Fetus in fetu: A rare presentation.

Sir,

With great interest, we read the recent article “Fetus in fetu: A rare case report” by Sharma et al.[1] Herein, we would like to add another case of fetus in fetu in abdomen and emphasize the preoperative diagnosis by computed tomography (CT) in such patients.

A 17-month-old male child was brought to our department by his parents when they noticed a lump in the lower abdomen for last 3 days. Abdominal ultrasonography (US) revealed a large, hyperechoic, and heterogeneous mass, measuring about 56 mm × 34 mm × 48 mm, in the lower abdomen. Then, CT scan was performed to verify a large, complex, soft-tissue mass with bony elements [Figure 1]. At laparotomy, a well-encapsulated retroperitoneal mass was found. Then, in toto excision of the mass was performed. On microscopic evaluation, well-developed vertebral and extremity bones plus differentiated connective and fat tissues were revealed. Based on the histopathology, a final diagnosis of fetus in fetu was confirmed.

Figure 1

Abdominal CT at different levels (a: Axial; b: Coronal; c: Sagittal) revealed a large, complex, soft-tissue mass with bony elements (white arrow)

The term “fetus in fetu” was first described by Johann Friedrich Meckel in 1800 and defined by Willis in 1953 as a rare condition where a malformed parasitic twin resides in the body of its host.[2] However, there is controversy as to whether fetus in fetu is a distinct entity or represents a highly organized teratoma. Spencer[3] suggested that a fetus in fetu must have one or more of the following conditions: (1) be enclosed within a distinct sac; (2) be partially or completely covered by normal skin; (3) have grossly recognizable anatomic parts; (4) be attached to the host by only a few relatively large blood vessels; (5) either be located immediately adjacent to one of the sites of attachment of conjoined twins or be associated with the neural tube or the gastrointestinal system. The cardinal differential point of fetus in fetu from mature teratoma is the presence of vertebral column along with the presence of complex and well-differentiated tissues.[45]

We agree with Sharma et al.[1] that CT scan is a very useful imaging modality in preoperative diagnosis. Identification of the vertebral column and the long bones of limbs in CT scan is an important indication for the diagnosis of fetus in fetu.[67]