Early prenatal diagnosis of axillary cystic hygroma.

Fetal axillary cystic hygroma has been reported rarely and only as a sonographic finding late in gestation. A retrospective study of 19,200 early second trimester screening ultrasonograms for anomalies revealed five cases of axillary cystic hygroma. All of the axillary hygromas were small, transient, nonloculated cysts. Three cysts were associated with chromosomal abnormalities: trisomy 21 in two cases and a single case of trisomy 18 in which structural abnormalities also were detected. Early fetal axillary cystic hygroma appears to be different from postnatal axillary cysts on the basis of differences in prevalence, structure, and appearance. It also may be a normal variant in the development of the fetal lymphatic system.