Prenatal sonographic findings of prominent fetal tricuspid annulus: A case report.

The tricuspid valve positioned between the right atrium and right ventricle is composed of 3 leaflets (anterior, posterior, and septal) anchored by a collagenous fibrous annulus, a saddle-shaped, oval structure, providing a firm yet dynamic structural support for the tricuspid valve. The annulus is considered to separate between the right atrium and right ventricle. Structural anomalies of the fetal tricuspid valve are rare and include Ebstein's anomaly, tricuspid atresia, partial absence, unguarded tricuspid orifice (absent leaflets) cleft, double orifice, bicuspid valve and Uhl anomaly (absence of the right ventricular myocardium with an apposing endocardium and epicardium). We present an unusual case in which a prominent peripheral circular structure was noted above the periphery of the fetal tricuspid valve at 31 weeks' gestation. Inflow across the tricuspid valve was unimpaired, with no tricuspid regurgitation. The right atrium appeared normal with a normal functioning foramen ovale, and the entire fetal cardiac anatomy and function were normal with no signs of congestive cardiac failure or fetal hydrops. The prominent non-obstructing circular structure in immediate proximity to the tricuspid valve leaflets was considered to represent a prominent tricuspid annulus. An appropriate for gestational age fetus was delivered at term and neonatal echocardiography was normal. This case emphasizes that normal variations in fetal anatomical structures should always be considered and specifically that unimpaired inflow across the tricuspid valve in diastole is key upon encountering an unusually prominent fetal tricuspid annulus, which may be noted at a considerable distance above the tricuspid leaflets within the right atrium.