Historically, the cardiac venous system has received less attention than its companion, the arterial system. The recent increase in the performance of sophisticated electrophysiologic and interventional cardiac procedures using the cardiac veins has renewed interest in the cardiac venous system.

This chapter provides a general overview of important facets of the cardiac venous system related to its embryologic development, anatomy, physiology, pathophysiology, and clinical significance. Although nomenclature for the cardiac venous system varies slightly across reviews and journal articles,^1,2 the more commonly accepted nomenclature has been used in this chapter.

Vessels develop by a process called vasculogenesis, which involves the coalescence of angioblasts into primary vessels. Subsequent branching and growth occur by angiogenesis, a process guided by cues from vascular endothelial and other growth factors.³ The coronary arteries and veins arise from an extensive mesenchymal cell–derived subepicardial capillary plexus in the embryonic heart. This plexus spreads along the anterior interventricular sulcus (AIVS), the atrioventricular sulcus (AVS), and the posterior interventricular sulcus (PIVS); around the bulbous cordis; and finally into the myocardium. Various molecular factors play a role in the differentiation of vessels into arteries and veins.^4,5,6,7 The venous side of the subepicardial capillary plexus subsequently grows toward and into the wall of the sinus venosus. The portions of the venous capillary plexus that persist during fetal growth develop into the great cardiac vein (GCV) in the AIVS, the middle cardiac vein (MCV) in the PIVS, and the right and left marginal veins (LMVs) running along the right and left cardiac margins toward the coronary sulcus. The venous side of the capillary plexus appears to form connections with the luminal circulation earlier than the arterial side.^8,9,10,11,12

In the fourth week of embryonic life, the heart tube forms a cardiac loop that brings the sinus venosus, a conduit between the veins and atrial cavity, posterior to the atrial cavity (Figure 23-1A). The sinus venosus receives venous blood from the right and left sinus horns and empties into a common atrial cavity through a wide sinuatrial orifice. The sinus horn on each side, in turn, receives venous blood from the vitelline, umbilical, and common cardinal veins (see Figure 23-1A). By the fifth week, the left-sided vitelline and umbilical veins obliterate, reducing the left sinus horn dimensions. The wide sinuatrial orifice shifts rightward from its central position, displacing the sinuatrial orifice toward the developing right atrium (Figure 23-1B). The right sinus horn and its veins enlarge as a result of blood shunting from left to right. The right and left atria also become more distinct. At this stage, the sinus venosus, represented predominantly by the right sinus horn, is the only venous system communication with the right atrium. The sinus venosus subsequently is incorporated into the right atrium. This incorporated portion of the right atrium is smooth walled and is called the sinus venarum in adults (Figure 23-2). The sinus venarum is separated from the rest of the trabeculated atrial cavity by the crista terminalis. By the tenth week, the left common cardinal vein (also called the left duct of Cuvier) obliterates, forming a vestigial ligament called the ligament of Marshal. Only the terminal portion of the left sinus horn remains, forming the oblique vein of the left atrium and the coronary sinus (CS) (Figure 23-3).³

The sinuatrial orifice into the right atrium is initially flanked by right and left venous valves (see Figure 23-2A). Later, the superior parts of the valves fuse to form the septum spurium. As the right sinus horn is incorporated into the right atrium, the inferior part of the left valve and septum spurium fuse with the developing atrial septum. At 9 to 15 weeks gestation, the inferior part of the right venous valve develops into the Thebesian valve of the CS and the Eustachian valve of inferior vena cava (IVC) (see Figure 23-2B).³ A few muscle strands originating from the sinus venosus persist around the CS beyond fetal life.¹³

The early embryonic heart receives its nutrition by diffusion through primitive trabeculae and sinuses that penetrate the atrial and ventricular walls. As the embryo develops, the trabecular network grows, obliterating most intertrabecular spaces and forming small myocardial sinusoids. These sinusoids most likely represent the small Thebesian veins of the heart.^9,10,14 The trabeculated right and left atrial appendages arise from the primitive atria. The adult smooth-walled atria arise from the right sinus horn on the right side and pulmonary veins on the left side.³

Most anatomic analyses of the cardiac venous system is based on the examination of human cadaveric hearts, and in recent years, various imaging techniques. Although the overall venous pattern of the human heart is relatively constant, individual variations in the size, number, angulation, and tortuosity of the vessels do exist. There are extensive anastomoses at all levels of the cardiac venous system that exceed those found in the arterial system. The highest density of these communications is found at the apex of the heart. Almost all subsidiary ramifications of the epicardial cardiac veins, except for the posterior vein of the left ventricle (PVLV) and the right marginal vein (RMV), accompany their arterial counterparts (see below).^10,15 The human cardiac venous system (Figures 23-4 and 23-5) is composed of:

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  The greater cardiac venous system (GCVS)

  
  
• 
  

  The smaller cardiac venous system (SVCS; also called the Thebesian veins)

  
  
• 
  

  The compound venous system, with features of both the GCVS and the SCVS

The GCVS only drains the outer two-thirds or three-quarters of the atrial and ventricular myocardium; the inner third or quarter is drained by tributaries of the SCVS. The right atrial appendage is drained by tributaries of the SCVS only. The walls of the atria frequently have variably sized subendocardial and intramural sinuses that belong to the compound venous system. In a healthy heart, the majority of venous drainage is maintained by the GCVS. However, extensive venous communications throughout the human heart provide the SCVS the capacity to drain the bulk of venous return in cases of occluded, atretic, or absent epicardial veins.^10,15,16,17

The Greater Cardiac Venous System

The veins of the GCVS have a predominantly epimural course and distribution (Figures 23-6). These veins generally have functional and sufficient ostial valves, although a few empty into subendocardial or intramural collecting tunnels or sinuses. The GCVS usually drains 90% to 95% of the cardiac venous return in a healthy heart. The major components of this system include the CS, GCV and its tributaries, MCV (also called the posterior interventricular vein), small (right) cardiac vein, RMV, and anterior cardiac veins. Most left and right atrial veins and a few miscellaneous cardiac veins are also included. The anterior and MCVs typically lie superficial to the right coronary artery. The GCV exhibits both deep and superficial intersection patterns with the left anterior descending and circumflex arteries.⁸

The CS, GCV, MCV, and PVLV are present in the majority of human hearts. The GCV arises in the AIVS and the MCV in the PIVS. The most common cardiac venous system configuration occurs when both the great and MCVs begin at the apex of the heart. In this circumstance, the venous system is considered to be codominant. In a few individuals, these two veins of equal caliber meet at the apex, forming a large venous arc. When the GCV begins in the PIVS and wraps around the apex to continue in the AIVS, this pattern is considered GCV dominant. This is the least common configuration. Similarly, in 37% of cases, when the MCV begins in the AIVS, the system is considered MCV dominant.^10,18

The CS is a 2- to 5-cm-long, superficial tubular structure with a luminal diameter of 6 to 16 mm, averaging 8 to 10 mm in the majority of individuals. The diameter of the CS is comparatively smaller in females and is also directly proportional to the left ventricular end-systolic diameter, end-diastolic diameter, and right atrial end-systolic dimensions.^19,20 The CS dimensions are larger in patients with heavier hearts or congestive heart failure.²¹ In patients with atrial reentrant tachycardia, the CS usually looks like a “windsock.”¹⁵

The CS is located in the posterior AVS on the diaphragmatic surface of the heart. The CS extends from the oblique vein ostium to its own ostium, emptying into the right atrium at the level of cardiac crux, which is the junction of the posterior AVS and the PIVS. The oblique vein usually marks the beginning of the CS. Other markers that can serve as the beginning of the CS are the left margin of the myocardial layer covering the CS or the width of the valve of Vieussens. The valve of Vieussens is the valve at the termination of the GCV into the CS. However, the high frequency of variation of these markers among individuals limits their applicability in defining the origin of the CS (Figures 23-7). The CS is typically superficial and in close proximity to the posterior descending coronary artery, the distal branches of the circumflex coronary artery, and the right coronary artery at the cardiac crux.^10,22,23

The CS travels almost parallel to the attachment of the posterior leaflet of the mitral valve, usually at a distance of 1 cm (Figure 23-8). In 77% of individuals, the CS takes a gentle superior curve away from the AV sulcus to a distance of 4 to 14 mm. The CS then gradually returns to the posterior AV sulcus before entry into the right atrium (Figure 23-9). The CS terminates into the right atrium posteromedially, gradually widening toward its opening into the right atrium. The ostium of the CS in the right atrium measures 2 to 9 mm and is flanked in 60% to 86% of individuals by a semilunar valve with a concave margin called the valve of Thebesius. The valve of Thebesius covers the ostium with considerable variation in its dimension and shape, and it may be absent in 15% to 40% of individuals. The valve may have crescent fenestrations; be fibrous bands or strands; be cribriform shaped; or appear as a large, redundant, fishnet-like structure continuous with a Chiari network (Figure 23-10). Rarely, the valve of Thebesius may occlude the ostium of the CS. An annular myocardial tissue or cuff surrounds the CS ostium. The fibers of this cuff may also extend into the valve of Thebesius. The function of this myocardial cuff and the valve of Thebesius are to prevent backflow of venous blood from the right atrium into the CS during atrial systole.^1,10,22 Therefore, the CS acts as a small contractile chamber with both inlet and outlet valves.

The CS is surrounded by a sleeve of myocardial fibers (see Figures 23-7 and 23-8) which contract rhythmically. The absence of these rhythmic contractions during atrial fibrillation suggests that the electrical activation of these fibers occurs largely from atrial inputs.²⁴ The fibers are arranged spirally, longitudinally, obliquely or axially. On the left CS margin, the cuff may extend onto the GCV or oblique vein of left ventricle (OV). The myocardial coat on the right margin is continuous with the posteroinferior wall of the right atrium. Histologically, the myocardial muscle sleeve surrounding the CS is formed from bands of muscle predominantly from the left atrium, except on the right margin of the CS, where the right atrium is the source (see Figure 23-8). In 8% of individuals, some myocardial fibers from the myocardial cuff on the inferior wall of the CS insert into the ventricular myocardium.^10,13,25

These myocardial cuffs may serve as arrhythmogenic foci for both micro- and macro-reentrant tachycardias, including biatrial flutter, atrial tachycardia, atrial fibrillation, and AV nodal reentrant tachycardias. These myocardial cuffs can also serve as substrate for accessory AV connections, thus propagating AV reentrant tachycardias. Recordings of local atrial electrograms around the CS suggested tight coupling of the muscle fibers around the CS but failed to show the same for muscle fibers around the GCV or MCV.²⁶ This finding supports the fact that the CS is probably the predominant generator of atrial arrhythmic foci compared with the GCV or MCV, which are clinically silent. The CS also provides access for both electrical mapping and ablation of epicardial ventricular tachycardias and other accessory pathway arrhythmias.^27,28,29

Coronary venous blood flow usually increases with exercise and stress. The pressure patterns in the CS may resemble right ventricular or right atrial pressures. The CS is maximally dilated during ventricular systole and minimally dilated during atrial systole. These rhythmic changes, however, are dampened in systolic heart failure or with the presence of a persistent left superior vena cava (LSVC).^30,31,32,33

The GCV is the longest vein of the heart and generally begins as the anterior interventricular vein near the apex of the heart. This vein receives venous return from the interventricular septum via septal veins (described later), the cardiac apex, the anterior aspects of both ventricles, and parts of the left atrium. The GCV receives tributaries from the LMV, the posterior vein of left the ventricle, the oblique vein of Marshall, the left adipose vein of Vieussens, and other left atrial veins before joining the CS. The GCV may also be covered by a myocardial cuff for about 2 to 11 mm from its anastomosis with the CS.The GCV arises predominantly from the lower third of the AIVS but may also arise in the middle third of the AIVS or the apex of the heart. In the AIVS, it is usually a single vessel (also called the anterior interventricular vein). Rarely, the GCV may begin as two vessels parallel to the left anterior descending artery (LAD) and form a common stem in the middle third of the AIVS. The GCV tributaries follow branches of the LAD.^{10,16,18,34,35,36}

The GCV courses superficial and adjacent to the LAD at a distance of 2 to 11 mm (average, 4.5 mm), predominantly to the right side of the LAD. As the GCV ascends the AIVS, the GCV usually crosses the LAD superficially and then curves gently to the left side, entering the left anterior AVS (refer to Figure 23-6A and 23-11). Here, the GCV frequently lies superficial and parallel to the circumflex coronary artery. The GCV then follows the curve of the left AV sulcus on the left heart margin and continues in the left posterior AV sulcus, lying adjacent to the circumflex coronary artery. At this curved location on the left heart margin, the GCV’s wall is often thin and is susceptible to perforation during manipulations with catheters or wires, especially if the vein is tortuous. Occasionally, at this curve, it may also intertwine with the circumflex artery.^37,38

The GCV empties into the CS at about 180 degrees 1.5 to 2 cm distal to the ostium of the PVLV. In one-third of cases, it may follow a sigmoid course in its terminal portion, lying on the posterolateral wall of the left atrium. The GCV may rarely drain into the SVC, right atrium, or internal thoracic vein.^18,36 Occasionally, the GCV may form a common stem with either the oblique vein of Marshall or the MCV. The luminal diameter of the GCV is 0.5 to 3 mm anteriorly and 1.3 to 6.7 mm (average, 3.5 mm) posteriorly.³⁸ The ostium of the GCV is usually 0.3 to 1 cm in diameter and ends with the valve of Vieussens in 80% to 90% of hearts. The morphology of valve of Vieussens is variable and is usually flimsy with one to three leaflets. In 13% of individuals in whom no valve is visible with the naked eye, the remnants may be seen with magnification.¹

As the GCV makes a left turn to enter the left anterior AVS from the AIVS, the GCV forms a triangle with the LAD and the circumflex coronary artery, named the triangle of Brocq and Mouchet (see Figure 23-11).^37,39 Depending on the relation of the GCV to the coronary arteries, the triangle may be “closed” or “open” (see Figure 23-11). One to three small branches of the LAD or sometimes a large diagonal branch of the LAD traverse this triangle dividing the triangle into two to three small, variable sized triangles. In this triangle, the GCV occasionally receives a venous branch from the superior part of the interventricular septum. Myocardial bridges may be present on the smaller tributaries of the GCV in 5% of individuals and on the GCV itself in 3% of individuals. The length of these bridges may range from 3 to 50 mm. If hyaline degeneration occurs, these bridges may, in rare circumstances, cause focal obstruction to the flow of the veins.^18,34 In systolic heart failure patients, the length of the GCV between the anterior interventricular portion and the LMV is increased.^25,31

The MCV, also called the posterior interventricular vein, usually begins at the apex of the heart in the PIVS (the groove between the right and left ventricles) and ascends posteriorly in this sulcus to empty into the CS at an obtuse angle or rarely, directly into the right atrium. The MCV drains part of the cardiac apex, the posterior portion of the interventricular septum, and the inferior walls of both ventricles. Although the MCV is consistently present, its caliber varies between 0.7 and 6.0 mm. The MCV usually has an ostial valve; however, its entrance into the CS may be dilated to form a diverticulum. This vein predominantly lies superficial to its corresponding coronary arteries. It is in close proximity to the right coronary artery, the posterior descending artery, and the AV nodal branch of the right coronary artery. Its tributaries often lie superficial to and follow branches of the posterior descending artery.

The size of the MCV and its nearness to the ostium of the CS make it a victim to the unintended insertion of a pacemaker lead, which may fluoroscopically appear to be in an appropriate right ventricular position on anteroposterior fluoroscopy. It may also be intentionally cannulated during electrophysiology procedures for approaching accessory AV pathways of the inferior pyramidal space.^1,8,10,23,35

The LMV lies perpendicular to the ventricular muscle on the left or obtuse margin of the heart. Its tributaries generally follow the branches of the obtuse marginal coronary artery. The LMV is typically single with a luminal diameter of 1 to 3 mm and is present in 80% to 90% of individuals. There can, however, be two to three small veins. The LMV usually drains into the GCV but may drain into the CS on rare occasions. An ostial valve may be present. The vein frequently lies superficial to the left obtuse marginal coronary artery with infrequent crossovers. In some instances, it may form a loop around this artery. The LMV drains the corresponding area around the left lateral margins of the heart and may be absent in patients with prior lateral infarction. Resurgence of interest in coronary venous anatomy has been primarily related to the use of this vein as a site for biventricular, synchronized pacing for patients with congestive heart failure.^1,10,23

Posterior Vein of the Left Ventricle

The PVLV usually courses on the diaphragmatic surface of left ventricle between the LMV and the MCV. The PVLV varies in number and size, ranging from two to five veins with a luminal diameter of 0.3 to 6.0 mm (average, 2.3 mm). The PVLV is absent in 5% of individuals. It typically drains into the CS, with its opening flanked by an ostial valve, although it may also empty into the GCV. Mostly, the PVLV enters the CS perpendicularly, but in 43% of individuals, it may enter at an acute angle.⁴⁰ The PVLV lies superficial to the posterolateral coronary arterial branches of the left ventricle, which arise either from the right coronary artery or the circumflex coronary artery, depending on the pattern of arterial dominance. However, the PVLV tributaries do not accompany any arterial branches. If the PVLV is of large caliber, the MCV and the GCV are correspondingly diminutive. When the PVLV is diminutive, the LMV is of large caliber. The PVLV is commonly absent in patients with prior lateral transmural myocardial infarction.^1,10,23

Oblique Vein of Marshall

The oblique vein of Marshall, also named the oblique vein of the left atrium, is a vestigial remnant of the embryonic left common cardinal vein and is one of the most consistently present cardiac veins. It drains the lateral and posterior wall of the left atrium. The OV courses diagonally on the lateral and posterior wall of the left atrium. At its beginning, it is attached to the ligament of Marshall. The ligament of Marshall contains sympathetic nerve trunks and sympathetic ganglia and is also richly innervated by parasympathetic nerves, making it potentially arrhythmogenic.⁴¹ The OV usually drains directly into the CS at a distance of 1 to 12 mm distal to the valve of Vieussens. The length of the OV rarely exceeds 2 cm, with an ostial diameter of 0.7 mm.^1,10,23 The vein is divided into three different types depending on its shape and branches. These types are dendritic, forked, and simple (Figure 23-12).⁴²

Given its constancy as a vein or cord, the OV serves as a relatively safe landmark for the beginning of the CS angiographically or intraoperatively. This vein may also play a role in the generation of various atrial arrhythmias, especially focal atrial tachycardia or atrial fibrillation. Ablation in this region has successfully resulted in the termination of these arrhythmias in some individuals.⁴²

Small (Right) Cardiac Vein

The small cardiac vein is present in 46% to 70% of individuals, with a male-to-female ratio of 6:1. The SCV runs in the right posterior AVS between the right atrium and right ventricle with a length of 9 to 65 mm (average, 26 mm). It is typically less than 1 mm in width but may be absent or reduced to a fibrous cord. The SCV predominantly drains into the MCV, with the ostium flanked by an ostial valve. Occasionally, the SCV may empty into the CS, the RMV, or the right atrium directly. In a minority of cases, the SCV may empty into both the CS and the RMV. The SCV typically receives venous blood from a few right atrial veins and the inferolateral wall of the right ventricle.^10,23,43,44

Right Marginal Vein

The RMV develops from a venous network at the cardiac apex. The RMV ascends the right margin of the heart and typically opens directly into the right atrium. It may also drain into the small cardiac vein or the anterior cardiac veins. The RMV has a diameter of 0.5 to 2.9 mm and receives tributaries from the posterior and anterior surfaces of the right ventricle. When the RMV is absent, the MCV receives small tributaries from the corresponding area of the RMV. Rarely, the RMV may be of large caliber reaching the cardiac apex.^1,10,18,23

Left Adipose Vein of Vieussens

The left adipose vein of Vieussens (LAVV) is present in 5% of individuals and drains into the GCV. The LAVV lies on the anterior surface of the left ventricle, superficial and to the right of the LAD coronary artery. The LAVV may communicate with the anterior cardiac veins or rarely with extracardiac veins. It usually receives venous return from adipose tissue around the conus arteriosus (see Figure 23-6A).^18,23

Anterior Cardiac Veins

The anterior cardiac veins are three to six small veins located on the anterior surface of the right ventricle. The superior branches receive venous return from the conus arteriosus and the upper third of the anterior and the anterolateral surfaces of right ventricle. The inferior branches receive venous blood from the middle and lower third of the anterior and the anterolateral surfaces of the right ventricle. In 50% of individuals, the diameter of at least two of these veins is more than 1 mm in size. The RMV, the right conus vein and the right AV veins also belong to the group of anterior cardiac veins. The right conus vein drains soft tissue between the aortic bulb and the pulmonary trunk. The right AV veins, as the name suggests, are numerous small vessels located in the anterior part of right AVS adjacent to the tricuspid annulus. The right AV veins collect blood from the anterior and lateral external surface of the right annulus fibrosus and empty into intramural sinuses of the right atrium. They also have extensive anastomoses with major tributaries of the CS.¹⁰

The anterior cardiac veins predominantly drain into one to three semicircular intramural sinuses (Figure 23-13) at the bases of anterior and lateral walls of right atrium parallel to the anterior AV sulcus and the fibrous annulus of tricuspid valve. The anterior cardiac veins generally enter the sinuses perpendicularly. These sinuses, in turn, open into the right atrium and may have insufficient threadlike ostial valves. The intramural sinuses vary from 1 to 8 cm in length and 1 to 4 cm in width. Infrequently, these sinuses run almost vertically in the posterior wall of the right atrial appendage, draining the anterior cardiac veins and emptying into the right atrium close to the right posterior AV sulcus. Each anterior cardiac vein may also empty directly into the right atrium or via a short common stem. Occasionally, the anterior cardiac veins collect very small veins of the right anterior atrial wall and sinus node. There may be myocardial cuffs around these veins that can create AV communications, thereby propagating supraventricular macro-reentrant tachycardias.^1,10,23

Atrial Veins

The atria are drained by veins (Figure 23-14) belonging to the GCVS and the SCVS. The SCVS drains the inner layers of the atrial myocardium. Various intramural sinuses that belong to the compound venous system also collect venous blood from a few atrial veins. These intramural sinuses connect veins that are epimurally and intramurally distributed.^10,15

Left Atrial Veins. The left atrial veins include the anteroseptal veins, posteroseptal veins, posterolateral veins, and posterosuperior veins (or the proper veins of the left atrium).^10,15

The anteroseptal veins are the most consistently present left atrial veins and drain the anterior and septal walls of the left atrium. They arise in close proximity to the right pulmonary veins, forming one or two stems. These stem(s) run rightward and cross the anterior interatrial sulcus. Subsequently, they penetrate the right atrial myocardium at the junction of SVC and sinus venarum anterosuperior to the fossa ovalis. Here the anteroseptal veins empty into intramural sinuses 1 to 3 mm in diameter. Their openings into the right atrium are rounded, funnel shaped, or slotlike and may be covered by unicuspid or bicuspid valves.

The posteroseptal veins drain the posteromedial and septal walls of the left atrium. They arise as one stem that runs on the posterior wall of the left atrium, frequently joined by an interatrial septal branch. The stem then crosses the posterior interatrial sulcus and empties into the right atrium via one to two subendocardial or intramural sinuses posterior to the fossa ovalis. The ostia of these sinuses may be covered by cribriform endocardial leaves, which are not real valves. Rarely, a large posteroseptal vein replaces the posterior atrial veins.

The posterolateral veins drain the left atrial appendage and the left posterior and lateral walls of the left atrium. The OV is also a part of the group of posterolateral veins. These veins follow intramyocardial courses for about 1 to 4 mm and then empty into the CS. They have unicuspid or bicuspid valves, which may be absent in 20% of individuals. Three to five small veins drain the left atrial appendage and lateral wall of the left atrium before emptying into the GCV. The openings of these small veins may also have ostial valves.

The posterosuperior part of the left atrium between the four pulmonary veins is also known as porta venosa of the heart. This region is usually drained by one to three small veins, termed the posterosuperior or proper veins of the left atrium. These veins course 2 to 3 cm on the epimural surface of the left atrium and empty into the left atrium via intramural sinuses. Occasionally, the posterosuperior veins may empty directly into the terminal portions of the pulmonary veins. The internal ostia of the posterosuperior veins may be round, funnel shaped, or slotlike flanked by unicuspid or bicuspid. The posterosuperior veins may also be interconnected with other right or left atrial veins. Sometimes these communicate with bronchial or mediastinal veins that abut the porta venosa of the heart. When the posterosuperior veins are absent, this area is drained by other left atrial veins.

Right Atrial Veins. The cavoatrial veins are present at the junction of the superior and IVC with the right atrium in 73% of individuals (see Figure 23-14). These short, very small veins empty into the right atrium through small internal ostia covered by translucent unicuspid valves.¹⁵ These veins drain the sinus venarum portion of the right atrium. The right atrial appendage is mostly drained by real Thebesian veins, a part of the SCVS.^10,15