The spectrum of transposition of the great arteries: with specific reference to developmental anatomy of the conus.

One hundred and sixty five cases of various types of transposition complexes were studied. Based on this and on recent studies of the embryology of the conotruncus, the following observations were made. Regardless of their relations with the ventricles, the semilunar valves may show d-transposition or i-transposition. In the situs solitus heart, the d-type of semilunar transposition is found in the bulboventricular heart, double outlet right ventricle type II, Taussig-Bing malformation, complete transposition of the great arteries, and double outlet left ventricle. This type of transposition of the great arteries results from lack of conotruncal inversion and the differences between the various entities are manifestations of varying degrees of leftward shift of the conoventricular junction and conal absorption. In i-transposition, the conotruncus rotates in the wrong direction. This may occur as an isolated process as in anatomic corrected transposition of the great arteries or with i-looping as in physiologic corrected transposition. Conal absorption and conoventricular shift account for the various entities in each of these two groups of 1-transposition. It is proposed that the term transposition of the great arteries should refer only to the mutual interrelationships of the semilunar valves regardless of their ventricular origin.