Fetus in fetu: report of two cases

Abstract

Fetus-in-fetu (FIF) is a rare and interesting entity characterized byincorporation of a malformed, monozygotic, diamnionic parasitic twin into the body of other normal twin partner. FIF is differentiated from teratoma by its embryological origin, its unusual location in the retroperitoneal space and the presence of vertebral column (axis) often with appropriate arrangement of other organs or limbs around this axis. We report two cases of FIF. Our first case presented at 18 months, while second at 9 year of age. FIF derived their blood supply directly from aorta in both the cases.Our FIF had distinct fetoid features, well developed axial skeleton with a complete spinal column, trunk, intestinal loops, four limbs, well developed fingers and toes, male external genitalia and abundant scalp hairs. Their weightwas 600 grams and 800 grams, respectively. Postoperative period was smooth and on long-term follow up no evidence of recurrence was seen in both the patients.

Keywords: Fetus-in-fetu; Monozygotic diamnionic twinning; Teratoma.

Figure 1:Top left-Barium enema showing displacement of colon due to soft-tissue mass. Bones and calcification in the mass is seen(curved black arrows). Top right- Well formed FIF seen after opening the sac(white arrow). Bottom left-FIF with rudimentary head(red arrow),well developed thorax, abdomen, upper and lower limbs and well developed external genitalia(straight black arrow).Bottom right- Dissection of the FIF from dorsal side showing-well developed vertebral column along with rib cage(green arrow).

Figure 2:Top left- A large retroperitoneal mass(white arrow) in the right hypochondrium, densely adherent to diaphragm superiorly, inferiorly to right kidney. Inferior vena cava is stretched and densely adherent to the anterior surface of the mass. Top right- Specimen excised in toto. Bottom left and Bottom right- A well formed FIF. The fetus is anencephalic; well developed upper(green arrows) and lower limbs(red arrows) with well formed male external genitalia, long hair also seen.