A one and a half-year-old girl was brought to us with a slowly growing abdominal mass, first noticed by her parents at 2 months of age. There were no bowel or urinary complaints. Abdominal examination revealed a firm, nontender, fixed, transversely placed mass measuring 20×15 cms. Laboratory test findings were unremarkable. A plain radiograph revealed a large, partially calcified soft tissue mass in the right side of the abdomen with long bone-like structures traversing the middle of the abdomen. Ultrasonography revealed a large, hyper-echoic, intra-abdominal mass with areas of calcifications. The MRI scan showed a large mass having a round head like structure in the right sub-hepatic space. The vertebral axis was visualized in its entire length going from the right upper abdomen to the left lower abdomen (Fig. 1). Multiple long bone-like structures were also identified. Based on the MRI findings, a preoperative diagnosis of fetus-in-fetu was made. The patient underwent laparotomy and complete excision of the mass. The radiograph of the specimen showed few calcified long bones with no identifiable vertebral bodies. The pathological examination revealed a large mass composed of adipose tissue and covered with skin. The mass also had evidence of bone formation. Vertebral bodies could be identified along the length of the fetiform mass with bone marrow formation. Sections taken between the vertebral bodies demonstrated formation of neural tissues.

Fig.1. MRI scan demonstrating the cranial ring in the right subhepatic space along with the vertebral axis in its entire length

Fetus-in-fetu is a term used to describe the inclusion of one fetus within the body of another. Fewer than 100 cases have been reported in litertature till date. It is controversial whether fetus-in-fetu is a distinct entity or represents a highly organized teratoma. The identification of a vertebral column suggests the diagnosis of fetus-in-fetu rather than teratoma. Occasionally, an underdeveloped and markedly dysplastic spinal column prevents the identification of the vertebral bodies at imaging(1). A recent review on the subject reported that a preoperative diagnosis of fetus-in-fetu was made in only 17.67% of all the cases till 1980 and the vertebral column was not identified in about 9% of cases even after the pathological examination(2). Though CT scan has proved very helpful in preoperative diagnosis, the non-visualization of the vertebral column on CT scan does not exclude this diagnosis(2). Although Magnetic Resonance Imaging (MRI) seems to be an ideal technique for demonstrating the wide range of tissue within such lesions, there are only a few reports of the use of MRI in the identification of the lesion(2,3). MRI allows imaging in the sagittal and coronal planes and does not rely on calcification for demonstrating tissues. This helps in identifying insufficiently calcified vertebrae and vertebral axis. In our case, the vertebral axis was demonstrated along the whole length on the coronal sections of the MRI. There was an excellent delineation of the tissues on MRI with good delineation of the cranial ring suggestive of the fetal skull which was not picked up on the conventional radographs including specimen radiographs.

We propose that MRI has the potential as imaging modality of choice for the diagnosis of fetus-in-fetu.

A. Sinha,
Y.K. Sarin,
M. Sengar,
Department of Pediatrics Surgery,
Maulana Azad Medical College,
New Delhi - 110 002, India.
E-mail: [email protected]

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1. 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: 483-489.

2. Hoeffel CC, Nguyen KQ, Tran TT, Fornes P. Fetus in fetu: A case report and literature review. Pediatrics 2000; 105: 1335-1344.

3. Hanquinet S, Damry N, Heimann P, Delaet MH, Perlmutter N. Association of a fetus in fetu and two teratomas: US and MRI. Pediatr Radiol 1997; 27: 336-338.