Melanocyte localization and distribution in human cholesteatoma

Introduction: Melanocytes in skin are derived from the neural crest and colonize the epidermis in the first trimester of gestation. Melanocytes have been observed in the nasopharyngeal, inner ear and oral mucosa and should therefore be present in the middle ear mucosa. Aims: To identify and determine the distribution of melanocytes in human cholesteatoma and normal meatal skin in Caucasian adults. Material and methods: Human cholesteatoma (n=18) and normal meatal skin samples (n=10) were investigated immunohistochemically with anti-HMB-45 and MART- 1 antibodies. Localization and distribution of melanocytes were assessed in the epidermis and cholesteatoma using an automatic analyzing system. Results: Regular skin exhibited melanocytes within the epidermis and accounted for 10% of the total cell number. They occurred partly as membrane-bound clusters. Cholesteatoma matrix melanocytes were observed in the basal layer and exhibited an oval or roundmorphology. Decreased numbers of melanocytes in the basal layer correlated with keratinization within cholesteatoma samples. Melanocytes revealed monomorphous nuclei, abundant cytoplasm containing particles of melanin. Found adjacent to glands and blood vessels, melanocytes were also scattered among the mesenchymal cells. Accounting for 2-6% of the total cell number within the squamous epithelium, melanocyte density was significantly lower in cholesteatoma tissue than in skin. Conclusions: The melanocyte distribution pattern was different when comparing the epithelia of skin and cholesteatoma. The presence of melanocytes in cholesteatoma may be due to an ingrowth, consequently controlled by keratinocyte-derived signals. In terms of the pathogenesis of cholesteatoma, neither squamous metaplasia nor melanocyte metaplasia can be excluded by our data