Left superior vena cava with left azygos vein.

An incidence of a left superior vena cava with a left azygos vein was found in a cadaver during an Osaka Dental University student's dissection practice session in 2002. The left superior vena cava began from the confluence between the right and left brachiocephalic veins, and extended directly into the left superior edge of the coronary sinus. No right superior vena cava was observed. The left azygos vein, receiving the bilateral intercostal veins, extended into the left superior vena cava. The developmental mechanism of the left superior vena cava was considered as follows; because the proximal part of the left anterior cardinal vein and the left common cardinal vein remained, and the proximal part of the right anterior cardinal vein and the right common cardinal vein degenerated and disappeared. The developmental mechanism of the left azygos vein was considered as follows; because the proximal part of the left posterior cardinal vein remained, and the root of the azygos vein was formed.