Double superior venae cavae with absence of the coronary sinus and anomalies of the azygos venous system

The superior vena cava is formed during the fetal period by the development of anastomoses between the right and left anterior cardinal veins, and the regression of the central part of the left anterior cardinal vein. The persistence of this part of the left anterior cardinal vein causes the formation of a left superior vena cava, which is a rare anomaly in cadaver dissection. We report the case of a persistent left superior vena cava with a normal right superior vena cava in a 95-year-old male cadaver, which was discovered during anatomical dissection for medical students at Kawasaki Medical School in 2016. The left superior vena cava was formed by the confluence of the left internal jugular and left subclavian veins and terminated in the right atrium via what would normally be the coronary sinus. The right and left superior venae cavae received intercostal veins via a right and left azygos vein, respectively. However, the right azygos vein was shorter than the normal azygos vein and received only the second to fifth intercostal veins, whereas the left azygos vein received the fifth to eleventh left intercostal veins and the sixth to eleventh right intercostal veins. We consider that the anomalies of the azygos venous system were the result of regression of right supracardinal vein and the persistence of the left supracardinal vein during development. An awareness of such variations of major thoracic veins is important for the interpretation of unusual CT images.