La tunisie Medicale - 2015 ; Vol 93 ( n°02 ) : 114-115
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Article
Anorectal melanoma is rare and has very poor prognosis with a median overall survival between 8 and 19 months [1]. The incidence has been reported to be 0.4%–3.0% of all malignant melanoma and 0.1%–4.6% of all anorectal malignant tumors [2,3]. The anorectum is the third most common location of malignant melanoma after the skin and retina. The most common symptom is rectal bleeding, which is often mistaken for bleeding associated with hemorrhoids. Diagnosis is very difficult, and initial diagnosis may be incorrect in 80% of all cases [4]. For patients with anorectal malignant melanoma, treatment strategy includes surgery, chemotherapy, and radiotherapy. Surgery is the mainstay of treatment. Chemotherapy and radiation therapy alone have not been shown to be effective, but may provide some benefit when used in an adjuvant way. The choice of wide local excision or abdominoperineal resection is also controversial [2,5]. We present one case of anorectal malignant melanoma initially wrongly diagnosed as thrombosed hemorroid and subsequently with a rapid and fatal course.

Case report

A 76-year-old woman was referred to our hospital for suspicion of external hemorrhoidal thrombosis. The patient complained of rectal bleeding, anal pain and a peri anal mass. The ano-rectal examination showed a brownish anal mass extruding the anal canal, and the digital examination revealed a circular hard and painful tumor (Figure 1).

Figure 1 : Image of the rectal tumor showing pigmented lesions.


The colonoscopy showed a pigmented ulcero-vegetant lesion in the anal region extending to the medium rectum. Laboratory data as well as serum carcinoembryonic antigen (CEA) and CA19-9 levels were almost normal. Biopsy of the rectal mass was performed. Histopathological examination showed a pattern of pleomorphic cells with melanin pigmentation of the cytoplasm (Figure 2).

Figure 2 : Histopathological examination of the rectal specimen showed the nest of melanocytic cells


expression of S-100 protein and HMB-45 and negative for the expression of cytokeratin AE1/AE3, CD34, CD117 CD45, actin ,desmin and synaptophysin. Computed tomography showed a thickening of the rectal wall and lymph node swelling of the circumference of an internal iliac artery; however, there was no evidence of distant metastasis. The patient was treated by abdominoperineal resection with dissection of lymph nodes. The resected specimen showed some pigmented lesions within the tumor and around the anal verge. Histopathological examination confirmed the diagnosis of malignant melanoma Pt4b N2. Postoperative adjuvant chemotherapy was administered. However, multiple liver metastases and multiple lung metastases appeared in the early phase after the operation. Metastases increased rapidly and the patient died one year after the operation.

Conclusion

In conclusion, anorectal melanoma is a rare and aggressive disease. Because of nonspecific symptoms, it is easily mistaken for hemorrhoids or rectal prolapsed. So it is imperative to have a high index of suspicion and to fully evaluate all complaints of lower gastrointestinal bleeding and pain.
 
Reference
  1. M. Ross, C. Pezzi, T. Pezzi et al. Patterns of failure in anorectal melanoma. A guide to surgical therapy. Arch Surg 1990:125; 313-6
  2. Thibault C, Sagar P, Nivatvongs S, Ilstrup DM, Wolff BG. Anorectal melanoma: an incurable disease? Dis Colon Rectum 1997; 40:661-8
  3. Heyn J, Placzek M, Ozimek A, Baumgaertner AK, Siebeck M, Volkenandt M. Malignant melanoma of the anal region. Clin Exp Dermatol 2007;32:603-7
  4. Maqbool A, Lintner R, Bokhari A, Habib T, Rahman I, Rao BK. Anorectal melanoma-3 Case reports and a review of the literature. Cutis 2004;73:409–13
  5. shizone S, Koide N, Karasawa F et al. Surgical treatment for anorectal malignant melanoma: report of five cases and review of 79 Japanese cases. Int J Colorectal Dis 2008; 23:1257–62.
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