The term Fetus in fetu was coined by Meckel during the late 18th century following which Willis described it as a rare condition where a malformed parasitic twin is found encased in the host especially in the retroperitoneal space. The other reported sites are abdomen, scrotum, cranium, kidneys, adrenals, mediastinum, and lymph nodes etc. FIF usually occurs as a single lesion however multiple FIF have also been reported, highest being 5. FIF is always a curiosity and to date about 200 cases have been reported in literature [3-6].
Most of the cases present during infancy, but late presentation has also been reported with the oldest patient presenting at 47-year. Male preponderance is noted in the reported cases. The major presenting complaint is a palpable abdominal mass, predominantly in upper abdomen. The other symptoms are secondary to the mass effect of the FIF such as, jaundice, hydronephrosis, intestinal obstruction, meconium peritonitis, respiratory distress, and vomiting [7-9].
Few reports describe antenatal diagnosis of FIF. Preoperative diagnosis can be made on plain radiographs and CT scan/MRI. The presence of vertebrae, long bones, bones of hands and feet etc are the common radiological findings. Visualization of a non-homogenous mass with bones especially vertebrae is considered pathognomonic of FIF. Failure to visualize vertebrae however does not rule out possibility of FIF. The other frequent differential is teratoma [1,5,10].
Most of the reported cases describe FIF suspended with an umbilical cord like stalk in an amnion like membrane containing fluid- equivalent to amniotic cavity. In few cases, the exact blood supply could be identified; in most of cases the blood supply was thought to come from the abdominal wall where amnion like membrane was in close approximation to it. Similarly, in our case the FIF was suspended in the fluid filled cavity with an umbilical cord like structure having two vessels in it. The FIF are usually anencephalic, with the vertebrae and limb-buds (long bones and bones of hands/feet can also present), and acardiac (rarely heart was found). In few cases vertebral column was not found however presence of mature enteric nervous plexi and melanocytes in the skin depicted the fetus would have passed the primitive streak stage of notochord development [1-5]. In our case the FIF was anencephalic, having primitive structures of nose, eyes and ears. One hand was well developed. The lower limbs were fused as in sirenomelia- long bones were palpable in the lower limbs.
Careful dissection of FIF should be done to avoid injury to the surrounding structures. A case of bile duct injury has been reported in literature. Complete excision of FIF along with covering membrane is necessary, as a case of malignant transformation of left over membrane is reported in literature. These cases are monitored with alpha-fetoprotein or beta-HCG, along with ultrasound and other radiological investigations [11,12]. We are following our patient on similar lines.