Fetus in fetu in a neonate: report of a case.

Fetus in fetu (FIF) is a rare condition in which a malformed fetus resides in the body of its host. The presence of a well-formed vertebral column secures the diagnosis of FIF and differentiates this entity from a teratoma. Although more than 100 cases of FIF have been reported in the literature, the presence of a well-formed vertebral column is not documented in many cases. We herein report the case of a 19-day-old female who presented with a lump in the abdomen. Plain radiograph of the abdomen showed the presence of a well-formed vertebral column with long bones, and the results were confirmed with ultrasonogram and CT scans. Therefore, a preoperative diagnosis of FIF was made, and the mass was successfully excised. Upon opening the sac of the mass, a malformed anencephalic fetus was found.