Congenital blood cysts of the heart valves.

Congenital blood cysts of the heart valves are found most commonly on the tricuspid and mitral valves of fetuses and infants. Hearts available following 38 random autopsies of fetuses and infants 2 years of age or younger were examined. Blood cysts were found in 18 cases (47 per cent) in which ages ranged from 26 weeks of gestation to 11 months. The cysts varied in diameter, from microscopic to 3 mm. Affected valves had from one to 20 cysts. Light microscopic examination of serially sectioned paraffin-embedded tissue and plastic-embedded tissue and scanning electron microscopic examination revealed connections between the cyst lumens and ventricles via small endothelium-lined channels. The cyst structure suggested formation from ventricular endothelial infoldings in the valve leaflet base, which bulged into the atrium because of the pressure gradient present during valve closure. Blood cysts are a common finding in neonates dying of various causes and probably have no clinical significance. There is no association with asphyxia as previously described. Blood cysts may persist and enlarge to form giant cysts of the heart valves.