ANATOMY OF THE 1 AND VESSELS

A fundamental knowledge of cardiac anat- cushion tissue, or primitive connective tissue, omy provides a concrete foundation for diag- begins to invade the cardiac jelly lying between nostic cardiovascular pathology and is requisite the endodermal and mesothelial layers (2). for understanding the clinical manifestations of Over the ensuing weeks, this heart tube will cardiac disease. In this introductory chapter, the form, through active and passive mechanisms, anatomy of the heart and blood vessels is pre- seven distinct septa. These divide it into a four- sented, with special emphasis on development, chamber structure with two pairs of valves, two gross structure, and histology to allow for a com- large , and typically six distinct venous plete understanding of the tumors and tumor- connections. like conditions described in this Fascicle. It follows from this brief overview that the heart and are derived entirely from CARDIAC EMBRYOLOGY mesodermal structures. All primary tumors of the heart and pericardium are also of mesodermal Formation of the Heart Tube origin. Cardiac tumors can also primarily consist Approximately 2 weeks after fertilization, a of mesodermal elements, such as fat, that become crescentic zone of thickened mesoderm, the entrapped during the process of septation. precursor of the heart and pericardium, appears The exceptions consist of tumors of mis- adjacent to the margin of the embryonic disc placed endodermal rests, and neural tumors, (1). A day or two later, this thickened zone of which are of ectodermal origin. Cardiac tumors mesoderm splits into somatic and splanchnic with endodermal elements, such as glandular layers, which surround the pericardial portion structures present in bronchogenic cysts, tumors of the coelomic cavity, or pericardial coelom. of the atrioventricular (AV) node, are presumed Endothelial tubes (cardiac primordial) form as to arise from embryologically misplaced tissues paired, lateral structures from the splanchnic (3). Theoretically, endodermal structures could mesodermal layer of the primitive pericardial be incorporated into cardiac tissue early in em- cavity where it lies close against the develop- bryogenesis when the foregut is adjacent to the ing foregut. By the third week, the endocardial laterally placed cardiogenic plates (4). Neural tubes have fused in the midline, forming the tumors of the heart are rare and are virtually primitive heart tube, consisting of three basic limited to paragangliomas and granular cell layers: the endocardial layer, intervening cardiac tumors of the epicardial surfaces and atria. “jelly,” and a mesothelial layer lining the peri- The histogenesis of some cardiac tumors, cardial coelom. The heart tube has arterial and such as cardiac myxoma, remains somewhat venous poles at the cranial and caudal aspects, controversial. The cardiac jelly, which supports respectively, and begins to beat. the epimyocardial layer and endothelial layer, is present from before 2 weeks of gestation (four- Looping of the Heart Tube and Septation somite embryo), and becomes infiltrated from Rapid bulboventricular growth of the tube, the endothelial surface by endocardial cushion which is tethered to the dorsal aspect of the cells (2). These cells are the putative cells of embryo and contained within the pericardial origin of cardiac myxoma, and are believed cavity, causes an anterior and rightward displace- to persist in some adults near the ment of the primitive ventricular portion and a (5). The rare occurrence of glandular structures posterior displacement of its primitive atrial and within cardiac myxoma is an incidental curios- venous portions. During this time, endocardial ity for the surgical pathologist, who should not

 Tumors of the Heart and Great Vessels

Figure 1-1 CARDIAC SILHOUETTE The size of the heart, in relation to the thorax, is demonstrated here on chest radiograph. The heart occupies less than 60 percent of the thorax in this view. Figure 1-2 PARIETAL PERICARDIUM ­mistake them for adenocarcinoma. It is difficult, With the anterior aspect of the parietal pericardium however, to satisfactorily explain their presence removed, the intrapericardial portions of the superior vena cava, , and pulmonary are apparent. from an embryologic view. In some cases, glan- dular cells appear to evolve from myxoma cells, casting doubt on the theory that they arise from the atria forming the base and the ventricles entrapped endodermal rests (6). It is also possible forming the apex, which is typically directed that cardiac myxoma is a true neoplasm of plu- leftward, anterior, and inferior. ripotent mesodermal cells (endocardial cushion External Cardiac Anatomy cells) and that the neoplastic alteration is capable of inciting these cells, which are of mesodermal The heart is covered and surrounded by origin, to form mucin-producing glands. the fluid-containing pericardial sac, which consists of both visceral and parietal portions. ANATOMY OF THE HEART The visceral pericardium, or epicardium, covers AND GREAT VESSELS the heart and intrapericardial portions of the great vessels, while the parietal pericardium Cardiac Position surrounds the heart, attaching along the great Consistent with their embryonic origins as vessels at the reflection of the visceral layer midline structures, the heart and great vessels (fig.1-2). The space between these two layers are situated in the mid-thorax, within the me- contains serous (25 mL or less diastinum. The heart, aortic arch, and descend- in adults) providing for friction-free movement ing thoracic aorta are located in the middle, within the chest. superior, and posterior regions, respectively. The AV groove is found at the plane of the Radiologically, the heart occupies less than 60 base of the heart and contains the circumflex percent of the thorax when viewed on a postero- and right , which travel in the anterior chest radiograph (fig.1 -1). The heart is a left and right AV grooves, respectively. The an- four-chambered, roughly conical structure, with terior and inferior interventricular grooves are

 Anatomy of the Heart and Blood Vessels

found at the plane of the ventricular septum and have an endocrine role by releasing natriuretic contain the anterior and posterior descending hormones in response to atrial stretch, helping coronary arteries, respectively. to maintain fluid homeostasis (7). The anterior and inferior free walls of the The atria consist of both septal and free wall right intersect to form the acute mar- portions. The free wall of the right is gin. The rounded lateral wall of the left ventricle smooth posteriorly and trabeculated anteriorly. forms a more ill-defined obtuse margin. Vessels The smooth portion, derived from the embry- supplying these regions are named accordingly; onic sinus venosus, receives the vena cavae and obtuse marginal branches have the circumflex is bordered anteriorly by the crista terminalis. coronary artery and acute marginal branches The trabeculated portion contains prominent of the right coronary artery. The intersection muscular bands, the , that of the major lines of division (atrioventricular, arise perpendicular to the crista terminalis and interventricular, and interatrial) is along the dia- extend anteriorly to involve the pyramidal right phragmatic surface of the heart and is referred atrial appendage (fig.1 -4, left). The free wall of to as the crux of the heart. the left atrium includes a dome-shaped body, Tumor location within the heart is relevant which receives the pulmonary veins, and a to not only its potential hemodynamic conse- worm-like atrial appendage (fig.1 -4, right). Like quences, but also often provides insights into the right atrium, the left atrial appendage con- the type of tumor (since certain cardiac tumors tains pectinate muscles, although they are not tend to have predilections for various locations prominent and are isolated to the periphery of within the heart). Thus, an understanding of not the appendage where they are radially arranged. only the normal size and shape of the cardiac The left atrium contains no crista terminalis. chambers and great vessels, but also their relative The atrial septum, when viewed from the positions three dimensionally, is required (fig.1 - right aspect, contains both an interatrial com- 3). The right atrium forms the right lateral border ponent (between the right and left atria) and an of the heart while the right ventricle is situated atrioventricular component (between the right so that it forms the anterior surface of the heart. atrium and the left ventricle). This is because the The left ventricle is a largely posterior structure, annulus is situated more apically also forming the left lateral heart border. The left than the annulus at the septum atrium lies in a midline-posterior position and (fig. 1-5). The interatrial portion contains the is really not a left-sided structure at all. fossa ovalis, with its two major components: The arises anterior, supe- a central sheet-like region (the valve of the rior, and to the left of the aorta. The superior fossa ovalis) surrounded by a horseshoe-shaped and inferior vena cavae are continuous with the muscular ridge referred to as the limbus of the right lateral heart border formed by the right fossa ovalis (fig. 1-6) (8). In some individuals, atrium. The coronary sinus is the major venous the valve and limbus do not fuse after birth and drainage conduit for the heart and travels in a potential passageway between the two atria the left AV groove (in parallel with the circum- persists and is referred to as a patent foramen flex coronary artery), emptying into the right ovale (9). The atrioventricular portion consists atrium near the atrial septum. The left and right of a muscular and membranous portion and pulmonary veins join the left atrium along its contains the AV node and penetrating bundle posterolateral aspect and typically consist of of His. When viewed from the left aspect, the a superior and an inferior vessel on each side, atrial septum is entirely interatrial and may totaling four pulmonary veins. be somewhat fenestrated in the region of the valve of the fossa ovalis, corresponding to the Internal Cardiac Anatomy embryologic ostium secundum. Atria. The right and left atria receive blood Ventricles. The ventricles receive blood draining from the systemic and pulmonary through their atrioventricular valves from venous systems, respectively, and pass the their respective atria and pump it across the blood into their corresponding ventricles. In semilunar valves into their great arteries. Dur- addition to their pumping functions, the atria ing ventricular systole, the ventricles decrease

 Tumors of the Heart and Great Vessels

Figure 1-3 EXTERNAL CARDIAC ANATOMY The heart and great vessels are exhibited from the anterior (A), inferior (B), left lateral (C), and right anterior oblique (D) anatomic perspectives. (SVC = superior vena cava; RA = right atrium; Ao = aorta; PA = pulmonary artery; LAA = left atrial appendage; RV = right ventricle; LV = left ventricle; LA = left atrium; LLPV = left lower pulmonary vein; RLPV = right lower pulmonary vein; IVC = inferior vena cava; LPA = left pulmonary artery; LUPV = left upper pulmonary vein; RPV = right-sided pulmonary veins; RAA = right atrial appendage.) their short axis diameters and also their base- The right ventricle is a crescent-shaped cham- apex lengths to expel blood into the arteries ber when viewed in the short axis plane. The and concomitantly close the atrioventricular inlet portion is associated with the tricuspid valves. They are divided into inlet, trabecular, valve with its septal cordal insertions. Antero- and outlet regions. apically, trabeculations of muscle extend from

 Anatomy of the Heart and Blood Vessels

Figure 1-4 COMPARISON OF THE RIGHT AND LEFT ATRIA Left: The right atrial free wall viewed from the left lateral perspective exhibits the crista terminalis (CT), with the perpendicularly oriented pectinate muscles (PM) extending from the CT, anteriorly. The superior vena cava (SVC) and inferior vena cava (IVC) empty into the smooth-walled portion of the atrium. The pyramidal appendage (RAA) is also evident. Right: The left atrial free wall viewed from the right lateral perspective exhibits the dome-shaped portion into which the left- and right-sided pulmonary veins (LPV and RPV, respectively) drain. Small radially oriented pectinate muscles are present only in the appendage (LAA).

Figure 1-5 CARDIAC SEPTA The interatrial, interven­ tricular, and atrioventricular (AVS) septa are exhibited in this four-chamber anatomic plane. The more apically positioned tricuspid valve annulus (TV) can be compared to the position of the mitral valve annulus (MV).

 Tumors of the Heart and Great Vessels

Figure 1-6 ATRIAL SEPTUM The opened right atrium exhibits the fossa ovalis portion of the atrial septum, consisting of the valvular component (VFO) as well as the horseshoe-shaped limbus. The opening of the coronary sinus (CS) is seen anteriorly, as well as the septal tricuspid valve leaflet (TV).

the septum to the free wall and serve as a con- shaped annulus, commissures, and leaflets) and a venient region in which to lodge pacemaker/ tensor apparatus (consisting of tendinous cords cardioverter-defibrillator leads or from which and papillary muscles) (fig.1 -8) (11,12). The leaf- to obtain endomyocardial biopsies (fig. 1-7). lets consist of fibrous connective tissue and have The remaining smooth-walled outlet region is an annular edge, free edge, and closing surface. often referred to as the infundibulum (meaning This closing surface is the surface of the leaflet funnel) or right ventricular outflow tract. that comes into contact with the apposing leaflet The left ventricle is a circular chamber when during ventricular systole. Tendinous cords ex- viewed in the short axis plane and is composed tend from papillary muscles, branching multiple of muscular myocyte bundles arranged in a com- times, to insert along the ventricular aspect and plex meshwork, with populations of myocytes free edge of the leaflet; upwards of 150 cords aligned both tangential to the epicardial and insert onto each valve, distributing the force endocardial surfaces and traversing the thickness along the undersurface of the leaflet (13,14). of the wall (10). This arrangement results in a The cords are anchored to the ventricular walls, twisting motion of the ventricle during systole, either by attaching directly to the ventricular wringing the blood into the outflow tract. The septum (a feature seen only in morphologic inflow region of the valve is bordered by the mi- tricuspid valves) or to papillary muscles located tral valve cords, which extend downward onto beneath the commissures. Contraction of the papillary muscles with no direct septal cordal papillary muscles during ventricular systole attachments (as opposed to the right ventricle). helps facilitate AV valve closure by bringing the The apical region is characterized by trabecula- leaflets into apposition. tions that are much shallower than those seen in The AV valves differ in their morphologic ap- the right ventricle (fig.1 -7). The outflow region pearance. The tricuspid valve has three distinct of the left ventricle is musculomembranous, leaflets, commissures, and papillary muscles consisting of not only the ventricular septum whereas the mitral has only two of each. As and anterobasal free wall anteriorly, but also the previously noted, the annulus of the tricuspid anterior mitral leaflet posteriorly. valve is situated more apically on the septum. Cardiac Valves. The AV valves allow for The mitral valve has an anterior leaflet (that unidirectional blood flow between the atria and forms part of the left ventricular outflow tract) the ventricles. They have two basic structural ele- as well as a more shallow, scalloped, posterior ments: a valvular apparatus (consisting of saddle- leaflet that has three segments (P1, P2, and P3)

 Anatomy of the Heart and Blood Vessels

Figure 1-7 INTERNAL CARDIAC ANATOMY Four-chamber views shown from the inferior (left) and superior (right) perspectives with the apex directed downward. (CS = coronary sinus; LCX = left circumflex coronary artery; LA = left atrium; MV = mitral valve; LV = left ventricle; VS = ventricular septum; RV = right ventricle; TV = tricuspid valve; RA = right atrium; RCA = right coronary artery; IVC = inferior vena cava; AV = atrioventricular septum; AS = atrial septum; PV = lower pulmonary veins.)

Figure 1-8 MITRAL APPARATUS The sail-like anterior mitral leaflet (Ant) is situated between a shallow, tri-scalloped (P1, P2, and P3) posterior leaflet. The posteromedial (PM) and anter­ olateral (AL) papillary muscles are located directly beneath the commissures (yellow arrow­ heads).

 Tumors of the Heart and Great Vessels

(fig.1 -8) (15). A morphologic tricuspid valve al- teries. Anatomically, they are simpler than their ways empties into a morphologic right ventricle, AV counterparts, consisting of an annulus and whereas a morphologic mitral valve always cusps devoid of a tensor apparatus (papillary empties into a morphologic left ventricle. muscles and tendinous cords). The annulus is The semilunar valves allow for unidirectional a complex three-dimensional structure, shaped blood flow between the ventricles and great ar- like a triradiate crown, with the three points at the level of the sinotubular junction demarcat- ing the commissures. These commissures are the points where two cusps meet. The cusps them- selves are half-moon–shaped (semilunar) struc- tures with various anatomic features (fig. 1-9). The nonannular edge is the free edge, beneath which is situated a biscalloped ridge referred to as the closing edge. The region between the free edge and the closing edge is often referred to as the closing surface, or lunula, and serves as the point of contact with the neighboring cusps (fig.1 -10) (16). The nodule of Arantius is a small fibrous mound situated at the free edge at the center of each cusp. The aortic and pulmonary semilunar valves are anatomically similar, with the being slightly thicker. The relationship of the four major cardiac valves is best understood by an examination Figure 1-9 of the cardiac base with the atria removed (so- AORTIC VALVE CUSP called surgeon’s view) (fig. 1-11). The aortic Each semilunar valve cusp has a free edge (white valve is situated in the middle and its annulus is arrowhead), a closing edge (black arrowhead), a nodule in continuity with the other three major valves: of Arantius (asterisk), and an annulus (dotted line). The left-posterior commissure to mitral valve, right- moon-shaped region between the free and closing edges is referred to as the lunula. posterior commissure to tricuspid valve, and

Figure 1-10 AORTIC VALVE The aortic valve is in closed position (ventricular diastole) (left), and open position (ventricular systole) (right). The left and right coronary ostia are located slightly above the free edges of the open cusps.

 Anatomy of the Heart and Blood Vessels

right-left commissure to . The After arising from the right , valves do not reside in the same plane or even the right coronary artery (RCA) wraps around parallel planes. Because of the intertwining of the the right lateral aspect of the heart within the great arteries, the aortic and pulmonary valves right AV groove to give rise to the posterior are skewed 60 to 90 degrees as the valvular ori- descending coronary artery about 70 percent fices are directed toward opposite shoulders. The of the time, making it the dominant coronary tricuspid and mitral valves are skewed 10 to 15 degrees with respect to one another, changing somewhat throughout the cardiac cycle. Vascular Supply and Drainage. The blood supply of the heart is derived primarily from the left and right epicardial coronary arteries, which arise from the left and right aortic sinuses (of Valsalva), respectively, typically just below the sinotubular junction. The left main coronary artery branches to become the left anterior descending (LAD) and left circumflex (LCX) coronary arteries (fig. 1-11). The LAD courses from the base to apex in the anterior interventricular sulcus and wraps pos- teriorly at the apex to a variable extent. Conse- quently, the LAD supplies the anterolateral and anteroseptal left ventricle, the basal- and mid- ventricular levels, and the entire left ventricle at the apical level. Branches arising from the LAD over the surface of the heart are referred to as Figure 1-11 diagonal branches. The LAD also gives rise to BASE OF THE HEART an extensive network of vessels branching into The centrally located aortic valve (AV) is adjacent to the anterior portion of the ventricular septum the three other major cardiac valves (mitral [MV], tricuspid (fig.1 -12). The LCX wraps around the left lateral [TV], and pulmonary [PV] valves). The distribution of the epicardial coronary arteries (LAD = left anterior descending aspect of the heart within the left AV groove, coronary artery; LCX = left circumflex coronary artery; RCA supplying the lateral left ventricle at the basal- = right coronary artery; CCA = conus coronary artery) and and mid-ventricular levels. the coronary sinus (CS) is also demonstrated in this view.

Figure 1-12 LEFT ANTERIOR DESCENDING CORONARY ARTERY The numerous branches, including the downwardly directed septal perforating branches that extend into the anterior ventricular septum, are seen.

 Tumors of the Heart and Great Vessels

artery. Approximately 10 percent of the time, than neural tissue, the heart and blood vessels the posterior descending coronary artery arises receive rich autonomic innervation from the from the LCX (so-called, left-dominant ). cervical sympathetic ganglia and parasympa- The remaining 20 percent of hearts are said to be thetic vagus nerves, from which neural neo- co-dominant, with both RCA and LCX contrib- plasms occasionally arise. uting to the supply of the posterior descending Examination of the cardiac conduction sys- coronary artery. tem is important when assessing for involve- The sinus node is supplied by the RCA in 60 ment by various tumors. The sinus node is evalu- percent of hearts and from the left circumflex in ated by procuring a rectangular portion of tissue the remaining 40 percent. The AV node, however, at the superior portion of the sulcus terminalis, derives its blood supply from the dominant just anterior to the junction of the superior vena coronary artery. cava and the right atrium (fig.1 -13) (18). Often, The venous circulation of the heart is com- a grossly visible artery, the sinus node artery, posed of the coronary sinus, anterior cardiac is seen running through the center of the rect- venous system, and thebesian venous system. angle, helping to confirm the correct anatomic The great cardiac vein is situated adjacent to area. The AV node is evaluated by procuring a the LAD and LCX and receives blood from rectangular portion of heart that includes the the territory supplied by both before draining so-called triangle of Koch, which is bordered by into the coronary sinus. The coronary sinus is the tricuspid valve annulus, the opening of the located adjacent to the posterior LCX and also coronary sinus, and the tendon of Todaro (fig. receives blood from various small cardiac veins 1-14). At the apex of this triangle, the AV node and tributaries; it drains directly into the right is reliably found. Both of these rectangles can atrium (17). Numerous small thebesian veins then be serially sectioned and submitted in a drain directly into the cardiac chambers, usually systematic way to allow for evaluation of the the right atrium and ventricle. conducting tissue contained within them. Conduction System. The cardiac conduction system typically refers to the specialized cardiac CARDIAC HISTOLOGY myocytes responsible for initiating the cardiac AND ULTRASTRUCTURE impulse and propagating it from the atria to Histologically, the myocardium contains the ventricles. Normally, the impulse begins in a number of cell types in addition to cardiac the heart’s pacemaker, the sinoatrial (or sinus) myocytes, which comprise the majority of the node, located subepicardially at the junction of heart’s mass. The myocardium also contains the sinus venosus and the right atrium, just an- fibroblasts (present in greater numbers than terior to the superior vena cava. From the sinus even cardiac myocytes), endothelial cells, and node, conduction propagates to the AV node, smooth muscle myocytes (19). Cardiac myo- located subendocardially in the AV septum, by cytes are 20 to 30 µm in diameter and generally way of several internodal tracts. From the AV about four times this in length (fig.1 -15). They node, the impulse is conducted through the are characterized by dense cross-bands, called by the penetrating bundle of intercalated discs, which represent highly spe- His, where it is transmitted to the left and right cialized intercellular attachment points that , and ultimately, the Purkinje create a branching network of muscle fibers, fibers and the ventricular myocardium. which are connected physically and electrically. In addition to being influenced by the sym- This allows for an electromechanical syncytium pathetic and parasympathetic nervous systems, that allows the heart to contract and relax in as well as circulating catecholamines and elec- an orderly fashion. Cardiac myocytes contain trolytes, the function of the conduction system one or two centrally placed nuclei, helping to can be influenced by tumors. Mass effect from ­differentiate cardiac-type striated muscle from histologically benign tumors can have devastat- the skeletal variety. The perinuclear region is rich ing arrhythmic consequences within the heart in glycogen, mitochondria, and often lipofuscin muscle. Despite the fact that the conduction pigment granules. Atrial myocytes also typically system tissue itself consists of myocytes, rather contain perinuclear granules (0.3 to 0.4 µm in

10 Anatomy of the Heart and Blood Vessels

Figure 1-13 SINOATRIAL (SINUS) NODE Left: The location of the epicardial sinus node is within the rectangular box. The sinus node artery is faintly seen running through the central portion of this area. Right: Serial sectioning of the rectangular box allows for histologic evaluation of the sinoatrial (SA) node.

Figure 1-14 The atrioventricular (AV) node is a subendocardial structure that lies within the triangle of Koch (A). Removal of this area (B), followed by serial sectioning (C), allows for histologic evaluation of the AV node.

11 Tumors of the Heart and Great Vessels

Figure 1-15 MYOCARDIUM Normal, branching cardiac myocytes (left, longitudinally oriented; right, oriented in cross section) are 20 to 30 µm in diameter and have one or two centrally placed nuclei.

Figure 1-16 ATRIAL NATRIURETIC PEPTIDE GRANULES Perinuclear granules are seen on ultrastructural analysis of the atrial myocardium.

size) that contain atrial natriuretic factor; they conducting it along anatomic pathways, allow- are best demonstrated on ultrastructural exami- ing for an organized pattern of contraction and nation (fig. 1-16). relaxation which results in optimal emptying As alluded to above, a specialized population and filling of the chambers. Nodal tissue contains of myocytes comprises the cardiac conduction four morphologic types of myocytes in varying system. Although all myocytes are capable of proportions: small, pale staining nodal or P cells; impulse conduction, this population of cells is re- contractile-type myocardial cells; transitional sponsible for generating the impulse and rapidly cells with a hybrid morphology of nodal- and

12 Anatomy of the Heart and Blood Vessels

contractile-type cells; and Purkinje cells (fig. 1- 17) (20,21). The Purkinje cells tend to be larger (up to 2 times) than contractile-type myocytes and are paler staining, owing to their glycogen content. While seen in variable quantities in the nodes, particularly the AV node, Purkinje cells are usu- ally identified in the subendocardium, where they form an extensive network by which impulses are conducted to the ventricular myocardium. Understanding the histomorphologic features of the various cell types, as well as their usual arrangement, is important in diagnosing certain types of cardiac tumors, particularly hamarto- mas. Hamartoma of mature cardiac myocytes, for example, is a grossly evident white mass that histologically is composed of enlarged myocytes in a haphazard distribution. A poorly under- Figure 1-17 stood entity, histiocytoid cardiomyopathy, is PURKINJE CELLS thought to represent a hamartomatous lesion Pale Purkinje cells (P) comprise part of the conduction composed of Purkinje-type cells. system. These cells contain abundant glycogen and are larger than the contractile cells of the heart (located in the ANATOMY AND HISTOLOGY upper segment of this figure). OF BLOOD VESSELS main pulmonary artery. The tubular ascending Elastic Arteries aorta transitions to the aortic arch at the takeoff The major elastic arteries include the aorta of the brachiocephalic artery, just beyond the and the pulmonary arteries. While the over- pericardial reflection. Consequently, the ascend- all diameters of these two vessels are similar ing aorta is almost entirely intrapericardial. The throughout life, the wall of the pulmonary aortic arch normally travels over the left bron- artery is typically less than half the thickness chus as well as the right pulmonary artery. The of the aortic wall. descending thoracic aorta is situated posterior to The main pulmonary artery arises from the the left atrium, adjacent to the esophagus. After right ventricle to the left of the , extending inferiorly to the diaphragm, the aorta directed toward the left shoulder. As it bifur- is referred to as the abdominal aorta before its cates, the left pulmonary artery continues as a iliac bifurcation at the level of the umbilicus. smooth arch and courses over the left bronchus, Histologically, elastic arteries are composed while the right pulmonary artery arises at a of lamellar units, typically arranged in parallel right angle and travels beneath the aortic arch, from the intimal surface to the adventitia (fig. posterior to the superior vena cava. 1-18). The elastic tissue in the pulmonary artery The aorta arises at the level of the aortic valve is somewhat discontinuous, imparting a slightly annulus and terminates at its bifurcation into more disorganized-appearing architecture (23). A the common iliac arteries. The aorta is divided lamellar unit consists of smooth muscle, collagen, into four primary regions: the ascending aorta and ground substance sandwiched between elas- (including the aortic root), aortic arch, descend- tic fiber plates. The orientation of the elastic ing thoracic aorta, and abdominal aorta. The fibers, as well as the relative amounts of muscle, ascending aorta and aortic arch are of neural collagen, and ground substance, vary between crest derivation, while the remaining portions elastic arteries as well as regionally within the are derived from the primitive vascular mesen- same elastic vessel (24). The composition and chyme (22). The ascending aorta is divided into structure of elastic arteries provide them with the aortic root (or sinus) and the tubular por- an amazing ability to stretch and accommodate tion, and arises to the right and posterior of the the pressures generated by the ventricles.

13 Tumors of the Heart and Great Vessels

Figure 1-18 ELASTIC ARTERY Parallel elastic membranes are located from the adventitial surface to the intimal surface. Juxtaposed between the elastic membranes are smooth muscle myocytes, collagen, and ground substance (aorta, Verhoeff-van Giesson stain).

Figure 1-19 MUSCULAR ARTERY Muscular arteries contain two prom­ inent elastic membranes: one at the intimal-medial junction and one at the medial-adventitial junction. The internal elastic lamina is typically more prom­ inent, as in this example. Between these membranes are abundant smooth muscle fibers arranged both concentrically and obliquely, maintaining vascular tone and modulating resistance (left anterior descending coronary artery, Verhoeff-van Giesson stain).

junction of the media and intima, and an external Muscular Arteries elastic layer between the media and adventitia. The epicardial coronary arteries, described Veins above, are the prototypical muscular arteries of the heart. While muscular arteries contain the The epicardial cardiac veins, running antipar- same basic components as elastic arteries, their allel to their arterial counterpart, are relatively relative quantities and the arrangement are thin-walled. In contrast to the muscular arter- strikingly different. Instead of parallel lamellar ies, the media is thin, consisting of bundles of units, a well-developed muscular media with little smooth muscle and collagen with a haphazard collagen or elastin characterizes muscular arteries arrangement of elastic fibers in the outer me- (fig. 1-19). Two distinct elastic layers are usually dia and adventitia. Cardiac veins do not have present: an inner internal elastic membrane at the distinct elastic membranes.

14 Anatomy of the Heart and Blood Vessels

REFERENCES

1. Gittenberger-de Groot AC, Bartelings MM, Deru- 13. Seccombe JF, Cahill DR, Edwards WD. Quanti- iter MC, Poelmann RE. Basics of cardiac develop- tative morphology of normal human tricuspid ment for the understanding of congenital : autopsy study of 24 cases. Clin Anat 1993; malformations. Pediatr Res 2005;57:169-176. 6:203-212. 2. Wessels A, Sedmera D. Developmental anatomy 14. Roberts WC. Morphologic features of the normal of the heart: a tale of mice and man. Physiol and abnormal mitral valve. Am J Cardiol 1983; Genomics 2003;5:165-176. 51:1005-1028. 3. Linder J, Shelburne JD, Sorge JP, Whalen RE, 15. Morris MF, Maleszewski JJ, Suri RM, et al. CT Hackel DB. Congenital endodermal heterotopia and MR imaging of the mitral valve: radiologic- of the atrioventricular node: evidence for the pathologic correlation. Radiographics 2010;30: endodermal origin of so-called mesothelio- 1603-1620. mas of the atrioventricular node. Hum Pathol 16. Bennett CJ, Maleszewski JJ, Araoz PA. CT and MR 1984;15:1093-1098. imaging of the aortic valve: radiologic-pathologic 4. Ariza S, Rafel E, Castillo JA, Garcia-Canton JA. correlation. Radiographics 2012;32:1399-1420. Intracardiac heterotopia—mesenchymal and 17. Noheria A, Desimone CV, Lachman N, et al. endodermal. Br Heart J 1978;40:325-327. Anatomy of the coronary sinus and epicardial 5. Orlandi A, Ciucci A, Ferlosio A, Genta R, Spag­ coronary venous system in 620 hearts: an elec- noli LG, Gabbiani G. Cardiac myxoma cells ex- trophysiology perspective. J Cardiovasc Electro- hibit embryonic endocardial stem cell features. physiol 2013;24:1-6. J Pathol 2006;209:231-239. 18. Anderson RH, Yanni J, Boyett MR, Chandler 6. Pucci A, Bartoloni G, Tessitore E, Carney JA, NJ, Dobrzynski H. The anatomy of the cardiac Papotti M. Cytokeratin profile and neuroendo- conduction system. Clin Anat 2009;22:99-113. crine cells in the glandular component of cardiac 19. Sarantitis I, Papanastasopoulos P, Manousi M, myxoma. Virchows Arch 2003;443:618-624. Baikoussis NG, Apostolakis E. The cytoskeleton of 7. Thibault G, Garcia R, Cantia M, Genest J. Atrial the cell. Hellenic J Cardiol 2012; natriuretic factor. Characterization and partial 53:367-379. purification. Hypertension1 983;5(Pt 2):I75-180. 20. Waller BF, Gering LE, Branyas NA, Slack JD. 8. Sweeney LJ, Rosenquist GC. The normal anatomy Anatomy, histology, and pathology of the cardiac of the atrial septum in the human heart. Am conduction system: Part I. Clin Cardiol 1993;16: Heart J 1979;98:194-199. 249-252. 9. Hagen PT, Scholz DG, Edwards WD. Incidence and 21. Waller BF, Gering LE, Branyas NA, Slack JD. size of patent foramen ovale during the first 10 Anatomy, histology, and pathology of the cardiac decades of life: an autopsy study of 965 normal conduction system: Part II. Clin Cardiol 1993; hearts. Mayo Clin Proc 1984;59:17-20. 16:347-352. 10. Anderson RH, Smerup M, Sanchez-Quintana 22. Jiang X, Rowitch DH, Soriano P, McMahon AP, D, Loukas M, Lunkenheimer PP. The three-di- Sucov HM. Fate of the mammalian cardiac neural mensional arrangement of the myocytes in the crest. Development 2000;127:1607-1616. ventricular walls. Clin Anat 2009;22:64-76. 23. de Sa M, Moshkovitz Y, Butany J, David TE. Histo- 11. Sonne C, Sugeng L, Watanabe N, et al. Age and logic abnormalities of the ascending aorta and pul- body surface area dependency of mitral valve and monary trunk in patients with bicuspid aortic valve papillary apparatus parameters: assessment by disease: clinical relevance to the Ross procedure. J real-time three-dimensional echocardiography. Thorac Cardiovasc Surg 1999;118:588-594. Eur J Echocardiogr 2009;10:287-294. 24. O’Connell MK, Murthy S, Phan S, et al. The 12. Badano LP, Agricola E, Perez de Isla L, Gianfagna three-dimensional micro- and nanostructure of P, Zamorano JL. Evaluation of the tricuspid valve the aortic medial lamellar unit measured using morphology and function by transthoracic real- 3D confocal and electron microscopy imaging. time three-dimensional echocardiography. Eur J Matrix Biol 2008;27:171-181. Echocardiogr 2009;10:477-484.

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