Primary Malignant Melanoma of Anorectum CT Findings: a Single Tertiary Center's Experience

Anorectal melanoma is a rare malignancy with very aggressive course. This case series emphasize the role of imaging, contrast-enhanced computed tomography in evaluating such cases before surgery. CT scan of four patients with pathologically proven primary anorectal malignant melanoma was included. CT findings were analyzed from the picture archiving and communication system for the site of involvement, morphological shape, presence of perirectal and anal infiltration, lymphadenopathy, liver metastasis, and occurrence of bowel obstruction for all the four patients. All the four patients presented as polypoidal mass that caused focal expansion and obscuration of rectal lumen without causing colonic obstruction. Perirectal infiltration was seen in 2/4 patients and involvement of anal canal was seen in 3 patients. Distant metastasis was seen in the liver in three out of four patients. In conclusion, primary anorectal malignant melanoma is a rare, highly aggressive tumor and should be considered in patients with a bulky intraluminal polypoid mass that does not cause colonic obstruction in the anorectal region with large-sized lymphadenopathy.