Lateral costal artery: accessory thoracic vessel of clinical interest.

The lateral costal artery (LCA), a supernumerary branch of the internal thoracic artery (ITA), occurs in several ethnic groups on one side of the thorax or on both, in 15-30% of cases. It has been considered responsible for the "steal-syndrome" of the coronary blood after coronary artery bypass grafting and it used occasionally for myocardial revascularization. To clarify its functional significance, an interpretation based on our findings and human and comparative anatomy and embryology has been attempted. We report on a case where a right LCA of about 2 mm in caliber, rising from the ITA 2.5 cm below the subclavian, coursed as far as the 4th intercostal space for a distance of 13 cm after the anterior axillary line. Anastomosing with the intercostal arteries, it can act as a blood derivative circuit of the thoracic wall. Embryologically, this artery, like the normal parietal arteries of the trunk, might form a longitudinal channel connecting the intersegmental arteries. In mammals having a thoracic cage transversely restricted (quadrupeds), the ITA is more lateral than in primates having a circular thorax, and gives off a ventral branch toward the sternum. It might be hypothesized that the sternal branch occurring in quadrupeds, undergoing adaptation to the thoracic shape of primates, may become the main trunk of the ITA, whereas the LCA may be the remnant of the ITA of quadrupeds. Because the LCA ran partly along the "milk line" of humans, it might be regarded as a supernumerary mammary artery.

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.