Primary extraskeletal osteosarcoma of the seminal vesicle: a case report and literature review.

A primary extraskeletal osteosarcoma (EOS) is a rare tumour. An EOS of the seminal vesicle has not been reported in the literature. We describe a case of a seminal vesicle EOS initially detected as a pre-rectal mass on a routine transrectal ultrasound in a 48-year-old man. A computed tomography (CT) scan confirmed the tumour to be arising from the left seminal vesicle. A robot-assisted laparoscopic seminal vesiculectomy was performed to avoid neurovascular bundle injury. Microscopic examination of the resected specimen showed a poorly differentiated osteosarcoma originating from the seminal vesicle. The patient received adjuvant chemotherapy. He is doing well without voiding or erectile dysfunction and he is tumour-free five months after surgery.