Difficulties encountered in the diagnosis of primary esophageal malignant melanoma by 18F-fluorodeoxyglucose positron emission tomography/computed tomography: a case report

Abstract: Primary malignant melanoma of the gastrointestinal mucosa is a rare tumor. Here, we report a case of a 60-year-old female patient with esophageal malignant melanoma. Combined with the related literature, the clinical manifestations, imaging, histopathological and immunohistochemical features of primary esophageal malignant melanoma were observed and analyzed. Imaging examination with 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18FDG-PET/CT) revealed multiple metastases in the patient's skull, bilateral acetabular, and bilateral cervical lymph nodes, but no radioactive uptake in the primary lesion. Endoscopy showed an area of abnormal pigmentation measuring approximately 0.8 cm in diameter in the lower esophageal mucosa, which was confirmed by pathological biopsy as primary malignant melanoma of the esophagus. The tumor cells are large, round, and diffused in sheets and nests, with visible nucleoli, thick chromatin granules, and abundant eosinophilic cytoplasm; melanin granules can be seen in the cytoplasm. The immune phenotype was as follows: tumor cells had diffuse expression of HMB45, Melan A, and S100. Diagnosing esophageal malignant melanoma using 18FDG-PET/CT imaging presents some difficulties, and new radio-targeted tracers need to be further developed to improve the diagnostic accuracy of this method. The combination of a morphological examination, pathological examination, and immunohistochemistry is helpful for diagnosing primary esophageal malignant melanoma.