Case of the Issue

June 16, 2008

Two-month-old girl with an abdominal mass since birth referred with suspected diagnosis of Wilms' tumor. Physical examination revealed a smooth, firm, nontender, right flank mass.

CLINICAL HISTORY

Two-month-old girl with an abdominal mass since birth referred with suspected diagnosis of Wilms' tumor. Physical examination revealed a smooth, firm, nontender, right flank mass.

FINDINGS

FIGURE 1. Anteroposterior abdominal radiograph demonstrates soft-tissue mass in right hemiabdomen. Mass contained calcified osseous-appearing structures of varying sizes and shapes.

FIGURE 2. Abdominal CT reveals large retroperitoneal soft-tissue mass. Long hyperdense opacities resembling fetal bones also observed.

Elective laparotomy found a large retroperitoneal cystic mass attached to the lower pole of the right kidney, pushing the hepatic flexure of the colon anteriorly. The sac contained a clear fluid. The fetus within had grossly visible limbs. The cystic component was decompressed and the mass dissected off the retroperitoneum with ligation of the feeding vessels.

FIGURE 3. Postoperative specimen shows a fairly well developed fetus lying on its back. Note rudimentary digits.

DIAGNOSIS

Fetus in fetu, a rare condition in which a malformed parasitic twin is found inside the body of its partner, usually in the abdominal cavity.

1,2

DIFFERENTIAL DIAGNOSES

Teratoma and meconium pseudocyst.

DISCUSSION

This pathology is rare, with an incidence of one per 500,000 births.3 Fewer than 100 cases have been reported worldwide, the majority occurring in infancy.4

Fetus in fetu occurs most commonly in the upper retroperitoneum. Uncommon sites include the oral cavity,1 sacrococcygeal region,5 and scrotum.4 It often is difficult to distinguish between teratomas and vestigial remnants resulting from abortive attempts at twinning. Teratoma usually occurs in the lower abdomen, ovaries, or sacrococcygeal region.6

Teratoma and meconium pseudocyst both often have calcified components and so can be difficult to differentiate from fetus in fetu on imaging.5 Identification of a vertebral column differentiates fetus in fetu from teratoma. Occasional cases have been reported in which the spinal column could not be identified at imaging.7 This can occur if the spinal column is underdeveloped and markedly dysplastic.8 The intra-abdominal fetus in fetu is usually contained in a complete sac without any major vascular connections to the host, as was the situation in this case.

Preoperative diagnoses of fetus in fetu have increased following the introduction of CT.9 In our case, however, imaging did not play a major role in our ability to diagnose pathology prior to surgery.

Complete excision is curative. After four years, our patient has shown no recurrence or complications and is leading a completely normal, healthy life.

Case submitted by Dr. Nisreen M. Khalifa, department of pediatric oncology, Dr. Doaa W. Maximous, department of surgical oncology, and Dr. Alaa A. Abd-Elsayed, department of public health and community medicine, Assiut University, Assiut, Egypt (Journal of Medical Case Reports 2008;2(2), [doi:10.1186/1752-1947-2-2]).

References

1. Senyüz OF, Rizalar R, Celayir S, Oz F. Fetus in fetu or giant epignathus protruding from the mouth. J Pediatr Surg 1992;27(12):1493-1495.
2. Willis RA. The borderland of embryology and pathology, 2nd ed. Washington, DC: Butterworth, 1962:442-462.
3. Hopkins KL, Dickson PK, Ball TI, et al. Fetus in fetu with malignant recurrence. J Pediatr Surg 1997;32(10):1476-1479.
4. Kakizoe T, Tahara M. Fetus in fetu located in the scrotal sac of a newborn infant: a case report. J Urol 1972;107(3):506-508.
5. Sanal M, Kucukcelebi A, Abasiyanik F, et al. Fetus in fetu and cystic rectal duplication in a newborn. Europ J Pediatr Surg 1997;7(2):120-121.
6. Thakral CL, Maji DC, Sajwani MJ. Fetus in fetu: a case report and review of literature. J Pediatr Surg 1998;33(9):1432-1434.
7. Knox JS, Webb AJ. The clinical features and treatment of fetus in fetu: two case reports and review of literature. J Pediatr Surg 1975;10(4):483-489.
8. Nocera RM, Davis M, Hayden CK Jr, et al. Fetus in fetu. AJR 1982;138(4):762-764.
9. Tsai CH, Lin JS, Tsai FJ. Intraventricular fetus in fetu: report of one case. Acta Paediatr Sin 1993;34(2):143-150.