Congenital downward displacement of the septal and posterior leaflets of the tricuspid valve is known as Ebstein anomaly. This downward displacement is associated with valvular dysplasia, resulting in tricuspid insufficiency (Schiebler et al., 1968). The displaced septal and posterior leaflets become adherent to the right ventricular walls, which may also be dysplastic. This results in division of the right ventricle into two segments, a proximal atrialized portion that forms a common enlarged chamber with the right atrium and a distal functional right ventricular chamber (Attenhoffer Jost et al., 2007). Significant right atrial enlargement is common, and atrial septal defects or patent foramen ovale is commonly seen during neonatal life (Attenhoffer Jost et al., 2007). Other cardiac malformations coexist with Ebstein anomaly in approximately one-third of cases (Celermajer et al., 1994). The most common additional malformations are pulmonary stenosis, pulmonary atresia with intact ventricular septum, ventricular septal defect, mitral-valve prolapse, aortic coarctation, patent ductus arteriosus, and right ventricular hypoplasia. Rarer coexisting malformations include tetralogy of Fallot, atrioventricular septal defect, aortic atresia, mitral dysplasia, and left ventricular diverticulum (Celermajer et al., 1994).

The incidence of Ebstein anomaly in the general population is approximately 1 in 10,000 livebirths (Hoffman and Kaplan, 2002). It accounts for 0.3% to 0.6% of congenital heart defects in children and occurs equally in males and females (Rao, 1990).

First trimester maternal lithium ingestion has been implicated in the occurrence of Ebstein anomaly for more than 20 years. Based on data from an international registry of mothers exposed to lithium during pregnancy it was suggested that the risk of Ebstein anomaly was 400 times greater in lithium-exposed infants than in the general population (Weinstein, 1976). From the registry of 225 infants born to women treated with lithium during the first trimester, there was an 8% incidence of all cardiac malformations and a 2.7% incidence specifically of Ebstein anomaly.

Subsequent controlled studies have suggested that the actual risk of Ebstein anomaly is considerably less than originally estimated from population registries. A total of two cohort studies and four case–control studies did not demonstrate as high a risk of Ebstein anomaly as was suggested from population registries, although the precise magnitude of the risk of Ebstein anomaly following first trimester lithium exposure is unclear (Cohen et al., 1994). It was estimated that first trimester lithium exposure is associated with a 4% to 12% incidence of congenital anomalies, as compared with a general population risk of from 2% to 4%.

Prenatally, Ebstein anomaly is suggested by an abnormal four-chamber cardiac view, in which the right atrium appears grossly enlarged (Figure 46-1) and the tricuspid valve is displaced downward toward the apex and below the level of the atrioventricular junction. Dysplasia of the valve appears as abnormal thickening, nodularity, and irregularity of the leaflets. The right ventricular wall may become dysplastic and appear thin (Roberson and Silverman, 1989). Pulsed and color Doppler evaluation may also demonstrate significant tricuspid regurgitation. As tricuspid regurgitation worsens, congestive heart failure may develop, leading to cardiac enlargement and eventually hydrops. On prenatal sonography, supraventricular tachycardia may also be noted in association with Ebstein anomaly (Sharf et al., 1983), and accessory conduction pathways resulting in Wolff–Parkinson–White syndrome may be common.

Ebstein anomaly has been graded in severity based on the volume of the right ventricle and degree of restriction of the anterior leaflet of the triscupid valve. With type A, the volume of the right ventricle is adequate; type B involves a significant amount of atrialization of the right ventricle but with no restriction in movement of the anterior triscupid leaflet; type C involves severe restriction in movement of the anterior tricuspid leaflet, with obstruction of the right ventricular outflow tract; type D demonstrates almost complete atrialization of the right ventricle (Carpentier et al., 1988). Another system for grading severity involves calculation of the ratio of the area of the right atrium plus atrialized right ventricle to the functional right ventricle area (Celermajer et al., 1994).

Prenatal sonographic diagnosis of Ebstein anomaly is accurate. In one series of 17 fetuses diagnosed prenatally with Ebstein anomaly, the diagnosis was confirmed postnatally in 15, either by autopsy, surgery, or neonatal imaging (Hornberger et al., 1991). In another series of 19 cases of prenatally identified tricuspid abnormalities, 6 of 10 cases of Ebstein anomaly were correctly diagnosed by fetal echocardiography; the remaining 4 were incorrectly described prenatally as valvular dysplasia without displacement (Oberhoffer et al., 1992).

The sonographic detection of right atrial enlargement should prompt a search for abnormalities of the tricuspid and pulmonary valves. The differential diagnosis of Ebstein anomaly includes isolated tricuspid valve dysplasia without significant downward displacement of valve leaflets. In its most severe form, such valve dysplasia may represent an unguarded tricuspid valve orifice. In each of these conditions, significant tricuspid regurgitation and cardiomegaly will most likely be present, but only in Ebstein anomaly will there be an abnormally located insertion site for the valve. However, the differentiation between Ebstein anomaly and tricuspid dysplasia is largely academic; both conditions can present clinically with heart failure and additional cardiac malformations (Sharland et al., 1991).

Echocardiography should easily distinguish pulmonary stenosis, anatomic pulmonary atresia, tricuspid atresia, transposition of the great vessels, Uhl anomaly, and tetralogy of Fallot from Ebstein anomaly (Rao, 1990). With pulmonary stenosis or atresia, significant right ventricular hypertrophy should be visible, together with a small pulmonary artery. Functional pulmonary atresia with diminished pulmonary flow may occur secondary to Ebstein anomaly, tricuspid dysplasia, and tricuspid insufficiency; these may be difficult to differentiate without neonatal imaging (Rao, 1990). In cases of tricuspid atresia, marked right atrial enlargement will be present, but forward flow across the site of the tricuspid valve will not be present. Uhl anomaly involves severe hypoplasia of the myocardium of the right ventricle, which may present with right atrial enlargement but with the tricuspid valve in a normal position (Benson et al., 1995).