ANATOMICAL CRITERIA FOR THE DIAGNOSIS OF SINUS VENOSUS DEFECTS

Background-The diagnosis of sinus venosus defects remains a matter of debate. It is crucial to provide solid anatomical criteria, by identif ying the very nature of the atrial septum relative to sinus venosus de fects, to diagnose and differentiate them from other interatrial commu nications. Objective-This study was designed to reestablish the anatom ical criteria for the diagnosis of sinus venosus defects. Methods-Five specimens with sinus venosus defects from the cardiopathological muse um were examined. Study of the abnormal hearts was supplemented by exa mining the extent and structure of the atrial septum in 10 normal hear ts. The echocardiograms and surgical notes were reviewed from 18 patie nts seen between July 1991 and August 1996 at the Royal Brompton Hospi tal in London diagnosed preoperatively to have a sinus venosus defect. Results-The nature of the oval fossa and its muscular borders were id entified in the normal hearts. In all three autopsied specimens of the superior variety of sinus venosus defect, the mouth of the superior c aval vein was overriding the intact muscular anterosuperior border of the oval fossa. Two specimens thought initially to have the inferior v ariety of sinus venosus defect were re-classified as having defects wi thin the oval fossa as it was the deficient oval fossa itself, rather than its intact muscular border, that was overridden by the mouth of t he inferior caval vein. Sixteen patients had been diagnosed echocardio graphically as exhibiting the superior variant of the defect. Retrospe ctive review showed overriding of the superior caval vein across the u pper rim of the oval fossa in 12 patients. These findings were confirm ed by surgery in 11 patients with the 12th awaiting operation. Overrid ing of the fossa by the caval vein was not found in the other four pat ients. Surgery in all of these showed the defect to be within the oval fossa. In two patients diagnosed echocardiographically as having infe rior defects, the surgical findings confirmed a biatrial connection of the inferior caval vein in one patient, the findings in the second we re equivocal. Conclusions-The key anatomical criterion for the diagnos is of sinus venosus defects is overriding of the mouth of the superior or inferior caval vein across the intact muscular border of the oval fossa. The interatrial communication is then formed within the mouth o f the overriding vein, and is outside the confines of the oval fossa.