Aneurysm of the fossa ovalis in infants: a pathologic study.

An aneurysm of the fossa ovalis was identified at autopsy in 17 infants. In each case the aneurysm of the fossa ovalis was considered to have resulted from excessive elevation of pressure in that atrium contralateral to the side into which the aneurysm bulged. The aneurysms were divided into two types: intrinsic (three cases) and extrinsic (14 cases). The intrinsic types of aneurysms of the fossa ovalis were considered to have started in fetal life and were consequences of abnormally narrow states of interatrial ostium II. Each intrinsic aneurysm bulged toward the left. Among the extrinsic types of aneurysm of the fossa ovalis, each was considered to have resulted from the hemodynamic consequences of a congenital anomaly in one side of the heart or other. Six aneurysms of extrinsic type bulged toward the left and eight toward the right. Aneurysm of the fossa ovalis should be included in the differential diagnosis of space-occupying conditions within the atria.