S3633 The Black Ampulla: A Melanoma in Disguise

Introduction: Malignant melanoma, which only constitutes 1% of all skin cancers, is responsible for the majority of skin cancer-related deaths. Its aggressive nature and potential for early metastasis make it a clinical challenge. Autopsy studies have indicated that up to 15% of patients with metastatic melanoma exhibit gallbladder involvement, yet clinical presentations involving the common bile duct (CBD) or ampulla of Vater are rare. We detail a unique presentation of metastatic melanoma with initially undetected primary, manifesting as biliary obstruction. Case Description/Methods: A 60-year-old woman presented with a 3-week history of nausea, vomiting, and diarrhea. She later developed jaundice, pale stools and intermittent right upper quadrant abdominal pain. Labs revealed: AST 205 U/L, ALT 285 U/L, alkaline phosphatase 263 U/L, total bilirubin 5.8 mg/dL, and lipase 735 U/L. Computed tomography of the abdomen and pelvis demonstrated dilated intra- and extrahepatic bile ducts, with CBD measuring 1.4 cm in diameter. Magnetic resonance cholangiopancreatography (MRCP) revealed a T1 hyperintense mass at the pancreaticoduodenal groove near the major papilla, measuring 2 × 1.5 cm, along with small T1 hyperintense lesions in the pancreas, peritoneum, and mesenteric lymph nodes. Endoscopic ultrasound identified a hypoechoic mass at the ampulla. Fine-needle biospy (FNB) of the lesion yielded black-colored fluid, which was confirmed to be melanoma after analysis. Esophagogastroduodenoscopy also revealed a non-bleeding cratered gastric body ulcer; biopsy of which also confirmed metastatic melanoma. Endoscopic retrograde cholangiopancreatography (ERCP) showed a pigmented, irregular ampulla consistent with melanomatous involvement. A sphincterotomy was performed, and a covered metal stent was placed to relieve the obstruction. A dermatological examination uncovered a red lesion on the patient's right lower abdomen, which upon biopsy, confirmed invasive malignant melanoma. Discussion: This case illustrates a rare instance where metastatic melanoma presented primarily as biliary obstruction. Absence of a known cutaneous primary lesion at the time of diagnosis is known as melanoma of unknown primary (MUP), which occurs in approximately 3.2% of all melanoma cases. The presence of T1 hyperintense lesions on MRCP can be indicative of melanoma due to melanin's para-magnetic properties. Endoscopic ultrasound-FNA played a pivotal role in obtaining diagnostic tissue, with the unusual finding of a black-colored aspirate further supporting the diagnosis. Management involved endoscopic intervention to alleviate biliary obstruction and systemic evaluation to identify the primary lesion.