Truncus arteriosus communis, an unusual anatomical variant of type I.

We present a case of type I truncus arteriosus communis characterized by the horizontal origin of the main pulmonary artery from the common trunk and by a winding course up to a total length of 11.5 cm to the point of bifurcation of the pulmonary artery. Other than cyanosis the patient had a normal clinical history, which was followed for 20 years. The length of the main pulmonary artery could be related to the lower site of the incomplete septation of the common trunk, and it seems that hemodynamic factors contributed to this unusual configuration.