Severe procedural complications during a TIPS procedure, including catastrophic bleeding or direct liver injury, are relatively uncommon. In the hands of an experienced physician, operative mortality is less than 1% [ medical citation needed ] . On the other hand, up to 25% of patients who undergo TIPS will experience transient post-operative  hepatic encephalopathy  caused by increased porto-systemic passage of nitrogen from the gut. [ 5 ]


A less common, but more serious complication, is hepatic ischemia causing acute liver failure. While healthy livers are predominantly oxygenated by portal blood supply, long-standing portal hypertension results in compensatory hypertrophy of and increased reliance on the hepatic artery for oxygenation. Thus, in people with advanced liver disease the shunting of portal blood away from hepatocytes is usually well tolerated. However, in some cases suddenly shunting portal blood flow away from the liver may result in acute liver failure secondary to hepatic ischemia. [ 6 ]  Acute hepatic dysfunction after TIPS may require emergent closure of the shunt. [ citation needed ]


A rare but serious complication is persistent TIPS infection, also known as endotipsitis. [ 7 ]


Lastly, the TIPS may become blocked by a blood clot or in-growth of endothelial cells and no longer function. This has been significantly reduced with the use of  polytetrafluoroethylene  (PTFE)–covered stents. [ 8 ]


Portal hypertension, an important consequence of liver disease, results in the development of significant  collateral circulation  between the portal system and systemic venous drainage (porto-caval circulation). Portal venous congestion causes venous blood leaving the stomach and intestines to be diverted along auxiliary routes of lesser resistance in order to drain to systemic circulation. With time, the small vessels that comprise a collateral path for porto-caval circulation become engorged and dilated. These vessels are fragile and often hemorrhage into the GI tract. ( See  esophageal ,  gastric ,  rectal varices ). [ citation needed ]


A TIPS procedure decreases the effective  vascular resistance  of the liver through the creation of an alternative pathway for portal venous circulation. By creating a shunt from the portal vein to the hepatic vein, this intervention allows portal blood an alternative avenue for draining into systemic circulation. In bypassing the flow-resistant liver, the net result is a reduced  pressure drop  across the liver and a decreased portal venous pressure. Decreased portal venous pressure in turn lessens congestive pressures along veins in the intestine so that future bleeding is less likely to occur.  The reduced pressure also makes less fluid develop, although this benefit may take weeks or months to occur. [ citation needed ]


Transjugular intrahepatic portosystemic shunts are typically placed by an interventional radiologist under  fluoroscopic  guidance. [ 9 ]  Access to the liver is gained, as the name 'transjugular' suggests, via the  internal jugular vein  in the  neck .  Once access to the jugular vein is confirmed, a guidewire and introducer sheath are typically placed to facilitate the  shunt 's placement.  This enables the interventional radiologist to gain access to the patient's  hepatic vein  by traveling from the  superior vena cava  into the  inferior vena cava  and finally the  hepatic vein .


Once the catheter is in the hepatic vein, a wedge pressure is obtained to calculate the pressure gradient in the liver. Following this, carbon dioxide is injected to locate the portal vein. Then, a special needle known as a Colapinto is advanced through the liver parenchyma to connect the hepatic vein to the large  portal vein , near the center of the liver.  The channel for the shunt is next created by inflating an angioplasty balloon within the liver along the tract created by the needle.  The shunt is completed by placing a special mesh tube known as a  stent  or endograft to maintain the tract between the higher-pressure portal vein and the lower-pressure hepatic vein.  After the procedure, fluoroscopic images are made to show placement. Pressure in the portal vein and inferior vena cava are often measured. [ citation needed ]


Uterine artery embolization (UAE, uterine fibroid embolization, or UFE)  is a procedure in which an  interventional radiologist  uses a  catheter  to deliver small particles that block the  blood  supply to the uterine body. The procedure is primarily done for the treatment of  uterine fibroids  and  adenomyosis . [ 1 ] [ 2 ]  Compared to surgical treatment for fibroids such as a hysterectomy, in which a woman's uterus is removed, uterine artery embolization may be beneficial in women who wish to retain their uterus. Other reasons for uterine artery embolization are postpartum hemorrhage and uterine  arteriovenous malformations . [ 3 ]


Uterine fibroids are the most common type of benign uterine tumor and are composed of smooth muscle. [ 4 ]  They often cause bulk-related symptoms, which can be characterized by back pain, heaviness in the pelvic area, abdominal bloating. [ 5 ]  Uterine artery embolization may be done to treat bothersome bulk-related symptoms as well as abnormal or  heavy uterine bleeding  due to  uterine fibroids . Fibroid size, number, and location are three potential predictors of a successful outcome. [ 6 ] [ 7 ] [ 8 ]  Specifically, studies have demonstrated that submucosal (directly underneath the uterine lining) fibroids demonstrated the largest reduction in size while subserosal (outer layer of the uterus) had the smallest reduction. [ 9 ]


Uterine artery embolization may also be appropriate for the treatment of adenomyosis, which is when the lining of the uterus aberrantly grows into the muscle of the uterus. [ 10 ]  Symptoms of adenomyosis include heavy or prolonged menstrual bleeding and painful menstrual periods. [ 11 ]


Uterine artery embolization can also be used to control heavy uterine bleeding for reasons other than fibroids, such as postpartum  obstetrical hemorrhage . [ 12 ]  Many women who experience postpartum hemorrhage may be successfully treated with medication or  uterine balloon tamponade . [ 13 ]  However, in cases where women continue to bleed, uterine artery embolization may be an appropriate option.


A less common indication for uterine artery embolization is for the treatment of uterine arteriovenous malformations which can be a cause of abnormal uterine bleeding or life-threatening bleeding. Roughly half of women with uterine arteriovenous malformations are born with them while the remaining form following surgical interventions or may be due to uterine tumors. [ 3 ]


Prior to undergoing UAE, the patient should be evaluated for the following absolute contra-indications to the procedure: a viable pregnancy, a current infection that is not being treated, or gynecologic malignancy (except for cases where UAE is being used as a procedure in addition to treatment for the cancer). [ 14 ]  Relative contra-indications for the procedure include a severe contrast allergy since contrast is necessary to visualize the arteries during the procedure, kidney impairment since contrast may cause damage to the kidneys, or  coagulopathy  (blood disorder that causes prolonged or excessive bleeding). [ 15 ]  However, all of the stated relative contra-indications can be managed with appropriate pre-operative planning.


The rate of serious complications is comparable to that of  myomectomy  or  hysterectomy . The advantage of somewhat faster recovery time is offset by a higher rate of minor complications and an increased likelihood of requiring surgical intervention within two to five years of the initial procedure. [ 16 ]  An analysis of 15,000 women found that those who had myomectomy required fewer additional procedures, including hysterectomies, to treat fibroids over the next five years than those who had uterine artery embolization. [ 17 ] [ 18 ]


Complications include the following:


Prior to a uterine artery embolization, patients should undergo a clinic visit with their  gynecologist , have a recent Pap smear, and an endometrial biopsy in cases where abnormal uterine bleeding is a presenting symptom. [ 27 ]  A clinic visit can then be made with the  interventional radiologist  performing the uterine artery embolization so that a thorough history and physical exam can be taken. Recent diagnostic imaging such as a pelvic  magnetic resonance imaging  (MRI) should also be reviewed by the interventional radiologist to rule out possible malignancy, evaluate uterine anatomy, and discuss the likelihood of fibroid passage with the patient. [ 27 ]


The procedure is performed by an  interventional radiologist  under conscious sedation. [ 25 ]  Access is commonly through the  radial  or  femoral artery  via the wrist or groin, respectively. [ 3 ] [ 25 ]  After anesthetizing the skin over the artery of choice, the artery is accessed by a needle puncture using the  Seldinger technique . [ 25 ]  Under  fluoroscopic  guidance, a catheter is then introduced into the artery and used to select the uterine vessels for subsequent embolization. Once at the level of the uterine artery an  angiogram  with contrast is performed to confirm placement of the catheter, and the embolizing agent (spheres or beads) is released. As more embolizing agent is administered, blood flow will slow down significantly. Over time, the decreased blood flow causes the fibroid to shrink. Both the left and right uterine arteries are embolized since unilateral UAEs have a high risk of failure. [ 28 ]  The procedure can be performed in a hospital or surgical center. More recently, there has been support for UAE as an outpatient procedure, but many doctors choose an overnight admission for pain control. [ 29 ]  Follow-up for the procedure may vary based on institution, but can include a clinic appointment at 1 to 3 months following the procedure and an MRI to see if the fibroids have shrunk from the preoperative MRI. [ 9 ]


The vast majority of women who undergo UAE experience elimination of abnormal uterine bleeding and improvement in bulk symptoms. [ 15 ]  Additionally, patient satisfaction following the procedure is about 80%. [ 14 ]  One drawback of UAE is that it appears to require more repeat procedures than if surgery was done initially. [ 30 ]  However, long-term patient satisfaction outcomes of UAE are similar to that of surgery and a short-term benefit is the reduction in hospital stay with UAE. [ 30 ] [ 15 ]


Currently the number of studies that compare pregnancy rates between UAE and myomectomy are limited. However, a 2020 systematic review assessing pregnancy outcomes after UAE for fibroids demonstrated that pregnancy rates between UAE and myomectomy are comparable. Additionally, they found that rates of pregnancy-related complications in women who underwent UAE were similar to that of the general population. [ 31 ]  Despite these findings, there is still a lack of randomized control trials that directly compare the outcomes of myomectomy and UAE for fibroids, so future studies are needed to determine which procedure yields better results.


For women with adenomyosis, the data regarding outcomes is limited. However, studies have demonstrated that about 83% of women with adenomyosis experienced an improvement in their symptoms. Additionally, the rate of improvement in symptoms increased to about 93% in women who had both adenomyosis and fibroids.


Regarding cost, the American Journal of Gynecology reports that uterine artery embolization costs 12% less than hysterectomy and 8% less than myomectomy. [ 32 ]


UAE was used for the first time in 1979 to control bleeding in a woman with postpartum hemorrhage that did not improve after surgical treatment. [ 33 ]  Since then studies have shown that UAE is a safe and effective procedure for postpartum hemorrhage with control of bleeding in greater than 90% of women. [ 34 ]  The initial use of UAE for patients with fibroids was to limit bleeding during myomectomy. [ 35 ]  During the 1990s, doctors began expanding the indications for UAE and started using it for the treatment of the fibroids specifically. [ 36 ]  Previously, the primary treatment methods for fibroids were myomectomy or hysterectomy. Compared to surgery, UAE can be advantageous because blood loss is typically minimal, surgery and general anesthesia is avoided, recovery is shorter, and women can retain their uterus (relative to hysterectomy). [ 37 ]  UAE is thought to treat fibroids by selectively decreasing blood flow to the tumor since it is highly vascular, which causes improvement in abnormal bleeding and the bulk symptoms that are often experienced with fibroids.


For removing uterine fibroids, myomectomy and uterine artery embolisation seem to be equally effective in improving  quality of life , as measured 4-yours after surgery. [ 38 ] [ 39 ]


Vascular closure devices  (VCDs) are medical devices used to achieve  hemostasis  of the small hole in the artery after a  cardiovascular  procedure of  endovascular surgery  requiring a  catheterization .


Cardiovascular procedures requiring catheterization include diagnostic procedures that help diagnose diseased blood vessels and interventional procedures such as  angioplasty , the placement of a  stent  and coronary  thrombectomy .


During such procedures, a small incision is made in the  groin  area and a hole is created in the  femoral artery  to gain access to the artery. This hole is referred to as the access site or puncture site. At the completion of the procedure, the hole needs to be closed. Metal clip-based and  suture -based VCDs may reduce time to hemostasis when compared with extrinsic (manual or mechanical) compression. However, no type of VCD has been shown to be more effective or safe than another. [ 1 ]


The main goal of a vascular closure device is to provide rapid  hemostasis  of the artery as well as reduce access site complications. [ 2 ]  VCD's also help reduce time to  ambulation  and time to hospital discharge. [ 3 ]  In addition, VCDs are more comfortable for the patient compared to manual compression.


Prior to the development of VCD's, the main method for closing the femoral artery was manual compression. Manual compression involves up to 30 minutes of manual pressure or mechanical clamps applied directly to the patient's groin, which is very painful, followed by up to 8 hours of bed rest in the hospital recovery room.


Vascular closure devices were introduced in the early 1990s in an effort to reduce the time to hemostasis, enable early ambulation and improve patient comfort. Initially, devices focused on technologies involving a  suture  or a  collagen  plug. [ 4 ]  These technologies are effective at closing the hole; however, they often leave an intravascular component in the artery, which can cause complications. In addition, these technologies failed to accurately address patient pain.


More recent methods to close the hole involve the use of novel materials that dissolve over a short period of time, such as  polyethylene glycol  found in the  Mynx vascular closure device . These technologies incorporate a more gentle deployment of the material to the outside of the artery and avoid the use of intravascular components, leaving nothing behind in the artery and consequently improving patient comfort. [ 5 ]


A  vascular snare  is an  endovascular  device that is used to remove  foreign bodies  from inside  arteries  and  veins . The snare consists of several  radiopaque  loops of wire inside a  catheter , which when extended flower out, and which collapse when withdrawn into the catheter.


Vascular snares are used to retrieve  inferior vena cava filters , lost  guide wires , or broken  central venous catheters . [ 1 ]


Vascular snaring is a component technique in  endovascular aneurysm repair  in some devices. [ citation needed ]


A snare catheter is inserted using the  Seldinger technique  under  fluoroscopic  guidance. The snare wire is advanced under direct visualization and flowered open. The object being retrieved is captured within the loops of snare, and retrieved with the snare wire and catheter, being carried out of the body at the tip of the catheter.


Vertebral augmentation , including  vertebroplasty  and  kyphoplasty , refers to similar  percutaneous  spinal procedures in which  bone cement  is injected through a small hole in the skin into a fractured  vertebra  in order to relieve  back pain  caused by a vertebral  compression fracture . After decades of  medical research  into the efficacy and safety of vertebral augmentation, there is still a lack of consensus regarding certain aspects of vertebroplasty and kyphoplasty.


Vertebroplasty  and  kyphoplasty  are the two most common procedures for spinal augmentation. These  medical terms  are  classical compounds  of the suffix  -plasty  meaning "molding or shaping surgically" (from  Ancient Greek   plastós  "molded, formed") and the prefixes  vertebro-  "vertebra" (from  Latin   vertebra  "joint, joint of the spine") and  kypho-  "humped; stooping forward" (from Ancient Greek  kyphos  "crooked"). [ 1 ]


Vertebroplasty is typically performed by a spine surgeon or  interventional radiologist . It is a minimally invasive procedure and patients usually go home the same or next day as the procedure. Patients are given local anesthesia and light sedation for the procedure, though it can be performed using only local anesthetic for patients with medical problems who cannot tolerate sedatives well.


During the procedure, bone cement is injected with a biopsy needle into the collapsed or fractured vertebra. The needle is placed with  fluoroscopic x-ray  guidance. The cement (most commonly  poly methyl methacrylate  (PMMA), although more modern cements are used as well) quickly hardens and forms a support structure within the vertebra that provide stabilization and strength. The needle makes a small puncture in the patient's skin that is easily covered with a small bandage after the procedure. [ 2 ]


Kyphoplasty is a variation of a vertebroplasty which attempts to restore the height and angle of  kyphosis  of a fractured  vertebra  (of certain types), followed by its stabilization using injected bone cement. The procedure typically includes the use of a small balloon that is inflated in the vertebral body to create a void within the cancellous bone prior to cement delivery.  Once the void is created, the procedure continues in a similar manner as a vertebroplasty, but the bone cement is typically delivered directly into the newly created void. [ 3 ]


In a 2011 review Medicare contractor NAS determined that there is no difference between vertebroplasty and kyphoplasty, stating, "No clear evidence demonstrates that one procedure is different from another in terms of short- or long-term efficacy, complications, mortality or any other parameter useful for differentiating coverage." [ 4 ]


As of 2019, the effectiveness of vertebroplasty is not supported. [ 5 ] [ 6 ]  A 2018 Cochrane review found no role for vertebroplasty for the treatment of acute or sub-acute osteoporotic vertebral fractures. [ 7 ]  The subjects in these trials had primarily non-acute fractures and prior to the release of the results they were considered the most ideal people to receive the procedure. After trial results were released vertebroplasty advocates pointed out that people with acute  vertebral fractures  were not investigated. [ 8 ] [ 9 ]  A number of non-blinded trials suggested effectiveness, [ 10 ]  but the lack of blinding limits what can be concluded from the results and some have been criticized because of being funded by the manufacturer. [ 8 ]  One analysis has attributed the difference to  selection bias . [ 11 ]


Some have suggested that this procedure only be done in those with fractures less than 8 weeks old; [ 12 ]  however, analysis of the two blinded trials appear not to support the procedure even in this acute subgroup. [ 13 ]  Others consider the procedure only appropriate for those with other health problems making rest possibly detrimental, those with metastatic  cancer  as the cause of the spine fracture, or those who do not improve with conservative management. [ 14 ]


Evidence does not support a benefit of kyphoplasty over vertebroplasty with respect to pain, but the procedures may differ in restoring lost vertebral height, and in safety issues like cement  extravasation  (leakage). [ 8 ]  As with vertebroplasty, several unblinded studies have suggested a benefit from balloon kyphoplasty. [ 15 ] [ 16 ]  As of 2012 [update] , no blinded studies have been performed, and since the procedure is a derivative of vertebroplasty, the unsuccessful results of these blinded studies have cast doubt upon the benefit of kyphoplasty generally. [ 17 ]


Some vertebroplasty practitioners and some health care professional organizations continue to advocate for the procedure. [ 18 ] [ 19 ] [ 20 ]   In 2010, the board of directors of the  American Academy of Orthopaedic Surgeons  released a statement recommending strongly against use of vertebroplasty for osteoporotic spinal compression fractures, [ 21 ]  while the Australian Medical Services Advisory Committee considers both vertebroplasty and kyphoplasty only to be appropriate in those who have failed to improve after a trial of conservative treatment, [ 22 ]  with conservative treatment (analgesics primarily) being effective in two-thirds of people. [ 23 ]  The  National Institute for Health and Care Excellence  similarly states that the procedure in those with osteoporotic fractures is only recommended as an option if there is severe ongoing pain from a recent fracture even with optimal pain management. [ 24 ]


Vertebral body stenting , also known by the brand Kiva, is a similar procedure which also has poor evidence to support its use. [ 6 ]


Some of the associated risks are from the leak of acrylic cement to outside of the vertebral body. Although severe complications are extremely rare, infection, bleeding, numbness, tingling, headache, and paralysis may ensue because of misplacement of the needle or cement. This particular risk is decreased by the use of X-ray or other radiological imaging to ensure proper placement of the cement. [ 2 ]  In those who have fractures due to cancer, the risk of serious adverse events appears to be greater at 2%. [ 23 ]


The risk of new fractures following these procedures does not appear to be changed; however, evidence is limited, [ 17 ]  and an increase risk as of 2012 is not ruled out. [ 25 ]  Pulmonary cement embolism is reported to occur in approximately 2-26% of procedures. [ 26 ]  It may occur with or without symptoms. [ 26 ]  Typically, if there are no symptoms, there are no long term issues. [ 26 ]  Symptoms do occur in about 1 in 2000 procedures. [ 22 ]  Other adverse effects include spinal cord injury in 0.6 per 1000. [ 22 ]


In the United States in 2003 approximately 25,000 vertebroplasty procedures were paid for by Medicare. [ 27 ]  As of 2011/2012 this number may be as high as 70,000-100,000 per year. [ 28 ]


Vertebroplasty had been performed as an open procedure for many decades to secure pedicle screws and fill tumorous voids. However, the results were not always worth the risk involved with an  open procedure , which was the reason for the development of  percutaneous  vertebroplasty.


The first percutaneous vertebroplasty was performed in 1984 at the University Hospital of Amiens, France to fill a vertebral void left after the removal of a benign  spinal tumor . A report of this and 6 other patients was published in 1987 and it was introduced in the United States in the early 1990s. Initially, the treatment was used primarily for tumors in Europe and vertebral compression fractures in the United States, although the distinction has largely gone away since then. [ 29 ]


The cost of vertebroplasty in Europe as of 2010 was ~2,500 Euro. [ 23 ]  As of 2010 in the United States, when done as an outpatient, vertebroplasty costs around US$3300 while kyphoplasty costs around US$8100 and when done as an inpatient vertebroplasty cost ~US$11,000 and kyphoplasty US$16,000. [ 30 ]  The cost difference is due to kyphoplasty being an in-patient procedure while vertebroplasty is outpatient, and due to the  balloons  used in the kyphoplasty procedure. [ 31 ]  Medicare in 2011 spent about US$1 billion on the procedures. [ 28 ]  A 2013 study found that "the average adjusted costs for vertebroplasty patients within the first quarter and the first 2 years postsurgery were $14,585 and $44,496, respectively. The corresponding average adjusted costs for kyphoplasty patients were $15,117 and $41,339. There were no significant differences in adjusted costs in the first 9 months postsurgery, but kyphoplasty patients were associated with significantly lower adjusted treatment costs by 6.8–7.9% in the remaining periods through two years postsurgery." [ 32 ]


In response to the NEJM articles and a medical record review showing misuse of vertebroplasty and kyphoplasty,  US Medicare   contractor  Noridian Administrative Services (NAS) conducted a literature review and formed a policy regarding reimbursement of the procedures. NAS states that in order to be reimbursable, a procedure must meet certain criteria, including, 1) a detailed and extensively documented medical record showing pain caused by a fracture, 2) radiographic confirmation of a fracture, 3) that other treatment plans were attempted for a reasonable amount of time, 4) that the procedure is not performed in the emergency department, and 5) that at least one year of follow-up is planned for, among others. The policy, as referenced, applies only to the region covered by Noridian and not all of Medicare's coverage area. The reimbursement policy became effective on 20 June 2011. [ 4 ]  A 2015 comparative study of Medicare patients with vertebral compression fractures found that those who received balloon kyphoplasty and vertebroplasty therapies experienced lower mortality and overall morbidity than those who received conservative nonoperative management. [ 33 ]


In 2015, it was reported by  The Atlantic  that a person associated with a medical device company that sells equipment related to the kyphoplasty procedure had edited the Wikipedia article on the subject to promote claims about its efficacy. [ 34 ]  Assertions about the positive effects of kyphoplasty have been found to be unsupported or disproven, according to independent researchers. [ 35 ]


A  contrast agent  (or  contrast medium ) is a  substance  used to increase the  contrast  of structures or fluids within the body in  medical imaging . [ 1 ]  Contrast agents absorb or alter external  electromagnetism  or  ultrasound , which is different from  radiopharmaceuticals , which emit  radiation  themselves. In  X-ray  imaging, contrast agents enhance the  radiodensity  in a target tissue or structure. In  magnetic resonance imaging  (MRI), contrast agents shorten (or in some instances increase) the relaxation times of  nuclei  within body tissues in order to alter the contrast in the image.


Contrast agents are commonly used to improve the visibility of  blood vessels  and the  gastrointestinal tract .


The types of contrast agent are classified according to their intended imaging modalities.


For  radiography , which is based on  X-rays ,  iodine  and  barium  are the most common types of contrast agent. Various sorts of iodinated contrast agents exist, with variations occurring between the  osmolarity ,  viscosity  and absolute iodine content. Non-ionic  dimers  are favored for their low osmolarity and low toxicity, but have a correspondingly higher cost attached to their use. [ 2 ]


Gadolinium  is used in  magnetic resonance imaging  as an  MRI contrast agent  or gadolinium-based contrast agent (GBCA). [ 3 ]  In the 3+ oxidation state, the metal has seven unpaired electrons. This causes water around the contrast agent to relax quickly, enhancing the quality of the MRI scan.


Microbubbles  are used as contrast agents for  sonographic  examination, specifically  echocardiograms , for the detection of a  cardiac shunt . These microbubbles are composed of agitated  saline solution , most of which are too large to pass through the  capillaries  (blood vessels) of the  lungs . Therefore, the only ones that reach the left side of the heart pass through an abnormal connection between the two sides of the heart, known as a  right-to-left shunt . In addition, pharmaceutically prepared microbubbles are composed of tiny amounts of  nitrogen  or  perfluorocarbons  strengthened and supported by a  protein ,  lipid , or  polymer  shell. [ 4 ]  These are small enough to pass through the capillaries and are used to increase the contrast in the left ventricle, improving the visualization of its walls. The drop in density on the interface between the gas in the bubble and the surrounding liquid strongly scatters and reflects the  ultrasound  back to the probe. This process of  backscattering  gives the liquid with these bubbles a high signal, which can be seen in the resulting image.


Abenacianine  for injection, also known as VGT-309, is a tumor-targeted  fluorescent  imaging agent developed by Vergent Bioscience to enhance tumor visualization during cancer surgeries. [ 1 ]  This compound binds to  cathepsins , a family of proteases that are over expressed in various solid tumors, facilitating the detection tumors. [ 2 ] [ 3 ] [ 4 ] [ 5 ]


Blood pool agents  (BPAs) are a class of  magnetic resonance angiography   contrast agents . [ 1 ] [ 2 ]  Blood pool agents (also known as intravascular contrast agents) are differentiated from other contrast agents due to their high molecular weight and higher  relaxivities . [ 3 ]  Their large size prevents diffusion through the  vascular   epithelium  and leakage into the  interstitial space , and because of this they stay in the vascular system for a longer time period. Most contrast agents, leave the vascular system within a few minutes, however blood pool agents remain in the circulation for up to an hour, extending the window available for imaging. Longer image acquisition times allow better  signal-to-noise ratio  and improved image resolution.


Due to their extended time in the  circulatory system , blood pool agents can be used for delayed steady-state imaging, and additionally these results can be combined with first pass arterial imaging. [ 2 ] [ 3 ]


This class of BPAs is based on the noncovalent binding of low molecular weight Gd 3+ -based complexes to  human serum albumin . The first commercial agent to be approved in this class is  gadofosveset trisodium [ 4 ]  (also known as Vasovist [ 5 ]  or Ablavar, [ 6 ]  and previously known as MS-325 [ 7 ] ). Many clinical and case studies documenting the use of this BPA have been published, [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ]  and its efficacy in enhancing blood vessels visibility has been demonstrated. [ 15 ]  The manufacturer ( Lantheus Medical ) discontinued production in 2017 though, due to poor sales. [ 16 ]


Gadocoletic acid (Bracco SpA), also known as B-22956 and B22956/1, is a Gd-DTPA derivative that is currently in development, but has not yet been approved for clinical use. [ 17 ]


Gadobenic acid  (MultiHance [ 18 ] ) is sometimes categorized as a BPA; however, as it only binds weakly to albumin and because hepatobiliary uptake of this compound occurs, this contrast agent should not be classified as a BPA.


Polymeric Gd 3+  chelates are large in size, which prevents leakage into the interstitial space, and provides long imaging windows. Several polymeric gadolinium-based BPAs are currently in development but have not yet been approved for clinical use:
Gadomelitol (Guerbet, France), also known as Vistarem and P792 [ 19 ]
Gadomer-17 (Schering AG, Berlin, Germany) also known as Gd-DTPA-17, SH L 643 A. [ 20 ]


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Relmapirazin  ( MB-102 ) is an investigational fluorescent tracer that is exclusively excreted renally and is used to measure  glomerular filtration rate  of the kidneys. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ]


Neuroradiology  is a subspecialty of  radiology  focusing on the diagnosis and characterization of abnormalities of the  central  and  peripheral nervous system ,  spine , and head and neck using  neuroimaging  techniques. Medical issues utilizing neuroradiology include  arteriovenous malformations ,  tumors ,  aneurysms , and  strokes .  [ 1 ]


The major professional association in the United States representing neuroradiologists is the American Society of Neuroradiology (ASNR). The ASNR publishes the  American Journal of Neuroradiology  (AJNR). The ASNR annual meeting rotates through different cities, and usually takes place between late April and early June. The specialty neuroradiology societies that are associated with the ASNR include the  American Society of Pediatric Neuroradiology  (ASPNR), the  American Society of Spine Radiology  (ASSR), the  American Society of Head and Neck Radiology  (ASHNR), and the  American Society of Functional Neuroradiology  (ASFNR). These societies contribute to the programming of the ASNR annual meeting and also hold their own annual meetings.


The major professional association in Europe is the  European Society of Neuroradiology  (ESNR). In Japan, it is the  Japanese Neuroradiological Society ; in the UK, it is the  British Society of Neuroradiologists  (BSNR); and in France, it is the  French Society of Neuroradiology  (SFNR). The ESNR and the Japanese society publish  Neuroradiology , and the SFNR publishes the  Journal of Neuroradiology .


A  radiologic sign  is an objective indication of some medical fact (that is, a  medical sign ) that is detected by a  physician  during  radiologic examination  with  medical imaging [ 1 ]  (for example, via an  X-ray ,  CT scan ,  MRI  scan, or  sonographic scan ).


Acorn cyst sign  is a  radiologic sign  indicating the presence of a  benign  uncomplicated  cyst  in  ultrasound examinations of the breast . [ 1 ]  It consists of a deep anechoic fluid portion resembling an  acorn , and a superficial echogenic layer resembling an acorn cap. This sign is helpful for radiologists to differentiate a benign uncomplicated cyst from a complex mass. [ 2 ]


This article about a  neoplasm  is a  stub . You can help Wikipedia by  expanding it .


In  radiology , the  air crescent sign  is a finding on  chest radiograph  and  computed tomography  that is  crescenteric  and  radiolucent , due to a  lung  cavity that is filled with  air  and has a round  radiopaque  mass. [ 1 ]   Classically, it is due to an  aspergilloma , a form of  aspergillosis , that occurs when the fungus  Aspergillus  grows in a cavity in the lung. [ 2 ]
It is also referred as Monad sign. [ 3 ]


This  medical sign  article is a  stub . You can help Wikipedia by  expanding it .


Aortic unfolding  is an  abnormality  visible on a  chest X-ray , that shows widening of the  mediastinum  which may mimic the appearance of a  thoracic aortic aneurysm . [ 1 ]


With aging, the ascending portion of the thoracic  aorta  increases in length by approximately 12% per decade, whereas the diameter increases by just 3% per decade. This elongation causes the ascending aorta to appear as a vertical shadow on the left  heart  border. Unfolding is often associated with aortic calcification which implies  aortic degeneration  and  hypertension .  [ 2 ]


Bat wing appearance  is a radiologic sign referring to bilateral perihilar lung shadowing seen in frontal chest X-ray and in chest CT. [ 1 ] [ 2 ]  The most common reason for bat wing appearance is the accumulation of oedema fluid in the lungs. [ 3 ]  The batwing sign is symmetrical, usually showing  ground glass appearance  and spares the lung cortices. [ 4 ]   This sign is seen in individuals with  pneumonia , inhalation injuries,  pulmonary haemorrhage ,  sarcoidosis , bronchoalveolar carcinoma and pulmonary alveolar proteinosis. [ 4 ]


This  pulmonology  article is a  stub . You can help Wikipedia by  expanding it .


The  black pleura sign  is a radiological feature observed in  pulmonary alveolar microlithiasis  (PAM), a rare lung disorder characterized by the accumulation of tiny calcium phosphate deposits, known as microliths, within the alveoli. [ 1 ]  This sign appears as a thin, dark (lucent) line beneath the ribs on imaging studies, contrasting with the diffusely dense, calcified lung parenchyma.


In PAM, microliths predominantly accumulate in the central portions of secondary pulmonary lobules, leading to widespread calcification of the lung tissue. However, the subpleural regions often remain relatively spared from these deposits and sometimes show subpleural cystic changes. This subpleural sparing creates a peripheral zone that appears less dense (more lucent) on imaging studies, resulting in the black pleura sign. [ 1 ]


The black pleura sign is considered a characteristic indicator of pulmonary alveolar microlithiasis. Its presence on imaging studies can aid radiologists and clinicians in differentiating PAM from other interstitial lung diseases that may not exhibit subpleural sparing. [ 4 ]


Blade of grass sign  (also known as  flame sign [ 1 ] ) is a radiologic sign referring to the lytic fronts seen in the leading edge of the long bone in  Paget's disease . [ 2 ]  It is usually seen as a wedge shaped area of radiolucency in the diaphysis of long bone. [ 1 ]


The boomerang sign is a radiological finding observed on magnetic resonance imaging (MRI) of the brain, particularly in diffusion-weighted imaging (DWI) sequences. It refers to a characteristic boomerang-shaped area of restricted diffusion in the splenium of the  corpus callosum  due to  cytotoxic edema . [ 1 ]  This sign is associated with various neurological conditions and is considered a non-specific marker of splenial pathology, often reversible depending on the underlying cause. [ 2 ] [ 3 ]


The splenium of the corpus callosum is the posterior part of the corpus callosum, a major white matter structure connecting the two cerebral hemispheres. On MRI, the boomerang sign appears as a boomerang-shaped hyperintense area on DWI. There is a corresponding low signal intensity on the apparent diffusion coefficient (ADC) map, indicating true restricted diffusion. The sign is often localized within the central or posterior splenium. [ 2 ]


The bowl of grapes sign is a descriptive radiological term used in the context of  synovial sarcoma , a malignant soft tissue tumor. [ 1 ]  This sign refers to the appearance of multiple small, rounded, fluid-containing spaces within a soft tissue mass, which resemble a cluster of grapes. [ 2 ]  These cystic spaces are typically attributed to hemorrhage, necrosis, or myxoid degeneration within the tumor, a common feature of synovial sarcoma.


The bowl of grapes sign is typically identified on magnetic resonance imaging and computed tomography, and occasionally on ultrasound. During ultrasound examination, mixed echogenicity is noted in synovial sarcoma, with hypoechoic or anechoic areas corresponding to the cystic regions.


The cystic spaces in synovial sarcoma appear hyperintense on T2-weighted images, reflecting fluid content. Solid tumor components often demonstrate heterogeneous enhancement after contrast administration. The mass may display a multilocular appearance with well-defined cystic and solid regions, contributing to the grape-like pattern. [ 3 ] [ 4 ]


The  bowler hat sign  is a  radiologic sign  seen on double-contrasted  barium enema  studies, indicating the presence of a  colonic polyp . [ 1 ]  A ring of barium collects at the base of the polyp and also along its dome, simulating the appearance of a bowler hat. [ 1 ]  This sign is present for growths that are an intermediate between flat and pedunculated. [ 2 ]  The  differential diagnosis  for this sign includes bubbles,  diverticula , and unusual projections of anatomic structures such as the  appendix . [ 2 ]


The  brim sign  or the  pelvic brim sign  is a  radiologic sign  seen in cases of  Paget’s disease  of bone involving the pelvis. [ 1 ]  It refers to thickened and sclerotic changes along the iliopubic line, the anteromedial portion of the pelvic brim. This sign is a key diagnostic marker for pelvic involvement in Paget’s disease and is typically identified on plain radiographs. [ 2 ]


Paget’s disease of bone is a chronic disorder characterized by abnormal bone remodeling. The pelvic brim sign arises due to excessive bone resorption due to increased osteoclastic activity in the early stages of the disease leads to localized bone loss, as well as excessive bone formation during the later stages of the diseases. Compensatory osteoblastic activity results in thickened, sclerotic bone along the iliopubic line.


The pelvic brim, being a weight-bearing area, shows pronounced changes, including thickening and increased density. These changes manifest radiologically as sclerosis and cortical thickening along the pelvic brim, creating the characteristic sign. [ 3 ]


A  bucket-handle tear  of the knee is a specific type of meniscal injury characterized by a longitudinal tear of the medial or lateral meniscus, where a displaced inner fragment resembles the appearance of a "bucket handle". [ 1 ]  This displaced meniscal fragment often remains attached at the anterior and posterior horns but dislocates into the intercondylar notch of the knee joint. Such injuries can cause mechanical symptoms, including locking and restricted movement of the knee.


The knee joint contains two crescent-shaped fibrocartilaginous structures, the menisci (medial and lateral), which serve as shock absorbers and stabilize the joint during movement. Each meniscus has an outer vascular zone (red-red zone), which has a good blood supply and healing potential as well as a central avascular zone (white-white zone), which has limited healing capability. [ 2 ]


The medial meniscus is more prone to injury due to its firm attachment to the joint capsule and limited mobility. The lateral meniscus is more mobile and less frequently injured.


A bucket-handle tear occurs when a significant longitudinal tear develops, often as a result of trauma or excessive twisting forces applied to the knee. The displaced fragment can flip into the intercondylar notch, impeding normal joint motion. The injury is most commonly seen in:


The injury frequently occurs in conjunction with anterior cruciate ligament (ACL) tears.


Patients with a bucket-handle tear typically present with the following symptoms: [ 3 ]


The patient may report a history of a twisting injury or sports-related trauma


Diagnosis of a bucket-handle tear is based on a combination of clinical examination and imaging studies:


Plain Radiographs (X-rays): While X-rays cannot visualize meniscal tears, they may rule out bony injuries. Occasionally, a joint effusion may be observed.


Management of bucket-handle tears is primarily surgical, as these tears often cause mechanical symptoms and are unlikely to heal on their own due to the displacement of the meniscal fragment. Treatment approaches include:


Postoperative care includes: [ 8 ]


Return to sports is usually permitted after 4–6 months, depending on the success of meniscus repair and concomitant injuries (e.g., ACL tear).


Butterfly vertebra  (also known as sagittal cleft vertebra) is a rare congenital spinal anomaly characterized by the presence of a sagittal cleft within a vertebral body, giving it a butterfly-like appearance on imaging. This condition arises due to incomplete fusion of the lateral halves of a vertebra during embryonic development. While often asymptomatic, butterfly vertebrae may occasionally be associated with spinal deformities or syndromic conditions. [ 1 ] [ 2 ]


The vertebral column develops from paired somites during embryogenesis. Normally, the right and left halves of each vertebra fuse in the midline to form a complete vertebral body. In butterfly vertebrae, this process is disrupted, leading to a persistent sagittal cleft. The defect is usually filled with fibrous or cartilaginous tissue, and the two halves of the vertebral body may remain connected by this intervening soft tissue.
The condition is most commonly observed in the thoracic and lumbar spine, although it can occur at any spinal level. The degree of clefting varies, resulting in a spectrum of appearances on imaging studies. [ 3 ]


Plain Radiography:  The vertebra appears divided into two symmetrical halves, separated by a vertical lucency that represents the cleft. The lateral portions of the vertebral body often appear sclerotic, and the shape resembles a butterfly when viewed in the anteroposterior projection.


CT imaging:  Provides greater detail regarding the bony anatomy, including the extent of clefting and the composition of the intervening tissue.


MRI:  Useful for evaluating associated spinal cord abnormalities or adjacent soft tissue changes. The sagittal cleft may appear as a hyperintense signal on T2-weighted images, representing cartilaginous or fibrous material. [ 4 ]


In  radiology ,  Canga's bead symptom  is the irregular appearance of  uterus  and  nodular  structures in  tuba uterina  observed in patients with genital  tuberculosis . [ 1 ]
It is named for  Serif Canga  (1906–1993), a Turkish Gynecologist, in 1971. [ 2 ]


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The  cannonball sign  is a radiological term used to describe the presence of multiple, well-circumscribed, round opacities seen on X-ray or CT imaging, typically in the lungs. [ 1 ]  This finding is most commonly associated with hematogenous metastases, where malignant cells spread to the lungs via the bloodstream, forming discrete nodules that resemble cannonballs. [ 2 ]  The term "cannonball" reflects the large, rounded appearance of these lesions, often evident on chest radiographs or CT scans.


Cannonball metastases result from the hematogenous dissemination of malignant cells, where tumor emboli travel through the bloodstream and lodge in the pulmonary vasculature. The lungs are a frequent site of metastases due to their rich vascular supply and filtration of venous blood. The characteristic rounded nodules represent distinct tumor foci that grow in a non-infiltrative pattern. [ 3 ]


This pattern is typically associated with malignancies that produce well-demarcated metastatic deposits rather than diffuse infiltrative changes. The size and number of nodules can vary depending on the primary tumor and the extent of metastatic spread.


Chest radiograph shows multiple, rounded opacities of varying sizes, typically bilateral but may be unilateral in early stages. Lesions are well-defined, mimicking cannonballs. [ 2 ]


CT has greater sensitivity in detecting small or early nodules. Nodules are round, well-circumscribed, and randomly distributed. [ 4 ]  The nodules may reveal additional features such as  necrosis  or calcification, depending on the tumor type.


Rarely used for initial identification but can assess metastatic activity, especially in borderline or ambiguous cases.


Cannonball metastases are classically seen in  renal cell carcinoma , [ 5 ]  also seen in  choriocarcinoma ,  endometrial cancer , [ 6 ]   prostate cancer  and some gastrointestinal malignancies.
The presence of cannonball metastases is a hallmark of advanced systemic malignancy. Identification of these lesions often triggers search for primary tumor. Detailed history, physical examination, and further imaging studies (e.g., abdominal or pelvic CT, mammography) are needed to locate the primary malignancy. Biopsy may be performed to confirm the metastatic origin and histopathology, particularly if the primary tumor is unknown.
Cannonball metastases often indicate a poor prognosis, reflecting widespread disease.


Celery stalking  or  celery stalk metaphysis  refers to the appearance of longitudinally aligned linear sclerotic bands extending from the  epiphysis  of the long bones. [ 1 ]  This finding is seen in conditions such as  osteopathia striata ,  congenital rubella [ 2 ]  and  congenital syphilis . [ 3 ]


Chang sign  is a radiologic sign for detecting  pulmonary embolism  in X-ray films. It refers to the dilatation and abrupt change in calibre of a previously normal descending pulmonary artery on a chest X-ray film. [ 1 ]  Chang sign usually appears within 24 hours of the onset of chest pain due to pulmonary embolism, [ 2 ]  and the maximal dilatation of the descending pulmonary artery often occurs in two to three days after the onset of pain. [ 3 ]


Chang sign is absent in case of co-existing pneumonia or other conditions causing central opacities, where the descending pulmonary artery cannot be visualised in the X-ray image. [ 3 ]


The  cheerio sign  is a  radiologic sign  that has been used to describe both pulmonary nodules and tears in the  glenoid labrum , named after its resemblance to the popular breakfast cereal " Cheerios ".


On  computed tomography  (CT) of the chest, the cheerio sign is seen as a ring-like structure with central  lucency  within the lung [ 1 ] . This sign most commonly indicates the presence of  pulmonary adenocarcinoma  or  Langerhans cell histiocytosis , but differential diagnosis includes  granulomatosis with polyangitis ,  rheumatoid nodules  and infections [ 1 ] .


The cheerio sign has also been demonstrated on  CT  arthograms of the shoulder in cases of anterior and posterior tears in the superior part of the  glenoid labrum . These tears are called SLAP lesions (superior labrum; anterior, posterior). This sign is specifically seen in type 3 SLAP lesions, which involve a "bucket-handle" tear of predominately the anterior labrum, often with displacement into the joint. On CT, this appears as a ring of contrast material and air surrounding a core of soft tissue [ 2 ] .


Chondrocalcinosis  or  cartilage calcification  is  calcification  (accumulation of  calcium  salts) in  hyaline cartilage  and/or  fibrocartilage . [ 1 ]  Chondrocalcinosis is an observation that can be visualized through diagnostic imaging tests such as  X-rays ,  CT ,  MRI , and  ultrasound . [ 2 ]


Buildup of  calcium phosphate  in the  ankle joints  has been found in about 50% of the general population, and may be associated with  osteoarthritis . [ 3 ]


Another common cause of chondrocalcinosis is  calcium pyrophosphate dihydrate crystal deposition disease  (CPPD). [ 4 ]  CPPD is estimated to affect 4–7% of the adult populations of Europe and the United States. [ 5 ]  Chondrocalcinosis can be seen in approximately 40% of those with CPPD. [ 6 ]  Previous studies have overestimated the prevalence by simply estimating the prevalence of chondrocalcinosis regardless of cause. [ 5 ]


A  magnesium deficiency  may cause chondrocalcinosis, and there is anecdotal evidence that magnesium supplementation may reduce or alleviate symptoms. [ 7 ]  In some cases,  arthritis  from  injury  can cause chondrocalcinosis. [ 8 ]
Other causes of chondrocalcinosis include: [ 4 ]


Chondrocalcinosis does not always lead to symptoms. However, chondrocalcinosis in the presence of CPPD may cause symptoms similar to Pseudogout, Pseudo-rheumatoid arthritis, and Pseudo-osteoarthritis. Chondrocalcinosis may be accompanied by joint pain, joint swelling, and decreased range of motion. [ 9 ]


Chondrocalcinosis affects common areas such as the knee, wrist, hand, and pelvis. [ 10 ]  Chondrocalcinosis can also be visualized affecting the spine. " Crowned Dens Syndrome " is an example of chondrocalcinosis affecting cervical vertebrae. [ 11 ]


Chondrocalcinosis can be visualized on  projectional radiography ,  CT scan ,  MRI ,  ultrasound , and  nuclear medicine . [ 1 ]  CT scans and MRIs show calcific masses (usually within the  ligamentum flavum  or joint capsule), however radiography is more successful. [ 1 ]  At ultrasound, chondrocalcinosis may be depicted as echogenic foci with no acoustic shadow within the hyaline cartilage. [ 12 ]  As with most conditions, chondrocalcinosis can present with similarity to other diseases such as  ankylosing spondylitis  and  gout . [ 1 ]


More research is needed on the role of genetics in the development of chondrocalcinosis and CPPD, but there is some evidence that  mutations of the ANKH gene may lead to chondrocalcinosis. [ 13 ]


The  cockade sign  is a radiological feature associated with  intraosseous lipoma , a rare benign tumor of the bone composed primarily of mature adipose tissue. [ 1 ] [ 2 ]  This sign describes the characteristic appearance of a central calcification or ossification surrounded by radiolucent fatty tissue on imaging, resembling a bullseye or  cockade . [ 3 ]


Intraosseous lipomas are thought to arise from the proliferation of adipose tissue within the medullary cavity of bone. Over time, ischemic changes within the lesion may lead to necrosis, calcification, or cystic transformation. These secondary changes are responsible for the imaging characteristics, including the cockade sign. The cockade sign develops due to central  calcification  or  ossification . The radiolucent fatty component forms the outer ring of the lesion. [ 4 ]


Codfish vertebra  refers to the biconcave appearance of the vertebra in sagittal radiographs due to pathological changes, such as demineralisation. [ 1 ] [ 2 ] [ 3 ]  Codfish appearance of the vertebra is seen in several conditions such as osteoporosis, steroid or heparin therapy,  Cushing syndrome , idiopathic,  sickle cell disease , leukemia,  Duchenne muscular dystrophy , and homo-cystinuria. [ 4 ]  Codfish vertebra sign is usually first seen in lumbar vertebrae. [ 5 ]


The  kidney bean sign  (more commonly called the  coffee bean sign;  also  bent inner tube sign ) is a  radiologic sign  observed on  abdominal radiographs  that indicates the presence of a  sigmoid volvulus , a form of bowel obstruction. It is seen as an area of hyperlucency resembling a coffee bean. [ 1 ]  The opposed walls of adjacent bowel loops form the central cleft while the two sides of the bean represent gas‐filled segments of dilated bowel that form an inverted U‐shape. [ 2 ]  Air-fluid levels may also be seen in the segments of dilated bowel. [ 1 ]


The  colon cut-off sign  is a radiographic finding seen on abdominal radiographs and computed tomography scans. It is characterized by a marked dilatation of the transverse colon, with an abrupt transition to collapsed distal colon, particularly the splenic flexure. [ 1 ]  This sign is indicative of underlying pathology, most commonly acute pancreatitis.


The colon cut-off sign is due to local inflammation or irritation. In acute pancreatitis, the inflammatory process involving the pancreas and surrounding tissues can extend to the adjacent transverse colon through the phrenicocolic ligament. [ 2 ]  This inflammation leads to spasm and localized ileus, causing a sharp demarcation between the dilated proximal bowel and the collapsed distal segment.


The colon cut-off sign is different from  sentinel loop  sign, where the dilated segment is a part of the small intestine.


The comb sign is a radiological sign seen on computed tomography or magnetic resonance imaging scans, primarily used to identify inflammation in the mesentery. [ 1 ]  It refers to the appearance of engorged mesenteric vessels resembling the teeth of a comb, which is a key feature seen in several abdominal conditions, particularly those associated with  inflammatory bowel diseases , such as  Crohn's disease . [ 2 ]  This sign was first described by Dr. Morton Mayers. [ 3 ]


The comb sign is characterized by the appearance of dilated, prominent vessels in the  mesentery  of the abdomen, which appears similar to the teeth of a comb. These engorged vessels result from inflammation and increased blood flow in the mesenteric vessels, which is a common response to acute or chronic inflammatory conditions in the gastrointestinal tract. [ 2 ]


This sign is most often seen in patients with Crohn's disease but can also be associated with other conditions that cause mesenteric inflammation. [ 4 ]


The mesentery may appear thickened, and the mesenteric vessels (which supply blood to the intestines) become dilated and appear to resemble a comb. This sign is best seen in the small intestine or colon and can be associated with peripheral fat stranding or mesenteric fat changes indicative of active inflammation. This sign is helpful in determining the acutiy of the inflammatory process. [ 3 ]


The  comet tail sign  is a radiological finding seen in chest CT. It refers to a specific appearance resembling a comet's tail, characterised by a bright, streaky opacity due to the presence of a round atelectasis in chest CT. [ 1 ]


In case of a round atelectatic mass, the nearby bronchovascular bundle appears to be pulled into the mass, resembling the tail of a comet. The comet tail usually extends from a central point in the lung periphery towards the hilum. If intravenous contrast is injected, homogenous enhancement is seen. [ 2 ]


The  continuous diaphragm sign  is a radiological finding seen on chest X-rays that indicates the presence of gas within the thoracic cavity, specifically in the mediastinum ( pneumomediastinum ), [ 1 ]  the peritoneal cavity ( pneumoperitoneum ) or pericardium ( pneumopericardium ). [ 2 ]  This sign is characterized by the uninterrupted visualization of the diaphragm's contour across the midline, underlining both the right and left hemidiaphragms, which is normally obscured by the overlying heart and mediastinum. [ 3 ]


The diaphragm typically appears as two separate, curved outlines (hemidiaphragms) on a chest X-ray due to the heart and mediastinum obscuring its central portion. When air accumulates in the mediastinum or peritoneal cavity, it outlines the diaphragm, making its central portion visible and creating the appearance of a continuous line. [ 4 ]  The continuous diaphragm sign is most commonly caused by the presence of free air in the mediastinum where air escapes from the lungs, airways, or other mediastinal structures. The causes for pneumomediastinum include trauma, alveolar rupture, asthma exacerbations, or esophageal perforation. The sign can also be seen in pneumoperitoneum, where free air enters the abdominal cavity due to gastrointestinal perforation or surgery. [ 1 ]


The  corduroy sign  is a radiological finding observed on spinal imaging in cases of  vertebral hemangiomas . It refers to a striated or vertically oriented linear pattern seen on imaging, resembling the appearance of corduroy fabric. [ 1 ]  This sign is most commonly identified on lateral radiographs or magnetic resonance imaging (MRI) of the spine and is an important diagnostic marker for benign conditions such as vertebral hemangiomas. Patients with the typical ‘corduroy appearance’ is extremely rare clinically. [ 2 ]


Vertebral hemangiomas are benign vascular tumors of the vertebral bodies. They arise due to a proliferation of thin-walled blood vessels within the bone and are often asymptomatic. The corduroy sign reflects the characteristic trabecular changes caused by the hemangioma, namely, thinning of trabeculae as well as thickened vertical struts, resulting from compensatory hypertrophy of the remaining trabeculae to maintain structural integrity. These vertical trabecular striations give rise to the " corduroy " appearance on imaging. [ 3 ]


On lateral radiographs and sagittal CT of the spine, the corduroy sign appears as vertical linear striations, which are alternating bands of radiolucency (representing vascular spaces) and radiodensity (representing thickened trabeculae) within the vertebral body. The vertebral body may retain its normal shape and size unless the lesion becomes aggressive. [ 4 ]


The  cottage loaf sign  is a radiological finding associated with  diaphragmatic rupture , often observed on imaging studies such as computed tomography (CT) or Magnetic Resonance Imaging (MRI). [ 1 ]  This sign refers to the appearance of herniated liver into the thoracic cavity, with a characteristic "stacked" or "two-tiered" morphology resembling a traditional British  cottage loaf —a smaller, rounded structure situated atop a larger one. It is a key indicator of diaphragmatic injury, typically resulting from blunt or penetrating trauma. [ 2 ]


Cœur en sabot  (French for "clog-shaped heart" or "boot-shaped heart" [ 1 ] ) is a  radiological sign  seen most commonly in patients with  tetralogy of Fallot , [ 2 ]  a cyanotic congenital heart disease. It is a radiological term to describe the following findings in the x-ray: [ citation needed ]


Echocardiography  has been used for confirmation and differentiation of congenital heart diseases. [ citation needed ]


Crazy paving  refers to a pattern seen on  computed tomography  of the chest, involving lobular  septal  thickening with variable  alveolar  filling. The finding is seen in  pulmonary alveolar proteinosis , [ 1 ]  and other diseases. [ 2 ]  Its name comes from its resemblance to irregular  paving stones , called  crazy pavings . [ 3 ]


There are variety of causes for crazy paving patterns: infection, cancer, blood related disorders, diseases caused by inhalation of particles, and  idiopathic disease . Specific lung disorders that can cause such patterns are:  pneumocystis pneumonia ,  mucinous bronchioloalveolar carcinoma , pulmonary alveolar proteinosis,  sarcoidosis , nonspecific interstitial pneumonia,  organizing pneumonia , exogenous lipoid pneumonia, adult respiratory distress syndrome, and pulmonary hemorrhage syndromes. [ 4 ]


The  cupola sign  is seen on a supine chest or abdominal radiograph in the presence of  pneumoperitoneum .


It refers to dependent air that rises within the  abdominal cavity  of the supine patient to accumulate underneath the central tendon of the  diaphragm  in the midline. It is seen as lucency overlying the lower thoracic vertebral bodies. The superior border is well defined, but the inferior margin is not.


"Cupola" is an architectural term, referring to a small dome (in particular, a small dome crowning a roof or a turret). The word derives from a Latin word for a "little cup".


Many conditions of or affecting the human integumentary system have associated features that may be found by performing an x-ray or CT scan of the affected person.


Dagger sign  is a radiologic sign seen in advanced cases of  ankylosing spondylitis . [ 1 ]  The appearance of a dagger is seen in the X-ray because of ossification of the supraspinous and infraspinous ligaments. [ 2 ]  As a result, a central dense line of sclerosis, resembling a dagger can be seen in the AP radiograph of spine and pelvis. [ 3 ]


In  radiology , the  deep sulcus sign  on a supine  chest radiograph  is an indirect indicator of a  pneumothorax . [ 1 ] [ 2 ]  In a  supine  film, it appears as a deep, lucent, ipsilateral costophrenic angle [ 3 ]  within the nondependent portions of the pleural space as opposed to the  apex  (of the  lung ) when the patient is upright.  The  costophrenic angle  is abnormally deepened when the pleural air collects laterally, producing the deep sulcus sign. [ 4 ]


Patients with  chronic obstructive pulmonary disease  (COPD) may exhibit deepened lateral costophrenic angles due to hyperinflation of the lungs and cause a false deep sulcus sign. [ 4 ]


In  medicine , the  dense artery sign  or  hyperdense artery sign  is an increased  radiodensity  of an artery as seen on  computer tomography  (CT) scans, and is a  radiologic sign  of early  ischemic stroke . [ 1 ]  In earlier studies of  medical imaging  in patients with strokes, it was the earliest sign of ischemic stroke in a significant minority of cases. [ 2 ]  Its appearance portends a poor prognosis for the patient. [ 3 ] [ 4 ]


The sign has been observed in the  middle cerebral artery  (MCA), [ 4 ]   posterior cerebral artery  (PCA), [ 5 ]   vertebral artery , [ 2 ]  and  basilar artery ; [ 6 ]  these have been called the  dense MCA sign ,  dense PCA sign ,  dense vertebral artery sign , and  dense basilar artery sign , respectively.


Rarely, a  hypodense artery sign  can occur due to fat embolism. [ 7 ]


Through  cerebral angiography , the sign has been demonstrated to correspond to  embolic  or  atherosclerotic  occlusion of an artery. [ 1 ]  Specifically, the hyperdensity is thought to be due to  calcification  or  hemorrhage  associated with an  atherosclerotic plaque . [ 1 ]


Identification of the dense artery sign is often based on subjective interpretation and  false positives  may occur. One study aiming to define criteria for the sign determined that measuring  Hounsfield units  on the CT scan could differentiate between the dense MCA sign associated with  ischemic stroke  and that caused by false positives. [ 8 ]  Specifically, the combination of greater than 43 Hounsfield units and an MCA density ratio of greater than 1.2 was diagnostic of a dense MCA sign associated with acute ischemic stroke. [ 8 ]


The  dense MCA sign  is a  dense artery sign  observed on non-contrast computed tomography (CT) of the brain and is an important early marker of acute ischemic stroke involving the  middle cerebral artery  territory. [ 1 ]  It refers to an abnormally increased attenuation (hyperdensity) of the MCA, reflecting an intraluminal thrombus or embolus. This sign is also referred to as the  hyperdense MCA sign .


The dense MCA sign is caused by a fresh thrombus or embolus occluding the lumen of the middle cerebral artery. A thrombus with a high concentration of red blood cells and fibrin has increased density relative to normal flowing blood, leading to its hyperattenuating appearance on a non-contrast CT scan.


The sign typically appears within the first few hours of arterial occlusion, often before visible ischemic changes develop in brain parenchyma. Early recognition of this sign is critical as it allows prompt diagnosis and initiation of treatment to restore perfusion and minimize brain damage.


Dense MCA sign stands for a hyperdense linear structure located along the course of the middle cerebral artery (MCA), typically in the Sylvian fissure in CT images. The sign may be seen unilaterally (on the affected side) compared to the contralateral MCA, which appears of normal attenuation. The sign is most commonly observed in the M1 segment of the MCA and less commonly in distal branches (M2/M3 segments), where it is termed the hyperdense MCA dot sign. [ 2 ]  The comparison of thrombus with the unaffected side improves diagnostic accuracy. [ 3 ]


The dense MCA sign is an early indicator of acute ischemic stroke caused by MCA occlusion. Its detection has important clinical implications:


The dense MCA sign may be the first and only sign of MCA occlusion within the first 1–2 hours of symptom onset, even before parenchymal hypodensity develops. Early recognition enables rapid initiation of treatment, such as intravenous thrombolysis (e.g., tissue plasminogen activator, tPA) or endovascular thrombectomy. [ 4 ]


Presence of the dense MCA sign suggests a large clot burden and is associated with more extensive infarction and worse functional outcomes if reperfusion is not achieved.Prompt recognition of the sign improves the chances of favorable recovery by allowing faster intervention.


Several conditions may mimic the dense MCA sign, leading to false positives. These include:


The dense MCA sign may not always be present, even in cases of acute MCA occlusion. However, the sign has good sensitivity, and high specificity. [ 6 ]  Thin-section CT and appropriate windowing (narrow window settings) improve detection.


The dense MCA sign is often accompanied by other early ischemic changes on CT, including:


The  double bronchial wall sign  is a radiological finding observed in cases of  pneumomediastinum , a condition characterized by the presence of air within the mediastinum. [ 1 ] [ 2 ]


Pneumomediastinum occurs due to the escape of air from ruptured alveoli or airways into the mediastinal space. The rupture of alveoli due to increased intrathoracic pressure (e.g., from coughing, vomiting, or trauma) leads to air tracking along the peribronchovascular interstitium which in turn accumulates in the mediastinum. As air accumulates, it dissects along the bronchial structures, creating a visible separation of the bronchial wall from the surrounding tissue. The result is the double bronchial wall appearance on imaging, a hallmark of pneumomediastinum. [ 3 ]


The double bronchial wall sign is best visualized on CT, which provides high-resolution images of the mediastinal structures. The double bronchial wall sign is commonly seen in the central bronchi, particularly in the trachea or mainstem bronchi, where air is more likely to outline the structures. Associated findings such as air surrounding other mediastinal structures, such as the esophagus or great vessels may be present. Subcutaneous emphysema or air tracking into the neck may also be seen. This sign may also be diagnosed in X-ray images, although the sensitivity is much lower than that of CT. [ 4 ]


In  radiology , the  double bubble  sign is a feature of pediatric imaging seen on  radiographs  or  prenatal   ultrasound  in which two air filled bubbles are seen in the abdomen, representing two discontiguous loops of bowel in a proximal, or 'high,' small bowel obstruction. The finding is typically pathologic, and implies either  duodenal atresia ,  duodenal web ,  annular pancreas , or on occasion  midgut volvulus , a distinction that requires close clinical correlation and, in most cases, surgical intervention. [ 1 ] [ 2 ] [ 3 ]


Distal gas is more often seen with midgut volvulus, duodenal stenosis and duodenal web, though this not always present. In such cases, distinguishing the diagnoses depends on clinical presentation. [ 4 ]


A  fluoroscopic  study known as an  upper gastrointestinal series  is often the next step in management in patients that are not critically ill, though if volvulus is suspected, emergent surgical intervention is mandated. If clinical findings are equivocal, caution with non water-soluble contrast is needed, as the usage of  barium  can impede surgical revision and lead to increased post operative complications. Non ionic water-soluble contrast should be used, as the hyperosmolar agents, if aspirated, can result in life-threatening  pulmonary edema . When reflective of duodenal atresia, associations with  Down syndrome  and  VACTERL sequence  abnormalities are often seen. [ 5 ]


Certain rare anatomic anomalies, such as congenital duodenal duplication [ 6 ]  and  pyloric atresia [ 7 ]  can cause  false positives  for the sign on radiographs. Congenital pyloric atresia usually causes a single bubble on radiographs without distal gas, though an intermittent double bubble sign is occasionally seen. [ 8 ]  Duodenal atresia, while typically without distal gas, has been reported with an absent double bubble, though this variant is quite rare. [ 9 ]  On neonatal ultrasound, a double bubble can also be caused by a  choledochal  cyst,  omental  cyst, or  enteric duplication cyst .


The  double duct sign  is a radiological finding characterized by the simultaneous dilation of the  common bile duct  and the  main pancreatic duct . This sign is significant because it often indicates an obstruction in the distal bile duct and pancreatic duct, frequently caused by serious underlying pathologies such as  pancreatic carcinoma  or  periampullary tumors . [ 1 ]  The double duct sign is most commonly visualized on imaging modalities such as computed tomography, magnetic resonance imaging, or  endoscopic retrograde cholangiopancreatography .


The double duct sign results from the anatomical convergence of the biliary and pancreatic ducts at the  ampulla of Vater , where obstructions can disrupt the drainage of both systems simultaneously. Common causes of such obstructions include  pancreatic adenocarcinoma ,  periampullary cancer ,  cholangiocarcinoma ,  chronic pancreatitis , gallstone-related obstruction and strictures. [ 1 ] [ 2 ]


The double duct sign is a red flag finding in radiology, with malignancies accounting for the majority of cases. Early identification is crucial for diagnosis, staging in case of malignancy, management and for performing therapeutic interventions.


The  double posterior cruciate ligament sign  (double PCL sign) is a radiological finding seen on magnetic resonance imaging of the knee, specifically in the context of a  bucket-handle tear  of the medial meniscus. It refers to the appearance of a duplicated posterior cruciate ligament, where the displaced fragment of the torn medial meniscus lies parallel and inferior to the PCL, mimicking a second ligament. [ 1 ]  The double PCL sign has high specificity for meniscal tears when noted on MRI. [ 2 ] [ 3 ]


A bucket-handle tear is a specific type of longitudinal meniscal tear in which a fragment of the torn meniscus displaces toward the intercondylar notch of the knee. The displaced fragment often remains attached at its anterior and posterior horns but flips centrally into the notch. [ 4 ]  This displacement causes the torn meniscal fragment to align closely and parallel to the PCL, resulting in the appearance of a "double PCL" on sagittal MRI sequences.


The double PCL sign is best observed on sagittal T2-weighted or proton density-weighted MRI images. [ 5 ]  Key features include: [ 6 ]


The  dripping candle wax sign  is a  radiologic sign  seen on  X-rays  of bone that indicates  melorheostosis (or Leri disease) , a rare benign bone disease characterized by bone  hypertrophy ,  dysplasia , and  sclerosis . [ 1 ]  The sclerosis typically affects one side of the  cortex  of the involved bone, appearing similar to wax melting down one side of a candle. [ 1 ]  Melorheostosis most commonly affects the  long bones  of the upper and lower extremities, but can also be seen in the hands and feet. [ 2 ]  It is usually an  incidental finding  and most patients are asymptomatic. [ 2 ]


The  drooping lily sign  is a radiological finding observed on imaging studies of the kidneys, most commonly associated with duplex collecting system and obstruction of the upper moiety. [ 1 ]  This sign is characterized by the appearance of a compressed, non-obstructed lower renal moiety, which takes on a "drooping" or displaced appearance due to the distension of the obstructed upper moiety. [ 2 ] [ 3 ]


The drooping lily sign is typically seen in the context of a duplex collecting system, a congenital anomaly in which the kidney has two separate ureters draining from two distinct renal segments (upper and lower poles). When the ureter draining the upper moiety becomes obstructed, often by a  ureterocele  (a cystic dilation of the distal ureter within the bladder), the upper moiety becomes dilated while the lower moiety remains functional and compressed.


The "drooping" appearance arises due to the enlarged upper moiety compressing and displacing the lower moiety downward and laterally. The non-obstructed lower moiety maintains normal function but appears smaller and distorted on imaging. [ 1 ]


The  dural tail sign  (also known as " dural thickening ", " flare sign ", or " meningeal sign ") is a radiological finding observed in  magnetic resonance imaging  (MRI) studies of the brain that refers to a thickening of the  dura mater  immediately adjacent to a mass lesion, such as a  brain tumor . [ 1 ]  Initially, the dural tail sign was thought to be  pathognomonic  of  meningioma , a slow-growing tumor that arises from the meninges. [ 1 ]  However, subsequent studies have shown that it can also be observed in various intra- and extra-cranial pathologies and in spinal lesions. [ 1 ]  It is not a completely  sensitive  finding, as it is seen in only 60-72% of cases. [ 2 ]  It is not completely specific either, as it has been described associated with lesions like  neuromas ,  chloromas ,  pituitary diseases ,  granulomatous disorders , cerebral  Erdheim-Chester disease ,  lymphomas ,  metastasis ,  hemangiopericytomas ,  schwannomas , and  gliomas  such as  glioblastoma multiforme  (GBM). [ 2 ] [ 3 ]  The final diagnosis should be further established through  cerebrospinal fluid analysis  or  histopathological examination  following a  biopsy . [ 3 ]


The dural tail sign was first described in 1989 by Wilms  et al. . [ 1 ] [ 4 ]  Histopathological correlation from different studies has at times revealed tumor infiltration into the dura mater, however, in most instances, it signifies a  hypervascular , non- neoplastic  response. [ 3 ]


One study showed that including the dural tail in the  stereotactic radiosurgery  (SRS) or fractionated stereotactic radiotherapy (FSRT) volumes for meningioma treatment did not seem to impact recurrence. [ 5 ]


The  empty sella sign  is a radiological finding characterized by the partial or complete filling of the  sella turcica  with  cerebrospinal fluid  (CSF), causing the  pituitary gland  to appear flattened or compressed against the walls of the sella. [ 1 ]  This results in the sella appearing "empty" on imaging, despite the presence of a compressed pituitary gland. The empty sella sign is typically identified on magnetic resonance imaging (MRI) or computed tomography (CT) and can be associated with various clinical conditions or incidental findings. [ 2 ]


The empty sella sign occurs due to herniation of the subarachnoid space into the sella turcica, displacing the pituitary gland and allowing CSF to occupy the space. [ 3 ]  This phenomenon is often linked to the following mechanisms: [ 4 ]


In both primary and secondary cases, the pituitary gland is often compressed but retains some degree of function.


MRI is the gold standard for diagnosing the empty sella sign. Key features include: [ 5 ]


On CT, the empty sella sign may appear as hypodensity in the sella, corresponding to CSF. There may be possible sellar floor thinning or remodeling due to chronic pressure changes.


Empty vertebral body sign  is a radiological sign used for diagnosing any injury with flexion-distraction mechanism of the vertebrae, particularly  Chance fracture  of the vertebrae. [ 1 ] [ 2 ]  In Chance fracture, there is disruption and angulation superiorly or inferiorly of posterior elements of the vertebrae. As a result, the affected vertebral body is seen as radiolucent in the anterio-posterior view. [ 3 ]


Endoexoenteric  refers to a specific  radiographic  manifestation of lymphoma of the bowel.


Lymphomas  are malignant neoplasms (cancers) arising from  lymphocytes  of the immune system. When they arise in the bowel tissue, they are referred to as primary. In other instances, the tumor can arise from the lymph nodes and "travel" to the bowel, so-called "extra-nodal" disease. [ citation needed ]


Marshak [ 1 ]  was the first to introduce the term "endoexoenteric" to refer to a specific radiographic pattern (seen on  x-rays ,  CT scans  or  PET scans ) of lymphomatous involvement of the bowel. This terminology derives from the fact that in this form of lymphomatous invasion of the bowel, the tumor extends throughout the entire width of the bowel wall, from the  luminal   or  mucosal  (endo) surface to the  serosal  (exo) surface. Enteric refers to the bowel itself. In Marshak's later textbook, published in 1980, [ 2 ]  he abandons this terminology.


Of the five patterns of bowel lymphoma described in Marshak's original work, endoexoenteric is the second most common type (the others being: infiltrative [most common], multiple nodules, polypoidal mass, and mesenteric.) [ 3 ] [ 4 ]


Specifically, the features of endoexoenteric lymphoma are an irregular collection of barium due to central ulceration, and displacement of adjacent bowel loops. In this form of lymphoma,  fistula  formation (an abnormal communication between the tumor and adjacent bowel loops) is common. Since the bowel is not sterile, infection can easily be introduced, leading to findings of  mesenteric  abscesses. [ 5 ] [ 6 ]


Imaging techniques, while very helpful in suggesting the presence of specific disease, cannot diagnose this (or any other  neoplastic  disease) with certainty. Definitive diagnosis is almost always achieved by  biopsy , followed by  microscopic ,  histologic  and  immunologic  examination of the tissues obtained. [ citation needed ]


Recognition of this type of lymphoma presentation is important, in that it may predict the future course and potential complications of this disease, thereby alerting clinicians to undertake surveillance and appropriate interventions. [ citation needed ]


The  eye of the tiger  sign is a  radiologic sign  observed on  T2-weighted   magnetic resonance  (MR) images of the brain. It appears as a central area of  hyperintense  signal surrounded by a ring of hypointensity in the anteromedial part of the  globus pallidus . [ 1 ]  The  eye of the tiger  sign is recognized as a diagnostic feature of  pantothenate kinase associated neurodegeneration , previously known as Hallervorden-Spatz syndrome. [ 2 ]  This is a neurodegenerative disorder associated with excess iron accumulation in the brain. The hypointense area is thought to be caused by the excess iron while the central hyperintensity is possibly a result of gliosis. [ 2 ]


The  fabella sign  is displacement of the  fabella  that is seen in cases of synovial  effusion  and  popliteal fossa  masses. [ 1 ]


The  fabella  is an accessory ossicle located inside the  gastrocnemius  lateral head  tendon  on the posterior side of the knee, in about 25% of people.  It can thus serve as a surrogate radio-opaque marker of the posterior border of the knee's  synovium .  On a lateral  radiograph  of the knee, an increase in the distance from the fabella to the  femur  or to the  tibia  can be suggestive of fluid or of a mass within the synovial fossa.  This is of particular use in radiographic detection of knee effusions, as the cause for the effusion may obscure the subcutaneous planes on x-ray that can also be used to determine presence of effusion or effusion size. [ 2 ]


The  falciform ligament sign  is a  radiological sign  observed on abdominal imaging in cases of  pneumoperitoneum , where free intraperitoneal air outlines the  falciform ligament . [ 1 ]  This sign is considered a diagnostic indicator of free air within the abdominal cavity and is most commonly identified on computed tomography (CT) scans and less frequently in abdominal radiographs. [ 2 ] [ 3 ] [ 4 ]


The falciform ligament is a double-layered fold of peritoneum that connects the anterior abdominal wall to the anterosuperior surface of the liver. It contains the  ligamentum teres  (a remnant of the umbilical vein) in its free edge and lies within the midline, extending from the umbilicus to the inferior surface of the diaphragm. [ 5 ] [ 6 ]  Under normal conditions, the falciform ligament is not visible on CT imaging unless surrounded by free air or fluid.


On CT, falciform ligament is seen as a linear high-attenuation structure outlined by low-attenuation free air. There may be associated findings such as the site for perforation or underlying pathology. [ 2 ]


The  fishhook ureter sign , also known as the "hockey stick" or "J-shaped"  ureter  sign, is a  radiologic sign  that has been used to describe the presence of a  retrocaval ureter , which is an anatomical anomaly where the ureter abnormally runs posterior to the  IVC . This abnormality often results in hydroureter or  hydronephrosis . [ 1 ]


The  fishook ureter sign  also describes the appearance of the ureter in patients with bladder outlet obstruction due to  benign prostatic hyperplasia  (BPH). [ 2 ]


This  biology  article is a  stub . You can help Wikipedia by  expanding it .


Fleischner sign  is a radiological sign that aids the diagnosis of pulmonary embolism. [ 1 ]  The sign indicates the dilatation of the proximal pulmonary arteries due to pulmonary embolism. [ 2 ]  It was named after  Felix Fleischner , who first described it. [ 3 ]  The Fleishner sign is seen both on X-ray and CT scan of chest/thorax.


Fogging phenomenon  in  computerized tomography (CT) scanning  of the  head  is vanishing signs of an  infarct  on the serial  CT  imaging in a patient with a recent  stroke . [ 1 ]  It is a reversal of the  hypodensity  on the CT after an acute  ischemic stroke . This happens as a result of re-nourishment of the infarcted area in subacute phase about one to three weeks after the stroke. [ 2 ]  In fact, resolution of the edema, which was caused by the accident, leads to increased  attenuation  of infarcted area that may regain near-normal density and mask the stroke. However, in the third week,  parenchymal  volume loss commonly appears as a hypoattenuation (decreased attenuation) with a  negative mass effect  (shrinkage). [ 3 ]


In  radiology , the  Golden S sign , also known as the  S sign of Golden , is a  radiologic sign  seen on  chest X-ray  that suggests a central  lung  mass or a  lung collapse . [ 1 ]  It was first described by, and subsequently named after, Dr Ross Golden (1889–1975) in 1925 in association with  bronchial carcinoma , [ 2 ]  but it is also seen in  metastatic cancer ,  enlarged lymph nodes , and collapse of the right upper lobe of the lung. [ 1 ]


The Golden S sign can be seen on  plain radiographs  as well as on  computed tomography  (CT) scans of the chest. [ 1 ] [ 3 ]  The sign is seen in the right lung as a distorted  minor fissure , whose lateral aspect is concave inferiorly and whose medial aspect is convex inferiorly. [ 1 ]  This produces a "reverse S" appearance, responsible for the sign being occasionally called the  reverse S sign of Golden . [ 1 ]


Ground-glass  opacity  ( GGO ) is a finding seen on  chest x-ray  (radiograph) or  computed tomography (CT)  imaging of the  lungs . It is typically defined as an area of hazy opacification (x-ray) or increased attenuation (CT) due to air displacement by fluid, airway collapse,  fibrosis , or a  neoplastic process . [ 1 ]  When a substance other than air fills an area of the lung it increases that area's density. On both x-ray and CT, this appears more grey or hazy as opposed to the normally dark-appearing lungs. Although it can sometimes be seen in normal lungs, common pathologic causes include  infections ,  interstitial lung disease , and  pulmonary edema . [ 2 ] [ 3 ]


In both CT and chest radiographs, normal lungs appear dark due to the relative lower  density  of air compared to the surrounding tissues. When air is replaced by another substance (e.g. fluid or fibrosis), the density of the area increases, causing the  tissue  to appear lighter or more grey. [ 4 ]


Ground-glass opacity is most often used to describe findings in  high-resolution CT  imaging of the  thorax , although it is also used when describing chest radiographs. In CT, the term refers to one or multiple areas of increased  attenuation  (density)  without  concealment of the  pulmonary vasculature . This appears more grey, as opposed to the normally dark-appearing (air-filled) lung on CT imaging. In chest radiographs, the term refers to one or multiple areas in which the normally darker-appearing (air-filled) lung appears more opaque, hazy, or cloudy. Ground-glass opacity is in contrast to  consolidation , in which the pulmonary vascular markings are obscured. [ 3 ] [ 5 ]  GGO can be used to describe both focal and diffuse areas of increased density. [ 5 ]  Subtypes of GGOs include diffuse, nodular, centrilobular, mosaic, crazy paving, halo sign, and reversed halo sign. [ 6 ]


The differential diagnosis for ground-glass opacities is broad. General etiologies include infections, interstitial lung diseases, pulmonary edema,  pulmonary hemorrhage , and neoplasm. A correlation of imaging with a patient's clinical features is useful in narrowing the diagnosis. [ 6 ] [ 7 ]  GGOs can be seen in normal lungs. Upon expiration there is less air in the lungs, leading to a relative increase in density of the tissue, and thus increased attenuation on CT. Furthermore, when a patient lays supine for a CT scan, the posterior lungs are in a dependent position, causing partial collapse of the posterior  alveoli . This leads to an increase in density of the tissue, resulting increased attenuation and a possible ground-glass appearance on CT. [ 3 ]


In the setting of  pneumonia , the presence of GGO (as opposed to consolidation) is a useful diagnostic clue. Most bacterial infections lead to lobar consolidation, while  atypical pneumonias  may cause GGOs. It is important to note that while many of the pulmonary infections listed below may lead to GGOs, this does not occur in every case. [ 2 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]


There are seven general patterns of ground-glass opacities. [ 6 ]  When combined with a patient's clinical signs and symptoms, the GGO pattern seen on imaging is useful in narrowing the differential diagnosis. It is important to note that while some disease processes present as only one pattern, many can present with a mixture of GGO patterns. [ 6 ]


The diffuse pattern typically refers to GGOs in multiple lobes of one or both lungs. Broadly, a diffuse pattern of GGO can be caused by displacement of air with fluid, inflammatory debris, or fibrosis.  Cardiogenic pulmonary edema  and ARDS are common causes of a fluid-filled lung.  Diffuse alveolar hemorrhage  is a rarer cause of diffuse GGO seen in some types of vasculitis, autoimmune conditions, and bleeding disorders. [ 6 ]


Inflammation  and fibrosis can also cause diffuse GGOs.  Pneumocystis  pneumonia, an infection typically seen in  immunocompromised  (e.g. patients with  AIDS ) or  immunosuppressed  individuals, is a classic cause of diffuse GGOs. Many viral pneumonias and idiopathic interstitial pneumonias can also lead to a diffuse GGO pattern. Radiation pneumonitis, a side effect of pulmonary radiation therapy, can lead to pulmonary fibrosis and diffuse GGOs. [ 6 ]


There are numerous potential causes of nodular GGOs which can be broadly separated into benign and malignant conditions. Benign conditions potentially leading to the formation of nodular GGOs include aspergillosis, acute eosinophilic pneumonia, focal interstitial fibrosis, granulomatosis with polyangiitis,  IgA vasculitis , organizing pneumonia, pulmonary contusion, pulmonary cryptococcus, and thoracic endometriosis. Focal interstitial fibrosis presents a unique challenge when differentiating from malignant nodular GGOs on CT imaging. It is typically persistent over long-term imaging follow-up and shares a similar appearance to malignant nodular GGOs. [ 9 ]


Pre-malignant or malignant causes of nodular GGOs include adenocarcinoma, adenocarcinoma in situ, and atypical adenomatous hyperplasia (AAH). One large review study found that 80% of nodular GGOs which were present on repeated CT imaging represented either pre-malignant or malignant growths. Differentiating between pre-malignancy and malignancy on the basis of CT alone can pose a challenge to radiologists; however, there are several features that are indicative of pre-malignant nodules. AAH is a pre-malignant cause of nodular GGO and is more commonly associated with lower attenuation on CT and smaller nodule size (<10 mm) compared to adenocarcinoma. [ 10 ]  In addition, AAH often lacks the solid features and spiculated appearance that are often associated with malignant growths. [ 9 ]  In contrast, as adenocarcinoma becomes invasive it will more often cause retraction of adjacent pleura and may show an increase in vascular markings. Nodules >15 mm almost always represent an invasive adenocarcinoma. [ 9 ] [ 10 ]


Centrilobular GGOs refer to opacities occurring within one or multiple secondary lobules of the lung, which consist of a respiratory bronchiole, small pulmonary artery, and the surrounding tissue. [ 3 ]  A defining feature of these GGOs is the lack of involvement of the interlobular septum. Potential causes of centrilobular GGOs include pulmonary calcifications from  metastatic disease , some types of idiopathic interstitial pneumonias, hypersensitivity pneumonitis, aspiration pneumonitis, cholesterol granulomas, and  pulmonary capillary hemangiomastosis . [ 6 ]


A  mosaic  pattern of GGO refers to multiple irregular areas of both increased attenuation and decreased attenuation on CT. It is often the result of occlusion of small pulmonary arteries or obstruction of small airways leading to air trapping. [ 6 ]  Sarcoidosis is an additional cause of a mosaic GGOs due to the formation of granulomas in interstitial areas. This may coexist with granulomatosis with polyangiitis, leading to diffuse areas of increased attenuation with ground-glass appearance. [ 6 ]


The crazy paving pattern may occur when there is both interlobular and intralobular widening. This sometimes resembles a road paved with irregular bricks or tiles. It is typically diffuse, involving larger areas of one or multiple lobes. There are a variety of potential causes, including Pneumocystis pneumonia, late-stage adenocarcinoma, pulmonary edema, some types of idiopathic interstitial pneumonias, diffuse alveolar hemorrhage, sarcoidosis, and pulmonary alveolar proteinosis. [ 6 ]  COVID-19 has also been shown to occasionally cause GGOs with a crazy paving pattern. [ 11 ]


A halo sign refers to a GGO that fills the area around a consolidation or nodule. This is a most commonly seen in various types of pulmonary infections, including CMV pneumonia, tuberculosis, nocardia infection, some fungal pneumonias, and septic emboli. Schistosomiasis, a  parasitic  infection, also commonly presents with the halo sign. Important non-infectious causes include granulomatosis with polyangiitis, metastatic disease with pulmonary hemorrhage, and some types of idiopathic interstitial pneumonias. [ 6 ]


A reversed halo sign is a central ground-glass opacity surrounded by denser  consolidation . According to published criteria, the consolidation should form more than three-fourths of a circle and be at least 2 mm thick. [ 12 ]  It is often suggestive of  organizing pneumonia , [ 13 ]  but is only seen in about 20% of individuals with this condition. [ 12 ]  It can also be present in  lung infarction  where the halo consists of hemorrhage, [ 14 ]  as well as in infectious diseases such as  paracoccidioidomycosis ,  tuberculosis , and  aspergillosis , as well as in  granulomatosis with polyangiitis ,  lymphomatoid granulomatosis , and  sarcoidosis . [ 15 ]


Ground-glass opacity is among the most common imaging findings in patients with confirmed  COVID-19 . [ 16 ] [ 17 ]  One systematic review found that among patients with COVID-19 and abnormal lung findings on CT, greater than 80% had GGOs, with greater than 50% having mixed GGOs and consolidation. [ 16 ]  GGOs with mixed consolidation has most often been found in elderly populations. [ 18 ]
Several studies have described a pattern among initial, intermediate, and hospital discharge imaging findings in the disease course of COVID-19. Most commonly, initial CT imaging reveals bilateral GGOs at the periphery of the lungs. During initial stages, this is most often found in the lower lobes, although involvement of the upper lobes and right middle lobe has also been reported early in the disease course. [ 16 ] [ 18 ]  This is in contrast to the two similar coronaviruses,  SARS  and  MERS , which more commonly involve only one lung on initial imaging. [ 19 ] [ 20 ]  As the COVID-19 infection progresses, GGOs typically become more diffuse and often progress to consolidation. [ 11 ] [ 18 ]  This is sometimes accompanied by the development of a crazy paving pattern and interlobular septal thickening. [ 18 ]  In many cases the most severe pulmonary CT abnormalities occurred within 2 weeks after symptoms began. [ 17 ]  At this point, many individuals begin showing resolution of consolidation and GGOs as symptoms improve. However, some patients have worsening symptoms and imaging findings, with further increase in septal thickening, GGOs, and consolidation. These patients may develop lung "white-out" with progression to  acute respiratory distress syndrome (ARDS)  requiring treatment escalation. [ 17 ] [ 21 ]


Preliminary reports have shown many patients have residual GGOs at time of discharge from the hospital. Due to the novelty of COVID-19, large studies investigating the long-term pulmonary CT changes have yet to be completed. However, long-term pulmonary changes have been seen in patients after recovery from SARS and MERS, suggesting the possibility of similar long-term complications in patients who have recovered from acute COVID-19 infection. [ 22 ]


The first usage of "ground-glass opacity" by a major radiological society occurred in a 1984 publication of the  American Journal of Roentgenology.  It was published as part of a glossary of recommended nomenclature from the  Fleischner Society , a group of thoracic imaging radiologists. [ 23 ]  The original published definition read as: "Any extended, finely granular pattern of pulmonary opacity within which normal anatomic details are partly obscured; from a fancied resemblance to etched or abraded glass." [ 23 ]  It was again included in an updated glossary by the Fleischner Society in 2008 with a more detailed definition. [ 24 ]


In  radiology , the  halo sign  is a finding of a dark halo around the arterial lumen on  ultrasound  that suggests the diagnosis of  temporal arteritis . [ 1 ]   The standard diagnostic test for temporal arteritis is  biopsy ; however,  ultrasound  and  MRI  show promise for replacing it. [ 2 ]


The halo sign of temporal arteritis should not be confused with  Deuel's halo sign , which is a sign of  fetal  death. [ 3 ]


The halo sign is also understood as a region of ground-glass attenuation surrounding a pulmonary nodule on an  X-ray computed tomography  (CT scan) of the chest. It can be associated with  hemorrhagic   nodules ,  tumors , or  inflammatory  processes, but is most commonly known as an early  radiographic  sign of invasive  pulmonary  infection by the fungus species  Aspergillus .


In  nursing , the halo sign is the result of a test to see if drainage from a head injury contains  cerebrospinal fluid . When a Dextrostix or Tes-Tape test gives a positive reading for glucose, the drainage must be further tested because glucose is also found in the blood. To perform the test, the leaking fluid is dripped onto a 4x4 gauze or towel. Positive results are indicated by blood coalescing into the center, leaving an outer ring of  cerebrospinal fluid .