Asymptomatic malignant melanoma of the gallbladder with multiple brain metastases diagnosed with endoscopic ultrasound-guided fine-needle aspiration cytology

Malignant melanoma of the gallbladder (MMG) is extremely rare and its early stage diagnosis is difficult. Most reports of MMG describe metastatic tumors. We herein report a rare case of presumed primary MMG diagnosed by endoscopic ultrasonography-guided fine-needle aspiration (EUS-FNA) cytology without surgical resection. A 72-year-old Japanese male was diagnosed with multiple brain metastases. Fluorodeoxyglucose (FDG) positron emission tomography showed an abnormal uptake of FDG at the gallbladder; enhanced CT and MRI also showed an enhanced gallbladder lesion, which indicated a malignancy. We performed endoscopic naso-gallbladder drainage. However, cytological examination of the drained bile showed no evidence of malignancy. Finally, EUS-FNA was performed to confirm the histological diagnosis; cytopathological assessment, including immunohistochemical analysis, showed a cluster of small to large-sized cells with nuclear pleomorphism and melanin pigment, which was compatible with malignant melanoma. The patient subsequently underwent chemotherapy; however, he died 2 months after diagnosis. In patients with gallbladder tumors, MMG should be suspected even in patients with no history of malignant melanoma or any cutaneous lesions. EUS-FNA is safe and useful to confirm histological diagnoses and to determine optimal treatment strategies.