Retroperitoneal mature cystic teratoma arising from intra-abdominal undescended testis in an adult.

Teratomas are a type of germ-cell tumour which may contain embryological tissues from more than one germ-cell layer, usually occurring in the gonads. Primary retroperitoneal teratomas account for 1-11% of retroperitoneal neoplasms and are most commonly found in neonates and young adults. In the clinical literature, retroperitoneal mature cystic teratoma arising from an intra-abdominal undescended testis in adult males has been very rarely reported. We report a case of surgically proven retroperitoneal mature cystic teratoma arising from an intra-abdominal undescended testis in an adult male by multislice helical computed tomography and magnetic resonance imaging.