A Case of Retrorectal Melanoma Presenting With Bleeding Per Rectum.

Rectal bleeding is a common presenting complaint in the emergency department (ED), most frequently due to benign conditions like hemorrhoids, anal fissures, and diverticulitis. Malignancies are a less common cause, with colorectal adenocarcinomas being more typical. Melanomas, malignant tumors of melanocytes, primarily occur on the skin but can arise in less visible sites, including mucosal surfaces and rarely as pelvic masses. We report a case of a 56-year-old female who presented to the ED with rectal bleeding. Initial examination did not reveal a mass, and a prior history of hemorrhoids led to an initial discharge without further workup. However, subsequent presentation with abdominal pain prompted further investigation, revealing significant leukocytosis and anemia. Imaging studies, including chest radiography and CT of the chest, abdomen, and pelvis, demonstrated multiple metastatic lesions in the lungs and liver, as well as a large retrorectal mass. Biopsies of a liver lesion and a rectal mass confirmed the diagnosis of metastatic melanoma. The patient was treated with immunotherapy but experienced clinical deterioration and ultimately elected for comfort measures, passing away approximately three months after the initial presentation, likely due to bowel obstruction secondary to the retrorectal melanoma. This report highlights the rare presentation of a stage IV retrorectal melanoma with initial rectal bleeding, emphasizing the importance of considering unusual malignancies in the differential diagnosis of this common symptom, particularly when initial assessments are non-diagnostic.