Bifurcation of the left superior pulmonary vein, associated with an anomalous connection with the left atrium

An unusual case of bifurcation of the left superior pulmonary vein (LSPV) just before it enters the pericardium is described. The LSPV, which at the hilus of the lung originated from normal confluence of a superior and inferior root, bifurcated near the left atrium (LAt) of the heart into anterior (AB) and posterior (PB) branches that, separately invaginating the parietal pericardium, formed two individual serous sheaths. The PB coursed almost horizontally and opened, as usual, into the supero-dorsal wall of the LAt. The AB turned downward, reached the superior margin of the left auricle (LAu) and emptied into it. Thus, the AB was interposed between the pulmonary trunk and the LAt, obstructing on the left side the communication between the transverse sinus of the pericardium and the pericardial cavity. The auricular opening of the AB was avalvular, but, unlike those of the normal pulmonary veins (PVs) which are surrounded by a large smooth inner surface, was, except for a narrow smooth-walled zone, close to the pectinate muscles. Moreover, an inferior muscular ridge at the inferior margin of its orifice of entrance into the LAu, separated it from the cavity of the LAt. It is well known that in development the PVs arise from convergence of capillaries belonging to the mediastinal part of the primitive splanchnic plexus and drain this into the systemic (cardinal and vitello-umbilical) veins of the embryo. As a consequence, it might be hypothesized that the AB of the LSPV probably represents a partial remnant either of a pulmonary-cardinal anastomotic mediastinal vein, or of a diverging vessel of the mediastinal plexus from which the PVs originate. In either case the AB became absorbed by the LAu, which, while it was developing on the left side of the primitive truncus arteriosus, drew the AB forward and downward, in the direction of its movement. The influence of such an anomaly of the PVs for altered intracardiac hemodynamics of the oxygenated blood flow has to be emphasized. Furthermore, the particular location of the AB, obstructing the communication between transverse sinus and pericardial cavity, can be a hindrance during cardio-pulmonary surgery.