Differential Diagnosis in Fetal Fetus in Fetu: A Case Report

Background: The rarest complication found in multiple gestations is fetus in fetu (FIF). In very young children, its clinical appearance in any number of locations is usually unexpected, making diagnosis challenging. Case description: A 27-year-old fourth-pregnancy patient diagnosed with fetal malformation consented to pregnancy termination. Autopsy reported developing twin fetus inside a lumbosacral mass; in the lower extremities, additional external male genitalia and a cystic cavity both belonged to the second twin. Conclusion: FIF refers to the fetal abnormality of one twin growing inside a cotwin’s body. Fetal viability and malformations are very complicated issues associated with severe maceration, absence of spinal cord or umbilical cord, complex duplications of some structures, conjoined fetuses, acardiac fetus, or teratoma. Clinical significance: Diagnosis in twin pregnancies is generally difficult, especially in cases such as the one presented here. We have applied an original algorithm to perinatal autopsies of complicated twin gestations.