'Posterior' transposition reconsidered.

Seven cases of transposition with an unusually posterior aorta and mitral-aortic fibrous continuity are described. The cases are similar to four cases published by Van Praagh et al. in 1971. The use of the term 'p' transposition is suggested to distinguish this unusual form of transposition from cases with a subaortic conus ('d' and 'l' transposition). The use of the term 'transposition' is considered justifiable on both semantic and morphogenetic grounds and a possible common embryological mechanism for all forms of transposition is discussed.