Left superior vena cava: revisited.

The persistence of a left-sided superior vena cava is the most common variant of systemic venous drainage. Increased utility of cardiac imaging, in particular cross-sectional techniques such as computed tomography and magnetic resonance (MR), will result in increased detection of the anomaly and its variants. Whilst in the typical form it is often haemodynamically insignificant, its discovery may have clinical significance nonetheless, and its mimics require exclusion. During cardiac development the anomaly results from a failure of the left anterior cardinal vein to obliterate. Recognized anatomical variants include the absence of the right superior vena cava and of an innominate bridging vein. Typical drainage is to the coronary sinus, dilatation of which may be the first hint to the anomaly. Clinical implications with respect to vascular access and arrhythmia are well described. A significant minority drain into the left atrium, potentially creating a haemodynamically significant lesion. Additionally, differentiation from anomalous left upper pulmonary venous drainage via a vertical vein is mandatory. A newly discovered variant runs an intra-atrial course with subsequent typical drainage, and if not recognized as such, may be confused with a left atrial mass. The use of 3D contrast-enhanced MR venography has proven extremely helpful in characterizing anomalous vasculature, and we demonstrate how such techniques can help delineate the anomaly and differentiate from its mimics.