The left innominate vein is usually located anterosuperior to the aortic arch, and connects with the right innominate vein, forming the SVC. However, it rarely courses via an alternative pathway. Kerschner reported the first case of an alternative course of the left innominate vein more than one hundred years ago (1). This rare anomaly has been reported in patients with cardiac anomalies. Its incidence is 0.55% among patients with congenital heart anomaly. It is commonly related to tetralogy of Fallot or right aortic arch (2). Cases of an isolated retroaortic innominate vein (RAIV) are extremely rare. Nagashima et al. reported that its incidence was 0.02% (1 of 4805) in patients without congenital heart anomaly (3). During normal fetal development, systemic veins develop from paired anterior and posterior cardinal veins. They unite on each side, and form common cardinal veins. Venous return eventually directs into the sinus venosus. The anterior cardinal veins continue to the bifurcation of the internal jugular veins and subclavian veins on each side. However, a large part of the left anterior cardinal vein vanishes. Venous flow from the left side of the head and arm directs into two anastomotic plexuses (superior and inferior channels), and eventually reaches the right anterior cardinal vein by the eighth week (2). Usually, the inferior transverse capillary plexus regresses, and the superior transverse capillary plexus becomes the left innominate vein. The left common cardinal vein becomes the coronary sinus. The oblique vein of Marshall is formed by the left anterior cardinal vein (4). It is not clear how the RAIV is formed. A possible explanation is failure of usual development of the superior transverse anastomosis and, as a result, an alternative pathway in the caudal position remains and forms the RAIV (4).
RAIV can be problematic if contrast CT is not performed in clinical settings. It may be difficult to insert a central venous catheter from the left jugular/subclavian vein. Permanent pacemaker lead insertion from the left subclavian vein can be hazardous. When surgery is performed in patients with AAAD using retrograde cardioplegia, insertion of the cannula into the coronary sinus under direct vision can be a problem. If insertion of the cannula without opening the RA under TEE guidance is used, RAIV does not cause a problem. If insertion of the cannula into the coronary sinus under direct vision with bicaval drainage is chosen, the site of SVC cannulation should be placed more caudally. Moreover, the SVC must be snared more caudally. Otherwise, blood from the RAIV returns into the RA, which makes it difficult to insert a retrograde cardioplegic cannula into the coronary sinus.
In the present case, we used a single venous cannula into the RA. Moreover, a retrograde cardioplegic cannula was inserted into the coronary sinus under TEE guidance. Blood from the RAIV did not cause a problem because we did not open the RA. However, if it is necessary to open the RA for tricuspid valve surgery or atrial septal defect closure, meticulous attention is required, as mentioned above.
Although we did not perform total arch replacement (TAR) in this patient, it is required when an intimal tear is located in the aortic arch. RAIV may prevent surgeons from looking at the distal aortic arch and performing maneuvers for anastomosis. When surgeons retract the RAIV to acquire a good operative field, laceration and subsequent bleeding may occur. When bleeding occurs from the junction between the RAIV and SVC, it might be difficult to control it. Furthermore, strong retraction for a long time can cause thrombosis in the RAIV, which might lead to catastrophic pulmonary embolism. If aortic surgery is required in patents with RAIV via left thoracotomy, the same attention is mandatory for proximal anastomosis.