Fetus in Fetu

A very rare but interesting congenital malformation is a Fetus in fetu (FIF), wherein a malformed fetus develops in fully formed another body. Fetus in fetu may be a parasitic twin fetus growing within its host twin. Its estimated incidence is 1: 500,000 live newborns. Its occurrence is exceedingly rare and only 200cases have been published in the literature. It is abnormal embryogenesis in a bi amniotic monochromic gestation in which one fetus is inside the other. Despite the detailed description in literature, its etiology and relationship with teratoma remained controversial. Fetiform Teratoma (FT) on the other hand is caused by the uncontrolled growth of pluripotential cells without organogenesis or vertebral segmentation. 

     We present the case of a 4 months old female child brought to Dr. Rajendra Salgare Hospital Chikodi with complaints of abdominal distension and poor oral intake for 2 months. On examination, the child had a large mass on the right side of the abdomen, and imaging studies showed a heterogeneous mass in the retroperitoneum pushing the Rt Kidney downwards and medially.

          Complete excision was planned with a clinical diagnosis of Retroperitoneal teratoma by Dr. Vijay Pujar. Surgery revealed a mass situated in the suprarenal fossa with solid and cystic components with large blood vessels supplying it. On Complete excision of the mass, it resembled FIF as it had fully formed Intestine, hair, nervous tissue, etc.

          The child did well in the post-op period and showed good weight gain and normal blood parameters at 1-month follow-up.

Discussion: Fetus in fetu is a developmental abnormality in which a mass of tissue resembling a fetus is formed inside the body. There have been controversies regarding its differentiation from teratoma. While the presence of axial skeleton has been considered mandatory for diagnosis. But recent literature questions this criterion and even the presence of well-organized organ tissues like intestine nervous tissue will also qualify it for Fetus in fetu like in our case. The existence of vertebral bodies in the FIF indicates that the parasitic fetus developed at the early embryogenic stage of the notochord i.e., the precursor of the spine. In contrast, Fetiform Teratoma (FT) is caused by the uncontrolled growth of pluripotential cells without organogenesis or vertebral segmentation. Also, unlike Fetiform teratoma, FIF does not usually present recurrences and is rarely malignant. As the majority of patients with FIF have a largely benign course but may result in significant complications due to pressure or obstruction to adjacent viscera.

Treatment of the two entities includes complete excision of the mass. An important aspect is to keep the patients in follow-up along with serum beta-HCG and alpha-fetoprotein and ultrasound monitoring for 2 years so that recurrences and malignant transformation can be diagnosed at an early stage

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