Aneurysm of the pars membranacea of the interventricular septum

Six cases of aneurysmal formation of the pars membranacea septi (AMS) are presented. Three cases associated with a ventricular septal defect (VSD) and one with VSD, prolapse of the right aortic cusp and aorto-right ventricular fistula, were operated on and the aneurysm, unsuspected preoperatively, was found at the operating table. Two cases, both with aortic coarctation (CA), have been diagnosed on the basis of selective angiocardiography and operated solely for resection of the coarctation. In three patients a mild pulmonary infundibular pressure gradient was present at catheterization. This anomaly is considered rare. It has been reported to complicate surgery, may not require surgery, and is considered by some to be a prelude to spontaneous closure of a VSD. The English medical literature concerning aneurysm of the membranous septum has been reviewed and our opinions on the management of these patients are presented. Including our own six patients, we are aware of approximately one hundred and sixty five reported cases, with possibly an additional 16 cases to be added.