Thanatophoric dysplasia: fetal manifestations and prenatal diagnosis.

This paper describes two fetuses with thanatophoric dysplasia (TD) diagnosed in utero by ultrasonography. The fetuses were found to have severely short (less than 3rd centile), mildly bowed bones in one of them at 20 weeks and straight bones in the other at 34 weeks; bell-shaped chest; abnormal ribs (broadened and flattened at their ends); severe lung hypoplasia; hypoplastic, round-shaped vertebral bodies with hypoplastic arches; abnormally small pelvic bones, phalanges, metacarpals, and metatarsals. There was also an incipient "cloverleaf" skull deformity produced by fused posterior sagittal and lambdoidal sutures in the 20-week fetus and a definitive cloverleaf skull with communicating hydrocephaly in the 34-week fetus. The autopsies did not show any other abnormality. By xeroradiography after delivery, marked abnormalities of the endochondral and perichondral bone structures could be demonstrated in the 20-week fetus but not in the 34-week fetus. They appear to constitute two different conditions. These cases are good examples of the possibilities brought by ultrasound to the analysis of the fetal phenotype in utero.