the  pleura . They are located peripherally in contact with the pleura, but are generally absent along fissural surfaces.  They may be seen in any zone but are most frequently observed at the lung bases at the  costophrenic angles  on the PA radiograph, and in the substernal region on lateral radiographs. [ 3 ]  Causes of Kerley B lines include pulmonary edema, lymphangitis carcinomatosa and malignant lymphoma, viral and mycoplasmal pneumonia, interstitial pulmonary fibrosis, pneumoconiosis, and sarcoidosis.  They can be an evanescent sign on the chest x-ray of a patient in and out of heart failure.


These are the least commonly seen of the Kerley lines. They are short, fine lines throughout the lungs, with a reticular appearance. They may represent thickening of anastomotic lymphatics or superimposition of many Kerley B lines.


Klemm's sign , also known as  air cushion sign , [ 1 ]  is a sign of chronic appendicitis.


Knuckle sign  is a radiologic sign used for diagnosing  pulmonary embolism . [ 1 ] [ 2 ]  The presence of a blood clot in the branch of a pulmonary artery can resemble a knuckle in CT and X-ray images, which is why it is called knuckle sign. [ 3 ]  It is frequently seen along with other signs of pulmonary embolism, such as the  Fleischner sign  and  Westermark sign . [ 2 ]


Leadpipe colon  is a term used in radiology to describe a specific, characteristic appearance of the colon, typically seen on barium enema radiographs. The term is associated with a rigid, non-distensible colon that has lost its normal  haustral  folds, presenting a smooth, tubular, or "pipe-like" appearance. [ 1 ]  This condition is most commonly linked to chronic  ulcerative colitis  and other forms of  inflammatory bowel disease .


In the leadpipe colon appearance, the colon appears straight and narrowed, with the absence of the usual haustral folds. Haustral folds are typically seen in the colon as segmental pouches or folds that help segment the large bowel. In leadpipe colon, these folds are obliterated or flattened, resulting in a smooth appearance. The colon takes on a rigid, tubular form, similar to a pipe, which is where the term "leadpipe" comes from, likening the colon to the appearance of a lead pipe. [ 2 ]


The classic leadpipe colon appearance is best observed on  barium enema  studies, a type of contrast X-ray imaging. During a barium enema, a contrast agent (barium sulfate) is introduced into the colon, and X-ray images are taken. In a leadpipe colon, the following features are seen: [ 3 ]


The  licked candy stick appearance  is a  radiologic sign  observed on  bone radiographs  that refers to the tapering of the tips of the hand bones ( metacarpals  and  phalanges ), foot bones ( metatarsals ), or  clavicles  that occurs in conditions such as  psoriatic arthritis ,  rheumatoid arthritis , and  leprosy . [ 1 ]


The  light bulb sign  is a radiological finding observed on plain radiographs in the context of posterior  shoulder dislocation . [ 1 ]  It refers to the abnormal, rounded appearance of the humeral head, which resembles a "light bulb," due to internal rotation of the arm following dislocation. [ 2 ]


In posterior shoulder dislocation, the humeral head is displaced posteriorly out of the glenoid cavity. This injury is frequently associated with internal rotation where the humeral head rotates internally, altering its usual elliptical contour to a more rounded shape, creating the "light bulb" appearance. On anteroposterior (AP) radiographs, the humeral head no longer overlaps the glenoid, further emphasizing its abnormal shape.


Posterior shoulder dislocations typically result from trauma such as seizures or electric shocks, which cause forceful contraction of the internal rotator muscles of the shoulder. [ 3 ] [ 4 ]


The light bulb sign is best observed on an AP radiograph of the shoulder. [ 5 ]  Key features include:


Radiologic signs  are the signs used for diagnosing physiological and pathological conditions in radiologic images. This list includes the names of radiologic signs in alphabetical order.


The  maiden waist deformity  is a  radiologic sign  associated with  retroperitoneal fibrosis , a condition resulting from the abnormal proliferation of fibrous tissue in the  retroperitoneal space . The fibrosis can extend to adjacent anatomical structures, frequently encompassing and obstructing the  ureters . [ 1 ]  This sign refers to the alteration in the normal course of the ureters: when the fibrosis causes both ureters to be pulled medially, they may form the appearance of a "narrow-waisted maiden". [ 2 ]


Mathe's sign  is an  ultrasonographic  sign that suggests the existence of an  abscess  in the proximity of a  kidney . Normally during  inspiration  when standing, the kidneys move  distally  to some extent. When one of them does not move at all or moves downwards scarcely, either in erect position or deep inspiration, the test is called positive. Along with  fever ,  urinary  symptoms, and  costovertebral angle tenderness , this will almost always indicate a  perinephric   abscess . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ better source needed ]


Mediastinal shift  is an abnormal movement of the  mediastinal structures  toward one side of the  chest cavity . A shift indicates a severe imbalance of pressures inside the chest. [ 1 ]  Mediastinal shifts are generally caused by increased lung volume, decreased lung volume, or abnormalities in the pleural space. Additionally, masses inside the mediastinum or musculoskeletal abnormalities can also lead to abnormal mediastinal arrangement. [ 2 ]  Typically, these shifts are observed on x-ray but also on computed tomography (CT) or magnetic resonance imaging (MRI). On chest x-ray,  tracheal deviation , or movement of the trachea away from its midline position can be used as a sign of a shift. Other structures, like the heart, can also be used as reference points. [ 3 ] [ 4 ]  Below are examples of pathologies that can cause a mediastinal shift and their appearance.


Tension pneumothorax is an emergent condition in which air gets trapped in the space between the chest wall and the lung. This space is referred to as the pleural space. Because air can't escape from this space, the air pocket grows larger and larger, resulting in the lung collapse closest to the pneumothorax. Forces are transmitted to the mediastinum and effectively "push" the mediastinal structures to the opposite side of the chest. [ 5 ]


A pleural effusion is an accumulation of fluid inside the pleural space. If this collection of fluid gets large enough, it can also push structures in the chest away from it and cause a mediastinal shift. However, a pleural effusion can also pull the mediastinal structure towards itself. If this is the case, then there is an underlying condition causing the collapse of the lung on that side. An example is a tumor obstructing a bronchus and causing lung collapse and pleural effusion. [ 3 ]


Hemothorax, or accumulation of blood in the pleural space, can result from trauma or surgical procedures in the chest. This accumulation of blood can grow large enough to compress the lung and push away other structures in the chest, thus causing a mediastinal shift. [ 6 ]  On a chest x-ray, a hemothorax can appear similarly to a pleural effusion with blunting of the pleural recess and white out of normal lung zones. [ 7 ]  In the setting of traumatic chest injury, rib fractures are also commonly observed on x-ray. [ 8 ]


An empyema is a collection of pus inside the pleural cavity. It is a complication of pneumonia or thoracic injury or surgery and also requires urgent diagnosis and treatment. [ 9 ]  Radiographic appearance is similar to that of a pleural effusion with costophrenic angle blunting and white out of lung zones. CT imaging is necessary to evaluate the structure of the empyema and evaluate for loculation or separation of the pus into different compartments. [ 10 ]  Finally, ultrasound is becoming a more commonly used imaging technique to evaluate an empyema. Ultrasound is more readily available at the bedside, is better at detecting pleural effusion, and can be used to guide thoracentesis to remove the empyema. [ 11 ]


Masses such as tumors can also cause compression and displacement of mediastinal structures. There are various mediastinal tumors, and they are classified by their location in the chest. Notable examples include germ cell tumors and lymphomas. [ 12 ]  Teratomas are a class of germ cell tumors that arise in the chest due to failure of germ cell migration during development. They can expand to large sizes and cause hemoptysis and pleural effusion. Radiographic features of teratomas typically include fluid and fat but also muscle, teeth, and bones inside the mass. [ 13 ]


Atelectasis is the partial collapse of a lung that is reversible. There are numerous etiologies, including post-operative atelectasis, surfactant deficiency, mucus plugging, and foreign body aspiration. Notably, post-operative atelectasis is thought to be caused by general anesthesia administration. Collapse of the affected lung shifts mediastinal structure towards the same side and can be observed on chest x-ray or CT. Radiographic features include increased opacification of collapsed lung and/or tracheal shift. [ 14 ]


Fetal conditions can also cause a mediastinal shift during development. For example, pulmonary hypoplasia is the underdevelopment of a lung due to various etiologies. These include agenesis due to gene mutation, fetal hydrothorax, and congenital diaphragmatic hernia. These conditions lead to incomplete development of lung tissue or hypoplasia. This can be unilateral or bilateral and is seen on x-ray as a mediastinal shift towards the side of the underdeveloped lung. [ 15 ] [ 16 ]  Additionally, mediastinal shifts can also be detected using antenatal ultrasonography. [ 17 ]


This condition is often called "funnel chest" and is observed as depression of the anterior chest at the xiphisternum. Pectus excavatum is commonly unilateral and, therefore, can lead to asymmetric distribution of thoracic organs. Therefore, a mediastinal shift can be seen in severe cases.  Radiographic features include a leftward deviation of the heart and deformed third to seventh ribs. Patients often present with exercise tolerance, cardiac arrhythmias, and heart murmur. [ 18 ]


A pneumonectomy is a surgical procedure in which an entire lung is removed. A common reason for performing this procedure is for lung cancer originating in the lung itself. [ 19 ]  This leads to a mediastinal shift towards the empty side of the thorax. Notably, patients can experience post pneumonectomy syndrome due to a severe mediastinal shift. This presents as difficulty breathing due to a shift of airways and rotation of the heart and great vessels. On x-ray, white out of the operated side and hyperinflation of the remaining lung is often observed. [ 20 ]


Foreign body aspiration is a major cause of death in young children due to their underdeveloped swallowing coordination. Young children most commonly ingest toys, coins, or food. [ 21 ]  On chest x-ray, the most frequent sign is air trapping that can lead to a mediastinal shift. Atelectasis and pneumothorax may also occur in the setting of foreign body aspiration. The diagnosis is made in conjunction with clinical symptoms and confirmed and treated with bronchoscopy. [ 22 ]


Bullous emphysema is a condition seen in patients with chronic obstructive pulmonary disease (COPD). The units making up the substructure of the lung (alveoli) become permanently enlarged due to the destruction of their walls. This leads to hyperinflation of the alveoli and, thus, the lungs. When this occurs asymmetrically, one lung can be larger than the other. [ 23 ]  A severe variant of this condition is called giant bullous emphysema. On chest x-ray, one lung will be significantly more inflated than the other, causing a mediastinal shift. Bullous emphysema's radiographic appearance on x-ray mimics a tension pneumothorax. This presents a medical challenge as these diseases are treated differently despite appearing similarly on x-ray. [ 24 ] [ 25 ]


Congenital pulmonary airway malformation (CPAM) is a rare disease in which the lung airways develop abnormally in the fetus. This leads to infants having pockets of air and cystic masses in their lungs. These can expand in size and cause a mediastinal shift, especially in the higher grades of CPAM. Diagnosis is usually made on ultrasound and supplemented with x-ray, CT, or MRI to further define the malformation. On chest x-ray, CPAM has varying appearances but may look like "bubbles" within the lung fields. [ 26 ]


Mercedes Benz sign  is a radiological sign seen due to the presence of  gallstones . [ 1 ]  It is a triradiate shadow, characteristic of the  Mercedes-Benz  automobile trademark. [ 2 ]  The sign occurs due to the gas fissuring within the gallstone.


Mumoli's sign  (also known as a  " Playboy Rabbit " sign ) is a  radiologic sign  seen in the normal  liver . It appears as a rabbit-shaped image caused by the confluence of the middle and right  hepatic veins  as they merge with the  inferior vena cava . It can be seen on  ultrasound images  of the  liver  with a transverse subcostal view during deep  inspiration .


The image was named after Nicola Mumoli of the Department of  Internal Medicine , Livorno Hospital, Livorno, Italy. [ 1 ]


The  Napoleon hat sign  (most commonly called " inverted Napoleon hat ") is a radiologic sign observed on frontal  radiographs  of the  spine  at the level of the fifth  lumbar vertebra  (L5) and the  sacrum  (S1) that indicates the presence of severe  spondylolisthesis  and/or severe  lumbar lordosis . When the L5 vertebra becomes severly displaced and overlaps the sacrum, the superimposed bones may appear as an inverted  Napoleon  hat (the L5 vertebral body represents the dome of the hat and the transverse processes represent the brim). [ 1 ]


Notching of the ribs  (or  rib notching ) is a  radiologic sign  where the surface of the rib is deformed. It can be characterized as unilateral or bilateral, and should be differentiated between affecting the upper (superior) or lower (inferior) surface of the rib.


Inferior rib notching can be associated with  aortic coarctation  (as a result of dilatation of  intercostal arteries [ 1 ] ),  superior vena caval obstruction ,  arteriovenous fistula , or following a  Blalock Taussig shunt .


Causes of inferior rib notching by etiology:


Arterial :  aortic coarctation , aortic thrombosis, pulmonary-oligemia/arteriovenous malformation,  Blalock Taussig shunt ,  Tetralogy of fallot  (TOF), absent pulmonary artery and pulmonary stenosis.


Venous : arteriovenous malformations of chest wall, superior vena cava or other central venous obstruction.


Neurogenic : intercostal neuroma,  Neurofibromatosis type 1 ,  poliomyelitis .


Osseous :  hyperparathyroidism ,  thalassemia ,  Melnick–Needles syndrome . [ 2 ]


Other causes of superior rib notching include:  poliomyelitis ,  osteogenesis imperfecta ,  neurofibromatosis ,  Marfan's syndrome ,  collagen vascular disease , and  hyperparathyroidism .


Omental cake  is a  radiologic sign  indicative of an abnormally thickened  greater omentum . [ 1 ]  It refers to  infiltration  of the normal omental structure by other types of soft-tissue or chronic  inflammation  resulting in a thickened, or cake-like appearance. [ 2 ]


Typically, it is caused by infiltration of  metastatic   tumors  arising from the  stomach ,  ovary , or  colon . This dissemination of cancerous cells that do not originate from the omentum itself is called  peritoneal carcinomatosis . It can occur other regional tumors such as  lymphoma  where it is associated with regional  lymphadenopathy . [ 3 ]  It can also rarely occur as a result of infectious causes such as  tuberculous   peritonitis , peritoneal  coccidioidomycosis , and  histoplasmosis . [ 4 ]


For the most common cause,  peritoneal carcinomatosis , omental caking is associated with a wide variety of symptoms.  Ascites  and intestinal  peristalsis  is known to have an effect on how diffusely the cancer cells are spread throughout the abdomen. This wide range of presentation makes omental caking difficult to diagnose based on symptoms alone. [ 5 ]


In patients with omental caking due to peritoneal lymphomatosis secondary to cancers such as  Non-Hodgkin's lymphoma  or  MALT lymphoma , the most frequent symptoms encountered are abdominal pain, gastric distention, and weight loss. [ 6 ]


Causes such as bacterial and fungal infections are associated with diffuse abdominal pain, intraperitoneal fluid accumulation, weight loss, fevers, and night sweats. The most common radiographic feature among patients with suspected tuberculous peritonitis was septated compartments of ascitic fluid on ultrasound and abnormal chest X-ray suggestive of previous tuberculosis. [ 7 ]


Due to the variety of symptoms experienced by patients with omental caking, [ 5 ]  omental cakes are most frequently discovered on abdominal  computed tomography (CT)  or  ultrasound . Plain film radiography ( X-ray ) is not a suggested modality for investigating the spread of cancerous cells in the abdomen due to the poor spatial resolution amongst soft-tissue densities. Contrast resolution obtained through CT allows radiologists to investigate omental caking for morphology, intraperitoneal fluid, and regional lymphadenopathy assists in proper diagnosis so clinicians, surgeons, and oncologists can plan the appropriate course of treatment. [ 8 ]


After omental cakes have been identified on CT or ultrasound, it may be appropriate to gain more information on the characteristics of the disease by undergoing  nuclear medicine  scans that can identify tissues where the cancerous cells may have spread [ 9 ]  or  magnetic resonance imaging  (MRI) for a higher degree of spatial resolution. [ 10 ]  Suspected infectious etiologies may require another degree of medical testing including blood antigen or antibody analysis. [ 11 ]  Yet, in both malignant and infectious cases, image-guided  biopsy  with pathologic correlation is the most definitive way to confirm the diagnosis.  [ 10 ]


The presence of omental cakes have long been seen as an indication of poor prognosis in patients with advanced-stage ovarian or gastrointestinal cancer, and medical teams usually address this through more advanced and aggressive treatments such as  cytoreductive surgery  and  hyperthermic-intraperitoneal chemotherapy  (HIPEC). [ 12 ]  During surgery, the presence of omental caking makes incomplete resection more likely. [ 13 ]  In patients where omental spread is completely removed, intestinal resections are more likely to be encountered due to the caked omentum's propensity for spreading malignancy to adjacent organs. [ 13 ] [ 14 ]  If malignant, as patients undergo treatment they are likely to undergo routine nuclear medicine imaging as surveillance for response to the treatment or recurrence of disease. [ 15 ]


Common disease presentations that are different but may appear similar include  pseudomyxoma peritonei , peritoneal  mesothelioma ,  splenosis  in patients with a history of  splenectomy , and diffuse peritoneal  leiomyomatosis. [ 16 ]  These diagnoses should be considered in patients with suspected omental caking and a history that makes malignant or infectious causes less likely. Image-guided biopsy with pathologic correlation is the gold-standard method for distinguishing these entities. [ 10 ]


Omental cakes have long been described during malignancy-related surgical interventions. In 1985, Drs. Stephen Rubesin and Marc Levine were the first to publish a radiographic review of omental caking and to describe the propensity for omental spread to facilitate colonic  metastases  due to the proximity of the greater omentum to bowel. [ 14 ]  Since then, many radiologists have adopted techniques to investigate omental thickening and irregularities in density using the  Hounsfield scale  and other radiographic tools to determine the extent of abdominal disease. [ 4 ]


Onion skin periosteal reaction  also known as  multilayered periosteal reaction  or  lamellated periosteal reaction  refers to the multi layered concentric layers of new bone adjacent to the bone cortex. It is called onion skin periosteal reaction because it resembles the layers of an onion. These layers are formed due to any pathological process that leads to the variable, excessive growth of the bone. [ 1 ]  Onion skin periosteal reaction is seen in  osteosarcoma , [ 2 ]   Ewing sarcoma  and  Langerhans cell histiocytosis . [ 3 ]  In radiological images, onion skin periosteal reaction is seen as radiolucent areas along the multiple layers of dense bone. [ 4 ]  The lucent areas may be occupied by tumors or inflammation.


This article related to  pathology  is a  stub . You can help Wikipedia by  expanding it .


Osteopathia striata  is a rare entity characterized by fine linear striations about 2- to 3-mm-thick, visible by  radiographic  examination, in the metaphyses and diaphyses of long or flat bones. [ 1 ]  It is often asymptomatic, and discovered incidentally most of the time.


Palla's sign  is a  clinical sign  in which an enlarged right descending  pulmonary artery  is seen on the  chest x-ray  in patients with  pulmonary embolism . It is of low  sensitivity , and its specificity is not known. It exhibits as a "sausage" appearance on X-ray.  [ 1 ]  It is named after italian radiologist Antonio Palla. In 1983, he published his observations that close to 25% of patients with pulmonary embolism had a chest x-ray sign of enlarged right descending pulmonary artery. [ 2 ] [ 3 ]


Pancake kidney  (also known as disc, shield or doughnut kidney [ 1 ] ) is a rare anomaly of the kidney with complete fusion of the superior, mild and inferior poles of both kidneys. The kidney is seen as a single, disc-shaped mass typically located in the pelvis. [ 2 ]  Each kidney has its own ureter that does not cross the midline. [ 1 ]


Pancake kidney is often associated with anomalies in other organs. Those with pancake kidneys are susceptible to urinary tract infections and renal stones due to anomalies in the collecting system of the kidneys and the short ureters. [ 1 ]


Ultrasound may initially suggest the condition, but computed tomography or magnetic resonance imaging provides a definitive diagnosis. [ 3 ]


Pencil-in-cup  is a radiologic sign indicating a deformity where fingers have the appearance of a pencil lying in a cup. [ 1 ] [ 2 ] [ 3 ]  This sign is classically seen in psoriatic arthritis, but it is also reported in systemic sclerosis and rheumatoid arthritis. [ 4 ]


Peribronchial cuffing , also referred to as  peribronchial thickening  or  bronchial wall thickening , is a  radiologic sign  which occurs when excess fluid or  mucus  buildup in the small airway passages of the  lung  causes localized patches of  atelectasis  (lung collapse). [ 1 ]  This causes the area around the  bronchus  to appear more prominent on an  X-ray . It has also been described as donut sign, considering the edge is thicker, and the center contains air.


Peribronchial cuffing is seen in a number of conditions including:


As peribronchial cuffing is a sign rather than a symptom or condition, there is no specific treatment except to treat the underlying cause.


Pneumatosis intestinalis  (also called  intestinal pneumatosis ,  pneumatosis cystoides intestinalis ,  pneumatosis coli , or  intramural bowel gas ) is  pneumatosis  of an  intestine , that is, gas  cysts  in the bowel wall. [ 1 ] [ 2 ]  As a  radiological sign  it is highly suggestive for  necrotizing enterocolitis . This is in contrast to gas in the  intestinal lumen  (which is relieved by  flatulence ). In  newborns , pneumatosis intestinalis is considered  diagnostic  for necrotizing enterocolitis, and the gas is produced by bacteria in the bowel wall. [ 3 ]  The pathogenesis of pneumatosis intestinalis is poorly understood and is likely multifactorial.  PI itself is not a disease, but rather a clinical sign.  In some cases, PI is an incidental finding, whereas in others, it portends a life-threatening intra-abdominal condition. [ citation needed ]


The  polka dot sign  is a radiological finding most commonly observed on axial computed tomography (CT) or magnetic resonance imaging (MRI) scans of the spine. [ 1 ]  It is a hallmark feature of  vertebral hemangiomas , a benign vascular tumor of the vertebral body. The sign refers to the appearance of multiple small, dot-like areas of sclerosis or hyperintensity within the vertebral body, resembling a pattern of polka dots. [ 2 ]


The polka dot sign arises due to the unique structural changes in vertebral hemangiomas. These changes include thickened vertical trabeculae, where the they apepar as small, discrete dots in axial imaging. There is also vascular proliferation and fat deposition that replaces normal bone marrow. This contributes to the mixed-density appearance of the lesion. [ 2 ]


The polka dot sign is best seen in CT imaging as multiple small, circular, sclerotic areas are seen within the vertebral body, representing cross-sections of the thickened vertical trabeculae. The background may appear lucent or hypodense due to vascular spaces and fat replacement. [ 2 ]  The sagittal view may demonstrate the  corduroy sign , which represents vertically oriented striations corresponding to the thickened trabeculae. [ 3 ]


Popcorn calcification  or  popcorn appearance  is the radiological appearance of  calcification  with irregular rings and arcs, which resembles  popcorns . The calcification patterns in chondroid lesions of the bone (such as  enchondroma  and  chondrosarcoma ), [ 1 ]   pulmonary hamartomas , [ 2 ]  degenerating fibroadenomas of the breast and calcified fibroids of the uterus have been described as 'popcorn calcification'.
In  osteogenesis imperfecta , popcorn calcifications are often seen around the knees and ankles in radiological imaging, and are associated with irregularity in the growth plate of the bone. [ 3 ] [ 4 ]


A  pulmonary consolidation  is a region of normally compressible  lung tissue  that has filled with liquid instead of air. [ 1 ]  The condition is marked by induration [ 2 ]  (swelling or hardening of normally soft tissue) of a normally aerated lung. It is considered a  radiologic sign . Consolidation occurs through accumulation of inflammatory cellular exudate in the  alveoli  and adjoining ducts. The liquid can be  pulmonary edema , inflammatory  exudate ,  pus , inhaled water, or blood (from bronchial tree or  hemorrhage  from a  pulmonary artery ). Consolidation must be present to diagnose  pneumonia : the signs of lobar pneumonia are characteristic and clinically referred to as consolidation. [ 3 ]


Signs that consolidation may have occurred include:


Putty kidney  is a radiological term describing a calcified kidney typically seen in the end stages of chronic  renal tuberculosis . The term "putty kidney" derives from the radiographic appearance of extensive amorphous calcification within the kidney, resembling the consistency of putty. This finding is a hallmark of advanced genitourinary tuberculosis, which is one of the types of extrapulmonary tuberculosis. The term 'putty kidney' was first used in 1906 by Dr. F Tilden Brown, a genitourinary surgeon. [ 1 ] [ 2 ]


Putty kidney represents the late-stage sequelae of renal tuberculosis, which results from hematogenous dissemination of  Mycobacterium tuberculosis  to the kidneys. Chronic inflammation and granuloma formation lead to: [ 3 ]


The advanced calcified state of a putty kidney is associated with a loss of renal function and often coexists with damage to the ureters and bladder. [ 3 ]


Dense, amorphous calcifications occupying the renal region. [ 1 ]


The  pyloric tit sign  is a radiological finding observed during barium studies in cases of hypertrophic pyloric stenosis. [ 1 ]  It appears as an outpouching on the lesser curvature of the stomach, just proximal to the impression created by the hypertrophied pyloric muscle. This sign represents the transient entrapment of contrast medium between a peristaltic wave and the thickened pyloric muscle. [ 2 ]


Rice grain calcification  is a distinctive radiological finding characterized by the presence of small, elongated, or oval calcific foci resembling grains of rice. This pattern of calcification is typically observed in soft tissues and is associated with certain infectious or inflammatory conditions. It is most commonly linked to  cysticercosis , a parasitic infection caused by the larval form of  Taenia solium . [ 1 ]


In cysticercosis, the calcifications represent the remnants of degenerated larvae of  Taenia solium . When the larvae die, they become calcified over time, forming the characteristic rice grain-like appearance. [ 1 ]


Rigler's triad  is a combination of findings on an  abdominal radiograph  of people with  gallstone ileus , a condition where a large  gallstone  causes  bowel obstruction . Rigler's triad consists of: (1) small bowel obstruction, (2) a gallstone outside the  gallbladder , and (3)  air in the bile ducts . [ 1 ]  It bears the name of  Leo George Rigler  (1896–1979), who described it in 1941. [ 2 ] [ 3 ]  It is not the same as  Rigler's sign .


It is most commonly seen in 6th to 7th decade of life and affects females more often. Most patients with gallstone ileus are  asymptomatic . Due to the fistula formation between the  small intestine  and gallbladder, large stones can lodge in the small bowel, leading to its obstruction.  Pneumobilia means air in the biliary tract. It is due to the transfer of air from bowel through the  fistula  into the biliary tract. [ citation needed ]


A  ring-enhancing lesion  is an abnormal  radiologic sign  on  MRI  or  CT scans  obtained using  radiocontrast . On the image, there is an area of decreased density (see  radiodensity ) surrounded by a bright rim from concentration of the enhancing contrast dye. This enhancement may represent breakdown of the blood-brain barrier and the development of an inflammatory capsule. This can be a finding in numerous disease states. In the brain, it can occur with an early  brain abscess  as well as in  Nocardia  infections associated with lung cavitary lesions. In patients with HIV, the major differential is between  CNS lymphoma  and CNS  toxoplasmosis , with CT imaging being the appropriate next step to differentiate between the two conditions. [ 1 ]


In  radiology , a  Romanus lesion  is the erosion of the anterior and posterior vertebral endplates in patients with an inflammatory  spondyloarthropathy  – such as  ankylosing spondylitis  or an  enteropathic arthropathy . [ 1 ] [ 2 ]  The anterior erosion in particular causes a loss of anterior vertebral body concavity, causing the vertebra to display a squared contour or even a barrel-shape. [ 1 ]  Healing of the erosion results in a  sclerotic  increase in density causing what is known as a  shiny corner sign , [ 1 ] [ 3 ]  which can later result in  syndesmophyte  formation. [ 4 ]  It is most easily diagnosed using  MRI , compared to conventional radiography. [ 2 ]


This type of erosion was initially described by Ragnar Romanus and Sven Ydén in a paper published in 1952. [ 5 ]


On a  chest X-ray , the  sail sign  is a  radiologic sign  that suggests  left lower lobe   collapse . [ 1 ]  In children, however, a sail sign could be normal, reflecting the shadow of the  thymus . [ 2 ]


The  thymic sail sign  or  spinnaker-sail sign  is due to elevation of the thymic lobes in the setting of  pneumomediastinum . [ 3 ]


Sandwich vertebral body  is a radiologic sign where the endplates of the vertebra are sclerotic, giving it the appearance of a sandwich. [ 1 ] [ 2 ]  This sign is seen in  osteopetrosis , particularly in the autosomal dominant variety. [ 3 ] [ 4 ]


Scottie dog sign  is a  radiological sign  which refers to the appearance of lumbar spine in oblique view X-ray. [ 1 ]  In the X-ray, the spine can be visualised as the lateral view of a  Scottie dog , [ 2 ]  with the pedicle as the eye, the transverse process as the nose, the superior articular facet as the ear and the inferior articular facet as the front leg, spinous process as the body. It was once used as a diagnostic sign for lumbar spondylolysis, but it is not commonly in use nowadays because of the advent of more sensitive diagnostic methods such as the  CT scan  and  MRI scan . [ 3 ]


A  sentinel loop  is a  sign  seen on a radiograph that indicates localized  ileus  from nearby inflammation. [ 1 ]  Simply put, it is the dilation of a segment of  small intestine  to be differentiated from  colonic cutoff sign  which is a dilation of a segment of large bowel. [ citation needed ]


An isolated distended loop of bowel is seen near the site of injured viscus or inflamed organ. This loop is called a "sentinel loop." It arises from the body's efforts to localize traumatic or inflammatory lesions. The local distention of that intestinal loop is due to local paralysis and accumulation of gas in the intestinal loop. In acute  pancreatitis , the sentinel loop is usually seen in the left  hypochondrium , while in acute  cholecystitis , it is seen in the right hypochondrium. In acute  appendicitis , the sentinel loop is seen in the  right lower quadrant . [ 2 ]


In  radiology , the  silhouette sign  refers to the loss of normal borders between  thoracic structures . [ 1 ]  It is usually caused by an  intrathoracic   radiopaque mass  that touches the border of the  heart  or  aorta . [ 2 ]  In other words, it is difficult to make out the borders of a particular structure - normal or otherwise - because it is next to another dense structure, both of which will appear white on a standard  X-ray . [ 3 ]  It may occur, for example, in  right middle lobe syndrome , where the right heart margin is obscured, and in  right lower lobe   pneumonia , where the border of the  diaphragm  on the right side is obscured, while the right heart margin remains distinct. [ 2 ]
Silhouette sign is very useful in localizing lung lesions as all structures forming cardiac silhouette are in contact with a specific portion of the lung.


The  small bowel feces sign  is a radiological finding observed in radiological imaging studies, particularly in cases of  small bowel obstruction . [ 1 ]  It is characterized by the presence of particulate matter resembling fecal material within the lumen of dilated small bowel loops. This sign is most commonly identified on  computed tomography  (CT) scans and, less frequently, on abdominal radiographs. [ 2 ]


The small bowel feces sign results from stagnation of enteric contents within dilated segments of the small intestine. [ 1 ]  When intestinal motility is impaired due to obstruction, progressive dehydration of luminal contents occurs, leading to the formation of solid particulate matter that mimics feces. [ 3 ]  This sign often indicates a chronic or subacute obstruction where bowel function is severely compromised. [ 4 ]


The composition of the particulate matter includes partially digested food, desquamated epithelial cells and mucus, giving it the characteristic heterogeneous appearance resembling colonic feces. This radiological finding suggests that the obstruction has persisted long enough to allow for these changes to occur. [ 3 ]


On CT imaging, the small bowel feces sign appears as a mottled, mixed-density pattern within a distended small bowel loop. It is typically located proximal to the site of obstruction and is often accompanied by other features of small bowel obstruction, such as: [ 5 ]


On plain radiographs, it may be difficult to discern this sign definitively due to its lower resolution and 2D view, compared to CT which has higher resolution and 3D orientation.


A  Sonographic Murphy sign  is a finding when performing diagnostic medical  sonography . It is different from the  Murphy sign  found on physical examination, but both signs are associated with  cholecystitis [ 1 ]  When the sonographer presses directly over the  gallbladder , and the  patient  expresses  pain , more than when the sonographer presses anywhere else, this is said to be a positive sonographic Murphy sign. [ 2 ] [ 3 ] [ 4 ]


A Sonographic Murphy sign is different from a Murphy sign on physical examination of the abdomen in three ways:


In  radiology , the  steeple sign  is a  radiologic sign  found on a frontal neck  radiograph  where  subglottic   tracheal  narrowing produces the shape of a  church   steeple  within the trachea itself. [ 1 ] [ 2 ]  The presence of the steeple sign supports a  diagnosis  of  croup , usually caused by  paramyxoviruses . [ 3 ]  It can also be defined as the replacement of the usual squared-shoulder appearance of the subglottic area by cone-shaped narrowing just distal to the vocal cords. This is called the steeple or pencil-point sign.


The  stepladder sign  is a radiological finding observed in the context of small bowel obstruction on abdominal X-rays or computed tomography scans. It refers to the appearance of multiple, dilated small bowel loops arranged in a step-like configuration, typically visible in upright or lateral decubitus imaging positions. This sign is indicative of bowel obstruction and is used to identify and localize the site of obstruction, aiding in diagnosis and management. [ 1 ]


In small bowel obstruction, a mechanical or functional blockage prevents normal passage of intestinal contents leading to increased peristaltic effort in the dilated loops causing bowel loops proximal to the obstruction to dilate. Gas and fluid accumulates proximal to the obstruction. [ 2 ]


Teacup calcifications , also known as the " teacup sign ," are a specific  radiologic sign  indicative of benign breast conditions, particularly milk of calcium within cysts. [ 1 ]  These calcifications exhibit a distinctive appearance on mammography, helping radiologists in distinguishing benign entities from malignant ones.


When horizontal x-ray beams, commonly used in lateral projections, are used to image the breast, the fluid inside the cysts, such as milk of calcium, is imaged tangentially. [ 2 ]  This technique often produces linear or curvilinear patterns of calcification. In some cases, a semilunar shape may appear, which is why this sign is called "teacup sign."


Teacup calcifications are typically benign and do not require follow up or sampling, per the  American College of Radiology  BI-RADS recommendation. [ 3 ]


In  radiology , the  Terry-Thomas sign  is a  scapholunate ligament  dissociation on an  anteroposterior  view of the wrist. [ 1 ] [ 2 ]  Most commonly a result of a fall on the outstretched hand ( FOOSH ), the  scapholunate ligament  ruptures resulting in separation of the  lunate  and  scaphoid bones . This burst causes the  scaphoid bone  to dorsally rotate. [ 3 ]  A gap of more than 3mm is  pathognomonic  for scapholunate dissociation. [ 4 ]


The resulting separation between the scaphoid and lunate bones leaves a space on the x-ray that is similar to the gap comedian  Terry-Thomas  had between his front teeth. For newer radiology students who do not know who Terry-Thomas was, this finding might also be known as the  David Letterman  sign. [ 3 ]


In  radiology , the  thumbprint sign , or  thumbprinting , is a  radiologic sign  found on a radiograph that suggests the diagnosis of either  epiglottitis  or  intestinal ischemia .


In a  lateral   C-spine   radiograph , the sign is caused by a thickened free edge of the  epiglottis , which causes it to appear more  radiopaque  than normal, resembling the distal  thumb .


In an abdominal  radiography , thumbprinting has an appearance of thumbs protruding into the  intestinal lumen , and is caused by thickened  edematous   mucosal folds . [ 1 ]  Abdominal thumbprinting is a  non-specific finding , though one potential cause is  intestinal ischemia . [ 2 ]


Tram tracks  or  tram-track signs  are  medical signs  that bear some resemblance to  tramway tracks .


When found in the  lungs , tram tracks are  radiologic signs  that are usually accompanied by  pulmonary edema  in cases of  congestive heart failure  and  bronchiectasis . Tram tracks are caused by  bronchial wall thickening , and can be detected on a lateral  chest X-ray . [ 1 ]


The term "tram tracks" is also used to describe the  basement membrane  duplication found on light microscopy that is characteristic of  membranoproliferative glomerulonephritis  (MPGN) type I. (It is less commonly associated with types II and III.) [ 2 ]


The term has also been used to describe findings associated with  optic nerve sheath meningioma . [ 3 ]


Tram track-shaped calcifications in the  cerebral cortex  indicate  Sturge–Weber syndrome . [ citation needed ]  where intracranial gyriform calcification (brain imaging) seen mostly in occipital and posterior parietal/temporal lobe ;this syndrome consists triad of port wine stain,seizure(usually focal but may become generalized),eye manifestation(e.g. glaucoma).


Tram track appearance in mammography/USG indicates Duct Ectasia. [ citation needed ]


In  radiology , the  tree-in-bud sign  is a finding on a  CT scan  that indicates some degree of  airway obstruction . [ 1 ]  The tree-in-bud sign is a nonspecific imaging finding that implies impaction within bronchioles, the smallest airway passages in the lung. The differential for this finding includes malignant and inflammatory etiologies, either infectious or sterile. This includes  fungal  infections, mycobacterial infections such as  tuberculosis  or  mycobacterium avium intracellulare ,  bronchopneumonia , chronic  aspiration pneumonia ,  cystic fibrosis  or cellular impaction from bronchovascular spread of malignancy, as can occur with breast cancer, leukemia or lymphoma. [ 2 ]  It also includes lung manifestations of autoimmune diseases such as  Sjögren syndrome  or  rheumatoid arthritis . [ 3 ] [ 4 ]


Histopathologic  studies have shown that the tree-in-bud pattern is caused by demarcation of the normally invisible branching course of the peripheral airways, which usually results from bronchioles being plugged or blocked with  mucus ,  pus  or  fluid . In addition,  dilated  and  thickened  walls of the peripheral airways and  peribronchitis  can make the affected bronchioles more easily visible, as is seen in patients with  cystic fibrosis . [ citation needed ]


Water Bottle Heart  is a descriptive term used in radiology to describe the appearance of the cardiac silhouette on a chest X-ray when it resembles the shape of a water bottle. This sign is associated with  pericardial effusion , a medical condition characterized by the accumulation of fluid in the  pericardial cavity  surrounding the heart. [ 1 ]


On a chest X-ray, the normal heart silhouette should have a clear and defined outline. However, in cases of pericardial effusion, the accumulation of fluid within the pericardial sac causes the heart to appear enlarged and assumes a shape that is reminiscent of a water bottle, with relatively smooth cardiac contours. [ 2 ]  This distinct appearance is what gives rise to the term "Water Bottle Heart."


Although water bottle heart is most commonly associated with pericardial effusion, it can also be seen in severe dilatation of the heart secondary to  valvular heart disease . [ 1 ]


Water lily sign  is a radiologic sign seen in  hydatid cyst  infection. [ 1 ]  It refers to floating laminated membranes of the cyst within a dense fibrous cystic wall, resembling the appearance of a water lily in radiographs. [ 2 ]


In  chest radiography , the  Westermark sign  is a  sign  that represents a focus of  oligemia  (hypovolemia) (leading to collapse of vessel) seen distal to a  pulmonary embolism  (PE). [ 1 ]  While the chest x-ray is normal in the majority of PE cases, [ 2 ]  the Westermark sign is seen in 2% of patients. [ 3 ]


Essentially, this is a plain X-ray version of a filling defect as seen on computed tomography pulmonary arteriogram.


The sign results from a combination of:


The Westermark sign, like  Hampton's hump  (a wedge shaped, pleural based consolidation associated with  pulmonary infarction ), has a low  sensitivity  (11%) and high  specificity  (92%) for the diagnosis of pulmonary embolism. [ 4 ]   Put more simply, the Westermark sign is seldom seen in pulmonary embolism. When visible on a chest X-ray, the Positive Predictive Value is only 33%. That is, 33% of the time that Westermark sign is seen on Chest XRay does a pulmonary embolism actually exist  [1] .


It is named after  Nils Westermark , a Swedish radiologist. [ 5 ]


The  Whirlpool sign  also known as the  Whirl sign [ 1 ]  is related to mesentery when the bowel rotates around the  mesentery  causing a swirling appearance of the mesentery around the mesenteric vessels. [ 2 ]


It can also be related to ovaries when twisting of the vascular pedicle of the ovaries takes place. [ 3 ] [ 4 ]


The  white cerebellum sign , also known as  reversal sign  or  dense cerebellum sign , is a radiological sign denoting the relatively white appearance of the  cerebellum  due to a generalized decrease in density of the  supratentorial  brain structures caused by extensive  edema . [ 1 ]


White cerebellum sign can be associated with raised intracranial pressure [ 2 ]  that occurs due to anoxic or ischemic changes in the brain. [ 3 ]  It can be found in:


Diffuse brain edema is the likely cause of this radiological change observed in CT or MRI. [ 2 ]


It was considered to indicate a bad prognosis. [ 4 ]  However, evidence suggests that it could be a non-specific indicator of diffuse brain edema which might not be as ominous as previously thought. [ 2 ]


Jha, Praveen.  "White cerebellum sign | Radiology Reference Article | Radiopaedia.org" .  radiopaedia.org . Retrieved  2017-03-26 .


Wilkinson's syndrome  (also known as  Sclerotic pedicle sign ) is a radiographic term which describes a unilaterally enlarged  pedicle  opposite a contralateral  pars defect . [ 1 ] [ 2 ]  The enlarged pedicle may due to stress hypertrophy, and changes may extend into the adjacent lamina and transverse processes. [ 1 ]


The characteristic radiographic feature of Wilkinson's syndrome is a missing pedicle with a thick, sclerotic contralateral pedicle at the same level. This is sometimes referred to as a "winking owl sign". [ 3 ]


The  Central Brain Tumor Registry of the United States  (CBTRUS) is the primary national database of malignant and benign  tumors  of the brain, "other  central nervous system  (CNS), tumors of the pituitary and pineal glands, olfactory tumors of the nasal cavity, and brain lymphoma and leukemia." [ 1 ]  A  non-profit , it was established in 1992. [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]


Computed tomography angiography  (also called  CT angiography  or  CTA ) is a  computed tomography  technique used for  angiography —the visualization of  arteries  and  veins —throughout the  human body . Using contrast injected into the blood vessels, images are created to look for blockages,  aneurysms  (dilations of walls),  dissections  (tearing of walls), and  stenosis  (narrowing of vessel). CTA can be used to visualize the vessels of the heart, the aorta and other large blood vessels, the lungs, the kidneys, the head and neck, and the arms and legs. [ citation needed ]  CTA can also be used to localise arterial or venous bleed of the gastrointestinal system. [ 1 ]


CTA can be used to examine blood vessels in many key areas of the body including the brain, kidneys, pelvis, and the lungs.


Coronary CT angiography  (CCTA) is the use of CT angiography to assess the  arteries  of the  heart . The patient receives an  intravenous injection  of  contrast  and then the heart is scanned using a high speed  CT scanner . With the advances in CT technology, patients are typically able to be scanned without needing medicines by simply holding their breath during the scan. CTA is used to assess heart or vessel irregularities, location of stents and whether they are still open, and occasionally to check for atherosclerotic disease. [ 2 ]  This method displays the anatomical detail of blood vessels more precisely than  magnetic resonance imaging  (MRI) or  ultrasound . Today, many patients can undergo CTA in place of a conventional  catheter   angiogram , a minor procedure during which a catheter is passed through the blood vessels all the way to the heart. However, CCTA has not fully replaced this procedure. CCTA is able to detect narrowing of blood vessels in time for corrective therapy to be done. CCTA is a useful way of screening for arterial disease because it is safer, much less time-consuming than catheter angiography, and is also a cost-effective procedure.


CTA can be used in the chest and abdomen to identify  aneurysms  in the aorta or other major blood vessels. These areas of weakened blood vessel walls that bulge out can life-threatening if they rupture. CTA is the test of choice when assessing aneurysm before and after endovascular stenting due to the ability to detect calcium within the wall. [ 3 ]  Another positive of CTA in abdominal aortic aneurysm assessment is that it allows for better estimation of blood vessel dilation and can better detect blood clots compared to standard  angiography . [ 4 ]


CTA is used also to identify  arterial dissection , including  aortic dissection  in the  aorta  or its major branches. Arterial dissection is when the layers of the artery wall peel away from each other; this causes pain and can be life-threatening. CTA is a quick and non-invasive method of identifying dissections and can show the extent of the disease and if there is leakage. [ 4 ]


CT pulmonary angiogram  (CTPA) is used to examine the pulmonary arteries in the lungs, most commonly to rule out  pulmonary embolism  (PE), a serious but treatable condition. It has become the technique of choice for detection of pulmonary embolism due to its wide availability, short exam time, ability to see other diseases that may present like pulmonary embolisms, and a high degree of confidence in the validity of the test. [ 3 ] [ 4 ]  In this test, a PE will appear as a dark spot inside the blood vessel or a sudden stop of the bright contrast material. [ 4 ]


CT angiography should not be used to evaluate for  pulmonary embolism  when other tests indicate that there is a low probability of a person having this condition. [ 5 ]  A  D-dimer  assay might be a preferred alternative to test for pulmonary embolism, and that test and a low clinical prediction score on the  Wells test  or  Geneva score  can exclude pulmonary embolism as a possibility. [ 5 ]


Visualization of blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders can be performed using CTA. Stenosis (narrowing) of a renal artery is a cause of  hypertension  (high blood pressure) in some patients and can be corrected. A special computerized method of viewing the images makes renal CT angiography a very accurate examination. [ 6 ]  CTA is also used in the  assessment of native and transplant renal arteries. [ 3 ]  While CTA is great for imaging of the kidneys, it lacks the ability to perform procedures at the same time. Thus traditional catheter angiography is used in cases of acute renal hemorrhage or acute arterial obstruction. [ 2 ]


CTA can be used assess acute stroke patients by identifying clots in the arteries of the brain. [ 2 ]  It can also be used to identify small aneurysms or  arteriovenous malformation  inside the brain that can be life-threatening. While CTA can produce high quality images of the  carotid arteries  for grading the level of  stenosis  (narrowing of the vessel), calcium deposits (calcified plaques) in the area where the vessels split can lead to interference with accurate stenosis grading. Because of this,  magnetic resonance angiography  is used more often for this purpose. [ 3 ]  Other applications of CTA are identifying  moyamoya disease , dissections of intracranial arteries, detection of  carotid-cavernous fistula , planning for intracranial-extracranial bypass surgery, and involvement of brain tumours such as  meningioma  with surrounding intracranial vessels. [ 7 ]


CTA can be used in the legs to detect atherosclerotic disease that has narrowed the arteries. It can also be used to image vessels in suspected blockages, trauma cases, or patients with surgical complications. [ 8 ]


CT angiography is a  contrast CT  where images are taken with a certain delay after injection of  radiocontrast  material. The contrast material is  radiodense  causing it to light up brightly within the blood vessels of interest. In order for the CT scanner to be able to scan the correct area where the contrast is, the scanner uses either automatic detectors which start scanning when enough contrast is present, or small test boluses. With the small test bolus, a small amount of contrast is injected in order to detect the speed that the contrast will move through the blood vessels. After determining this speed, the full bolus is injected and the scan is begun at the timing determined by the test bolus. After the scan is completed the images are post-processed to better visualize the vessels and can even be created in the 3D images. [ 8 ]


Harms of overuse of CT angiography include radiation exposure and the possibility of finding then seeking treatment for a clinically insignificant pulmonary embolism which ought not be treated. [ 5 ]


A reaction may occur whenever iodine contrast is injected. These reactions range in severity and it is difficult to predict if they will occur. With the current practice of using low-osmolar contrast these adverse reactions only occur in ~0.1% of cases. [ 4 ]  The severity of the reaction can be broken down into three groups:


A patient with a history of allergy to contrast may be advised to take medications such as corticosteroids or histamine (H1) blockers before CTA to lessen the risk of allergic reaction or to undergo a different exam that does not call for contrast material injection. [ 4 ] [ 9 ]  Patients should also be well hydrated in order to minimize possible adverse effects of contrast. [ 9 ]


Contrary to popular belief there is no correlation between seafood allergies and reactions to iodine contrast, as shown by many recent studies. [ 10 ] [ 11 ]


Historically it has been thought that contrast material can lead to  contrast-induced nephropathy  (also called CIN) in any patient. However, recent studies have shown that the risk of kidney injury caused by  contrast agent  in patients with no history of kidney problems occurs extremely infrequently. [ 12 ] [ 13 ] [ 14 ]


The use of CTA in people with  kidney failure , kidney disease or long-standing severe diabetes should be weighed carefully as the use of IV iodine contrast material may further harm kidney function. The decision not to use contrast agents must be weighed against the possibility of misdiagnoses if contrast is not used. [ 13 ] [ 14 ]


Compared with other imaging modalities, CTA is associated with a significant dose of ionizing radiation. Varying significantly with patient age, sex, and exam protocol, radiation risk models predict coronary CTA to increase lifetime cancer risk. [ 15 ]


CT angiography should not be performed in patients who are pregnant as the contrast and radiation may lead to harm to the fetus. The extent of harm to the fetus has not been fully determined. [ 9 ]


By 1994 CT angiography began to replace conventional angiography in diagnosing and characterizing most cardiovascular abnormalities. [ 16 ]  Prior to this, conventional angiography had been in use for 70 years. [ 16 ]


Computed tomography of the abdomen and pelvis  is an application of  computed tomography  (CT) and is a sensitive method for diagnosis of  abdominal  diseases. It is used frequently to determine stage of cancer and to follow progress. It is also a useful test to investigate acute abdominal pain (especially of the lower quadrants, whereas ultrasound is the preferred first line investigation for  right upper quadrant  pain).  Renal stones ,  appendicitis ,  pancreatitis ,  diverticulitis ,  abdominal aortic aneurysm , and  bowel obstruction  are conditions that are readily diagnosed and assessed with CT. CT is also the first line for detecting solid organ injury after trauma.


Multidetector CT (MDCT) can clearly delineate anatomic structures in the abdomen, which is critical in the diagnosis of internal diaphragmatic and other nonpalpable or unsuspected hernias. MDCT also offers clear detail of the abdominal wall allowing wall hernias to be identified accurately. [ 1 ]


Abdominal imaging is associated with many potential uses for the different  phases of contrast CT . The majority of abdominal and pelvic CT's can be performed using a single-phase, but the evaluation of some tumor types (hepatic/pancreatic/renal), the urinary collecting system, and trauma patients among others, may be best performed with multiple phases. [ citation needed ]


In discussing the numerous phases and indications for CT, best patient care requires individualized CT protocols based upon each patient's specific symptoms, pathology, and underlying co-morbidities. Although labor intensive, this provides the highest likelihood of an accurate diagnosis with the lowest necessary radiation dose. The following discussion will provide a basic outline of current best practice, but not all clinical scenarios can be accounted for. [ 2 ]


Contrast enhanced CT examinations can be acquired at a variety of specific time points after intravenous contrast injection (timing is dependent on the phase of contrast enhancement needed and organ system being evaluated). The timing should be chosen specifically to optimize contrast distribution within the solid organ parenchyma in question. [ citation needed ]


In cases of suspected bowel leak or perforation, gastrointestinal fistula, interloop abscess or other fluid collection, oncologic staging and surveillance, and CT colonography, oral positive contrast is useful in delineating the lesions. [ 3 ]  1% dilute barium solution can be administered orally for bowel preparation for CT scan of the abdomen. [ 4 ]


Non-contrast CT scans Figure 1a (left) and 1b (right) are of limited use for the differentiation of soft tissue structures. However, materials like blood, calcium (renal stones, vascular atherosclerosis), bone, and pulmonary parenchyma are highly visible and can usually be adequately assessed with non-contrast CT. For example, in the abdomen and pelvis, there are several indications for non-contrast imaging. These include: evaluation of renal calculi; assessment for gross intra-abdominal hemorrhage; and post-endostent volume measurements. In addition, non-contrast images are often obtained in conjunction with contrast enhanced images in evaluating potential renal transplant donors and in the evaluation of the pancreas (in combination with contrast phases). Of note, dual-energy CT and the development of virtual "non-contrast" images (VNC imaging) may ultimately obviate the combination scans. Additionally, CT angiography examinations performed for pathologies like aneurysms and dissection are frequently performed in conjunction with non-contrast imaging. The non-contrast images facilitate the differentiation of active extravasation or acute bleeding from vascular calcifications. [ citation needed ]


The most common technique is to perform portal venous phase imaging in the abdomen and pelvis (approximately 60–90 seconds after contrast administration, figure 2). This results in near optimal contrast opacification of the majority of the solid abdominal organs and it is used for a wide variety of indications: nonspecific abdominal pain; hernia; infection; masses (with a few exceptions such as hypervascular, renal, and some hepatic tumors); and in most follow-up examinations. As a general rule, this single phase is adequate unless there is a specific clinical indication that has been shown to benefit from other phases. [ citation needed ]


CT angiography (CTA) is highly effective for evaluation of the arterial system, and has largely replaced conventional angiography due to the lower risk profile and ability to survey the entire abdomen. Images are acquired after a rapid bolus of intravenous contrast material (3-7 cc/s) during the arterial phase (15–35 seconds after injection) when the concentration of contrast material in the arterial system is high (figures 3). Images are usually acquired using narrow collimation (<1 mm) and can be retrospectively reconstructed using dedicated 3-dimensional workstations and software. CTA is commonly used in the head and chest in the evaluation of pulmonary emboli, aneurysms, vascular malformations, dissection, bleeding and ischemia. Indications for early arterial phase imaging include: evaluation of aneurysms or dissections (cerebral, aortic, etc.), hepatic, splanchnic or renal arterial anatomy, and arterial imaging in liver or kidney transplantation. Single phase arterial imaging is often used in the evaluation of trauma patients either a complete chest/abdomen/pelvis examination with arterial phase imaging of the chest and portal venous phase imaging of the abdomen/pelvis or just a portal venous phase of abdomen and pelvis depending on the mechanism and severity of the trauma. CTA is also commonly performed in the abdomen and pelvis for evaluating vascular malformations and in the evaluation of bleeding. Mesenteric ischemia can also be evaluated using CT angiography. CTA of the abdomen and pelvis is often performed in combination with a CTA for evaluating the extremity vasculature. [ citation needed ]


The late arterial phase is timed to correspond to the peak concentration of contrast material in highly vascular tumors and is performed approximately 20–35 seconds after the injection of intravenous contrast. Early arterial phase imaging is predominantly utilized for angiography and will be discussed separately. Late arterial phase imaging is almost always performed in conjunction with other phases (e.g. portal venous phase) to allow more complete characterization of any identified abnormalities (figure 4). The primary indication for a late arterial phase is for the evaluation of hypervascular tumors of the liver such as hepatocellular carcinoma or hypervascular metastases (figure 4). Typical hypervascular tumors for which this would be used include: hepatocellular carcinoma; renal cell carcinoma; melanoma; carcinoid/neuroendocrine tumors; some sarcomas; choriocarcinoma; and thyroid carcinoma. Although a "hypervascular", biphasic evaluation would generally be used for these patients, note that a single phase is often adequate for follow up imaging. [ citation needed ]


CT imaging specific for the venous structures is performed uncommonly. Most venous structures are partially opacified on the routine contrast enhancing images and suffice for most examinations. However, occasionally evaluation of the inferior vena cava is desired, such as prior to IVC filter placement/removal or evaluation of IVC thrombosis. [ citation needed ]


Delayed phase imaging (figure 5) encompasses scanning at a variety of different times following contrast administration, and depends on the pathology in question. Typical delayed imaging times range from a few minutes to up to 15 minutes or longer. The most common indications for delayed phase imaging are evaluation of the kidneys, collecting system (ureters and bladder) and specific kidney, liver, and adrenal tumors. Evaluation of the kidneys, ureters and bladder are discussed separately in the renal imaging section. Cholangiocarcinoma occurring within the extrahepatic biliary tree or intrahepatic cholangiocarcinomas are a common reason for delayed imaging. Cholangiocarcinomas are fibrotic tumors which enhance slowly, and are usually imaged following a 10-15 minute delay. Similarly, adrenal masses can be evaluated with multiphase imaging including an unenhanced CT, portal venous phase and a 10 minute delay CT which allows for evaluation and calculation of the enhancement and washout characteristics aiding in distinguishing benign adrenal adenomas from other adrenal masses. [ citation needed ]


Outside of the evaluation of masses, delayed phase images can be used in the evaluation of active vascular extravasation in trauma patients, vascular malformations, and aneurysm disruption.


When evaluating hepatic masses, it can be advantageous to have both late arterial and portal venous phase images (biphasic imaging, figure 4) since some tumors enhance briskly during the arterial phase (hepatocellular carcinoma, hepatic adenoma, follicular nodular hyperplasia (FNH), and hypervascular metastasis), but may be occult or difficult to characterize on portal venous phase imaging alone (figure 6). However, it should be stressed that the addition of late arterial phase images is only indicated if one of these tumors is suspected, or if there is a need for further characterization of a hepatic mass, since the large majority of patients will not benefit from the addition of this phase. In addition, if there is a need to definitively characterize a hepatic mass, MRI is generally more sensitive and specific, with no associated radiation dose. [ citation needed ]


Transient hepatic attenuation differences  in the arterial phase may mimic diseases of the liver. [ citation needed ]


Detection and characterization of renal parenchymal masses is a frequent indication for CT. An initial noncontrast CT is important for detecting calcium or fat in a lesion, and to provide baseline attenuation of any renal masses. Following noncontrast scanning, intravenous contrast is injected and a corticomedullary phase is obtained at approximately 70 seconds (figure 7a, 7b). The corticomedullary phase is characterized by enhancement of the renal cortex as well as the renal vasculature. This phase is valuable in the evaluation of benign renal variants, lymphadenopathy and vasculature, however certain medullary renal masses may not be visible during this phase due to minimal enhancement of the medulla and collecting system. The parenchymal phase is obtained approximately 100–200 seconds after the injection of contrast material (figure 7c). Parenchymal phase imaging demonstrates continued enhancement of the cortex, enhancement of the medulla, and various levels of contrast material in the collecting system. The parenchymal phase is highly important for the detection and characterization of renal masses, parenchymal abnormalities, and the renal collecting system. This method of imaging does not evaluate for abnormalities of the collecting system. [ citation needed ]


Common renal masses can occasionally be differentiated from each other using this imaging technique. Renal cell carcinomas and oncocytomas typically demonstrate intense heterogeneous enhancement on the parenchymal phase images and cannot be reliably differentiated from each other but can be distinguished from other renal masses. Angiomyolipomas (AML's) also demonstrate intense contrast enhancement but characteristically contain macroscopic fat which can be detected on the noncontrast images, and can help to differentiate AML's from renal cell carcinomas and oncocytomas. Renal lymphoma on the other hand, will often have decreased enhancement when compared to the renal parenchyma on the parenchymal phase images. [ citation needed ]


CT urography  (CTU) is commonly used in the evaluation of hematuria, and specifically tailored to image the renal collecting system, ureters and bladder in addition to the renal parenchyma. Initial imaging includes a noncontrast phase to detect renal calculi as a source of hematuria. Note that dual energy CT may eventually allow the noncontrast phase to be eliminated. Contrast enhancement techniques for CTU vary from institution to institution. A common technique is a double bolus, single phase imaging algorithm. Excretory phase imaging allows for not only evaluation of the ureteral lumen, but also periureteral abnormalities including external masses and lymphadenopathy. [ citation needed ]


Pancreatic masses are often evaluated using both an early arterial (to evaluate for vascular involvement and thus resectability, figure 9a) and a later "pancreatic" phase (which optimizes pancreatic parenchymal enhancement and thus is best at differentiating pancreatic tumors from pancreatic parenchyma, figure 9b). Pancreatic adenocarcinoma typically is hypoenhancing when compared to the surrounding parenchyma. Most other common pancreatic tumors are hypervascular with avid enhancement (such as pancreatic neuroendocrine tumors) and appear brighter than the surrounding pancreatic parenchyma after the injection of intravenous contrast material. [ citation needed ]


CT imaging should be performed to evaluate the specific clinical question, however incidental findings are noted in approximately 5-16 % of patients scanned for an unrelated reasons. It is not acceptable practice to anticipate the possibility of incidental lesions given their low incidence and prospectively add additional phases to routine protocols. Unfortunately, several recent surveys demonstrated that this practice is more common than might be anticipated, and contributes to unnecessary medical radiation exposure to a large population of patients. Even more egregious is the fact that many of these findings could potentially be more accurately evaluated with other non-radiation imaging modalities such as MRI or ultrasound. [ citation needed ]


Although the management of incidental findings is not the focus of this chapter, some of these findings will require complete characterization with further CT phases such as arterial phase (certain liver tumors) or delayed images (adrenal lesions). Management of incidental findings has been controversial since they are relatively common, especially in the elderly, and more CT scanning may be required for further characterization of what is frequently a benign finding. In an effort to provide guidance on which incidental findings should be appropriately further evaluated and what the appropriate imaging modality should be, the ACR published a white paper on management of incidental findings detected at CT of the abdomen in 2010. [ citation needed ]


Multiphase CT examinations are very important for the detection and characterization of certain clinical conditions, but should not be generalized for every patient undergoing CT of the abdomen and pelvis. A recent survey demonstrated that many physicians are routinely performing multiphase CT for the majority of patients in an attempt to prospectively characterize potential lesions detected during the scan. However, unindicated multiphase CT examinations are an important source of medical radiation that does not contribute to the care of patients. Adherence to published standards such as the ACR appropriateness criteria can both decrease medical radiation and optimize imaging for the specific clinical indication. [ citation needed ]


Computed tomography of the chest  or  chest CT  is a group of  computed tomography scan   protocols  used in  medical imaging  to evaluate the  lungs  and search for  lung disorders .


Contrast agents  are sometimes used in CT scans of the chest to accentuate or enhance the differences in  radiopacity  between  vascularized  and less vascularized structures, but a standard chest CT scan is usually non-contrasted (i.e. "plain") and relies on different  algorithms  to produce various series of digitalized images known as  view  or " window ". Modern detail-oriented scans such as  high-resolution computed tomography  (HRCT) is the  gold standard  in  respiratory medicine  and  thoracic surgery  for investigating disorders of the lung  parenchyma  ( alveoli ).


Contrasted CT scans of the chest are usually used to confirm diagnosis of for  lung cancer  and  abscesses , as well as to assess  lymph node  status at the  hila  and the  mediastinum .  CT pulmonary angiogram , which uses time-matched ("phased") protocols to assess the lung perfusion and the patency of  great arteries  and  veins , particularly to look for  pulmonary embolism . [ 1 ]


Computed tomography of the head  uses a series of  X-rays  in a  CT scan  of the  head  taken from many different directions; the resulting data is transformed into a series of cross sections of the brain using a computer program. [ 1 ]  CT images of the head are used to investigate and diagnose  brain injuries  and other neurological conditions, as well as other conditions involving the skull or  sinuses ; it used to guide some brain surgery procedures as well. [ 2 ]   CT scans expose the person getting them to  ionizing radiation  which has a risk of eventually causing cancer; some people have allergic reactions to  contrast agents  that are used in some CT procedures. [ 2 ]


Computed tomography (CT) has become the diagnostic modality of choice for head trauma due to its accuracy, reliability, safety, and wide availability. The changes in microcirculation, impaired auto-regulation, cerebral edema, and axonal injury start as soon as head injury occurs and manifest as clinical, biochemical, and radiological changes. Proper therapeutic management of brain injury is based on correct diagnosis and appreciation of the temporal course of the disease process. CT scan detects and precisely localizes the intracranial hematomas,  cerebral contusions , edema and foreign bodies. [ 2 ]


Even in emergency situations, when a head injury is minor as determined by a physician's evaluation and based on established guidelines, CT of the head should be avoided for adults and delayed pending clinical observation in the emergency department for children. [ 3 ]  Many people visit emergency departments for minor head injuries. CT scans of the head can confirm a diagnosis of skull fracture or brain bleeding, but even in the  emergency department , such things are uncommon and not minor injuries, so CT of the head is usually not necessary. [ 3 ]  Clinical trials have shown the efficacy and safety of using CT of the head in emergency settings only when indicated, which would be at the indication of evidence-based guidelines following the physical examination and a review of the person's history. [ 3 ]


Concussion  is not a routine indication for having brain CT or brain MRI and can be diagnosed by a healthcare provider trained to manage concussions. [ 4 ]  People with concussions usually do not have relevant abnormalities about which brain imaging could give insight, so brain imaging should not routinely be ordered for people with concussions. [ 4 ]  If there is concern about a skull fracture, focal neurological symptoms present or worsening symptoms, then CT imaging may be useful. [ 4 ]  MRI may be useful for people whose symptoms worsen over time or when structural pathology is suspected. [ 4 ]


CT of the head is sometimes used for people who have sudden hearing loss. [ 5 ]  However, when there are not other neurological findings, a history of trauma, or a history of ear disease, CT scans are not useful and should not be used in response to sudden hearing loss. [ 5 ]


CT of the head is also used in CT- guided   stereotactic surgery  and  radiosurgery  for treatment of intracranial tumors, arteriovenous malformations and other surgically treatable conditions. [ 6 ] [ 7 ]


Special views focusing  on the  orbit  of the  eye  may be taken to investigate concerns relating to the eye. [ 8 ]   CT scans are used by  physicians  specializing in treating the eye ( ophthalmologists ) to detect  foreign bodies  (especially metallic objects),  fractures ,  abscesses ,  cellulitis ,  sinusitis , bleeding within the skull ( intracranial bleeding ),  proptosis ,  Graves disease  changes in the eye, and evaluation of the orbital apex and  cavernous sinus . [ 8 ]


Magnetic resonance imaging  (MRI) of the head provides superior information as compared to CT scans when seeking information about headache to confirm a diagnosis of  neoplasm ,  vascular disease ,  posterior cranial fossa  lesions, cervicomedullary lesions, or  intracranial pressure  disorders. [ 9 ]  It also does not carry the risks of exposing the person to  ionizing radiation . [ 9 ]  CT scans may be used to diagnose headaches when  neuroimaging  is indicated and MRI is not available, or in emergency settings when hemorrhage,  stroke , or  traumatic brain injury  is suspected. [ 9 ]


MRI (magnetic resonance imaging)  provides more sensitivity in the evaluation of the cavernous sinus and the orbital apex. [ 8 ]


One advantage over a  brain MRI  is in the evaluation of intracerebral calcifications. [ 10 ]


Several different views of the head are available, including  axial ,  coronal , reformatted coronal, and reformatted  sagittal  images.  However, coronal images require the person to   hyperextend  their neck, which must be avoided if any possibility of neck injury exists. [ 8 ]


CT scans of the head increase the risk of  brain cancer , especially for children. As of 2018, it appeared that there was a risk of one excess cancer per 3,000–10,000 head CT exams in children under the age of 10. [ 11 ]


In  CT scan  of the  thyroid , focal and diffuse  thyroid abnormalities  are commonly encountered. These findings can often lead to a diagnostic dilemma, as the CT reflects nonspecific appearances.  Ultrasound  (US) examination has a superior  spatial resolution  and is considered the modality of choice for thyroid evaluation. Nevertheless, CT detects incidental  thyroid nodules  (ITNs) and plays an important role in the  evaluation  of  thyroid cancer . [ 1 ]


This pictorial review covers a wide spectrum of common and uncommon, incidental and non-incidental thyroid findings from  CT scans . It will also include the most common incidental thyroid findings. In addition, the role of imaging in the assessment of  thyroid carcinoma  (before and after treatment) and  preoperative  thyroid  goiter  is explored, as well as localization of  ectopic  and  congenital thyroid tissue . [ 1 ]


Thyroid ultrasonography  is the modality of choice for thyroid evaluation. [ 1 ]  Yet, focal and diffuse thyroid abnormalities [ 2 ]  are commonly encountered during the interpretation of  computed tomography  (CT) exams performed for various  clinical purposes . [ 1 ]  For example, CT often detects incidental  thyroid nodules  (ITNs). It plays an important role in the evaluation of abnormal structures including  thyroid cancer . [ 1 ]


Thyroid disorders  are common and include many entities. They can be  symptomatic ,  asymptomatic ,  diffuse , focal,  neoplastic , or non-neoplastic processes. Neck ultrasound (US), with the prospect of proceeding to  fine needle aspiration  (FNA), is the first line of investigation; however, other options are available. Thyroid Uptake Scans using  Tc-99 m  or I-123 are typically reserved for specific clinical scenarios. Cross-sectional imaging including  computed tomography (CT)  and  magnetic resonance imaging  ( MRI ) detect incidental  thyroid nodules  (ITNs) and can be used in the evaluation of  thyroid cancers  and  goiter . The aim of this article is to provide a pictorial review of a broad spectrum of incidental and non-incidental thyroid findings on CT scans. [ 1 ]


The  thyroid gland  is a  vascular , encapsulated structure made up of right and left  lobes , which are connected at the midline by the isthmus. Each lobe is about 2 cm thick, 3 cm wide, and 5 cm long. The thyroid apex is located superiorly at the level of the mid- thyroid cartilage . The inferior margin of the  gland  is at the level of the fifth or sixth  tracheal ring . The  thyroid gland  is encapsulated by the middle layer of  deep cervical fascia  and is part of the visceral space in the infrahyoid neck. It wraps around the  trachea  and is separated from the  esophagus  by the  tracheoesophageal  groove on each side, which houses the  recurrent laryngeal nerves . The thyroid has variable lymphatic drainage to the  internal jugular  chain, para-tracheal region,  mediastinum , and  retropharyngeal  area. It has homogeneous high attenuation values on a  CT scan , as compared to adjacent muscles, due to its high  iodine   concentration . It shows avid iodine contrast enhancement due to its  hypervascularity . [ 1 ]


Multi-detector volumetric acquisition from the  skull base  to the  tracheal bifurcation  is usually obtained. Multiplanar 2-mm  axial ,  coronal , and  sagittal  images are typically available. Examination can be acquired with or without administration of  intravenous (IV)  iodinated contrast. [ 1 ]


The thyroid gland can have variable CT scan findings, such as  calcifications , single or multiple nodules,  cysts , or diffuse enlargement. [ 1 ]


Thyroid calcifications on a CT scan can be seen in both benign and malignant thyroid  lesions .  Sonographic  examination of the thyroid can differentiate between micro-calcifications, which are highly associated with  papillary thyroid carcinoma , and eggshell calcifications, which favour a benign process such as  colloid cysts  (Figs. 1 and 2). In a retrospective review of preoperative CT scan, 35% (135 of 383) of the patients had detectable intrathyroidal calcifications. Among them, 48% had a  histopathologically  proven thyroid cancer. Calcified nodules had a significantly higher incidence of thyroid cancer and  lymph node  metastases. The incidence of thyroid cancer among nodules with different calcifications patterns was 79% of nodules with multiple punctate calcifications, 58% of nodules with a single punctate calcification, 21% of nodules with coarse calcification, and 22% of nodules with peripheral calcification. Most of the single calcified nodules were  malignant . However, this did not include patients with ITNs and the sample is skewed towards malignancy. Another study evaluated the presence of ITNs on CT scans and found that 12% of thyroid nodules were calcified, with no significant correlation between malignant or potentially malignant histology and punctate calcifications. As a result, some researchers believe that calcification per se is not a suspicious CT sign, and have suggested that calcified thyroid nodules on CT scans should be treated the same as non-calcified nodules. [ 1 ]


Thyroid cystic changes are variable, ranging from simple cysts with a thin wall to complex cysts with septations and solid components. An  adenoma  may undergo cystic degeneration. It is important to note that papillary carcinoma may mimic a benign-looking cyst. Simple serous cysts appear with fluid density on a CT scan, whereas a cyst with haemorrhage or high thyroglobulin content is iso-dense to muscle. [ 1 ]


Thyroid nodules that are detected by an imaging study but have not been previously detected or suspected clinically are considered to be ITNs. ITNs are one of the most common incidental findings on neck imaging. ITNs are reported in up to 25% of chest CT scans, and in 16–18 % of cervical region cross-sectional imaging, including CT and MRI scans. The rate of malignancy in the detected ITNs on CT and MRI scans varies from 0% to 11%. Incidentally detected thyroid carcinomas are more likely to be papillary thyroid carcinomas (PTCs) (Fig. 3). Incidentally detected cancers tend to be smaller in size and less likely to have distant metastasis, as compared to clinically suspected thyroid cancers. [ 1 ]


On CT scans, a malignant lesion is suspected when the margins are ill-defined and there is extra-thyroid extension, lymph node involvement, or invasion of the surrounding structures. The absence of these features does not exclude malignant tumours, especially papillary,  follicular , and  medullary  thyroid carcinomas (Fig. 3). Therefore, ultrasound is the modality of choice for thyroid lesion evaluation, due to its superior spatial resolution compared to CT examinations. Sonographic features of malignancy are micro-calcifications,  acoustic shadowing , anti-parallel orientation, marked hypoechogenicity, irregular or microlobulated margins, and increased vascularity. CT scans lack the ability to detect these reliable sonographic signs of malignancy. Therefore, further management of ITNs, if required, usually begins with thyroid ultrasound and FNA should be considered according to the ultrasound findings. [ 1 ]


The  American College of Radiology  (ACR) flowchart and recommendations for ITNs detected by CT or MRI offer general guidance and are not applicable to all patients. The recommendations are primarily based on the presence or absence of suspicious features, nodule size, patient's age, patient's life expectancy, and patient's comorbidities. Suspicious features that can be detected on CT scans include signs of local invasion and abnormal lymph nodes. Abnormal lymph nodes may show cystic components, calcifications, and/or increased enhancement. Mere nodal enlargement is less specific for thyroid cancer metastasis; however, further evaluation should be considered if the ITN has ipsilateral jugulodigastric lymph nodes > 1.5 cm on the short axis or > 1 cm for other groups. Cervical Level IV and VI lymphadenopathies raise a higher suspicion of thyroid carcinoma metastasis. Almost all patients with ITNs and suspicious imaging features should be evaluated with a neck ultrasound. Patients with  comorbidities  or limited life expectancy without suspicious features should not undergo further evaluation. Nevertheless, further workup might be necessary for such individuals if it is clinically warranted, or specifically requested by the referring physician or the patient. [ 1 ]


In patients with ITNs, it is important to inquire about pertinent historical factors predicting malignancy. These factors include a history of childhood or adolescent head and neck or total body radiation exposure, and familial thyroid carcinoma or thyroid cancer syndrome. Syndromes associated with thyroid cancer include  multiple endocrine neoplasia 2 , familial  adenomatous polyposis ,  Carney complex ,  Cowden's disease , and  Werner syndrome / progeria . If a patient has a first-degree relative with such a syndrome, screening based on the various components of that syndrome is advised. Nevertheless, there are no guidelines specifically addressing ITNs detected on CT scans in patients at risk of thyroid cancer. Therefore, in the absence of suspicious features on the CT scan, other criteria such as nodule size on the CT scan, patient age, and levels of  thyroid stimulating hormone  (TSH) are important in guiding management in such a patient population. [ 1 ]


Although the correlation between thyroid nodule size and malignancy risk is limited, nodule size affects prognosis in malignant nodules. Small thyroid cancers (less than 2 cm) tend to have an indolent course, with favourable prognosis even if not treated. Less than 7% of the imaging-detected ITNs are seen in younger populations. However, Shetty et al.  found a higher rate of malignancy in the ITNs detected on CT scans among patients younger than 35 years. Ito et al. found a higher tumour progression risk among young patients (<40 years) with subclinical, low-risk PTCs who undergo observation rather than surgery. Therefore, nodule size and patient age should determine the need for workup in the general population without suspicious imaging features and with normal life expectancy. Further evaluation with ultrasound is required for patients less than 35 years old with nodules measuring more than 1 cm in the  axial plane . The cutoff size for further evaluation is raised to 1.5 cm for patients more than 35 years old. This recommendation should be applied to the largest thyroid nodule in cases of multiple thyroid nodules. Incidentally discovered heterogeneous and enlarged thyroid glands should undergo dedicated ultrasound if the patient has no limited life expectancy or serious comorbidities. [ 1 ]


Primary thyroid carcinomas include papillary, follicular, medullary, and  anaplastic  carcinomas. Lymphoma and metastasis of other primary malignancies to the thyroid gland represent a minority of thyroid carcinomas. Differentiated thyroid carcinomas (DTCs) originate from follicular epithelial cells and encompass PTCs and follicular thyroid carcinomas, including the  Hurthle cell  variant of follicular carcinoma. DTCs have an excellent prognosis and fortunately represent the majority of thyroid carcinomas. PTCs and follicular thyroid carcinomas represent 88% and 8%, respectively, of all thyroid malignancies. Medullary thyroid carcinoma arises from  neuroendocrine C-cells  and has a good prognosis. Anaplastic carcinoma is an aggressive undifferentiated tumour that usually affects the elderly and tends to have a worse prognosis. [ 1 ]


Surgery is the primary mode of treatment for DTCs. Post total  thyroidectomy  radioactive iodine (RAI)  ablation  is an option, especially in patients with distant metastasis, tumours larger than 4 cm, or extra-thyroidal disease extension. Ultrasound examination is usually adequate in evaluating primary tumours and cervical lymph nodes. Preoperative cross-sectional imaging with CT or MRI is indicated if there is a concern for local invasion that may alter the patient's staging as well as surgical approach (Figs. 4, 55 and 6)6) . Some thyroid primaries may be small, diffuse, or multifocal and therefore may be occult on imaging (Fig. 4) . [ 1 ]


In patients with known thyroid malignancies, a non-enhanced exam is preferred due to the possible undesired interference of free iodide contrast medium with thyroid iodide I-131 uptake for 6–8 weeks or more. This would adversely affect the management of these patients by delaying diagnostic thyroid scintigraphy and radioiodine ablation in patients with DTCs for 2–6 months. [ 1 ]


The radiologist must evaluate the central structures draping the thyroid gland including the  trachea , oesophagus,  larynx , and  pharynx , as well as the recurrent  laryngeal nerve . Invasion is suspected if the thyroid mass abuts the airway or oesophagus for more than 180 degrees. Luminal deformity,  mucosal  thickening and mucosal focal irregularity are more specific indicators of invasion. Obliteration of the fat planes of the tracheoesophageal groove in three axial images and signs of  vocal cord paralysis  are indicative of recurrent laryngeal nerve invasion. Invasion of these central structures meets the criteria for T4a disease (Figs. 5 and and6)6). [ 1 ]


Arterial invasion constitutes T4b disease, which may preclude curative surgery. More than 180 degrees of arterial encasement is suggestive of invasion, however, arterial deformity or narrowing is much more suspicious for invasion. The  carotid artery  is the most commonly involved artery; however, the mediastinal vessels should also be examined. Encasement of the carotid artery or mediastinal vessels for more than 270 degrees is unlikely to be resectable. On the other hand, occlusion or effacement of the internal jugular vein can occur without invasion and does not influence surgical resectability or staging. Asymmetry of the strap muscle and the tumour abutting its external surface are signs of an invasion. However, invasion of the pre-vertebral musculature is more challenging, as a large lesion can compress the muscle without invasion (Figs. 5 and and6)6). [ 1 ]


Finally, the possibility of metastatic disease should be excluded. PTCs and medullary thyroid carcinomas tend to metastasize to regional lymph nodes. According to the AJCC/UICC TNM staging system, the nodal stage is classified by site: N1a indicates level VI nodal involvement, including paratracheal nodes; N1b indicates unilateral or bilateral lateral cervical nodal disease or superior mediastinal nodal disease (Figs. 4, 55 and and6)6). [ 1 ]