Pigmented perianal macules.

Primary mucosal melanoma occurs in under 2% of melanomas. Anorectal melanoma is a rare disorder, approximately accounting for 1% of all anorectal carcinomas. Primary anorectal melanoma presents predominantly in women, in the 4th-6th decade of life. Typical clinical manifestations include rectal bleeding and tenesmus. The prognosis remains poor.

Photo Quiz

A 64‐year‐old woman presented with 6–8 sharply demarcated, darkly pigmented macules around the anus (Fig. 1) and a 3‐month history of intermittent rectal bleeding. The patient underwent a colonoscopy and an ulcerated 3.6 cm in diameter, polypoid, pigmented tumor of the anorectal verge was found (Fig. 2).

Figure 1

Dark pigmented macules around the anus.

Figure 2

An ulcerated, polypoid tumor of the anorectal verge was seen at colonoscopy.

Question

Based on the patient's history and physical examination findings, which one of the following is the most likely diagnosis?

Peutz‐Jeghers syndrome.

Genital warts.

Neurofibromatosis type 1.

Acrodermatitis enteropathica.

Metastatic anorectal melanoma.

Discussion

The correct answer is E: Metastatic anorectal melanoma.

Numerous biopsies were taken from the tumor at the time of colonoscopy and pathologic results were consistent with the diagnosis of melanoma. The patient proceeded to an abdominoperineal resection. Histopathology of the operative specimen showed a primary melanoma (HMB45 and S‐100 stains positive) with a Breslow thickness of 1.4 mm. Regional lymph nodes were free from any signs of the disease. A 3 mm‐punch biopsy from the hyperpigmented macules confirmed the perianal metastases of melanoma. Abdominal ultrasonography and contrast CT‐scan of chest, abdomen, and pelvis showed no evidence of metastases.

Primary mucosal melanoma occurs in under 2% of melanomas 1. Anorectal malignancies are commonly adenocarcinomas. Anorectal melanoma is a rare disorder, approximately accounting for 1% of all anorectal carcinomas 2. The anorectum is the third most common location for melanoma following cutaneous and ocular melanoma. Primary rectal melanoma presents in the fourth decade with an increase of incidence in the fifth or sixth decade of life. It appears predominantly in women.

Conflict of Interest

None declared.