Cervical ribs: useful marker of monosomy X in fetal hydrops.

Cervical ribs were observed in six hydropic fetuses with 45X karyotype. To test the usefulness of this observation in the macerated hydropic fetus where chromosome culture is problematic, a group of 36 hydropic fetuses was examined. Cases were chosen to include fetuses with several karyotypic and pathological abnormalities known to be associated with fetal hydrops. Whole-body anteroposterior radiographs were evaluated without knowledge of the fetal karyotype or pathological findings. Twenty-five fetuses had an abnormal karyotype, seven had a normal karyotype and in four culture failed. In the last group, the number of X, 21 and 18 chromosomes per nucleus was estimated using FISH. Radiographic analysis demonstrated that among the 16 fetuses with 45,X karyotype or a single copy of X and female phenotype, 12 had a pair of cervical ribs. Three other fetuses had a single cervical rib. Only one fetus had no cervical ribs. The last fetus had tubular hypoplasia of the aortic arch and persistent mesocolon. Twelve of the sixteen 45,X fetuses had tubular hypoplasia of the aortic arch. Seven had other cardiovascular anomalies, five had renal anomalies, and five had anomalies of intestinal rotation. Cervical rib appears to be more common than other frequently recorded associations of 45,X. It is a useful and easily demonstrated mark in the evaluation of the macerated hydropic fetus.