Left sided superior vena cava

Left sided superior vena cava (SVC) is the most common congenital venous anomaly in the chest, and in a minority of cases can result in a right to left shunt 3-4.


A left sided SVC is seen in 0.3 - 0.5% of the normal population and in 4.4% of those with congenital heart disease 3.

It commonly (90%) occurs with a persistent normal right sided SVC which is also termed SVC duplication. However in 10% of cases it is found isolation with no right sided vessel.


The embryology of a left sided SVC is simply a failure of obliteration of the left anterior cardinal vein. The abnormal vessel passes anterior to the left hilum and lateral to the aortic arch before rejoining conventional circulation. There are a number of possible drainage sites.

In approximately 92% of cases the left sided SVC enters the coronary sinus. In this configuration there is little if any functional impact as blood from the head and arms still reaches the right atrium 3.

In the remaining 8% of cases, drainage is into the left atrium in which case the patient has a right to left shunt 3.

In the vast majority of cases (82 - 90%) a normal (but small) right sided SVC is also present, and a persistent bridging vein (left brachiocephalic vein) is seen in 25 - 35% of cases 3.

Other configurations are possible, with the left superior intercostal vein forming a communication between the left SVC and the accessory hemiazygous vein forming a left sided azygous arch.

Clinical presentation

The vast majority of cases are asymptomatic and the presence of the vessel is only identified incidentally during CT scanning of the chest, or as a result of line placement.

In the small minority of patients who have a right to left shunt as a result of drainage directly into the left atrium, the shunt is usually not large enough to present with cyanosis (draining only the left upper limb, and left side of the head and neck).

A number of associations are recognised, which may result in investigation and identification of the abnormal vessel. They include:

* congenital heart defects : present in 4.4% of patients with CHD 3
o atrial septal defect (ASD) : most common
o single atrium
o ventricular septal defect (VSD)
o tetralogy of Fallot
o coarctation of the aorta
o pulmonary stenosis
o anomalous pulmonary venous return
* arrhythmias

Radiographic features

Plain film

Direct visualisation of a left sided SVC is not possible however its presence can be implied if a catheter or line is in an unexpected left paramediastinal location.


CT, especially with contrast, is able to elegantly demonstrate the anomalous vessel coursing inferiorly to the left of the arch of the aorta and anterior the the left hilum. It is in direct continuation of the confluence of the left jugular vein and the left subclavian vein. A communication between the normal right SVC (which is present in 82 - 90% of cases) may also be seen.

Depending on the timing of the scan and the side of the injection variable amounts of contrast may be seen within the vessel.

CT is also able, especially with the benefit of reformats, to delineate the site of drainage (usually coronary sinus).

Nuclear medicine

The diagnosis may be suspected in cases of left arm injection for a VQ scan, in patients with drainage into the left atrium. In such cases essentially all the radio-tracer will appear in the systemic circulation rather than the normal 2% which cross the lung due to intrapulmonary shunts 3.

Treatment and prognosis

Except in cases where a large right to left shunt is present, a left sided SVC has essentially no physiologic impact and is entirely asymptomatic.

Its importance stems from venous procedures, such as line placement or pacemaker implantation where failure to recognise this variant can result in incorrect positioning 4.

Differential diagnoses

When able to be traced on CT there is no differential.

An abnormal catheter position on chest x-ray, which runs to the left of the mediastinum has a limited differential : see differential of left paramediastinal catheter position 5.


Left sided superior vena cava - CXR with PPM


Left sided SVC


Bilateral SVC CT

Article Author : Dr Frank Gaillard, Radiopaedia


  1. Kellman GM, Alpern MB, Sandler MA et-al. Computed tomography of vena caval anomalies with embryologic correlation. Radiographics. 1988;8 (3): 533-56. Radiographics (abstract) - Pubmed citation
  2. Padhani AR, Hale HL. Mediastinal venous anomalies: potential pitfalls in cancer diagnosis. Br J Radiol. 1998;71 (847): 792-8. Br J Radiol (abstract) - Pubmed citation
  3. Pretorius PM, Gleeson FV. Case 74: right-sided superior vena cava draining into left atrium in a patient with persistent left-sided superior vena cava. Radiology. 2004;232 (3): 730-4. doi:10.1148/radiol.2323021092 - Pubmed citation
  4. Smyth YM, Barrett CD, Fahy GJ. Images in cardiology. Biventricular pacemaker implant in a patient with persistent left sided superior vena cava. Heart. 2005;91 (11): 1427. doi:10.1136/hrt.2005.060707 - Free text at pubmed - Pubmed citation
  5. Kazerooni EA, Gross BH. Cardiopulmonary imaging. Lippincott Williams & Wilkins. (2004) ISBN:0781736552. Read it at Google Books - Find it at Amazon
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