This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
A persistent left superior vena cava usually drains into 
Select and explain. 
A. Right atrium, B. Inferior vena cava, C. Coronary sinus, D. Right superior vena cava
C: Coronary sinus
Answer: C: Coronary sinus 
Explanation: Persistent left superior vena cava (PLSVC) is the most common thoracic venous anomaly. Autopsy studies in unselected patients have shown that the frequency of PLSVC is 0.3%. This anomaly is frequently observed in patients with congenital hea disease and has occasionally been repoed in patients without evidence of other congenital abnormalities.1, 2 Persistent left superior vena cava is the result of a persistent patency of an embryological vessel (left anterior cardinal vein) that is present during the early developmental period. It usually drains into the right atrium through a dilated coronary sinus.3, 4 However, in some cases, it may drain directly into the left atrium producing a right-to-left shunt,5, 6 or directly into the right atrium. In most of these cases the right superior vena cava may be present and may or may not communicate with the left superior vena cava.7 Persistent left superior vena cava is generally discovered fouitously without clinical signs.