The radiology corner. Anorectal melanoma.

A case of malignant anorectal melanoma is presented together with a short review of the literature. The lesion arises from the melanocytes normally present within the squamous epithelium of the anal canal. It presents as a small polypoid tumor and spreads rapidly into rectum, perirectal tissues, pelvic and inguinal nodes. It should be considered in the differential diagnosis of sessile lesions located or involving the anal canal.