Aneurysm of the Atrioventricular Membranous Septum Appearing as a Right Atrial Cystic Mass

Abstract

6-mo-old infant was referred for closure of aventricular septal defect (VSD). Transthoracic echo-cardiography obtained for evaluation of a cardiacmurmur at 2 mo of age demonstrated a largeperimembranous VSD. Subsequent examination re-vealed partial occlusion of the defect by surround-ing aneurysmal tissue, billowing of this tissue intothe right atrium (RA), and the concern for a leftventricular (LV)-to-RA communication. Surgical in-tervention was undertaken in view of the clinicalevidence of a moderate intracardiac shunt.After induction of anesthesia, transesophageal echo-cardiography (TEE) was performed. Two-dimensionalimaging demonstrated a large, septated, cystic mass inthe posteroinferior aspect of the RA (Fig. 1; please seevideo clip available at www.anesthesia-analgesia.org).Color flow Doppler interrogation identified shuntingfrom the LV into the saccular structure, and from thisinto the right ventricle (RV) (Please see video clipavailableatwww.anesthesia-analgesia.org).Notricus-pid inflow obstruction was detected. A second area ofleft-to-right shunting was noted in the adjacent mem-branous ventricular septum.Surgical inspection demonstrated aneurysmal fi-brotic degeneration of the atrioventricular (AV) mem-branous septum protruding into the RA. Fenestrationsin the aneurysmal sac, in immediate proximity to thetricuspid valve (TV), appeared to allow for the egressof blood directly into the RV. Two distinct anatomiccommunications were identified in the membranousseptum: one between the LV and aneurysmal sacwithin the RA, and another between the ventricles.The intervention consisted of pericardial patch closureof the defects and repair of a TV leaflet incisionrequired for anatomic exposure. Because of the con-cern for creating AV block, the aneurysmal tissuecould not be resected in its entirety and a few fenes-trations remained on the septal aspect of the tricuspidannulus. Postoperative TEE demonstrated a smalleraneurysmal sac, mild tricuspid regurgitation, and noevidence of residual septal defect shunting. Agitatedsaline injection into a central venous catheter showeda small systolic stream from the RV into the aneurysm,consistent with residual fenestrations along the septalTV leaflet (Please see video clip available at www.anesthesia-analgesia.org).The membranous ventricular septum is divided bythe attachment of the septal leaflet of the TV into twocomponents: the AV portion, or region immediately