Question

A left-sided superior vena cava drains into:

• A. Right atrium
• B. Left atrium
• C. Coronary sinus
• D. Pericardial space

Hint:

The left horn of the sinus venosus becomes the coronary sinus; the persistent left vein drains there.

Answer 1

The Correct Option is C

Note on the key: The recalled paper printed option A (right atrium). The classic and medically correct answer is the coronary sinus, so the key has been corrected to option C, with the reasoning below.

Step 1: A persistent left superior vena cava (LSVC) is the commonest thoracic venous anomaly. It results from failure of the left anterior cardinal vein to obliterate during development.

Step 2: The left common cardinal vein and the left horn of the sinus venosus normally regress; the left horn of the sinus venosus persists as the coronary sinus. When the left anterior cardinal vein fails to involute, it persists as an LSVC, which descends on the left, receives the left brachiocephalic territory, and drains into the coronary sinus.

Step 3: The dilated coronary sinus then empties into the right atrium in the usual way, so blood ultimately reaches the right atrium but through the coronary sinus. The direct termination of the LSVC is the coronary sinus, which is what this question asks.

Step 4: In the rare variant where the LSVC drains into the left atrium it causes a right-to-left shunt, but the typical, expected answer for this question is the coronary sinus, so options A, B and D are not the best answer.

Answer: C. Coronary sinus