Anorectal malignant melanoma: preoperative usefulness of magnetic resonance imaging

Abstract

Magnetic resonance imaging (MRI) findings in three patients with primary anorectal malignant melanoma are described. Two patients had melanotic and one had amelanotic anorectal melanoma. The findings of MRI with a pelvic coil and an endorectal coil were consistent with pathologic findings. MRI with a pelvic coil demonstrated the melanotic component as high signal intensity on T1-weighted imaging. MRI with a pelvic coil and an endorectal coil was useful for staging anorectal melanoma. This article describes the initial report of the use of an endorectal coil for malignant melanoma of the anorectum.

Importance of clear resection margins in anorectal malignant melanoma

“…Today, preoperative magnetic resonance imaging (MRI) is often of great importance when planning rectal cancer surgery16. In a recent report of three patients, MRI findings in anorectal melanoma were consistent with pathological findings with regard to tumour extension and nodal stage17, indicating that MRI may also be a useful tool when planning surgery for anorectal melanoma. Combined positron emission tomography and CT (PET/CT) scanners are increasingly available, and promising results regarding head and neck melanomas have been published18.…”

Malignant Melanoma of the Rectum

“…[11] Extraluminal extent of the lesion is better demonstrated by MRI imaging. Other rectal mass lesions show hypointense signal on T1-weighted imaging.…”

MRI Findings of Rectal Submucosal Tumors

“…Melanoma cells carry melanin pigments that contain free radicals, and this makes the cells paramagnetic, which consequently shortens the T1 relaxation time and increases the T2 relaxation time on MRI. This accounts for the high-in-low intensity seen on T1WI and the mixed intensity seen on T2WI (18, 20). Based on these MRI features, a few reports have stated that MRI is useful for the characterization of malignant melanoma (20).…”

“…This accounts for the high-in-low intensity seen on T1WI and the mixed intensity seen on T2WI (18, 20). Based on these MRI features, a few reports have stated that MRI is useful for the characterization of malignant melanoma (20). However, approximately 10% to 29% of anorectal melanomas are known to be the amelanotic type, and the MRI findings resemble rectal cancer (18, 20).…”

“…Based on these MRI features, a few reports have stated that MRI is useful for the characterization of malignant melanoma (20). However, approximately 10% to 29% of anorectal melanomas are known to be the amelanotic type, and the MRI findings resemble rectal cancer (18, 20). Sometimes metastatic lymph nodes might contain pooled hemorrhage, and this presents as a high-intensity signal on MRI (20).…”