In utero ultrasound detection of a large fetal sarcoma of the back.

A congenital fibrosarcoma, a very rare soft-tissue tumor of infancy, was suspected on prenatal ultrasound at 23 weeks' gestation. On sonography, a large soft tissue growth on the left side of the fetal back, measuring 53 x 65 x 22 mm, was observed. The diagnosis was further validated by magnetic resonance imaging. Delivery by Cesarian section occurred at 31 weeks of gestation, due to fetal distress. The baby underwent an unusual embolization of the tumor-feeding arteries and an operation at the age of 1 month to remove the tumor. The pathological and cytogenetic examinations were consistent with the diagnosis of a fibrosarcoma.