Fetus in Fetu: A Rare Cause of an Abdominal Lump.

Fetus in fetu (FIF) is a rare anomaly characterized by the presence of a monozygotic twin that becomes incorporated into the abdomen of its sibling during fetal development. FIF is a rare congenital condition typically identified in infancy. We present a case of FIF in a 16-year-old male, which is an extremely rare presentation during adolescence. Teratoma is one of the differentials; however, FIF can be distinguished from teratoma by the presence of a vertebral column, often accompanied by a proper arrangement of other organs or limbs around it. Computed tomography (CT) imaging preoperatively diagnosed the FIF, prompting the decision for exploratory laparotomy. Histopathological analysis confirmed the diagnosis of FIF. Surgical excision is considered the optimal treatment.