In one case, a left pulmonary vein opened into the left brachiocephalic vein. These unusual connections between the pulmonary veins and neighboring, many adversely inappropriate, veins are explicable only on the basis of very early embryonic stages in which the developing foregut, trachea, and lung buds are supplied by a common plexus of small channels that network in all directions through the loose mesenchyme and communicate with the primitive cardinal veins in many places. With the development of certain channels in this primitive vascular bed to form the pulmonary veins leading to the left atrium, the primitive connections with the cardinal veins usually disappear. The unusual development of one or more of them, and its retention by the adult derivative of the particular part of the cardinal system involved, are most probably responsible for the occurrence of these unusual pulmonary connections. Steinberg and Finby classified the congenital anomalies of the pulmonary circulation as follows A. Malformations of the Pulmonary Artery.
Valvular stenosis Requires surgical treatment.
B. Malformation of a Branch of the Pulmonary Artery. No treatment required, prognosis good. Compatible with normal life. C. Pulmonary Arteriovenous fistulas Requires surgical treatment. D. Alteration of Pulmonary Circulation.