Intrauterine closure of membranous ventricular septal defects: mechanism of closure in two autopsy specimens.

Anatomic evidence of intrauterine closure of ventricular septal defects (VSDs) has been reported rarely. Between 1985 and 1990, 112 autopsies were performed at the Mayo Clinic on third trimester stillborns and infants who died during the first week of life. There were 21 (19%) cases of congenital heart disease. VSD was found in 12 (11%) cases: in eight (7%) as a part of a more complex heart defect and in four (4%) as an isolated lesion. Two cases with membranous VSDs with tricuspid valve tissue partially occluding the ventricular septal defect were found. A 2280-g female infant (case 1) with trisomy 18 died at 4 days of age. Autopsy revealed bilateral superior venae cavae, a large atrial septal defect, cor triatriatum, an atypical tricuspid valve with large septal leaflet partially obstructing a large membranous VSD, a hypoplastic right ventricle, and severe pulmonic stenosis. A 2610-g female infant (case 2), born with congenital heart block died at 4 days of age. Autopsy revealed cor triatriatum dexter obstructing the tricuspid orifice, a large membranous VSD partially obstructed by the septal leaflet of the tricuspid valve, four small muscular VSDs, and pulmonic stenosis. These cases suggest that closure of membranous VSDs may begin in utero and the mechanism of closure is similar to that reported postnatally.