Giant intra-abdominal mature cystic teratoma (dermoid cyst) in an adult man, with male genitourinary tissue including prostatic and penile elements.

We describe a case of a giant intra-abdominal mature cystic teratoma in a 36-year-old man, which comprised typical features of differentiated teratoma/dermoid cyst but which contained a macroscopic rudimentary penis, with vasoformative erectile tissue-like structures consistent with corpora cavernosa, as well as scrotal-type skin and prostatic tissue. The genitourinary structures were well formed both grossly and microscopically and sharply demarcated from the rest of the neoplasm, which comprised typical differentiated teratoma, without any other macroscopic foci of organoid differentiation or of other histologic differentiation. The plasticity of the cells of differentiated teratoma, which enables it to undergo multidirectional differentiation, is well recognized, but the factors determining this distinct path of differentiation remain to be established.