Intratesticular Fetus in Fetu Arising from an Intra-Abdominal Undescended Right Testis: A Case Report

Fetus in fetu (FIF) is a rare congenital anomaly. The most common location of FIF is the retroperitoneum. FIF of testicular origin is extremely rare, with only 9 cases reported previously. We present a case of intratesticular FIF within an intra-abdominal undescended right testis and review previously reported cases to discuss the possibility of intratesticular FIF.

A male neonate was born through normal vaginal delivery at 37 weeks and 5 days of gestation, with a birth weight of 2648 g. An abdominal mass suspected to be a FIF was prenatally detected. At 26 weeks of gestation, fetal ultrasonography revealed a mass measuring 20 mm in diameter that contains structures resembling an embryo and an umbilical cord in the abdominal cavity; however, these structures were no longer identifiable after 29 weeks of gestation. Postnatally, a mass measuring 20 mm in diameter was found in the right lower abdomen. The mass was mobile, well defined, heterogeneous, hypovascular, and showed calcifications at its margins. The normal right testis was not identified. The patient's general condition was stable; therefore, elective laparotomy was performed on the 15th day of life. Intraoperatively, a 20-mm oval mass with a smooth surface was identified in the right lower abdomen. The mass was tethered by a thin fibrous band attached to the right internal inguinal ring, which was presumed to be the feeding vessel. The normal right testis was not observed. Gross examination of the excised specimens revealed massive hematomas and solid structures arranged in a ladder-like configuration, connected to the inner wall of the mass via a cord-like structure. Histopathological examination demonstrated cartilage within the solid structures, which were regularly and segmentally arranged, consistent with vertebral elements. No remnants of testicular, epididymal, or spermatic cord tissue were observed within the mass.

This case was considered most consistent with FIF arising within an intra-abdominal undescended right testis based on the macroscopic testis-like morphology, absence of a normal right testis, and localization of the lesion in proximity to the normal pathway of testicular descent.