Anorectal Melanoma as an Unexpected Diagnosis for a Pigmented Mass Resembling a Thrombosed Hemorrhoid.

Abstract

A 71-year-old woman presented with a sensation of an anal mass, episodes of rectal bleeding, and a 2-kg weight loss over the past year. She had a prior diagnosis of hemorrhoids, which had been managed with warm sitz baths and antihemorrhoidal cream. On rectal examination, a pedunculated, hard mass was identified. Colonoscopy revealed an irregular, ulcerated, blackish, hard, and friable mass located at the confluence of the lower rectum and anal canal. Histological analysis confirmed a malignant intraepithelial proliferation of melanocytes, consistent with anorectal melanoma. Magnetic resonance imaging (MRI) showed a mass at the anorectal junction occupying 50% of the luminal circumference, without evidence of obstruction. The patient underwent a laparoscopic abdominoperineal resection, with a favorable postoperative recovery and discharge on the fifth day.