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

Isolated Aneurysms of the Membranous Ventricular Septum Without Residual Shunts: Systematic Review and Description of 3 Cases in Adults

“…A variety of pathologic factors have been proposed to explain the occurrence of aneurysms at this location . The most common is spontaneous closure of a preexisting ventricular septal defect arising from the margins of the defect and usually incorporating the septal leaflet of the tricuspid valve . The rate of spontaneous closure of ventricular septal defects was 18.4% in 1873 patients in a single report .…”

“…The size and direction of the aneurysmal defect are governed by the pressure gradient on both sides of its walls . The latter will give rise to the characteristic outpouching “windsock” appearance on echocardiography, resulting from aneurysmal distension during ventricular systole . The sizes of the aneurysm have varied from 8 × 25 mm in one report to as large as 5 × 7 cm in others (Figure ) …”

“…Transesophageal echocardiography is used when results from the transthoracic approach are inconclusive . Saline contrast echocardiography can delineate the borders of the aneurysm and help differentiate it from other outflow tract masses (Figure ) . Despite its limited utility for the assessment of membranous ventricular septal aneurysms, myocardial perfusion imaging may show a correlative perfusion defect secondary to aneurysmal formation (Figure ).…”

“…In rare cases, it can protrude outside the heart between the root of the pulmonary artery and the ascending aorta, giving the appearance of a mediastinal mass . Less commonly, a left ventricular‐to‐right atrial communication can occur with a “Gerbode defect,” increasing the risk of complications . The strategic localization of the aneurysm and the traction imposed by ventricular systole to the atrioventricular bundle and its branches helps explain the genesis of certain conduction defects .…”

“…9 Less commonly, a left ventricular-to-right atrial communication can occur with a "Gerbode defect," increasing the risk of complications. 19 The strategic localization of the aneurysm and the traction imposed by ventricular systole to the atrioventricular bundle and its branches helps explain the genesis of certain conduction defects. 9,13,14,20 Life-threatening complications are related to thrombus formation, endocarditis, and related systemic emboli, persistent cardiac arrhythmias, and acute right-to-left shunts secondary to aneurysmal rupture.…”