Diagnosis of primary biliary melanoma with distinct imaging features: a case report and literature review

Abstract

Primary biliary melanoma arises from proliferating melanocytes in the mucosal surface of the bile duct and is extremely rare. Since the vast majority of biliary melanomas represent metastases of cutaneous origin, accurate preoperative diagnosis of melanoma and exclusion of other primary sources are vital in cases involving primary lesions. Although melanomas with pigmented cells have typical signal characteristics, obtaining a non-invasive pre-treatment diagnosis remains difficult, due to their low incidence. Here, the case of a 61-year-old male Asian patient who presented with upper quadrant abdominal pain, swelling and jaundice for 2 weeks, and who was diagnosed with primary biliary melanoma following extensive preoperative blood analyses, computed tomography (CT) and magnetic resonance imaging (MRI), is described. Post-resection immunohistochemistry confirmed the diagnosis and the patient received six chemotherapy cycles of temozolomide and cisplatin, however, progression of multiple liver metastases was observed at the 18-month follow-up CT. The patient continued with pembrolizumab and died 17 months later. The present case of primary biliary melanoma is the first reported diagnosis based on typical MRI features and the exhaustive exclusion of a separate primary origin.

Keywords: Bile duct; imaging features.; immunohistochemistry; jaundice; magnetic resonance imaging; malignant melanoma.

Figure 1.

Computed tomography (CT) images from a 61-year-old Asian male patient diagnosed with primary biliary melanoma: (a) CT plain scan image showing a round, slightly hypodense lesion (arrow) in the common bile duct; (b and c) arterial and delayed-phase CT scan images after injection of contrast agent, demonstrating arterial marked and mild heterogeneous enhancement, and uniform slightly reduced later enhancement; and (d) coronal reconstruction image showing a distal biliary lesion (arrow) causing extrahepatic bile duct dilatation.

Figure 2.

Axial magnetic resonance images from a 61-year old male Asian patient diagnosed with primary biliary melanoma: (a) magnetic resonance cholangiopancreatography image clearly showing a lesion (arrow) with smooth margin in the distal common bile duct causing biliary dilatation; (b) a T1-weighted fat-suppressed sequence image showing a biliary lesion (arrow) that is hyperintense versus the adjacent muscle; (c) a T2-weighted image showing the lesion (arrow) as slightly hyperintense versus the adjacent muscle; (d) diffusion weighted image showing the lesion (arrow) as hyperintense versus the adjacent muscle; and (e and f) arterial and delayed-phase dynamic contrast-enhanced fat-saturated T1-weighted images demonstrating arterial slight heterogeneous enhancement and later progressive and more homogeneous enhancement.

Figure 3.

Representative tumour histopathology photomicrographs from a 61-year old male Asian patient diagnosed with primary biliary melanoma: (a) haematoxylin and eosin-stained section showing pleomorphic malignant cells and some with pigmentation; (b) strong and diffuse positive staining for S-100 protein; (c) strong and diffuse positive staining for HMB-45; and (d) strong and diffuse positive staining for melan-A (all original magnification, × 200).