Fetus-in-fetu: parasite or neoplasm? A study of two cases.

INTRODUCTION: Fetus-in-fetu is a rare congenital fetiform mass whose etiology is still controversial. We report two cases of fetus-in-fetu. CASE 1: A fetal retroperitoneal cystic tumor including two masses was detected by ultrasonography at 26 gestational weeks. The masses showed distinctive structures resembling a vertebral axis and were prenatally diagnosed as fetus-in-fetu. A resected specimen revealed two fetiform masses. CASE 2: An intracranial tumor with hydrocephalus was detected by ultrasonography at 19 gestational weeks. The pregnancy was terminated, and a postmortem examination revealed six fetiform masses with immature teratoma. DISCUSSION: The tumors may possibly consist of parasitic monozygotic diamniotic twins or highly differentiated teratomas. Copyright 2007 S. Karger AG, Basel.