Primary anorectal melanoma on FDG PET/CT

Area of Science:

• Oncology
• Medical Imaging
• Gastroenterology

Background:

• Primary anorectal melanoma is an exceptionally rare and aggressive malignancy.
• It is associated with a poor patient prognosis.
• Early and accurate diagnosis is crucial for effective management.

Observation:

• A 76-year-old male presented with a 2-month history of rectal bleeding, anal pain, and tenesmus.
• F-FDG PET/CT imaging demonstrated abnormal focal FDG uptake in the lower rectum.
• The scan also revealed multiple intensely FDG-avid lesions in pelvic lymph nodes, bones, liver, and lungs.

Findings:

• The imaging findings were highly suggestive of advanced malignancy, leading to a provisional diagnosis of rectal carcinoma.
• Histopathological analysis of a biopsy from the lower rectal lesion confirmed primary anorectal melanoma.
• This highlights the importance of considering rare diagnoses even with seemingly typical presentations.

Implications:

• This case underscores the diagnostic challenges posed by primary anorectal melanoma.
• F-FDG PET/CT can identify metastatic disease but requires histopathological confirmation for definitive diagnosis.
• Accurate diagnosis is essential for appropriate staging and treatment planning of this rare cancer.