Chapter 28 - Fossa ovalis, patent foramen ovale, and cardiac masses

Abstract

The fossa ovalis forms an oval shaped depression in the wall of the interatrial septum. It is a remnant of the embryonic ostium secundum in the septum primum (the dividing membrane between right and left atrium) of the heart. Its morphology changes in certain disease conditions. Of note is the morphological variant of fossa ovalis, the patent foramen ovale (PFO) which is the result of an incomplete union of the embryonic septum secundum against the septum primum, found in about 25% of the population. The patent foramen ovale provides a channel not only for blood but also potentially for thrombi and gas and fat emboli to cross into the systemic circulation, bypassing the pulmonary circuit via such “paradoxical” embolism. Aneurysms associated with the fossa ovalis have also been implicated in giving rise to the arterial emboli. Hence, a patent foramen ovale has been associated with pathologies including cryptogenic stroke, decompression sickness, migraine, and platypnea–orthodeoxia syndrome—among other less studied ailments. The fossa ovalis is also used as a surgical plane for traversing into the left heart from the right atrium and is of surgical significance for multiple cardiac procedures including removal of the cardiac myxomas. Cardiac myxomas form the majority of the cardiac masses encountered clinically in the vicinity of the fossa ovalis. Cardiac masses are clinically divided into benign and malignant tumors of primary and secondary origin, and nonneoplastic entities like thrombi and vegetations.