Right atrioventricular valve atresia: anatomic evaluation with MR imaging.

MR was used to differentiate the classical form of tricuspid atresia, in which the atrioventricular connection is absent, from a rare type of right atrioventricular obstruction, in which the valve is imperforate, and from some Ebstein's malformations in which atrioventricular flow is obstructed by a displaced tricuspid valve. ECG-gated, T1-weighted spin-echo MR imaging was performed at 0.3 or 1.0 T in six patients with classical tricuspid atresia, in one patient with tricuspid atresia due to an imperforate tricuspid valve, and in two with Ebstein's malformation. In the patients with classical tricuspid atresia, epicardial fat within the atrioventricular sulcus that was interposed between the right atrium and the ventricular mass caused increased intensity. This finding was not present in the patients with imperforate tricuspid valve or Ebstein's malformation in whom the sulcus appeared normal. Postmortem examination of five other hearts with classical tricuspid atresia revealed epicardial fat extending into the atrioventricular sulcus, which separated the right atrium and the ventricular mass. In three hearts with Ebstein's malformation, the sulcus extended only to the level of the atrioventricular junction. The characteristic MR appearance of fat adjacent to the muscular floor of the right atrium, therefore, serves to identify the atrioventricular sulcus and allows differentiation of the types of right atrioventricular valve atresia.