case_images: PMC3985785_01
case_images: Anorectal mass, biopsy specimen: hematoxylin and eosin stain (x20) showing an atypical spindle cell proliferation with mitotic activity and without melanin. The neoplastic spindle cells have increased nuclear/cytoplasmic ratios and nucleoli.
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case_images: F1
case_images: A biopsy of the mass demonstrated an invasive, poorly differentiated carcinoma (fig. 1).
case_images: CT scan of the abdomen and pelvis showing an abnormal soft tissue mass occupying the anorectal junction, extending to the right lateral wall of the rectum.
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case_images: F2
case_images: A CT of the abdomen and pelvis demonstrated an abnormal mass at the anorectal junction, with no evidence of lymph nodes or liver metastases in September 2013 (fig. 2).
case_images: PET/CT scan showing a 1-cm metabolically active, precoccygeal lymph node.
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case_images: F3
case_images: PET combined with a CT scan demonstrated marked metabolic activity in the primary anal mass and a 1-cm perirectal lymph node near the coccyx, suggesting a node-positive disease in October 2013 (fig. 3).
case_images: MRI of the pelvis showing a thickening of the anal wall and a mild surrounding soft tissue enhancement.
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case_images: F4
case_images: An MRI of the pelvis confirmed the PET/CT findings (fig. 4).
case_images: APR specimen: hematoxylin and eosin stain showing spindle cells with marked nuclear pleomorphism and abnormal mitotic activity.
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case_images: F5
case_images: The pathologic specimen confirmed a malignant melanoma arising in the anal skin and extending into the rectum, involving the anal and perirectal soft tissue and 6 regional lymph nodes (fig. 5).
case_images: APR specimen: immunochemical stain for HMB45 is diffusely positive, confirmatory of malignant melanoma.
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case_images: F6
case_images: T2N1M0 according to the tumor-node-metastasis classification of colorectal cancer. Immunohistochemical analysis results were positive for the expression of the S-100 protein, HMB-45 and vimentin, whereas negative for the expression of cytokeratin and SMA (fig. 6). The patient agreed to the plan of starting chemotherapy with mitomycin and 5-fluorouracil (for the anorectal melanoma).