Extragonadal retroperitoneal endodermal sinus tumor in an eight-month-old female infant.

We describe a rare case of an extragonadal retroperitoneal endodermal sinus (yolk sac) tumor in the minor pelvis. Radiologic investigation, which included abdominal ultrasound and computed tomography (CT), showed a large soft tissue mass occupying the pelvic cavity. Radionuclide bone scans demonstrated bone metastases. The serum alpha fetoprotein was elevated. Pathologic examination of the surgical specimen revealed extragonadal yolk sac tumor. Immunohistochemically, the tumor was positive for a-feto-protein and cytokeratins. After postoperative combination therapy, follow-up CT showed decreasing tumoral disease, while serum alpha fetoprotein returned to normal.