Fetus-in-fetu with testicular vessel involvement and ipsilateral testicular absence: a case report

Fetus-in-fetu (FIF) is a rare congenital anomaly. It is differentiated from a mature teratoma by the presence of an axial skeleton and organized organogenesis. The vascular supply derived from gonadal vessels is exceptionally uncommon. A male neonate, diagnosed antenatally at 27 weeks of gestation with a retroperitoneal mass, was transferred to our hospital. He has a palpable left abdominal mass and absence of the left testis. A magnetic resonance imaging showed a well-encapsulated mass with a vertebral column, limbs, and rudimentary head. An exploratory laparotomy revealed a 7 × 7 cm encapsulated FIF supplied by the left testicular vessels and vas deferens, with no left testis identified. The mass was completely excised. Histopathology was declined by the patient’s parents due to cultural and religious reasons; the diagnosis was confirmed by imaging and gross intraoperative findings. The recovery was uneventful. Fetus-in-fetu can be associated with ipsilateral testicular absence.