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A 68-year-old woman presented with cellulitis of the left leg. She had a history of hypertension, obesity, and chronic lymphedema of the lower left leg. On admission, roentgenography of the chest showed possible cardiomegaly, but other cardiovascular findings were normal. An initial transthoracic echocardiogram was thought to show a right atrial mass that measured 1.2 × 1.6 cm (Fig. 1). The suspected mass appeared to arise from the interatrial septum. Transesophageal echocardiography (Fig. 2) showed a normal right atrium. An unusually prominent eustachian valve arose normally from the ostium of the inferior vena cava and was attached to the interatrial septum just below the level of the fossa ovalis (Figs. 2 and and3).3). The valve measured 1.2 × 2.6 cm in its greatest thickness and partitioned the right atrium into roughly 2 chambers (Figs. 4 and and5).5). Intravenous saline contrast injection (Fig. 5) showed partitioning of the right atrium into 2 chambers by this membrane. Inferior vena caval flow was not obstructed. These findings were consis-tent with cor triatriatum dexter.
Cor triatriatum dexter, or partitioning of the right atrium to form a triatrial heart, is an extremely rare congenital anomaly that is caused by persistence of the right valve of the sinus venosus.1 In most cases, the anomaly is recorded at necropsy, either as an isolated finding in an otherwise normal heart or as an accompaniment to other congenital heart lesions.2,3 Typically, the right atrial partition is due to exaggerated fetal eustachian and thebesian valves, which together form an incomplete septum across the lower part of the atrium. This septum may range from a reticulum to a substantial sheet of tissue.4,5
Normally, during embryogenesis, the right horn of the sinus venosus gradually incorporates itself into the right atrium to form the smooth posterior portion of the right atrium or the sinus venarum, whereas the original embryologic right atrium forms the trabeculated anterior portion. The right horn of the sinus venosus and the embryologic right atrium are then connected through the sinoatrial orifice, which, on either side, has 2 folds called the right and left venous valves. During this incorporation, the left valve becomes part of the septum secundum, and the right valve of the right horn of the sinus venosus divides the right atrium into 2 chambers. This right valve forms as a sheet that serves to direct oxygen-ated blood from the inferior vena cava across the foramen ovale to the left side of the heart during fetal life. Normally, the network regresses by 12 weeks, leaving behind the crista terminalis superiorly and the eustachian valve of the inferior vena cava and the thebesian valve of the coronary sinus inferiorly.5 Complete persistence of the right sinus valve results in a separation between the smooth and trabeculated portions of the right atrium, constituting cor triatriatum dexter.6–8 Cor triatriatum dexter has varying clinical manifestations depending on the degree of partitioning or septation of the right atrium. When the septation is mild, the condition is often asymptomatic and is an incidental finding frequently made at postmortem examination; more severe septation can cause right-sided heart failure and elevated central venous pressures due to obstruction of the tricuspid valve, the right ventricular outflow tract, or the inferior vena cava.
In our patient, a cor triatriatum dexter deformity was at first mistaken for a right atrial mass on surface echo-cardiography. After diagnosis, the membrane appeared to have no hemodynamic significance and required no treatment.
Address for reprints: Raymond F. Stainback, MD, 6624 Fannin, Suite 2480, Houston, TX 77030. E-mail: moc.hels@kcabniatsr