Double superior vena cava
Incidental finding on a chest CT scan done as a metastatic work-up in a newly diagnosed patient of prostate cancer.
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Contrast enhanced CT chest axial sections show an anomalous vessel coursing inferiorly to the left of the aortic arch and anterior to the left hilum. It is in direct continuation with the confluence of the left subclavian vein and the left internal jugular vein. Superiorly it is communicating with a normal right sided SVC via a hypoplastic left brachiocephalic vein. Inferiorly it drains into the coronary sinus, and thus into the right atrium. Findings are consistent with double SVC due to the presence of a persistent left SVC (anatomical variant) along with a normal right SVC.
Double SVC is a rare anatomical variant that results from a persistent left superior vena cava, which is due to the embryological failure of regression of the anterior cardinal vein.
The left sided SVC drains into the right atrium in 90% of cases via a dilated coronary sinus, alternative sites include the inferior vena cava, a hepatic vein and the left atrium. Atypical left SVC drainage into the left atrium results in a right to left shunt, which can cause cyanosis and has been linked in cases of septic embolism.
A right sided SVC is seen in 82-90% of cases of double SVC. Absence of right SVC or a left SVC draining into the left atrium has been associated with increased incidence of congenital heart diseases such as ASD,VSD and TOF.
It is important to be aware of this normal variant especially during upper limb central venous catheterisation on the left side.
- Webb WR, Gamsu G, Speckman JM et al. Computed tomographic demonstration of mediastinal venous anomalies. AJR Am J Roentjenol. 1982;139(1): 157-61.