Successful excision of a congenital, prenatally diagnosed fibrosarcoma involving the entire right ovary.

This report describes a congenital fibrosarcoma (CFS) of the ovary presenting as an abdominal mass on prenatal ultrasonography. Few cases of intrauterine CFS have been reported to date. When CFS develops prenatally, it usually grows rapidly, and resection is difficult at birth. We successfully resected a tumor after birth, and there has been no recurrence after 2 years. This patient is the first known survivor of CFS diagnosed prenatally.