Embryology, anatomy, and physiology: Anatomical variations, lipomatous hypertrophy, atrial septal aneurysm, eustachian valve, chiari network, combination with other atrial septal defects

Knowledge of the embryological development of the interatrial septum can provide the basis for understanding the morphogenesis of some congenital cardiac malformations. The interatrial septum consists of several embryological components including the septum primum, the anterosuperior and the posteroinferior cushions of the atrioventricular canal, the septum secundum, and the left sinus valve. Normally the interatrial communication closes soon after birth. However, in about 25% of the population, this passage will persist and is known as a patent foramen ovale (PFO). A PFO can be a risk factor for several serious clinical syndromes, including paradoxical systemic embolism such as ischemic stroke or myocardial infarction, decompression sickness in divers, and profound hypoxemia. Recent evidence further implicates PFO as a possible cause of migraine headache through mechanisms that are not fully understood. A PFO is amenable to interventional percutaneous closure, and multiple novel technologies are either available or under development for closure of this defect. A PFO may be associated with various anatomic anomalies such as an atrial septal aneurysm, a Eustachian valve, or a Chiari network. The pathology, pathophysiology, and clinical impact of PFO should serve as a knowledge base as multiple approaches to percutaneous closure become available for clinical application.