ANOMALIES OF THE GREAT SYSTEMIC VEINS
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| CARDIAC VEIN ANOMALIES |
Anomalies can involve the large systemic venous trunks because of the complex embryogenesis and tremendous variability of the venous system in general. Abnormal channels almost always empty into other systemic veins and rarely cause functional changes disturbing to the patient, usually discovered incidentally at postmortem examination or during cardiovascular diagnostic or surgical procedures. Venous trunk anomalies may occur as isolated malformations but more often are associated with other cardiovascular anomalies. The presence of an anomaly, if unsuspected, may lead to troublesome or even dangerous situations when total cardiopulmonary bypass techniques are employed.
By far the most common clinically
significant anomaly of the great systemic veins is persistence of the left
superior vena cava (SVC). This vein, after being formed by the confluence of
the left jugular and subclavian veins, descends into the chest parallel to the
right superior vena cava and anterior to the left-lung hilus, usually entering
the greatly dilated coronary sinus along a course normally occupied by the
ligament and vein of Marshall. This topographic position is expected because
embryologically, a persistent left SVC represents retention of the left anterior
and common cardinal veins and the left sinus horn. Anatomically, the hemiazygos
vein resembles the normal right-side azygos vein and may approximate it in size
(see Plate 5-2).
The right SVC is usually present as
well but may be absent. The two venae cavae may be equal in size, or one
(generally the left) may be smaller than its counterpart. The left innominate
vein, if present, is smaller than normal or may be more or less plexiform.
The coronary sinus ostium (coronary
os) is very large because of the increased blood flow through it, detected
easily by cardiac ultrasound. Occasionally, a defect is present in the wall
between the sinus and left atrium (unroofed coronary sinus). Generally,
such a defect results in a left-to-right shunt; that is, left atrial blood
enters the coronary sinus and is carried to the right atrium. Hemodynamically,
therefore, the anomaly resembles an atrial septal defect. If the defect is
extremely large, particularly if the coronary os is small or atretic, the left
SVC is said to “enter the left atrium.” Patients with persistent left SVC
present a typical clinical picture consisting of moderate central cyanosis
without other symptoms. There is no murmur, and the heart is normal in size.
The electrocardiogram (ECG) generally shows signs of left ventricular
hypertrophy. Similar but more pronounced findings have been described in the
rare cases of isolated drainage of the inferior
vena cava into the left atrium.
Azygos Drainage Of Inferior Vena Cava
Absence of the hepatic segment of
the inferior vena cava (IVC) is an uncommon anomaly in which the prehepatic portion of the IVC drains into the
right atrium by way of an enormously enlarged azygos vein. The hepatic veins
empty into the right atrium by way of a short common stem that normally forms
the most proximal part of the IVC (see Plate 5-2). Although azygos drainage of the IVC occurs rarely as an isolated lesion, usually it is associated with other
serious cardiac anomalies (e.g., asplenia or polysplenia syndrome).
Double Inferior Vena Cava
Other systemic venous anomalies,
including double inferior vena cava (see Plate 5-2), generally involve the IVC bed and are of more importance to
general surgeons and urologists than cardiologists and cardiac surgeons. Patients with significant cardiac
anomalies associated with various types of partial inversion of the thoracic or
abdominal viscera are particularly prone to harbor anomalies of the great
systemic venous trunks. Because such anomalies may cause difficulties at
surgery, their presence or absence should be clearly established as part of the
diagnostic workup, most easily through angiocardiography, computed tomography
(CT), or magnetic resonance imaging (MRI).
