Anorectal malignant melanoma with multiple organ metastases

Introduction: Anal malignant melanoma (ARMM) is a fatal malignancy with high malignant potential and poor patient prognosis. The ARMM incidence account for 0.4% to 1.6% of all malignant melanomas (MM), and 37% of patients already have distant or local metastases during the initial diagnosis. However, the low ARMM incidence and the lack of definitive studies have led to a very high rate of misdiagnosis and missed diagnosis. This case report describes brain metastasis and liver metastasis in ARMM patient. Patient Concerns: The patient, a 49-year-old Chinese male, was admitted to the hospital because of altered defecation habits for four years, hematochezia, and difficult defecation for 2 months. Diagnoses: Rectal palpation found a mass 2 cm from the anus. Colonoscopy revealed an infiltrative growing mass 2 cm from the anus. Pathological results confirmed MM. The diagnosis was Rectal MM with incomplete intestinal obstruction. Interventions: The patient underwent laparoscopic assisted combined abdominal perineal resection under general anesthesia. Outcomes: On the second day after surgery, the patient developed sensory impairment and motor dysfunction in the right upper extremity. Cranial computed tomography and magnetic resonance imaging suggested multiple occupying lesions in the brain. On the eighth postoperative day, the patient's condition deteriorated. The patient died after a one-month follow-up. Conclusions: This study describes a ARMM patient with brain and liver metastases that was diagnosed late. Pathology combined with immunohistochemistry is important to diagnose ARMM and proper auxiliary examinations can help in early diagnosis.