Multilocular cystic adenomyoma of the pelvic cavity: A rare clinical and histological entity in a young man.

We report a large complex cystic pelvic mass encountered in a 16-year-old man complaining of perineal discomfort. A large and elastic hard mass was palpated on the right anterior wall of the rectum with no discernible prostate on digital rectal examination. Prostatic tumor markers were elevated. Excretory urography and urethrocystography showed a filling defect with a smooth edge on the right side of the bladder. Magnetic resonance imaging demonstrated a mass with a mosaic pattern between the right side of the bladder and the rectum. We performed ultrasound-guided transrectal needle core biopsy of the mass. The pathologist suspected hyperplastic glandular epithelium of prostatic origin with focal inflammatory cell infiltration, but there was no sign of malignancy. We thought that the tumor arose from the prostate. Surgery was successfully performed. The tumor was located on the right side of the pelvic cavity and adhered to the right lobe of the seminal vesicle. En bloc excision was performed. This lesion histologically proved to be a multilocular prostatic tissue with a seminal vesicle component, without communication to the surrounding tissue. Such a lesion has not previously been reported in the literature.