Unusual variation in upper-body venous anatomy found with cardiovascular MRI

It is not uncommon to find patients with a persistent left SVC draining into the coronary sinus along with a normal right SVC; this occurs in 0.3% of the general population and is considered a normal variant of systemic venous return.1 In such patients, blood from the left jugular and subclavian veins reaches the right atrium via a left SVC and the coronary sinus while the right brachiocephalic vein drains into the normal right SVC. However, it is fairly rare to find a patient such as ours, with a persistent left SVC in the absence of a right-sided SVC and with normal visceroatrial orientation (situs solitus), which occurs in less than 0.1% of the general population.2 Nearly half of patients with left SVC (46%) have associated congenital abnormalities (Box i), which are often significant enough to be detected before or just after birth. However, half of patients with a persistent left SVC and absent right SVC are asymptomatic and have no associated cardiac malformations. For an MRJ animation of our patient's anatomy, see Appendix 1 (available at www.cmaj.ca /cgi/content/full/175/1/27/DC1). Fig. 3: The development of persistent left-sided superior vena cava (SVC). Left panel: The embryonic venous system, in which the superior and inferior caval veins (CVs) join into the common caval vein. At 8 weeks, the innominate vein links the superior CVs. Centre: The left superior CV normally obliterates distally to the innominate vein; the right-sided SVC develops from the right superior CV and part of the right common CV. The coronary sinus, which collects myocardial venous blood, develops from the left common CV. Right panel: A persistent left SVC connects to the coronary sinus. The rightsided SVC is absent because of persistence of the distal superior CV segment on the left and involution on the right. AntCV = superior caval veins, CCV = common caval vein, CS = coronary sinus, InV = innominate vein, LSVC = leftsided superior vena cava, PostCV = inferior caval veins.