Review of Critical Care Medicine

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Anatomy Thorax

Posted by Dr KAMAL DEEP on May 17, 2011

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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;
  • marks the superior limit of the pulmonary trunk.

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The major structures found in the superior mediastinum include:

  • thymus,
  • right and left brachiocephalic veins,
  • left superior intercostal vein,
  • superior vena cava,
  • arch of the aorta with its three large branches,
  • trachea,
  • esophagus,
  • phrenic nerves,
  • vagus nerves,
  • left recurrent laryngeal branch of the left vagus nerve, (not right one as left vagus goes very low down to present in sup aperture giving rec branch there)
  • thoracic duct, and
  • other small nerves, blood vessels, and lymphatics

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The commonest variation in the arteries arising from the arch of aorta is:
A.Absence of brachiocephalic trunk
B.Left vertebral artery arising from the arch
C.Left common carotid artery arising from brachio cephalic trunk
D.Presence of retroesophageal subclavian artery

Branches Three branches arise from the convex aspect of the arch: the brachiocephalic trunk, left common carotid and left subclavian arteries (Figs 31.15, 60.6). They may branch from the beginning of the arch or the upper part of the ascending aorta. The distance between these origins varies, the most frequent being approximation of the left common carotid artery to the brachiocephalic trunk.

Primary branches from the aortic arch may be reduced to one, but more commonly two. The left common carotid may arise from the brachiocephalic trunk (7%). More rarely, the left common carotid and subclavian arteries may arise from a left brachiocephalic trunk, or the right common carotid and right subclavian may arise separately, in which case the latter more often branches from the left end of the arch and passes behind the oesophagus. The left vertebral artery may arise between the left common carotid and the subclavian arteries. Very rarely, external and internal carotid arteries arise separately, the common carotid being absent on one or both sides, or both carotids and one or both vertebral arteries may be separate branches. When a ‘right aorta’ occurs, the arrangement of its three branches is reversed. The common carotids may have a single trunk. Other arteries may branch from it, most commonly one or both bronchial arteries and the thyroid ima artery.

An analysis of variation in branches from 1000 aortic arches showed the usual pattern in 65%; a left common carotid shared the brachiocephalic trunk in 27% (contrast percentage quoted above) and the four large arteries branched separately in 2.5%. The remaining 5% showed a great variety of patterns, the most common (1.2%) being symmetric right and left brachiocephalic trunks

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Figure 59.5 Transverse section of thorax through the middle of the fourth thoracic vertebra and aortic arch; obtained by computed tomography.

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Transverse section of thorax at the level of the lower border of the fourth thoracic vertebra, just at the level of the tracheal bifurcation; obtained by computed tomography.

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Transverse section of thorax at the upper border of the sixth thoracic vertebra, below the carina at the level of the pulmonary trunk and the right main pulmonary artery; obtained by computed tomography

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Transverse section of thorax through the lower portion of the seventh thoracic vertebra, passing through the aortic root; obtained by computed tomography

The structure found in a cross-section of the thorax at
T4 vertebra is :
A.Azygos vein
B.Brachiocephalic artery
C.Arch of the aorta
D.Left Subclavian artery

Azygous vein also present at T4 level but more accurate answer is arch of aorta. As azygous is at lower level of T4.

The hilum of the right lung is arched by
A.Recurrent laryngeal nerve
B.Azygos vein
C.Thoracic duct
D.Vagus nerve

Bochdalek hernia occurs in
A.Anterolateral part of diaphragm
B.Posterolateral part of diaphragm
C.Retrosternal area
D.Posterior to diaphragm

 

A diaphragmatic hernia is defined as a communication between the abdominal and thoracic cavities with or without abdominal contents in the thorax  The etiology may be congenital or traumatic. The symptoms and prognosis depend on the location of the defect and associated anomalies. The defect may be at the esophageal hiatus (hiatal), paraesophageal (adjacent to the hiatus), retrosternal (Morgagni), or at the posterolateral (Bochdalek) portion of the diaphragm. The term congenital diaphragmatic hernia (CDH) typically refers to the Bochdalek form. These lesions may cause significant respiratory distress at birth, can be associated with other congenital anomalies, and have a significant mortality and long-term morbidity. The overall survival from the CDH Study Group is 67%. The Bochdalek hernia accounts for up to 90% of the hernias seen in the newborn period, with 80–90% occurring on the left side

FORMATION OF THE DIAPHRAGM

The separation of the pleural and peritoneal cavities is effected by development of the diaphragm (Fig. 65.1). This forms from a portion of the septum transversum mesenchyme above the developing liver. The septum transversum is a population of mesenchymal cells that arises from the coelomic wall of the caudal part of the pericardial cavity. As the population proliferates, it forms a condensation of mesenchyme, caudal to the pericardial cavity and extending from the ventral and lateral regions of the body wall to the foregut. Dorsal to it on each side is the relatively narrow pleuroperitoneal canal. The endodermal hepatic bud grows into the caudal part of the septum transversum, whereas the cranial portion will form the diaphragm.

Medial to the pleuroperitoneal canals are the oesophagus and stomach with their dorsal mesentery and, at the root of the latter, the dorsal aorta. Dorsolateral to the canals are the pleuroperitoneal membranes, which remain small. Dorsally are the mesonephric ridges, suprarenal (adrenal) glands and gonads. Just as the enlargement of the pleural cavity cranially and ventrally is effected by a process of burrowing into the body wall, so its caudodorsal enlargement is effected in the same way. The expanding pleural cavities extend into the mesenchyme dorsal to the suprarenal glands, the gonads and (degenerating) mesonephric ridges. Thus somatopleuric mesenchyme is peeled off the dorsal body wall to form a substantial portion of the dorsolumbar part of the diaphragm. The pleuroperitoneal canal is closed by the fusion of its edges, which are carried together from posterolaterally to anteromedially by growth of the organs surrounding it and in particular that of the suprarenal gland. The right pleuroperitoneal canal closes earlier than the left, which presumably explains why an abnormal communication persisting between the pleural and peritoneal cavities is more frequently encountered on the left.

The diaphragm is a dome-shaped musculotendinous structure that is derived from four distinct fused structures. The septum transversum gives rise to the central tendon and separates the pericardial and peritoneal cavities. The central tendon constitutes 30% of the diaphragm and is the largest portion. The pleuroperitoneal membranes give rise to the dorsal lateral portions of the diaphragm; this separates the paired pleural cavities and the “fetal diaphragm” at approximately 8 wk gestation. The esophageal mesentery forms the dorsal crura and the intercostal muscle groups give rise to the muscular portion of the diaphragm. CDH may be due to defective formation of the pleuroperitoneal membrane. When the abdominal contents return to the abdomen from the umbilical sac at 10 wk gestation, herniation of the abdominal contents may occur.

 

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

 

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 with sternum. Their costal cartilages are small, only covering their tips.

There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage

Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs:

  • the costal cartilages of ribs VIII to X articulate anteriorly with the costal cartilages of the ribs above;
  • ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs.

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A, Superior and B, inferior aspects of the first rib. (Photographs by Sarah-Jane Smith.)

The superior surface of the rib is characterized by a distinct tubercle, the scalene tubercle, which separates two smooth grooves that cross the rib approximately midway along the shaft. The anterior groove is caused by the subclavian vein, and the posterior groove is caused by the subclavian artery. Anterior and posterior to these grooves, the shaft is roughened by muscle and ligament attachments.

The insertion of scalenus medius on the elongated rough area behind the groove for subclavian artery.

The external border is convex, thick posteriorly and thin anteriorly. It is covered behind by scalenus posterior descending to the second rib. The first digitation of serratus anterior is, in part, attached to it, behind the subclavian (arterial) groove. The internal border is concave and thin, and the scalene tubercle is near its midpoint. The suprapleural membrane, which covers the cervical dome of the pleura, is attached to the internal border.

The superior surface of the flattened shaft is crossed obliquely by two shallow grooves, separated by a slight ridge, which usually ends at the internal border as a small pointed projection, the scalene tubercle, to which scalenus anterior is attached. The groove anterior to the scalene tubercle forms a bed for the subclavian vein, and the rough area between this and the first costal cartilage gives attachment to the costoclavicular ligament and, more anteriorly, to subclavius. The subclavian artery and (usually) the lower trunk of the brachial plexus pass in the groove behind the tubercle. Behind this, scalenus medius is attached as far as the costal tubercle.

  • the superior costal facets on the body of vertebra TI are complete and articulate with a single facet on the head of its own rib-in other words, the head of rib I does not articulate with vertebra CVII;
  • similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body;
  • vertebrae TXI and TXII articulate only with the heads of their own ribs-they lack transverse costal facets and have only a single complete facet on each side of their bodies.

Costal cartilages articulate with small concavities on the lateral sternal borders (chondrosternal articulations, Fig. 57.16). Perichondrium and periosteum are continuous. The first sternocostal joint is an unusual variety of synarthrosis, often inaccurately called a synchondrosis. The second to seventh costal cartilages articulate by synovial joints

The manubriosternal joint lies between the manubrium and sternal body, and is usually a symphysis. The bony surfaces are covered by hyaline cartilage and connected by a fibrocartilage

COSTOCHONDRAL JUNCTIONS :- Artificially separated from its rib, a costal cartilage has a rounded end that fits a reciprocal depression in the rib. Periosteum and perichondrium are continuous across the costochondral junctions, and the collagen of the osseous and cartilaginous matrices blend. No movement occurs at costochondral junctions.

Intercostal muscles

The intercostal muscles are three flat muscles found in each intercostal space that pass between adjacent ribs (Fig. 3.27). Individual muscles in this group are named according to their positions:

  • the external intercostal muscles are the most superficial;
  • the internal intercostal muscles are sandwiched between the external and innermost muscles

External intercostal muscles :-The eleven pairs of external intercostal muscles extend from the inferior edges of the ribs above to the superior surfaces of the ribs below. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely anteroinferiorly (Fig. 3.27). The muscles extend around the thoracic wall from the regions of the tubercles of the ribs to the costal cartilages, where each layer continues as a thin connective tissue aponeurosis termed the external intercostal membrane. The external intercostal muscles are most active in inspiration.

Internal intercostal muscles :-The eleven pairs of internal intercostal muscles pass between the most inferior lateral edge of the costal grooves of the ribs above, to the superior surface of the ribs below. They extend from parasternal regions, where the muscles course between adjacent costal cartilages, to the angle of the ribs posteriorly (Fig. 3.27). This layer continues medially toward the vertebral column, in each intercostal space, as the internal intercostal membrane. The muscle fibers pass in the opposite direction to those of the external intercostal muscles. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely posteroinferiorly. The internal intercostal muscles are most active during expiration.

 

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Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles.

In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below.

Innervation of the thoracic wall is mainly by the intercostal nerves, which are the anterior rami of spinal nerves T1 to T11 and lie in the intercostal spaces between adjacent ribs. The anterior ramus of spinal nerve T12 (the subcostal nerve) is inferior to rib XII

A typical intercostal nerve passes laterally around the thoracic wall in an intercostal space. The largest of the branches is the lateral cutaneous branch, which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin

In addition to innervating the thoracic wall, intercostal nerves innervate other regions:

  • the anterior ramus of T1 contributes to the brachial plexus;
  • the lateral cutaneous branch of the second intercostal nerve (the intercostobrachial nerve) contributes to cutaneous innervation of the medial surface of the upper arm;
  • the lower intercostal nerves supply muscles, skin, and peritoneum of the abdominal wall

Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces (Fig. 3.29). These arteries originate from the aorta and internal thoracic arteries, which in turn arise from the subclavian arteries in the root of the neck. Together, the intercostal arteries form a basket-like pattern of vascular supply around the thoracic wall.

Posterior intercostal arteries originate from vessels associated with the posterior thoracic wall. The upper two posterior intercostal arteries on each side are derived from the supreme intercostal artery, which descends into the thorax as a branch of the costocervical trunk in the neck. The costocervical trunk is a posterior branch of the subclavian artery (Fig. 3.29).

The remaining nine pairs of posterior intercostal arteries arise from the posterior surface of the thoracic aorta. Because the aorta is on the left side of the vertebral column, those posterior intercostal vessels passing to the right side of the thoracic wall cross the midline anterior to the bodies of the vertebrae and therefore are longer than the corresponding vessels on the left.

In addition to having numerous branches that supply various components of the wall, the posterior intercostal arteries have branches that accompany lateral cutaneous branches of the intercostal nerves to superficial regions.

Venous drainage :-

Venous drainage from the thoracic wall generally parallels the pattern of arterial supply 

Centrally, the intercostal veins ultimately drain into the azygos system of veins or into internal thoracic veins, which connect with the brachiocephalic veins in the neck.

Often the upper posterior intercostal veins on the left side come together and form the left superior intercostal vein, which empties into the left brachiocephalic vein.

Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein.

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Figure 3.30 Veins of the thoracic wall.                                                                                                                                                             Recess

The largest and clinically most important recesses are the costodiaphragmatic recesses, which occur in each pleural cavity between the costal pleura and diaphragmatic pleura . The costodiaphragmatic recesses are the regions between the inferior margin of the lungs and inferior margin of the pleural cavities. They are deepest after forced expiration and shallowest after forced inspiration.

During quiet respiration, the inferior margin of the lung crosses rib VI in the midclavicular line, rib VIII in the midaxillary line, and then courses somewhat horizontally to reach the vertebral column at vertebral level TX. From the midclavicular line and around the thoracic wall to the vertebral column, the inferior margin of the lung can be approximated by a line running between rib VI, rib VIII, and vertebra TX. The inferior margin of the pleural cavity at the same points is rib VIII, rib X, and vertebra TXII. The costodiaphragmatic recess is the region between the two margins.

The right costo-phrenic recess extends up to the level of which rib in the mid-axillary line
A.6th
B.10th
C.8th

D.12th

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imageFigure 60.12 Principal elements of the fibrous skeleton of the heart. For clarity, the view is from the right posterosuperior aspect. Perspective causes the pulmonary anulus to appear smaller than the aortic anulus, whereas in fact the reverse is the case. Consult text for an extended discussion. Key: red, mitral and aortic ‘anuli’; blue, tricuspid and pulmonary ‘anuli’; green, tendon of the infundibulum. (Copyright from The Royal College of Surgeons of England. .)image

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                                          Left Dominance

Variations in the distribution patterns of coronary arteries

Several major variations in the basic distribution patterns of the coronary arteries occur:

  • The distribution pattern described above for both right and left coronary arteries is the most common and consists of a right dominant coronary artery. This means that the posterior interventricular branch arises from the right coronary artery. The right coronary artery therefore supplies a large portion of the posterior wall of the left ventricle and the circumflex branch of the left coronary artery is relatively small.
  • In contrast, in hearts with a left dominant coronary artery, the posterior interventricular branch arises from an enlarged circumflex branch and supplies most of the posterior wall of the left ventricle (Fig. 3.73).
  • Another point of variation relates to the arterial supply to the sinu-atrial and atrioventricular nodes. In most cases, these two structures are supplied by the right coronary artery. However, vessels from the circumflex branch of the left coronary artery occasionally supply these structures

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Anterior views of the coronary arterial system, with the principal variations. The right coronary arterial tree is shown in magenta, the left in full red. In both cases posterior distribution is shown in a paler shade. A, The most common arrangement. B, A common variation in the origin of the sinuatrial nodal artery. C, An example of left ‘dominance’ by the left coronary artery, showing also an uncommon origin of the sinu-atrial artery.

 

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 B. Left anterior oblique view of right coronary artery. C. Right anterior oblique view of left coronary artery

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From two to nine large left anterior ventricular arteries branch at acute angles from the anterior interventricular (descending) artery and cross the anterior aspect of the left ventricle diagonally; larger terminals reach the rounded (obtuse) left border. One is often large and may arise separately from the left coronary trunk (which then ends by trifurcation). This left diagonal artery, reported in 33-50% or more individuals, is sometimes duplicated (20%). A small left conus artery frequently leaves the anterior interventricular (descending) artery near its start, and anastomoses on the conus with its counterpart from the right coronary artery and with the vasa vasorum of the pulmonary artery and aorta. The anterior septal branches leave the anterior interventricular (descending) artery almost perpendicularly, and pass back and down in the septum, usually supplying its ventral two-thirds. Small posterior septal branches from the same source supply the posterior one-third of the septum for a variable distance from the cardiac apex.

The circumflex artery, comparable to the anterior interventricular (descending) in calibre, curves left in the atrioventricular groove, continuing round the left cardiac border into the posterior part of the groove and ending left of the crux in most hearts, but sometimes continuing as a posterior interventricular (descending) artery. Proximally, the left atrial auricle usually overlaps it. In c.90%, a large ventricular branch, the left marginal artery, arises perpendicularly from the circumflex artery and ramifies over the rounded ‘obtuse’ margin, supplying much of the adjacent left ventricle, usually to the apex. Smaller anterior and posterior branches of the circumflex artery also supply the left ventricle. Anterior ventricular branches (from one to five, commonly two or three) course parallel to the diagonal artery, when it is present, and replace it when it is absent. Posterior ventricular branches are smaller and fewer; the left ventricle is partly supplied by the posterior interventricular (descending) artery. When this is small or absent, it is accompanied or replaced by an interventricular continuation of the circumflex artery, which is frequently double or triple. The circumflex artery may supply the left atrium via anterior, lateral and posterior atrial branches.

The right coronary artery supplies the right atrium and right ventricle, the sinu-atrial and atrioventricular nodes, the interatrial septum, a portion of the left atrium, the posteroinferior one-third of the interventricular septum, and a portion of the posterior part of the left ventricle

The distribution pattern of the left coronary artery enables it to supply most of the left atrium and left ventricle, and most of the interventricular septum, including the atrioventricular bundle and its branches.

Occlusion of the ant descending branch of LAD will
lead to infarction of which area?
A.Posterior part of the interventricular septum
B.
Anterior wall of the left ventricle
C.Lateral part of the heart
D.Inferior surface of right ventricle

All of the following are true about coronary artery except :
A.Right coronary artery lies in right anterior coronary salcus
B.Left anterior descending artey is a branch of left coronary artery
C.Usually 3 obtuse marginal arteries arise from left coronary artery   It is single.Diagonal branches are 2-3 sometimes.
D.In 85% cases posterior descending
interventricular artery arises from right co. art.

The right coronary artery supplies all of the following parts of the conducting system in the heart except:
A.SA Node
B.AV Node
C.AV Bundle
D.Right Bundle branch

Most commonly, the right coronary artery supplies all the right ventricle (except a small region right of the anterior interventricular groove), a variable part of the left ventricular diaphragmatic aspect, the posteroinferior one-third of the intraventricular septum, the right atrium and part of the left, and the conducting system as far as the proximal parts of the right and left crura. Left coronary distribution is reciprocal, and includes most of the left ventricle, a narrow strip of right ventricle, the anterior two-thirds of the interventricular septum and most of the left atrium

As the right and left bundle branches runs in Interventricular septum so it must be supplied by Left coronary artery

The middle cardiac vein is located at the:
A.Anterior interventricular sulcus
B.Posterior interventricular sulcus
C.Posterior AV groove
D.Anterior AV groove

Right coronary artery

The right coronary artery originates from the right aortic sinus of the ascending aorta. It passes anteriorly and to the right between the right auricle and the pulmonary trunk and then descends vertically in the coronary sulcus, between the right atrium and right ventricle .On reaching the inferior margin of the heart, it turns posteriorly and continues in the sulcus onto the diaphragmatic surface and base of the heart. During this course, several branches arise from the main stem of the vessel:

  • an early atrial branch passes in the groove between the right auricle and ascending aorta, and gives off the sinu-atrial nodal branch, which passes posteriorly around the superior vena cava to supply the sinu-atrial node;
  • a right marginal branch is given off as the right coronary artery approaches the inferior (acute) margin of the heart and continues along this border toward the apex of the heart;
  • as the right coronary artery continues on the base/diaphragmatic surface of the heart, it supplies a small branch to the atrioventricular node before giving off its final major branch, the posterior interventricular branch, which lies in the posterior interventricular sulcus.

The left coronary artery originates from the left aortic sinus of the ascending aorta. It passes between the pulmonary trunk and the left auricle before entering the coronary sulcus. While still posterior to the pulmonary trunk, the artery divides into its two terminal branches, the anterior interventricular and the circumflex

  • the anterior interventricular branch (left anterior descending artery-LAD), which continues
  • around the left side of the pulmonary trunk and descends obliquely toward the apex of the heart in the anterior interventricular sulcus during its course, one or two large diagonal branches may arise and descend diagonally across the anterior surface of the left ventricle;
  • the circumflex branch, which courses toward the left, in the coronary sulcus and onto the base/diaphragmatic surface of the heart and usually ends before reaching the posterior interventricular sulcus-a large branch, the left marginal artery, usually arises from it and continues across the rounded obtuse margin of the heart

The coronary sulcus circles the heart, separating the atria from the ventricles. As it circles the heart, it contains the right coronary artery, the small cardiac vein, the coronary sinus, and the circumflex branch of the left coronary artery.

The anterior and posterior interventricular sulci separate the two ventricles-the anterior interventricular sulcus is on the anterior surface of the heart and contains the anterior interventricular artery and the great cardiac vein, and the posterior interventricular sulcus is on the diaphragmatic surface of the heart and contains the posterior interventricular artery and the middle cardiac vein

  • the right and left margins are the same as the right and left pulmonary surfaces of the heart;
  • the inferior margin is defined as the sharp edge between the anterior and diaphragmatic surfaces of the heart (Figs 3.56 and 3.58)-it is formed mostly by the right ventricle and a small portion of the left ventricle near the apex;
  • the obtuse margin separates the anterior and left pulmonary surfaces (Fig. 3.56)-it is round and extends from the left auricle to the cardiac apex (Fig. 3.58), and is formed mostly by the left ventricle and superiorly by a small portion of the left auricle

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CORONARY DISTRIBUTION

Details of coronary distribution require integration into a concept of total cardiac supply. Most commonly, the right coronary artery supplies all the right ventricle (except a small region right of the anterior interventricular groove), a variable part of the left ventricular diaphragmatic aspect, the posteroinferior one-third of the intraventricular septum, the right atrium and part of the left, and the conducting system as far as the proximal parts of the right and left crura.

Left coronary distribution is reciprocal, and includes most of the left ventricle, a narrow strip of right ventricle, the anterior two-thirds of the interventricular septum and most of the left atrium. As noted (Figs 60.23, 60.24), variations in the coronary arterial system mainly affect the diaphragmatic aspect of the ventricles; they consist of the relative ‘dominance’ of supply by the left or the right coronary artery. The term is misleading, as the left artery almost always supplies a greater volume of tissue.

.In ‘right dominance’, the posterior interventricular (descending) artery is derived from the right coronary; in ‘left dominance’ it derives from the left. In the so-called ‘balanced’ pattern, branches of both arteries run in or near the groove. Less is known of variation in atrial supply because the small vessels involved are not easily preserved in the corrosion casts that are used for analysis. In more than 50% of individuals, the right atrium is supplied only by the right coronary; in the remainder the supply is dual. More than 62% of left atria are largely supplied by the left and c.27% by the right coronary; in each group a small accessory supply from the other coronary artery exists, and 11% are supplied almost equally by both arteries. Sinu-atrial and atrioventricular supplies also vary. Various studies have reported that the right and left coronary arteries supply the sinu-atrial node in 51-65% and 35-45% respectively (fewer than 10% of nodes receive a bilateral supply). The atrioventricular node is supplied by the right coronary (80-90%) and left coronary arteries (10-20%).

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The large majority of cardiac veins drain into the wide coronary sinus, c.2 or 3 cm long, lying in the posterior atrioventricular groove between the left atrium and ventricle (Figs 60.2, 60.25). The sinus opens into the right atrium between the opening of the inferior vena cava and the right atrioventricular orifice; the opening is guarded by an endocardial fold (semilunar valve of the coronary sinus; Fig. 60.7). Its tributaries are the great, small and middle cardiac veins, the posterior vein of the left ventricle and the oblique vein of the left atrium; all except the last have valves at their orifices.

The great cardiac vein begins at the cardiac apex, ascends in the anterior interventricular groove to the atrioventricular groove and follows this, passing to the left and posteriorly to enter the coronary sinus at its origin .It receives tributaries from the left atrium and both ventricles, including the large left marginal vein that ascends the left aspect (‘obtuse border’) of the heart

The small cardiac vein lies in the posterior atrioventricular groove between the right atrium and ventricle and opens into the coronary sinus near its atrial end (Fig. 60.25). It receives blood from the posterior part of the right atrium and ventricle. The right marginal vein passes right, along the inferior cardiac margin (‘acute border’). It may join the small cardiac vein in the atrioventricular groove, but more often opens directly into the right atrium

The middle cardiac vein (Fig. 60.25) begins at the cardiac apex, and runs back in the posterior interventricular groove to end in the coronary sinus near its atrial end.

Posterior vein of the left ventricle  The posterior vein of the left ventricle (Fig. 60.25) is found on the diaphragmatic surface of the left ventricle a little to the left of the middle cardiac vein. It usually opens into the centre of the coronary sinus, but sometimes opens into the great cardiac vein.

Oblique vein of the left atrium  The small vessel that is the oblique vein of the left atrium (Fig. 60.25) descends obliquely on the back of the left atrium to join the coronary sinus near its end. It is continuous above with the ligament of the left vena cava. The two structures are remnants of the left common cardinal vein.

ANTERIOR CARDIAC VEINS

The anterior cardiac veins drain the anterior part of the right ventricle. Usually two or three, sometimes even five, they ascend in subepicardial tissue to cross the right part of the atrioventricular groove, passing deep or superficial to the right coronary artery. They end in the right atrium, near the groove, separately or in variable combinations. A subendocardial collecting channel, into which all may open, has been described. The right marginal vein courses along the inferior (‘acute’) cardiac margin, draining adjacent parts of the right ventricle, and usually opens separately into the right atrium. It may join the anterior cardiac veins or, less often, the coronary sinus. Because it is commonly independent, it is often grouped with the small cardiac veins, but it is larger in calibre, being comparable to the anterior cardiac veins or even wider.

SMALL CARDIAC VEINS

The existence of small cardiac veins, opening into all cardiac cavities, has been confirmed, but they are more difficult to demonstrate than larger cardiac vessels. Their numbers and size are highly variable: up to 2 mm in diameter opening into the right atrium and c.0.5 mm into the right ventricle. Numerous small cardiac veins have been identified in the right atrium and ventricle, but they are rare in the left atrium and left ventricle

The toughest layer of the esophagus is the
A.Mucosa
B.Submucosa
C.Muscularis
D.Adventitia

IInd constriction in oesophagus is seen at the following site :
(A)Where it crosses left main bronchus
(B)Crossing of aorta
(C)At pharyngoesophageal junction
(D)Where it pierces the diaphragm

Oesophagus is constricted at the beginning (15 cm (6 in) from the incisor teeth), where it is crossed by the aortic arch (22.5 cm (9 in) from the incisor teeth), where it is crossed by the left principal bronchus (27.5 cm (11 in) from the incisors) and as it passes through the diaphragm (40 cm (16 in) from the incisors). …ref gray

there are 3 constrictions ;second one by aortic arch and bronchus…..ref schwartz and sabiston…

imageimage

                                           Schwartz                                                                                                                                                                                                   Gray

 

 

Oesophagus receives supply from all of the following except :
(A)Bronchial artery
(B)Internal mammary artery
(C)Inferior phrenic artery
(D)Inferior thyroid artery

The cervical oesophagus is supplied by the inferior thyroid artery. The thoracic oesophagus is supplied by bronchial arteries and oesophageal arteries. There are four or five oesophageal arteries, which arise anteriorly from the aorta and descend obliquely to the oesophagus. They form a vascular chain on the oesophagus that anastomoses above with the oesophageal branches of the inferior thyroid arteries and below with ascending branches from the left phrenic and left gastric arteries.(The arterial supply and venous drainage of the esophagus in the posterior mediastinum involves many vessels. Esophageal arteries arise from the thoracic aorta, bronchial arteries, and ascending branches of the left gastric artery in the abdomen)

In a patient with a tumor in superior mediatinurn compressing the superior vena cava, all of the following veins would serve as alternate pathways for the blood to return to the right atrium, except:         AI 2003

A.Lateral thoracic vein
B.Internal thoracic vein
C.Hemiazygos vein
D.Vertebral venous plexus

?

All of the above can provide alternate pathways.

Im not able to find the answer to this Question

EXPLAINATION GIVEN BELOW:- Reference Snell Anatomy

image

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The possible collateral circulations of the superior and interior venae cavae. Note the alternative pathways that exist for blood to return to the right atrium of the heart if the superior vena cava becomes blocked below the entrance of the azygos vein (upper black bar). Similar pathways exist if the inferior vena cava becomes blocked below the renal veins (lower black bar). Note also the connections that exist between the portal circulation and the systemic veins in the anal canal.

The inferior vena cava is commonly compressed by the enlarged uterus during the later stages of pregnancy. This produces edema of the ankles and feet and temporary varicose veins. Malignant retroperitoneal tumors can cause severe compression and eventual blockage of the inferior vena cava. This results in the dilatation of the extensive anastomoses of the tributaries (see CD Fig. 8-3). This alternative pathway for the blood to return to the right atrium of the heart is commonly referred to as the caval–caval shunt. The “same pathway” comes into effect in patients with a superior mediastinal tumor compressing the superior vena cava. “Clinically”, the enlarged subcutaneous anastomosis between the lateral thoracic vein, a tributary of the axillary vein, and the superficial epigastric vein, a tributary of the femoral vein, may be seen on the thoracoabdominal wall (see CD Fig. 8-3). “Anatomically” many are present.

Reference Snell

Chronic thrombosis of the inferior vena cava

A medical student was asked to inspect the abdomen of two patients. On the first patient he noted irregular veins radiating from the umbilicus. On the second patient he noted irregular veins, coursing in a caudal to cranial direction, over the anterior abdominal wall from the groin to the chest. He was asked to explain his findings and determine the significance of these features.

In the first patient the veins were draining radially away from the periumbilical region. In normal individuals, enlarged veins do not radiate from the umbilicus. In patients with portal hypertension the portal venous pressure is increased as a result of hepatic disease. Small collateral veins develop at, and around, the obliterated umbilical vein. These veins pass through the umbilicus and drain onto the anterior abdominal wall, forming a portosystemic anastomosis. The eventual diagnosis for this patient was cirrhosis of the liver.

The veins draining in a caudocranial direction on the anterior abdominal wall in the second patient is not a typical appearance of veins on the anterior abdominal wall. When veins are so prominent it usually implies that there is an obstruction to the normal route of venous drainage and an alternative route has been taken. Typically, blood from the lower limbs and the retroperitoneal organs drains into the inferior cava and from here to the right atrium of the heart. This patient had a chronic thrombosis of the inferior vena cava preventing blood returning to the heart by the ‘usual’ route.

Blood from the lower limbs and the pelvis may drain via a series of collateral vessels, some of which include the superficial inferior epigastric veins, which run in the superficial fascia. These anastomose with the superior, superficial, and deep epigastric venous systems to drain into the internal thoracic veins, which in turn drain into the brachiocephalic veins and the superior vena cava.

After the initial inferior vena cava thrombosis, the veins of the anterior abdominal wall and other collateral pathways hypertrophy to accommodate the increase in blood flow.

52-year-old man presented with headaches and shortness of breath. He also complained of coughing up small volumes of blood. Clinical examination revealed multiple dilated veins around the neck. A chest radiograph demonstrated an elevated diaphragm on the right and a tumor mass, which was believed to be a primary bronchogenic carcinoma.

 

By observing the clinical findings and applying anatomical knowledge, the site of the tumor can be inferred.

The multiple dilated veins around the neck are indicative of venous obstruction. The veins are dilated on both sides of the neck, implying that the obstruction must be within a common vessel, the superior vena cava. Anterior to the superior vena cava in the right side of the chest is the phrenic nerve, which supplies the diaphragm. Because the diaphragm is elevated, suggesting paralysis, it is clear that the phrenic nerve has been involved with the tumor.

clip_image002

Four pairs of lumbar veins collect blood by dorsal tributaries from the lumbar muscles and skin. These branches anastomose with tributaries of the lumbar origin of the azygos and hemiazygos veins .The abdominal tributaries to the lumbar veins drain blood from the posterior, lateral and anterior abdominal walls, including the parietal peritoneum. Anteriorly, the abdominal tributaries anastomose with branches of the inferior and superior epigastric veins. These anastomoses provide routes of continued venous drainage from the pelvis and lower limb to the heart in the event of inferior vena caval obstruction. The abdominal tributaries drain into the superior epigastric veins and hence via the internal thoracic veins to the superior vena cava, whereas the dorsal tributaries carry blood into the azygos and hemiazygos system and hence into the superior vena cava. Near the vertebral column, the lumbar veins drain the vertebral plexuses and are connected by the ascending lumbar vein, which is a vessel running longitudinally anterior to the roots of the transverse processes of the lumbar vertebrae

Collaterals in inferior vena caval occlusion

Occlusion of the inferior vena cava may follow thrombosis resulting from hypercoagulable conditions, or embolism from lower limb or pelvic thromboses. The increased pressure within the lower body circulation leads to oedema of the legs and back, without ascites. Collateral venous circulation is established through a wide range of anastomoses between branches that drain ultimately to the superior vena cava. The lumbar veins connect to branches of the superior epigastric, circumflex iliac, lateral thoracic and posterior intercostal veins. They also anastomose with tributaries of the azygos, hemiazygos and lumbar azygos veins. The interconnecting vertebral venous plexuses provide an additional route of collateral circulation between the vena cavae

SUPERIOR VENA CAVAL OBSTRUCTION

 

Superior vena caval obstruction is characterized by headaches, facial congestion and facial oedema. It is often caused by bronchial carcinoma involving the right upper lobe of the lung or metastatic involvement of the right paratracheal lymph nodes causing circumferential narrowing or complete obstruction of the superior vena cava. This impairs venous drainage of the head, neck and upper arms. This is usually considered to be an oncological emergency and symptoms may be relieved by insertion of a vascular stent or by radiotherapy to the affected region after a tissue diagnosis is established.

The level of SVC obstruction relative to the insertion of the azygous vein is predictive of the patient’s degree of symptoms. Obstruction of the SVC above the insertion of the azygous vein may cause fewer symptoms, because the azygous vein provides venous drainage for the head and upper extremities. If the level of obstruction is below the azygous vein, then venous drainage occurs via collaterals to the inferior vena cava.

.An obstructed superior vena cava (SVC) initiates collateral venous return to the heart from the upper half of the body through 4 principal pathways. The first and most important pathway is the azygous venous system, which includes the azygous vein, the hemiazygous vein, and the connecting intercostal veins. The second pathway is the internal mammary venous system plus tributaries and secondary communications to the superior and inferior epigastric veins. The long thoracic venous system, with its connections to the femoral veins and vertebral veins, provides the third and fourth collateral routes, respectively

INFERIOR VENA CAVA

The thoracic part is very short, partly inside and partly outside the pericardial sac. The extrapericardial part is separated from the right pleura and lung by the right phrenic nerve. The intrapericardial part is covered, except posteriorly, by inflected serous pericardium. The venous drainage from the tissues below the diaphragm finally ends in the inferior vena cava. The inferior vena cava traverses the diaphragm at the level of the eight and ninth thoracic vertebrae between the right and central tendon of the diaphragm (p. 1081). It then passes through the pericardium and drains into the inferoposterior part of the right atrium.

COLLATERAL VENOUS CHANNELS

In obstruction of the upper inferior vena cava, the azygos and hemiazygos veins and vertebral venous plexuses are the main collateral channels maintaining venous circulation. They connect the superior and inferior venae cavae and communicate with the common iliac vein by the ascending lumbar veins and with many tributaries of the inferior vena cava.

Veins of the vertebral column form intricate plexuses along the entire column, external and internal to the vertebral canal. Both groups are devoid of valves, anastomose freely with each other, and join the intervertebral veins. Interconnections are widely established between these plexuses and longitudinal veins early in fetal life. When development is complete, the plexuses drain into the caval and azygos/ascending lumbar systems via named veins which accompany the arteries described above. The veins also communicate with cranial dural venous sinuses and with the deep veins of the neck and pelvis. The venous complexes associated with the vertebral column can dilate considerably, and can form alternative routes of venous return in patients with major venous obstruction in the neck, chest or abdomen. The absence of valves allows pathways for the wide and sometimes paradoxical spread of malignant disease and sepsis. Pressure changes in the body cavities are transmitted to these venous plexuses and thus to the CSF, though the cord itself may be protected from such congestion by valves in the small veins which drain from the cord into the internal vertebral plexus.

14 Responses to “Anatomy Thorax”

  1. […] Anterior views of the coronary arterial system, with the principal variations. The right coronary arterial tree is shown in magenta, the left in full red. In both cases posterior distribution is shown in a paler shade. A, The most common arrangement. B, A common variation in the origin of the sinuatrial nodal artery. C, An example of left ‘dominance’ by the left coronary artery, showing also an uncommon origin of the sinuatrial artery. (Text and images retrieved from: http://pgmcqs.com/2011/05/17/anatomy-thorax/) […]

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