Melanotic oncocytic metaplasia of the nasopharynx: A case report discussing the pathogenesis of a lesion

Background: Melanotic oncocytic metaplasia is a rare non-neoplastic lesion. It has been described as a phenomenon in which cells change their morphology to adapt to various stimuli. The incidence of melanotic oncocytic metaplasia is higher in middle-aged Asian males and smokers. The nasopharynx is the most common site of occurrence. Clinically, it is necessary to distinguish this lesion from malignant melanoma. Case: The patient was a man in his sixties and a heavy smoker. Brownish lesions were observed at bilateral pharyngeal openings of the eustachian tube through nasopharyngoscopy. Histopathologically, oncocytic cells without atypia having abundant granular cytoplasm and brownish pigmented granules were observed in the biopsy specimen obtained from the lesion. Immunohistochemically, most of these cells showed positive reaction for anti-mitochondria, S100, and Melan A, but not for HMB45. Discussion: The characteristic histological finding of this lesion was the presence of abundant mitochondria and melanin pigments in the cytoplasm. The former may be the result of a mitochondrial response to various stimuli, while the latter may be transported from dendritic cells mixed in the surrounding mucosal epithelium. Conclusion: It is important that otolaryngologists understand the features of this lesion, perform thorough observations, and reach a diagnosis through biopsy.