Classification of persistent left superior vena cava considering presence and development of both superior venae cavae, the anastomotic ramus between superior venae cavae, and the azygos venous system.

Subjects with persistent left superior vena cava were classified on the basis of the presence and thickness of both superior venae cavae, the anastomotic ramus between the superior venae cavae (anastomotic ramus), and the presence of both azygos veins. Among subjects with persistent left superior vena cava, the percentage of those with weak development of the anastomotic ramus (41.5 %) or absence of an anastomotic ramus (35.8 %) was 77.3 %. In addition, 54.7 % of subjects had a left azygos vein. However, 88.7 % of subjects had a right azygos vein. In this classification, the most frequently observed types included the presence of both superior venae cavae, an anastomotic ramus, and both azygos veins (20.8 %). During student dissection practice sessions performed on 337 cadavers that were carried out from 2002 through 2010, a subject having a left superior vena cava (in 2002) and a subject having both superior venae cavae (in 2003) were detected. The former case was reported previously. The latter case is reported in this paper. The incidence of persistent left superior vena cava was 0.59 % (2/337 cadavers).