Müllerian-type epithelial tumor arising within a torsed appendix testis.

Because it is a remnant of the müllerian duct system, the appendix testis contains müllerian epithelium that theoretically may produce epithelial tumors similar to those that occur in the female genital tract. Few reports of tumors of müllerian origin arising in the testis exist, and rarely are neoplasms arising from the appendix testis identified. We present a case of a serous cystic neoplasm of low malignant potential derived from müllerian-type epithelium that was located in the torsed appendix testis of a young, otherwise healthy, boy.