Malignant melanoma of the rectum

Abstract

Malignant melanoma of the rectum is an extremely rare disease. It typically presents in the fifth or sixth decade of life with nonspecific complaints such as rectal bleeding or anal pain. A timely diagnosis of anal melanoma is made even more difficult by the fact that most of the lesions lack obvious pigmentation and are even histologically amelanotic. Prognosis is very poor. Anorectal malignant melanomas spread along submucosal planes and are often beyond complete resection at the time of diagnosis. We present the radiological and pathological features seen in a 43-year-old woman diagnosed with melanoma of the rectum.

Keywords: Imaging; malignant; melanoma; rectum.

Figure 1

43-year-old woman with protruding anal lesion diagnosed with melanoma of the rectum. Contrast-enhanced axial CT scan images of pelvis shows heterogeneous mass lesion in rectum with extension into mesorectal fat (white solid arrow).

Figure 2

43-year-old woman with protruding anal lesion diagnosed with melanoma of the rectum. T2- weighted axial MR images of pelvis show irregular lobulated mass of rectum with intra- and extra-mural extension with involvement of posterolateral wall of vagina (white solid arrow).

Figure 3

43-year-old woman with protruding anal lesion diagnosed with melanoma of the rectum. T2 weighted sagittal MR image of pelvis shows lobulated mass of rectum (white solid arrow) with variable signal intensity.

Figure 4

43-year-old woman with protruding anal lesion diagnosed with melanoma of the rectum. Histopathological biopsy sample stained with hematoxylin and eosin (× 100) shows pleomorphic lesions with melanin pigment (white solid arrows) suggestive of malignant melanoma.