Systemic venous anomalies of the thorax are the result of complex variations in the persistence and regression of segments of three pairs of venous channels during the first 4 weeks of fetal development. All these three venous channels drain into the sinus venosus: the omphalomesenteric (vitelline) veins, carrying blood from the yolk sac; the umbilical vein, originating in the chorionic villi and carrying oxygenated blood from placenta; and the common cardinal veins (ducts of Cuvier), draining the body of the embryo.

The right and left common cardinal veins are formed by the confluence of the anterior and posterior cardinal veins [1, 21, 22] (Fig. 26.2). The anterior cardinal vein drains the cephalic portion of the embryo, and the posterior cardinal vein drains the remainder of its body. The left vitelline and cardinal veins regress during embryogenesis. The right vitelline vein forms hepatic segment of the IVC (hepatocardiac channel). The right horn of the sinus venosus and the right common cardinal vein will be developed and eventually form the posterior wall of the right atrium (RA) and the SVC, respectively. The left horn of the sinus venosus, in conjunction with the regressing left common cardinal vein, forms the coronary sinus (CS) and the ligament or vein of the left atrium (Marshall) (Fig. 26.2). A bridging venous plexus forms between the right and left anterior cardinal veins around 24 mm crown-rump embryonic stage and develops to be the left brachiocephalic vein [23]. The left anterior cardinal vein below this connection gradually obliterates. Its upper portion remains as part of the left superior intercostal vein (SICV). The right anterior and common cardinal veins persist and form the SVC.

The right sinus valve persists as the valve of the IVC (eustachian valve) and the valve of the coronary sinus (thebesian valve) [24]. A double SVC is the result of persistence of the left anterior cardinal vein. If, in addition, the normally persistent right cardinal vein regresses, then there is only one SVC on left. In the normal atrial situs, persistence of the left anterior cardinal vein connected to the left atrium (LA) is an infrequent occurrence, this vein usually draining into the RA via the coronary sinus. In atrial isomerism, conversely, the left anterior cardinal vein usually persists, draining either into the roof of the left-sided atrium (mainly in right atrial isomerism) or into the CS (usually in left atrial isomerism).

The SVC starts at the confluence of the right and left brachiocephalic veins. It travels 5–7 cm on the right anterior aspect of the upper mediastinum from the level of first sternocostal junction to the superior cavoatrial junction. At the junction with the RA, the SVC is located posterolateral to the ascending aorta, anterior to the right pulmonary artery, and anteromedial to the right superior pulmonary vein (Fig. 26.3). Isolated anomalies of the right SVC are rare [25]. Anomalous low insertion of the right SVC into the right atrium can be seen as an isolated anomaly. Anomalous high insertion of IVC can be seen in congenital heart diseases (CHD). A case of cyanotic CHD with left ventricular hypertrophy described that cardiac catheterization showed a right SVC draining into the left atrium without other cardiovascular abnormality [26]. Congenital aneurysmal dilatation of the SVC may be mistaken with a mass [27] (Fig. 26.4). It may involve the SVC only or multiple veins in the upper mediastinum (Fig. 26.5). This anomaly is usually an incidental finding but has been associated with thrombosis leading to embolization and SVC obstruction [28]. Congenital aneurysmal dilatation can be associated with cystic hygromas [29]. Agenesis of the SVC with two brachiocephalic veins draining separately is also reported without intracardiac malformations [30].

The left SVC is the most common anomalous systemic vein drainage in the thorax, incidentally found in one out of 200 (0.5 %) of CT or MRI studies of chest. In patients with congenital heart malformation, it is more common and may be seen in 5–10 % of patients [1, 31–33]. Isolated left SVC is less common than duplicated SVC. Similar to PAVR of the left upper lobe, it results from failure of parts of the left anterior and common cardinal veins to regress. The left SVC drains the tributaries of the left subclavian and jugular veins into the CS via the oblique vein of the left atrium (vein of Marshall). The LSIV becomes a tributary of the left LVC in 20 % of cases and may connect it to the accessory hemiazygos, analogous to the azygos arch on the right that connects the right SVC to the azygos vein (Fig. 26.6). In 80–90 % of patients, the left and right SVCs coexist, although the left is usually smaller especially when the left brachiocephalic vein bridges the two veins (Fig. 26.7). In about 40–60 % of cases, the left brachiocephalic vein connecting the two SVCs is absent [31, 34]. In this situation the left SVC is larger (Fig. 26.8). In persistent left SVC, especially isolated left SVC, the incidence of CHD increases including atrial septal defect (ASD), tetralogy of Fallot, heterotaxy, coarctation of aorta , pulmonary atresia or stenosis, cor triatriatum, atrioventricular septal defects, double-outlet right ventricle, and anomalous pulmonary venous drainage [1, 35] (Fig. 26.9).

The left SVC descends lateral to the aortic arch and anterior to the hilum, enters the pericardium in the posterior atrioventricular groove, and in almost all cases drains into the CS (90 %) with no significant hemodynamic effects (Figs. 26.8 and 26.10). The CS is large especially when the brachiocephalic vein is absent and will be heavily opacified in CT or MR angiographies when contrast is injected in the left arm. Rarely (8 %), the drainage of the left SVC is not into the CS, but instead into the left atrium or left superior pulmonary vein. In these cases as well, the incidence of CHD increases (Fig. 26.11). Isolated connection of the left SVC to the left atrial roof is very rare [36–38]. Patients with an isolated left SVC draining into the left atrium usually have a right-to-left shunt, unless there is a big bridging vein between the two SVCs, which may allow a left-to-right shunt, instead. Usually, the left SVC draining into the left atrium causes mild cyanosis and polycythemia. Patients are minimally symptomatic or asymptomatic. Cardiac examination, chest X-ray, and electrocardiogram are usually normal. As a result, these rare cases are often an incidental finding during other diagnostic exams [36]. A major complication of this form of hidden right-to-left shunt would be paradoxical embolism with complication such as cryptogenic stroke (Fig. 26.11). Similar situation can occur in cases of left SVC with an unroofed CS especially if the CS ostium to the right atrium is atretic. The anomalies can also interfere with catheterization and may cause difficulty placing a cardiac pacer or defibrillator leads when a left arm approach is used. During the development of the embryo, the left SVC draining into the CS causes an enlargement of this vessel and dissolution of the wall of the CS adjacent to the LA causing either a coronary sinus–left atrium fenestration (unroofing) or an interatrial communication through the mouth of the CS (coronary sinus type ASD) [39]. Therefore, unroofed CS is mostly associated with a left SVC, with or without a connection between both the two SVCs. The diagnosis of this lesion is important to the prognosis of the patient because of the consequences of brain abscess or cerebral emboli that may result from a right-to-left shunt [40, 41]. Injection of contrast in the arm during CT or MR angiography can improve demonstration of this anomaly and associated right-to-left shunting.

Bilateral SVCs are seen in 60–70 % of patients with situs anomalies [35, 42]. In right atrial isomerism, the left SVC drains into the roof of the left-sided atrium. In the hearts with right atrial isomerism, a coronary sinus defect does not exist as there is no orifice of the CS [39]. Whereas in left atrial isomerism, bilateral SVCs are usually present, and both tend to connect low on the atrial wall near the atrioventricular junction [36]. In 50 % of the cases, the left SVC connects to the right-sided atrium through a CS, but both veins can connect directly into the superior atrial wall.

In situs anomalies, the current trend is to divide and anastomose both SVCs to the pulmonary arteries in a bidirectional cavopulmonary anastomosis, hemi-Fontan, or Fontan procedure [43]. However, a small-caliber left SVC, especially when associated with a large innominate vein, may not be considered worthy of anastomosing and may simply be ligated. In adult repaired CHD the residual of a ligated left SVC can seen in CT or MR (Fig. 26.9). If the left SVC draining the CS is preserved during the Glenn and Fontan-type operations, the ensuing systemic venous hypertension could adversely affect the coronary flow and myocardial perfusion. A persistent left SVC is rarely associated with coronary sinus orifice atresia [44, 45]. Other congenital cardiac lesions associated with coronary sinus orifice atresia with left SVC include ASD, ventricular septal defect, transposition of the great arteries, tricuspid atresia, and mitral atresia [32].

During the fourth to sixth weeks of embryologic development, a pair of posterior cardinal veins drain all but the cephalic portion of the embryo [31, 53, 54]. Later at sixth week, a second new pairs of vein, the subcardinal veins, develop which become dominant at 7 weeks while most of the posterior cardinal veins gradually disappear (Fig. 26.2). Important anastomoses develop between the right and left subcardinal veins anterior to the aorta. The right subcardinal vein further develops to the renal and suprarenal portions of the IVC which connect with the posthepatic segment of IVC (derived from vitelline vein). At 8 weeks, the posterior cardinal veins will be replaced proximally by a third pair of veins, the supracardinal veins, which develop medial and dorsal to the posterior cardinal veins and later anatomose each other behind the aorta. The azygos vein derives mainly from the upper right supracardinal vein but the azygos arch seems to originate from the remaining of the cranial segment of the right posterior cardinal vein. Similarly, upper left supracardinal vein turns into the hemiazygos vein, and the residual of the cranial segment of the left posterior cardinal vein may form the posterior portion of LSICV. The IVC development is complex and five embryological segments contribute to its composition. In caudal–cranial order, these segments include posterior cardinal veins (iliac segment), right supracardinal vein (infrarenal segment), anastomosis between the right supra- and subcardinal veins (renal segment), right subcardinal vein (suprarenal segment), and hepatocardiac canal (hepatic segment).