Tetralogy of Fallot. Occlusion of the ventricular septal defect due to accessory tricuspid valve leaflet and an associated membranous aneurysm.

A unique case of tetralogy of Fallot is presented in a 3 7/12-yr-old white female. At surgical repair, a ventricular septal defect smaller than usual was demonstrated in the usual infracristal position. The ventricular septal defect was partially obstructed from the right side of the ventricular septum by adherence of an accessory tricuspid leaflet. An associated membranous aneurysm, presumably acquired, was occluding the ventricular septal defect at its outlet almost completely. The literature has been reviewed and the pathophysiology of this lesion is discussed, underlining the nature and plausible development of the membranous aneurysm.