Morphological findings in Ebstein's anomaly.

This is a report on the anatomical findings of 6 cases of typical Ebstein's anomaly found in a review of 1300 autopsy specimens. In addition 2 cases with pulmonary atresia and 1 with atresia of the malformed tricuspid valve showing morphologically similar anomalies were found, as well as 29 cases with tricuspid valvular dysplasia (21 of them coexisting with pulmonary atresia with intact ventricular septum). The right ventricle was divided, in each case, in 2 parts separated by the abnormal valvular leaflets. The infundibular septum was very hypoplastic, its antero-medial prolongation forming a morphologically abnormal band superimposed upon the right side of the interventricular septum, ending inferiorly at the base of the anterior papillary muscle. The interventricular septum was thinner than normal, and so was the right ventricular free wall. A constant finding was a superiorly placed valvular orifice, limited by anterior and septal leaflets. In three cases an apical orifice was found, limited by the septal and posterior leaflets and by a zone of the posterior wall of the right ventricle with no recognizable leaflet insertion. The leaflets were rather easily identified. The anterior leaflet was demarcated by the 2 commissures of the superior orifice. The septal leaflet attached to the septum along an oblique line. The posterior leaflet, the least differentiated, inserted in the annulus, with its inferior border adherent to the ventricular muscular wall, forming a blind cavity in which chordae tendineae in different stages of development were found. Microscopic findings included: myocytolysis, substitution of muscle fibers by connective tissue with some small scars, a great deal of capillaries and disorganization of muscle bundles, none of them being constant.