Aneurysm of fossa ovalis in adults: a pathologic study.

BACKGROUND: Aneurysm of the fossa ovalis is an out pouching, space-occupying, interatrial septal structure. The anatomic morphology and characteristics of this aneurysm are of interest for pathologists and cardiologists alike. METHODS: We identified 33 specimens of adult hearts with a large size aneurysm of the fossa ovalis (length equal to or more than 10 mm from the plane of the atrial septum) in a registry of cardiovascular disease. Anatomic-morphologic features of these aneurysms were examined by macroscopic and histopathologic studies. RESULTS: Nineteen aneurysms were from females (57%) and 14 were from males (43%). Most aneurysms had a dome shape with maximal length of the aneurysmal excursion into an atrium varying from 10 to 35 mm (mean 16+/-5 mm) and width varying from 16 to 40 mm (mean 24+/-6 mm). Twenty-four aneurysms (73%) protruded into the right atrium while only nine (27%) penetrated into the left atrium. In 24 patients the interatrial ostium II was patent, and in 22 (91%) of them, abnormal increased intracardiac pressure was deemed responsible for the formation of the aneurysm. Among nine patients in whom the foramen ovale was closed, eight (89%) had an aneurysm protruding into the right atrium, and only one aneurysm penetrated into the left atrium. In six patients, the aneurysm further stretched an already patent foramen ovale resulting in creation of an atrial septal defect so that bidirectional shunting could occur, and in three cases, the aneurysm narrowed the inferior vena caval orifice. In three hearts, the aneurysm wall had endocardial fibrosis, and in three other specimens, a focal mural thrombus was present on the aneurysmal surface. Most common associated cardiac conditions in this series included atherosclerotic coronary artery disease (51%), aortic valvular disease (21%) and mitral valve disease (24%). CONCLUSIONS: Aneurysm of the fossa ovalis is a space-occupying, redundant structure, most commonly with a dome shape. In a majority of cases, the formation of this aneurysm relates to the effect of extrinsic mechanisms, which create abnormally elevated intracardiac pressures. The aneurysm protruded into the right atrium in 73% of cases. Endocardial fibrosis and a focal mural thrombus were present in several cases on the aneurysmal wall. Bidirectional shunt via stretched patent foramen ovale and distal embolization can contribute to complications related to the aneurysm.