awinml/medqa-textbooks-chunked · Datasets at Hugging Face

id stringlengths 14 28	file_name stringclasses 18 values	content stringlengths 1 722k
Anatomy_Gray_900	Anatomy_Gray.txt	It was deduced that the blood pressure measurements were obtained in different arms, and both were reassessed.
Anatomy_Gray_901	Anatomy_Gray.txt	The blood pressure measurements were true. In the right arm the blood pressure measured 120/80 mm Hg and in the left arm the blood pressure measured 80/40 mm Hg. This would imply a deficiency of blood to the left arm.
Anatomy_Gray_902	Anatomy_Gray.txt	The patient was transferred from the emergency department to the CT scanner, and a scan was performed that included the chest, abdomen, and pelvis.
Anatomy_Gray_903	Anatomy_Gray.txt	The CT scan demonstrated a dissecting thoracic aortic aneurysm. Aortic dissection occurs when the tunica intima and part of the tunica media of the wall of the aorta become separated from the remainder of the tunica media and the tunica adventitia of the aorta wall. This produces a false lumen. Blood passes not only in the true aortic lumen but also through a small hole into the wall of the aorta and into the false lumen. It often reenters the true aortic lumen inferiorly. This produces two channels through which blood may flow. The process of the aortic dissection produces considerable pain for the patient and is usually of rapid onset. Typically the pain is felt between the shoulder blades and radiating into the back, and although the pain is not from the back musculature or the vertebral column, careful consideration of structures other than the back should always be sought.
Anatomy_Gray_904	Anatomy_Gray.txt	The difference in the blood pressure between the two arms indicates the level at which the dissection has begun. The “point of entry” is proximal to the left subclavian artery. At this level a small flap has been created, which limits the blood flow to the left upper limb, giving the low blood pressure recording. The brachiocephalic trunk has not been affected by the aortic dissection, and hence blood flow remains appropriate to the right upper limb.
Anatomy_Gray_905	Anatomy_Gray.txt	The paraplegia was caused by ischemia to the spinal cord.
Anatomy_Gray_906	Anatomy_Gray.txt	The blood supply to the spinal cord is from a single anterior spinal artery and two posterior spinal arteries. These arteries are fed via segmental spinal arteries at every vertebral level. There are a number of reinforcing arteries (segmental medullary arteries) along the length of the spinal cord—the largest of which is the artery of Adamkiewicz. This artery of Adamkiewicz, a segmental medullary artery, typically arises from the lower thoracic or upper lumbar region, and unfortunately during this patient’s aortic dissection, the origin of this vessel was disrupted. This produces acute spinal cord ischemia and has produced the paraplegia in the patient.
Anatomy_Gray_907	Anatomy_Gray.txt	Unfortunately, the dissection extended, the aorta ruptured, and the patient succumbed.
Anatomy_Gray_908	Anatomy_Gray.txt	A 55-year-old woman came to her physician with sensory alteration in the right gluteal (buttock) region and in the intergluteal (natal) cleft. Examination also demonstrated low-grade weakness of the muscles of the foot and subtle weakness of the extensor hallucis longus, extensor digitorum longus, and fibularis tertius on the right. The patient also complained of some mild pain symptoms posteriorly in the right gluteal region.
Anatomy_Gray_909	Anatomy_Gray.txt	A lesion was postulated in the left sacrum.
Anatomy_Gray_910	Anatomy_Gray.txt	Pain in the right sacro-iliac region could easily be attributed to the sacro-iliac joint, which is often very sensitive to pain. The weakness of the intrinsic muscles of the foot and the extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles raises the possibility of an abnormality affecting the nerves exiting the sacrum and possibly the lumbosacral junction. The altered sensation around the gluteal region toward the anus would also support these anatomical localizing features.
Anatomy_Gray_911	Anatomy_Gray.txt	An X-ray was obtained of the pelvis.
Anatomy_Gray_912	Anatomy_Gray.txt	The X-ray appeared on first inspection unremarkable. However, the patient underwent further investigation, including CT and MRI, which demonstrated a large destructive lesion involving the whole of the left sacrum extending into the anterior sacral foramina at the S1, S2, and S3 levels. Interestingly, plain radiographs of the sacrum may often appear normal on first inspection, and further imaging should always be sought in patients with a suspected sacral abnormality.
Anatomy_Gray_913	Anatomy_Gray.txt	The lesion was expansile and lytic.
Anatomy_Gray_914	Anatomy_Gray.txt	Most bony metastases are typically nonexpansile. They may well erode the bone, producing lytic type of lesions, or may become very sclerotic (prostate metastases and breast metastases). From time to time we see a mixed pattern of lytic and sclerotic.
Anatomy_Gray_915	Anatomy_Gray.txt	There are a number of uncommon instances in which certain metastases are expansile and lytic. These typically occur in renal metastases and may be seen in multiple myeloma. The anatomical importance of these specific tumors is that they often expand and impinge upon other structures. The expansile nature of this patient’s tumor within the sacrum was the cause for compression of the sacral nerve roots, producing her symptoms.
Anatomy_Gray_916	Anatomy_Gray.txt	The patient underwent a course of radiotherapy, had the renal tumor excised, and is currently undergoing a course of chemoimmunotherapy.
Anatomy_Gray_917	Anatomy_Gray.txt	122.e1 122.e2
Anatomy_Gray_918	Anatomy_Gray.txt	Conceptual Overview
Anatomy_Gray_919	Anatomy_Gray.txt	Relationship to Other Regions
Anatomy_Gray_920	Anatomy_Gray.txt	Fig. 2.20, cont’d
Anatomy_Gray_921	Anatomy_Gray.txt	Fig. 2.20, cont’d
Anatomy_Gray_922	Anatomy_Gray.txt	In the clinic—cont’d
Anatomy_Gray_923	Anatomy_Gray.txt	Fig. 2.55, cont’d
Anatomy_Gray_924	Anatomy_Gray.txt	Fig. 2.68, cont’d
Anatomy_Gray_925	Anatomy_Gray.txt	Fig. 2.69, cont’d
Anatomy_Gray_926	Anatomy_Gray.txt	The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly (Fig. 3.1). The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm.
Anatomy_Gray_927	Anatomy_Gray.txt	The musculoskeletal wall of the thorax is flexible and consists of segmentally arranged vertebrae, ribs, and muscles and the sternum.
Anatomy_Gray_928	Anatomy_Gray.txt	The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments: a left and a right pleural cavity, each surrounding a lung, and the mediastinum.
Anatomy_Gray_929	Anatomy_Gray.txt	The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position. It contains the heart, esophagus, trachea, major nerves, and major systemic blood vessels.
Anatomy_Gray_930	Anatomy_Gray.txt	The pleural cavities are completely separated from each other by the mediastinum. Therefore abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities.
Anatomy_Gray_931	Anatomy_Gray.txt	Another important feature of the pleural cavities is that they extend above the level of rib I. The apex of each lung actually extends into the root of the neck. As a consequence, abnormal events in the root of the neck can involve the adjacent pleura and lung, and events in the adjacent pleura and lung can involve the root of the neck.
Anatomy_Gray_932	Anatomy_Gray.txt	One of the most important functions of the thorax is breathing. The thorax not only contains the lungs but also provides the machinery necessary—the diaphragm, thoracic wall, and ribs—for effectively moving air into and out of the lungs.
Anatomy_Gray_933	Anatomy_Gray.txt	Up and down movements of the diaphragm and changes in the lateral and anterior dimensions of the thoracic wall, caused by movements of the ribs, alter the volume of the thoracic cavity and are key elements in breathing.
Anatomy_Gray_934	Anatomy_Gray.txt	Protection of vital organs
Anatomy_Gray_935	Anatomy_Gray.txt	The thorax houses and protects the heart, lungs, and great vessels. Because of the upward domed shape of the diaphragm, the thoracic wall also offers protection to some important abdominal viscera.
Anatomy_Gray_936	Anatomy_Gray.txt	Much of the liver lies under the right dome of the diaphragm, and the stomach and spleen lie under the left. The posterior aspects of the superior poles of the kidneys lie on the diaphragm and are anterior to rib XII, on the right, and to ribs XI and XII, on the left.
Anatomy_Gray_937	Anatomy_Gray.txt	The mediastinum acts as a conduit for structures that pass completely through the thorax from one body region to another and for structures that connect organs in the thorax to other body regions.
Anatomy_Gray_938	Anatomy_Gray.txt	The esophagus, vagus nerves, and thoracic duct pass through the mediastinum as they course between the abdomen and neck.
Anatomy_Gray_939	Anatomy_Gray.txt	The phrenic nerves, which originate in the neck, also pass through the mediastinum to penetrate and supply the diaphragm.
Anatomy_Gray_940	Anatomy_Gray.txt	Other structures such as the trachea, thoracic aorta, and superior vena cava course within the mediastinum en route to and from major visceral organs in the thorax.
Anatomy_Gray_941	Anatomy_Gray.txt	The thoracic wall consists of skeletal elements and muscles (Fig. 3.1):
Anatomy_Gray_942	Anatomy_Gray.txt	Posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs;
Anatomy_Gray_943	Anatomy_Gray.txt	Laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces;
Anatomy_Gray_944	Anatomy_Gray.txt	Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.
Anatomy_Gray_945	Anatomy_Gray.txt	The manubrium of sternum, angled posteriorly on the body of sternum at the manubriosternal joint, forms the sternal angle, which is a major surface landmark used by clinicians in performing physical examinations of the thorax.
Anatomy_Gray_946	Anatomy_Gray.txt	The anterior (distal) end of each rib is composed of costal cartilage, which contributes to the mobility and elasticity of the wall.
Anatomy_Gray_947	Anatomy_Gray.txt	All ribs articulate with thoracic vertebrae posteriorly. Most ribs (from rib II to IX) have three articulations with the vertebral column. The head of each rib articulates with the body of its own vertebra and with the body of the vertebra above (Fig. 3.2). As these ribs curve posteriorly, each also articulates with the transverse process of its vertebra.
Anatomy_Gray_948	Anatomy_Gray.txt	Anteriorly, the costal cartilages of ribs I to VII articulate with the sternum.
Anatomy_Gray_949	Anatomy_Gray.txt	The costal cartilages of ribs VIII to X articulate with the inferior margins of the costal cartilages above them. Ribs XI and XII are called floating ribs because they do not articulate with other ribs, costal cartilages, or the sternum. Their costal cartilages are small, only covering their tips.
Anatomy_Gray_950	Anatomy_Gray.txt	The skeletal framework of the thoracic wall provides extensive attachment sites for muscles of the neck, abdomen, back, and upper limbs.
Anatomy_Gray_951	Anatomy_Gray.txt	A number of these muscles attach to ribs and function as accessory respiratory muscles; some of them also stabilize the position of the first and last ribs.
Anatomy_Gray_952	Anatomy_Gray.txt	Completely surrounded by skeletal elements, the superior thoracic aperture consists of the body of vertebra TI posteriorly, the medial margin of rib I on each side, and the manubrium anteriorly.
Anatomy_Gray_953	Anatomy_Gray.txt	The superior margin of the manubrium is in approximately the same horizontal plane as the intervertebral disc between vertebrae TII and TIII.
Anatomy_Gray_954	Anatomy_Gray.txt	The first ribs slope inferiorly from their posterior articulation with vertebra TI to their anterior attachment to the manubrium. Consequently, the plane of the superior thoracic aperture is at an oblique angle, facing somewhat anteriorly.
Anatomy_Gray_955	Anatomy_Gray.txt	At the superior thoracic aperture, the superior aspects of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum (Fig. 3.3).
Anatomy_Gray_956	Anatomy_Gray.txt	Structures that pass between the upper limb and thorax pass over rib I and the superior part of the pleural cavity as they enter and leave the mediastinum. Structures that pass between the neck and head and the thorax pass more vertically through the superior thoracic aperture.
Anatomy_Gray_957	Anatomy_Gray.txt	The inferior thoracic aperture is large and expandable. Bone, cartilage, and ligaments form its margin (Fig. 3.4A).
Anatomy_Gray_958	Anatomy_Gray.txt	The inferior thoracic aperture is closed by the diaphragm, and structures passing between the abdomen and thorax pierce or pass posteriorly to the diaphragm.
Anatomy_Gray_959	Anatomy_Gray.txt	Skeletal elements of the inferior thoracic aperture are: the body of vertebra TXII posteriorly, rib XII and the distal end of rib XI posterolaterally, the distal cartilaginous ends of ribs VII to X, which unite to form the costal margin anterolaterally, and the xiphoid process anteriorly.
Anatomy_Gray_960	Anatomy_Gray.txt	The joint between the costal margin and sternum lies roughly in the same horizontal plane as the intervertebral disc between vertebrae TIX and TX. In other words, the posterior margin of the inferior thoracic aperture is inferior to the anterior margin.
Anatomy_Gray_961	Anatomy_Gray.txt	When viewed anteriorly, the inferior thoracic aperture is tilted superiorly.
Anatomy_Gray_962	Anatomy_Gray.txt	The musculotendinous diaphragm seals the inferior thoracic aperture (Fig. 3.4B).
Anatomy_Gray_963	Anatomy_Gray.txt	Generally, muscle fibers of the diaphragm arise radially, from the margins of the inferior thoracic aperture, and converge into a large central tendon.
Anatomy_Gray_964	Anatomy_Gray.txt	Because of the oblique angle of the inferior thoracic aperture, the posterior attachment of the diaphragm is inferior to the anterior attachment.
Anatomy_Gray_965	Anatomy_Gray.txt	The diaphragm is not flat; rather, it “balloons” superiorly, on both the right and left sides, to form domes. The right dome is higher than the left, reaching as far as rib V.
Anatomy_Gray_966	Anatomy_Gray.txt	As the diaphragm contracts, the height of the domes decreases and the volume of the thorax increases.
Anatomy_Gray_967	Anatomy_Gray.txt	The esophagus and inferior vena cava penetrate the diaphragm; the aorta passes posterior to the diaphragm.
Anatomy_Gray_968	Anatomy_Gray.txt	The mediastinum is a thick midline partition that extends from the sternum anteriorly to the thoracic vertebrae posteriorly, and from the superior thoracic aperture to the inferior thoracic aperture.
Anatomy_Gray_969	Anatomy_Gray.txt	A horizontal plane passing through the sternal angle and the intervertebral disc between vertebrae TIV and TV separates the mediastinum into superior and inferior parts (Fig. 3.5). The inferior part is further subdivided by the pericardium, which encloses the pericardial cavity surrounding the heart. The pericardium and heart constitute the middle mediastinum.
Anatomy_Gray_970	Anatomy_Gray.txt	The anterior mediastinum lies between the sternum and the pericardium; the posterior mediastinum lies between the pericardium and thoracic vertebrae.
Anatomy_Gray_971	Anatomy_Gray.txt	The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6).
Anatomy_Gray_972	Anatomy_Gray.txt	Each pleural cavity is completely lined by a mesothelial membrane called the pleura.
Anatomy_Gray_973	Anatomy_Gray.txt	During development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura.
Anatomy_Gray_974	Anatomy_Gray.txt	Each lung remains attached to the mediastinum by a root formed by the airway, pulmonary blood vessels, lymphatic tissues, and nerves.
Anatomy_Gray_975	Anatomy_Gray.txt	The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs is the visceral pleura. Only a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity.
Anatomy_Gray_976	Anatomy_Gray.txt	The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm.
Anatomy_Gray_977	Anatomy_Gray.txt	The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7).
Anatomy_Gray_978	Anatomy_Gray.txt	The superior aspect of each pleural cavity extends approximately 2 to 3 cm above rib I and the costal cartilage into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately anterior to the esophagus. Major blood vessels and nerves pass in and out of the thorax at the superior thoracic aperture anteriorly and laterally to these structures.
Anatomy_Gray_979	Anatomy_Gray.txt	An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axillary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7).
Anatomy_Gray_980	Anatomy_Gray.txt	Each axillary inlet is formed by: the superior margin of the scapula posteriorly, the clavicle anteriorly, and the lateral margin of rib I medially.
Anatomy_Gray_981	Anatomy_Gray.txt	The apex of each triangular inlet is directed laterally and is formed by the medial margin of the coracoid process, which extends anteriorly from the superior margin of the scapula.
Anatomy_Gray_982	Anatomy_Gray.txt	The base of the axillary inlet’s triangular opening is the lateral margin of rib I.
Anatomy_Gray_983	Anatomy_Gray.txt	Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over rib I.
Anatomy_Gray_984	Anatomy_Gray.txt	Proximal parts of the brachial plexus also pass between the neck and upper limb by passing through the axillary inlet.
Anatomy_Gray_985	Anatomy_Gray.txt	The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it (Fig. 3.8):
Anatomy_Gray_986	Anatomy_Gray.txt	The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII.
Anatomy_Gray_987	Anatomy_Gray.txt	The esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX.
Anatomy_Gray_988	Anatomy_Gray.txt	The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII.
Anatomy_Gray_989	Anatomy_Gray.txt	Numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm.
Anatomy_Gray_990	Anatomy_Gray.txt	The breasts, consisting of mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9).
Anatomy_Gray_991	Anatomy_Gray.txt	Vessels, lymphatics, and nerves associated with the breast are as follows:
Anatomy_Gray_992	Anatomy_Gray.txt	Branches from the internal thoracic arteries and veins perforate the anterior chest wall on each side of the sternum to supply anterior aspects of the thoracic wall. Those branches associated mainly with the second to fourth intercostal spaces also supply the anteromedial parts of each breast.
Anatomy_Gray_993	Anatomy_Gray.txt	Lymphatic vessels from the medial part of the breast accompany the perforating arteries and drain into the parasternal nodes on the deep surface of the thoracic wall.
Anatomy_Gray_994	Anatomy_Gray.txt	Vessels and lymphatics associated with lateral parts of the breast emerge from or drain into the axillary region of the upper limb.
Anatomy_Gray_995	Anatomy_Gray.txt	Lateral and anterior branches of the fourth to sixth intercostal nerves carry general sensation from the skin of the breast.
Anatomy_Gray_996	Anatomy_Gray.txt	When working with patients, physicians use vertebral levels to determine the position of important anatomical structures within body regions.
Anatomy_Gray_997	Anatomy_Gray.txt	The horizontal plane passing through the disc that separates thoracic vertebrae TIV and TV is one of the most significant planes in the body (Fig. 3.10) because it: passes through the sternal angle anteriorly, marking the position of the anterior articulation of the costal cartilage of rib II with the sternum. The sternal angle is used to find the position of rib II as a reference for counting ribs (because of the overlying clavicle, rib I is not palpable); separates the superior mediastinum from the inferior mediastinum and marks the position of the superior limit of the pericardium; marks where the arch of the aorta begins and ends; passes through the site where the superior vena cava penetrates the pericardium to enter the heart; is the level at which the trachea bifurcates into right and left main bronchi; and marks the superior limit of the pulmonary trunk.
Anatomy_Gray_998	Anatomy_Gray.txt	Venous shunts from left to right
Anatomy_Gray_999	Anatomy_Gray.txt	The right atrium is the chamber of the heart that receives deoxygenated blood returning from the body. It lies on the right side of the midline, and the two major veins, the superior and inferior venae cavae, that drain into it are also located on the right side of the body. This means that, to get to the right side of the body, all blood coming from the left side has to cross the midline. This left-to-right shunting is carried out by a number of important and, in some cases, very large veins, several of which are in the thorax (Fig. 3.11).

Anatomy_Gray_900

Anatomy_Gray.txt

It was deduced that the blood pressure measurements were obtained in different arms, and both were reassessed.

Anatomy_Gray_901

Anatomy_Gray.txt

The blood pressure measurements were true. In the right arm the blood pressure measured 120/80 mm Hg and in the left arm the blood pressure measured 80/40 mm Hg. This would imply a deficiency of blood to the left arm.

Anatomy_Gray_902

Anatomy_Gray.txt

The patient was transferred from the emergency department to the CT scanner, and a scan was performed that included the chest, abdomen, and pelvis.

Anatomy_Gray_903

Anatomy_Gray.txt

The CT scan demonstrated a dissecting thoracic aortic aneurysm. Aortic dissection occurs when the tunica intima and part of the tunica media of the wall of the aorta become separated from the remainder of the tunica media and the tunica adventitia of the aorta wall. This produces a false lumen. Blood passes not only in the true aortic lumen but also through a small hole into the wall of the aorta and into the false lumen. It often reenters the true aortic lumen inferiorly. This produces two channels through which blood may flow. The process of the aortic dissection produces considerable pain for the patient and is usually of rapid onset. Typically the pain is felt between the shoulder blades and radiating into the back, and although the pain is not from the back musculature or the vertebral column, careful consideration of structures other than the back should always be sought.

Anatomy_Gray_904

Anatomy_Gray.txt

The difference in the blood pressure between the two arms indicates the level at which the dissection has begun. The “point of entry” is proximal to the left subclavian artery. At this level a small flap has been created, which limits the blood flow to the left upper limb, giving the low blood pressure recording. The brachiocephalic trunk has not been affected by the aortic dissection, and hence blood flow remains appropriate to the right upper limb.

Anatomy_Gray_905

Anatomy_Gray.txt

The paraplegia was caused by ischemia to the spinal cord.

Anatomy_Gray_906

Anatomy_Gray.txt

The blood supply to the spinal cord is from a single anterior spinal artery and two posterior spinal arteries. These arteries are fed via segmental spinal arteries at every vertebral level. There are a number of reinforcing arteries (segmental medullary arteries) along the length of the spinal cord—the largest of which is the artery of Adamkiewicz. This artery of Adamkiewicz, a segmental medullary artery, typically arises from the lower thoracic or upper lumbar region, and unfortunately during this patient’s aortic dissection, the origin of this vessel was disrupted. This produces acute spinal cord ischemia and has produced the paraplegia in the patient.

Anatomy_Gray_907

Anatomy_Gray.txt

Unfortunately, the dissection extended, the aorta ruptured, and the patient succumbed.

Anatomy_Gray_908

Anatomy_Gray.txt

A 55-year-old woman came to her physician with sensory alteration in the right gluteal (buttock) region and in the intergluteal (natal) cleft. Examination also demonstrated low-grade weakness of the muscles of the foot and subtle weakness of the extensor hallucis longus, extensor digitorum longus, and fibularis tertius on the right. The patient also complained of some mild pain symptoms posteriorly in the right gluteal region.

Anatomy_Gray_909

Anatomy_Gray.txt

A lesion was postulated in the left sacrum.

Anatomy_Gray_910

Anatomy_Gray.txt

Pain in the right sacro-iliac region could easily be attributed to the sacro-iliac joint, which is often very sensitive to pain. The weakness of the intrinsic muscles of the foot and the extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles raises the possibility of an abnormality affecting the nerves exiting the sacrum and possibly the lumbosacral junction. The altered sensation around the gluteal region toward the anus would also support these anatomical localizing features.

Anatomy_Gray_911

Anatomy_Gray.txt

An X-ray was obtained of the pelvis.

Anatomy_Gray_912

Anatomy_Gray.txt

The X-ray appeared on first inspection unremarkable. However, the patient underwent further investigation, including CT and MRI, which demonstrated a large destructive lesion involving the whole of the left sacrum extending into the anterior sacral foramina at the S1, S2, and S3 levels. Interestingly, plain radiographs of the sacrum may often appear normal on first inspection, and further imaging should always be sought in patients with a suspected sacral abnormality.

Anatomy_Gray_913

Anatomy_Gray.txt

The lesion was expansile and lytic.

Anatomy_Gray_914

Anatomy_Gray.txt

Most bony metastases are typically nonexpansile. They may well erode the bone, producing lytic type of lesions, or may become very sclerotic (prostate metastases and breast metastases). From time to time we see a mixed pattern of lytic and sclerotic.

Anatomy_Gray_915

Anatomy_Gray.txt

There are a number of uncommon instances in which certain metastases are expansile and lytic. These typically occur in renal metastases and may be seen in multiple myeloma. The anatomical importance of these specific tumors is that they often expand and impinge upon other structures. The expansile nature of this patient’s tumor within the sacrum was the cause for compression of the sacral nerve roots, producing her symptoms.

Anatomy_Gray_916

Anatomy_Gray.txt

The patient underwent a course of radiotherapy, had the renal tumor excised, and is currently undergoing a course of chemoimmunotherapy.

Anatomy_Gray_917

Anatomy_Gray.txt

122.e1 122.e2

Anatomy_Gray_918

Anatomy_Gray.txt

Conceptual Overview

Anatomy_Gray_919

Anatomy_Gray.txt

Relationship to Other Regions

Anatomy_Gray_920

Anatomy_Gray.txt

Fig. 2.20, cont’d

Anatomy_Gray_921

Anatomy_Gray.txt

Fig. 2.20, cont’d

Anatomy_Gray_922

Anatomy_Gray.txt

In the clinic—cont’d

Anatomy_Gray_923

Anatomy_Gray.txt

Fig. 2.55, cont’d

Anatomy_Gray_924

Anatomy_Gray.txt

Fig. 2.68, cont’d

Anatomy_Gray_925

Anatomy_Gray.txt

Fig. 2.69, cont’d

Anatomy_Gray_926

Anatomy_Gray.txt

The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly (Fig. 3.1). The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm.

Anatomy_Gray_927

Anatomy_Gray.txt

The musculoskeletal wall of the thorax is flexible and consists of segmentally arranged vertebrae, ribs, and muscles and the sternum.

Anatomy_Gray_928

Anatomy_Gray.txt

The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments: a left and a right pleural cavity, each surrounding a lung, and the mediastinum.

Anatomy_Gray_929

Anatomy_Gray.txt

The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position. It contains the heart, esophagus, trachea, major nerves, and major systemic blood vessels.

Anatomy_Gray_930

Anatomy_Gray.txt

The pleural cavities are completely separated from each other by the mediastinum. Therefore abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities.

Anatomy_Gray_931

Anatomy_Gray.txt

Another important feature of the pleural cavities is that they extend above the level of rib I. The apex of each lung actually extends into the root of the neck. As a consequence, abnormal events in the root of the neck can involve the adjacent pleura and lung, and events in the adjacent pleura and lung can involve the root of the neck.

Anatomy_Gray_932

Anatomy_Gray.txt

One of the most important functions of the thorax is breathing. The thorax not only contains the lungs but also provides the machinery necessary—the diaphragm, thoracic wall, and ribs—for effectively moving air into and out of the lungs.

Anatomy_Gray_933

Anatomy_Gray.txt

Up and down movements of the diaphragm and changes in the lateral and anterior dimensions of the thoracic wall, caused by movements of the ribs, alter the volume of the thoracic cavity and are key elements in breathing.

Anatomy_Gray_934

Anatomy_Gray.txt

Protection of vital organs

Anatomy_Gray_935

Anatomy_Gray.txt

The thorax houses and protects the heart, lungs, and great vessels. Because of the upward domed shape of the diaphragm, the thoracic wall also offers protection to some important abdominal viscera.

Anatomy_Gray_936

Anatomy_Gray.txt

Much of the liver lies under the right dome of the diaphragm, and the stomach and spleen lie under the left. The posterior aspects of the superior poles of the kidneys lie on the diaphragm and are anterior to rib XII, on the right, and to ribs XI and XII, on the left.

Anatomy_Gray_937

Anatomy_Gray.txt

The mediastinum acts as a conduit for structures that pass completely through the thorax from one body region to another and for structures that connect organs in the thorax to other body regions.

Anatomy_Gray_938

Anatomy_Gray.txt

The esophagus, vagus nerves, and thoracic duct pass through the mediastinum as they course between the abdomen and neck.

Anatomy_Gray_939

Anatomy_Gray.txt

The phrenic nerves, which originate in the neck, also pass through the mediastinum to penetrate and supply the diaphragm.

Anatomy_Gray_940

Anatomy_Gray.txt

Other structures such as the trachea, thoracic aorta, and superior vena cava course within the mediastinum en route to and from major visceral organs in the thorax.

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The thoracic wall consists of skeletal elements and muscles (Fig. 3.1):

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Posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs;

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Laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces;

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Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.

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The manubrium of sternum, angled posteriorly on the body of sternum at the manubriosternal joint, forms the sternal angle, which is a major surface landmark used by clinicians in performing physical examinations of the thorax.

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The anterior (distal) end of each rib is composed of costal cartilage, which contributes to the mobility and elasticity of the wall.

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All ribs articulate with thoracic vertebrae posteriorly. Most ribs (from rib II to IX) have three articulations with the vertebral column. The head of each rib articulates with the body of its own vertebra and with the body of the vertebra above (Fig. 3.2). As these ribs curve posteriorly, each also articulates with the transverse process of its vertebra.

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Anteriorly, the costal cartilages of ribs I to VII articulate with the sternum.

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The costal cartilages of ribs VIII to X articulate with the inferior margins of the costal cartilages above them. Ribs XI and XII are called floating ribs because they do not articulate with other ribs, costal cartilages, or the sternum. Their costal cartilages are small, only covering their tips.

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The skeletal framework of the thoracic wall provides extensive attachment sites for muscles of the neck, abdomen, back, and upper limbs.

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A number of these muscles attach to ribs and function as accessory respiratory muscles; some of them also stabilize the position of the first and last ribs.

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Completely surrounded by skeletal elements, the superior thoracic aperture consists of the body of vertebra TI posteriorly, the medial margin of rib I on each side, and the manubrium anteriorly.

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The superior margin of the manubrium is in approximately the same horizontal plane as the intervertebral disc between vertebrae TII and TIII.

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The first ribs slope inferiorly from their posterior articulation with vertebra TI to their anterior attachment to the manubrium. Consequently, the plane of the superior thoracic aperture is at an oblique angle, facing somewhat anteriorly.

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At the superior thoracic aperture, the superior aspects of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum (Fig. 3.3).

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Structures that pass between the upper limb and thorax pass over rib I and the superior part of the pleural cavity as they enter and leave the mediastinum. Structures that pass between the neck and head and the thorax pass more vertically through the superior thoracic aperture.

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The inferior thoracic aperture is large and expandable. Bone, cartilage, and ligaments form its margin (Fig. 3.4A).

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The inferior thoracic aperture is closed by the diaphragm, and structures passing between the abdomen and thorax pierce or pass posteriorly to the diaphragm.

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Skeletal elements of the inferior thoracic aperture are: the body of vertebra TXII posteriorly, rib XII and the distal end of rib XI posterolaterally, the distal cartilaginous ends of ribs VII to X, which unite to form the costal margin anterolaterally, and the xiphoid process anteriorly.

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The joint between the costal margin and sternum lies roughly in the same horizontal plane as the intervertebral disc between vertebrae TIX and TX. In other words, the posterior margin of the inferior thoracic aperture is inferior to the anterior margin.

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When viewed anteriorly, the inferior thoracic aperture is tilted superiorly.

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The musculotendinous diaphragm seals the inferior thoracic aperture (Fig. 3.4B).

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Generally, muscle fibers of the diaphragm arise radially, from the margins of the inferior thoracic aperture, and converge into a large central tendon.

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Because of the oblique angle of the inferior thoracic aperture, the posterior attachment of the diaphragm is inferior to the anterior attachment.

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The diaphragm is not flat; rather, it “balloons” superiorly, on both the right and left sides, to form domes. The right dome is higher than the left, reaching as far as rib V.

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As the diaphragm contracts, the height of the domes decreases and the volume of the thorax increases.

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The esophagus and inferior vena cava penetrate the diaphragm; the aorta passes posterior to the diaphragm.

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The mediastinum is a thick midline partition that extends from the sternum anteriorly to the thoracic vertebrae posteriorly, and from the superior thoracic aperture to the inferior thoracic aperture.

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A horizontal plane passing through the sternal angle and the intervertebral disc between vertebrae TIV and TV separates the mediastinum into superior and inferior parts (Fig. 3.5). The inferior part is further subdivided by the pericardium, which encloses the pericardial cavity surrounding the heart. The pericardium and heart constitute the middle mediastinum.

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The anterior mediastinum lies between the sternum and the pericardium; the posterior mediastinum lies between the pericardium and thoracic vertebrae.

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The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6).

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Each pleural cavity is completely lined by a mesothelial membrane called the pleura.

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During development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura.

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Each lung remains attached to the mediastinum by a root formed by the airway, pulmonary blood vessels, lymphatic tissues, and nerves.

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The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs is the visceral pleura. Only a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity.

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The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm.

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The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7).

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The superior aspect of each pleural cavity extends approximately 2 to 3 cm above rib I and the costal cartilage into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately anterior to the esophagus. Major blood vessels and nerves pass in and out of the thorax at the superior thoracic aperture anteriorly and laterally to these structures.

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An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axillary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7).

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Each axillary inlet is formed by: the superior margin of the scapula posteriorly, the clavicle anteriorly, and the lateral margin of rib I medially.

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The apex of each triangular inlet is directed laterally and is formed by the medial margin of the coracoid process, which extends anteriorly from the superior margin of the scapula.

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The base of the axillary inlet’s triangular opening is the lateral margin of rib I.

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Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over rib I.

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Proximal parts of the brachial plexus also pass between the neck and upper limb by passing through the axillary inlet.

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The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it (Fig. 3.8):

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The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII.

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The esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX.

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The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII.

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Numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm.

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The breasts, consisting of mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9).

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Vessels, lymphatics, and nerves associated with the breast are as follows:

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Branches from the internal thoracic arteries and veins perforate the anterior chest wall on each side of the sternum to supply anterior aspects of the thoracic wall. Those branches associated mainly with the second to fourth intercostal spaces also supply the anteromedial parts of each breast.

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Lymphatic vessels from the medial part of the breast accompany the perforating arteries and drain into the parasternal nodes on the deep surface of the thoracic wall.

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Vessels and lymphatics associated with lateral parts of the breast emerge from or drain into the axillary region of the upper limb.

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Lateral and anterior branches of the fourth to sixth intercostal nerves carry general sensation from the skin of the breast.

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When working with patients, physicians use vertebral levels to determine the position of important anatomical structures within body regions.

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The horizontal plane passing through the disc that separates thoracic vertebrae TIV and TV is one of the most significant planes in the body (Fig. 3.10) because it: passes through the sternal angle anteriorly, marking the position of the anterior articulation of the costal cartilage of rib II with the sternum. The sternal angle is used to find the position of rib II as a reference for counting ribs (because of the overlying clavicle, rib I is not palpable); separates the superior mediastinum from the inferior mediastinum and marks the position of the superior limit of the pericardium; marks where the arch of the aorta begins and ends; passes through the site where the superior vena cava penetrates the pericardium to enter the heart; is the level at which the trachea bifurcates into right and left main bronchi; and marks the superior limit of the pulmonary trunk.

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Venous shunts from left to right

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The right atrium is the chamber of the heart that receives deoxygenated blood returning from the body. It lies on the right side of the midline, and the two major veins, the superior and inferior venae cavae, that drain into it are also located on the right side of the body. This means that, to get to the right side of the body, all blood coming from the left side has to cross the midline. This left-to-right shunting is carried out by a number of important and, in some cases, very large veins, several of which are in the thorax (Fig. 3.11).