Fetus in fetu or a retroperitoneal teratoma--a controversy revisited. A case report and review of literature.

A 25 year old man male presented with a lump in the left side of the abdomen. Ultrasonography revealed an echogenic retroperitoneal mass with hyperechoic areas within it suggestive of bone. CT scan confirmed the presence of a large retroperitoneal mass with bone within it. On exploration there was a large encapsulated retroperitoneal lump. There was a soft tissue mass within the lump surrounded by a yellow pultaceous material admixed with pus. Examination of the specimen showed a bone at the cephalic end with teeth embedded within it. There were two limb buds near the cephalic end. The whole specimen was covered with skin with all its appendages. There was coelomic cavity present. The distinction between fetus in fetus and teratoma has for long been the subject of controversy. According to the criteria described by Willis, there should be a vertebral axis present to make the diagnosis of fetus in fetu. But there have been a few reports where cases have been described as fetus in fetu even in the absence of a vertebral axis. A review of the literature concerning this controversy is briefly given.