Left superior vena cava continuing to the accessory hemiazygos without anastomosis with the coronary sinus

A case of double superior vena cava lacking the left brachiocephalic vein was found. The left superior vena cava directly continued to the accessory hemiazygos vein without anastomosis with the coronary sinus. Therefore, the blood from the left superior vena cava drained into the right superior vena cava via the transverse anastomosis between the left and right azygos lines. It was thought that embryologically 1) the inter-precardinal vein was not formed, and 2) the left precardinal vein did not continue to the common cardinal vein, rather it drained into the left azygos line. This case may represent one of the most basic arrangements of the superior caval system.