Left Superior Caval Vein to Coronary Sinus without Coronary Sinus Ostial Atresia

Embryologically, left superior caval vein to the coronary sinus is thought to be due to the persistence of the left anterior and common cardinal veins. The left superior caval vein descends anterior to the aortic arch and left pulmonary hilum. It enters the pericardium and contacts the heart at the left posterior atrioventricular groove, where it continues into the right atrium as the coronary sinus (Figure 37.1A). The right atrial orifice of the coronary sinus is usually dilated in proportion to the size of the left superior caval vein. While the majority of patients also have a right superior caval vein, the size of this contralateral vessel is usually inversely proportional to the size of the left superior caval vein. For example, when the left superior caval vein is large the right superior caval vein is usually small and vice versa. In 24% of cases the right superior caval vein is hypoplastic or even atretic (Figure 37.1B) [14–16]. In 75% of cases the left innominate vein is absent or severely hypoplastic [7]. When an adequately sized left innominate vein is present, it provides an important alternate pathway for left superior caval vein flow to the right atrium in addition to the coronary sinus. Left superior caval vein to the coronary sinus can coexist with azygos continuation of the inferior caval vein to the right superior caval vein (9%), hemiazygos continuation of the inferior caval vein to the left superior caval vein (7%), and separate entrance of the inferior caval vein and hepatic veins into the right atrium (2%) [14]. While left superior caval vein to the coronary sinus rarely can be an isolated anomaly, it is most commonly associated with septal defects (atrial septal defect [ASD], ventricular septal defect [VSD], or common atrium), tetralogy of Fallot, atrioventricular septal defects, transposition of the great arteries, and other more complex defects [14]. While the true incidence of this anomaly is not known, it may occur in as many as 3–10% of patients with congenital heart disease. It appears to occur in 0.1–0.5% of the general population [17].

Left Superior Caval Vein with Coronary Sinus Ostial Atresia

Coronary sinus ostial atresia with persistent left superior caval vein is a rare cardiac anomaly, with 35 total cases reported in the world literature. Of these reported cases, 11 were diagnosed in living patients either by angiography or intraoperatively and the remainder were identified at autopsy [18]. Anatomically these lesions consist of a membranous occlusion of the coronary sinus ostium, thereby disconnecting the usual direct drainage of the coronary sinus (and left superior caval vein) to the right atrium (Figure 37.1C). The gap between the blind end of the coronary sinus and the right atrium can be either a short‐ or a long‐segment interruption [19]. The anomalous left superior caval vein provides the major route for venous drainage from the coronary sinus; however, there can be small communicating veins between the coronary sinus and the right atrium [20]. Retrograde flow from the coronary sinus to the left superior caval vein and across the innominate vein to the right superior caval vein is most commonly found (Figure 37.1C) However, other venous connections can exist between the left superior caval vein and the right superior caval vein. For example, the left superior caval vein can drain into the right superior caval vein through a hemiazygos–azygos connection. Other cardiac malformations coexist in 56% of the reported cases of coronary sinus ostial atresia [18].

Unroofed Coronary Sinus Syndrome

Unroofed coronary sinus syndrome (UCSS) is a spectrum of congenital cardiac anomalies consisting of partial or complete absence of the partition between the coronary sinus and the left atrium. All patients have an interatrial communication. A left superior caval vein is usually present, but is not a requirement for UCSS. Since the coronary sinus itself is a systemic vein, UCSS should be considered a subset of ASVC regardless of whether a left superior caval vein coexists.

Persistence of the left anterior and common cardinal veins draining into the left sinus horn with failure of the normal invagination process that separates the left sinus horn (future coronary sinus) from the left atrium is a possible embryologic mechanism for the development of UCSS [10, 13, 21].

UCSS can consist of either complete or partial unroofing [22, 23]. In complete unroofing the entire length of the partition between the coronary sinus and the left atrium is absent. A left superior caval vein is usually present, but can be absent. In partial unroofing only a segment of the partition between the coronary sinus and the left atrium is absent. This partial unroofing can occur in the midportion or the distal portion (right atrial end) of the coronary sinus.

Complete Unroofing with Left Superior Caval Vein

The left superior caval vein forms as the confluence of the left internal jugular vein and the left subclavian vein. Its vertical descent is anterior to the distal transverse left‐sided aortic arch and the left pulmonary hilum. The left superior caval vein terminates in the superior left aspect of the left atrium (Figure 37.2A). The position of its left atrial orifice appears to be relatively constant with the left superior pulmonary vein orifice located posteriorly and inferiorly and the orifice of the left atrial appendage located anteriorly. There can be a valve‐like structure or a ridge near the left superior caval vein ostium. The hemiazygos vein joins the left superior caval vein after arching superiorly and anteriorly over the left mainstem bronchus. The left innominate vein is absent in 80–90% of cases. The right superior caval vein is usually smaller than the left superior caval vein or it can be absent, with the right internal jugular and subclavian veins draining into the left superior caval vein through a right innominate vein. There may be hemiazygos continuation of the inferior caval vein to the left superior caval vein. In this situation the hepatic veins enter the inferior right atrium separately. Occasionally the hepatic veins may enter the left atrium posterior to the interatrial septum. This, in combination with a left superior caval vein and hemiazygos continuation of the inferior caval vein, produces total anomalous systemic venous connection.

A coronary sinus ASD is located posteriorly and inferiorly in the interatrial septum in the position usually occupied by the right atrial orifice of the coronary sinus. When the interatrial communication is an isolated coronary sinus defect, it is separated from the atrioventricular valve annulus by an anterior remnant of interatrial septal tissue. It is also bounded superiorly and inferiorly by interatrial septal tissue and posteriorly by the posterior atrial free wall. There may be an associated secundum ASD separated from the coronary sinus ASD by interatrial septal tissue. Alternatively, the coronary sinus ASD may be confluent with a secundum and/or primum ASD. When a primum ASD coexists in confluence with the coronary sinus ASD, the anterior leaflet of the mitral valve is frequently cleft. Occasionally the complete absence of interatrial tissue creates a common atrium (Figure 37.2B) [10, 22–25].

In the presence of complete unroofing of the coronary sinus with left superior caval vein, the pulmonary veins can enter the left atrium more superiorly than usual. This can create an apparent narrowing between the area of the left atrium into which the pulmonary veins enter and the portion of the left atrium to which the left superior caval vein, left atrial appendage, and mitral valve are attached [23].

Complete Unroofing without Left Superior Caval Vein

In this case complete unroofing of the coronary sinus exists in the presence of a coronary sinus type ASD, but without a left superior caval vein (Figure 37.2C).

Partially Unroofed Coronary Sinus with or without Left Superior Caval Vein

Partial absence of the partition between the coronary sinus and the left atrium can occur in the middle (Figure 37.2D) [26, 27] or the distal [22, 23] coronary sinus, with or without a left superior caval vein. Distal unroofing of the coronary sinus occurs most commonly in the presence of atrioventricular canal defects. In this situation the distal coronary sinus, including its right atrial orifice, can be unroofed, resulting in a displacement of the distal opening of the coronary sinus into the left atrium (Figure 37.2E). Conversely, the distal coronary sinus may be unroofed just prior to its right atrial orifice, resulting in a coronary sinus ASD (Figure 37.2F) [22, 27].

While situs solitus of the atria and viscera with levocardia are usually present, anomalies that can coexist with UCSS include dextrocardia, situs inversus, and atrial appendage isomerism with asplenia or polysplenia. UCSS has been reported in association with partial atrioventricular canal defect, complete atrioventricular canal defect, common atrium, tetralogy of Fallot, double‐outlet right ventricle, pulmonary stenosis, total anomalous pulmonary venous connection, and hypoplastic left ventricle [22, 23].

Right Superior Caval Vein to the Left Atrium

A right superior caval vein draining to the left atrium is very rare as an isolated lesion, and was first reported by Kirsch and colleagues (Figure 37.3A) [28]. True cases must be differentiated from the sinus venosus type of ASD with a superior caval vein overriding the interatrial septum.

Direct Inferior Caval Vein Connections

The inferior caval vein normally receives the hepatic veins and then connects directly to the inferior aspect of the right‐sided morphologic right atrium. Very rarely the inferior caval vein connects to the right atrium through the coronary sinus. This latter anomaly has been reported in a patient with a left superior caval vein to the coronary sinus, absent right superior caval vein, left‐sided hypoplasia (small left ventricle, parachute mitral valve, bicuspid aortic valve, hypoplastic arch, and coarctation of the aorta), primum ASD, and secundum ASD [29]. Direct connection of the inferior caval vein to the left‐sided morphologically left atrium can occur either as an isolated lesion or in association with other cardiac anomalies (Figure 37.3B) [30–34]. One very unusual case of left‐sided superior and inferior caval veins draining into the left atrium in association with normal right superior and inferior caval veins and an ASD has been reported [35].

Indirect Inferior Caval Vein Connections

Indirect inferior caval vein connections exist when the inferior caval vein does not connect to the atrium from below, but rather “continues” as an extension of either the azygos or hemiazygos veins. In azygos continuation the inferior caval vein passes up the right paravertebral gutter and arches over to join the right superior caval vein as a dilated azygos vein (Figure 37.4A). In hemiazygos continuation the inferior caval vein courses up the left paravertebral gutter to join the left superior caval vein as a dilated hemiazygos vein (Figure 37.4B). Both azygos and hemiazygos continuation have been collectively referred to as “anomalous inferior caval vein with azygos continuation” or “infrahepatic interruption of the inferior caval vein” [36]. When there is azygos or hemiazygos continuation of the inferior caval vein, the hepatic veins always connect directly to the atrial mass and never via the anomalous inferior caval vein.

The incidence of indirect inferior caval vein connections is 0.6% of patients with congenital heart defects. Its incidence in patients without congenital heart defects is probably much less than the 0.3% incidence quoted for left superior caval vein under the same circumstances [36].

Although indirect inferior caval vein connections can rarely be found in individuals with otherwise normal hearts [37], the vast majority of them occur in association with other congenital cardiac abnormalities such as atrial appendage isomerism, atrioventricular canal defect, anomalous pulmonary venous connection, double‐outlet right ventricle, common atrium, pulmonary atresia, superior caval vein anomalies (especially bilateral superior caval vein), and others.

Atrial (Appendage) Isomerism

Heterotaxy (Greek heteros, other than, and taxis, arrangement) is synonymous with the terms “visceral heterotaxy” and “heterotaxy syndrome.” It is literally defined as a pattern of anatomic organization of the thoracic and the abdominal organs that is neither situs solitus (the usual or normal arrangement) nor complete situs inversus (the unusual or mirror‐image arrangement of normal) [38]. If asymmetry of the thoracic and abdominal viscera is the usual or normal situation, then the heterotaxy syndrome includes patients with an unusual degree of thoracic and abdominal visceral symmetry. Admittedly, this broad term includes patients with a wide variety of very complex cardiac lesions and is a term that has generated confusion and controversy in the literature. The definition of heterotaxy that currently enjoys the greatest consensus in the literature is “an abnormality where the internal thoraco‐abdominal organs demonstrate abnormal arrangement across the left‐right axis of the body. By convention, heterotaxy does not include patients with either the expected usual or normal arrangement of the internal organs along the left‐right axis, also known as ‘situs solitus,’ nor patients with complete mirror‐imaged arrangement of the internal organs along the left‐right axis also known as ‘situs inversus’” [39]. One way to impose order upon this diverse group of cardiac lesions is to stratify them according to the morphology of the atrial appendages [40]. This is accomplished by applying the chemistry term isomerism to congenital cardiac morphology. Isomerism, in the context of the congenitally malformed heart, is defined as a situation where some paired structures on opposite sides of the left–right axis of the body are, in morphologic terms, symmetric mirror images of each other [39]. In atrial appendage isomerism, both atrial appendages are similar rather than displaying their usual distinctive right and left morphology. Right or left atrial appendage isomerism exist when both atria have right or left atrial appendage morphologic characteristics, respectively. Right atrial appendage isomerism is frequently, but not always, associated with bilaterally trilobed lungs (each with short bronchi) and asplenia. Left atrial appendage isomerism is frequently, but not always, associated with bilaterally bilobed lungs (each with long bronchi) and polysplenia.

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