Persistent left superior vena cava

A persistent left superior vena cava is the most common variation of the thoracic venous system, found in roughly 0.3 to 0.5 percent of people. It is an embryologic remnant that arises when the left-sided vein fails to involute during development. In the typical form the left brachiocephalic vein does not develop fully, so blood from the left arm, head and neck drains into the right atrium through the coronary sinus. On its own it is considered benign and often goes unnoticed, but it is frequently found alongside cardiac abnormalities such as ventricular or atrioventricular septal defects, which carry real mortality and morbidity. It may be picked up on a prenatal ultrasound and confirmed by fetal echocardiogram, or seen as a pipe sign on CT or MRI. If it drains into the left atrium, cyanosis may occur; otherwise it is usually left untreated.