Developmental anatomy and origins of LSVC
When the right atrium is developing at the eighth week of gestational stage, the sino-atrial chamber differentiates into the sinus venosus and the atrial chamber. The cephalic portions of the anterior cardinal veins form the internal jugular veins while the caudal portions of the right anterior and a part of the corresponding common cardinal vein form the normal right-sided superior vena cava. The left anterior cardinal vein, caudal to the innominate vein, obliterates to form “the ligament of Marshall”, which was described as a “vestigial fold of pericardium” (6).
The left common cardinal vein normally persists as coronary sinus and oblique vein. The congenital malformation LSVC represents the persistence of the left anterior cardinal vein that continues into the left sinus horn (left duct of Cuvier) during the early developmental period (6).
Subaortic membrane remains an important differential diagnosis in hypertrophic cardiomyopathy with left ventricular outflow tract (LVOT) obstruction and in aortic stenosis. The coexistence of subaortic membrane and persistent SVCs is very rare.