Anatomic causes of pulmonary stenosis in complete transposition.

Among 166 specimens with classical complete transposition, pulmonary or subpulmonary stenosis was present in 22 cases. The bases for obstruction were pulmonary valvular stenosis (one case), membranous subpulmonary stenosis (nine cases), anomalous attachment of the mitral valve to the ventricular septum (five cases) and combinations of causes (seven cases). Conditions contributing to combinations of causes included the above, in addition to accessory mitral or pulmonary valvular tissue and herniation of a tricuspid valvular pouch through a related ventricular septal defect. In addition to the 166 cases mentioned, our collection contained six cases of atypical complete transposition characterized by a conus being present in the each ventricel. In three of these six, subpulmonary stenosis was present and caused by a narrow inlet to the left ventricular conus.