case_images: PMC11752850_01
case_images: Positron emission tomography (PET-CT) scan. The images show the region corresponding to the anal canal. A and B show the affected anatomical region in axial slices. (A) Shows the anal canal with slight asymmetrical thickening predominantly on the left side, with no suspicious adenopathies; (B) shows uptake corresponding to the increase in local metabolism secondary to the tumor lesion (white arrow). C and D show sagittal slices of the pelvic region, where uptake is observed at the level of the anal canal (white arrow).
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case_images: A positron emission tomography (PET-CT) scan demonstrated heightened metabolic activity at the level of the anal canal, without evidence of suspicious lymph nodes or distant metastases (Fig. 1).
case_images: Lesion corresponding to anorectal melanoma. Observe in (A) and (B) the lesion with left lateral predominance, ulcerated surface, and irregular hyperpigmented borders.
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case_images: Surgical exploration of the anal canal revealed a hyperpigmented tumor-like lesion originating from the anal canal and involving the anterior quadrants of the perianal skin (Fig. 2).
case_images: Wide local excision surgical specimen. (A) There is an exophytic tumor with irregular borders. (B) Nodular, submucosal, poorly demarcated tumor.
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case_images: Subsequently, a wide local excision of the lesion was performed (Fig. 3).
case_images: Hematoxylin and eosin staining. (A) Display of malignant neoplasm with solid growth pattern and forming nests (*). (B, C) At higher magnification, pleomorphic, polygonal cells with vesicular nuclei, prominent nucleolus, and abundant cytoplasm are observed. Note the pigment in the cytoplasm of the cells, which corresponds to melanin.
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case_images: Histopathological examination confirmed the diagnosis of a poorly differentiated invasive nodular melanoma, measuring 3.3 x 2.8 cm, with a Clark level of IV and a Breslow depth of 6 mm (Fig. 4).