Fetus in fetu: a medical curiosity—considerations based upon an intracranially located case

INTRODUCTION: “Fetus in fetu” (FIF) is defined as the abnormal monozygotic twin inside the body of its “host twin.” Intracranial FIFs are extremely rare. CASE PRESENTATION: A male premature newborn was admitted to the hospital due to a large intracranial tumor diagnosed in the 31st week of gestation. The child died before surgical treatment because of failure of the respiratory system due to fetal respiratory distress syndrome. During general autopsy, a large intracranial tumor with four relatively well-developed limbs was found. Microscopically, apart from relatively well-formed musculoskeletal structures of limbs that were covered with skin, there were haphazardly distributed different tissues or fragments of organs. However, various neuroectodermal derivatives were dominant. CONCLUSION: We believe that intracranial FIFs, theoretically with poor prognosis, can be successfully curable in cases revealed prenatally, provided that optimal treatment is introduced and the achievement of proper pulmonary maturity of the host is accomplished prior to the operation of the tumor.