Cytokeratin profile supports developmental origin of cerebellopontine angle epidermoid cysts

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Introduction: Epidermoid cysts (EC) of the cerebellopontine angle (CPA) are thought to arise from ectopic ectodermal cells trapped during the neural tube closure. CPA ECs are sometimes referred to as cholesteatomas, which have an identical histological structure to CPA EC. Reoperations are frequent and malignant transformation can occur. Cytokeratins (CK) are structural proteins of epithelial cell cytoskeleton that may be used to determine developmental lineages of epithelia. Research question: To explore the epithelial origin of CPA ECs, we analyzed their CK expression patterns. Material and methods: We analyzed 26 histological samples, including two malignant cases, from 23 patients operated for CPA EC using immunohistochemical methods. Staining for simple epithelia (CK7, CK8, CK18, CK19, CK20), stratified epithelia (CK14) and cell proliferation marker Ki67 were performed. Results: CK14 was strongly and consistently expressed in all samples of CPA EC epithelium. Variable CK19 expression was seen in all samples, mainly in the basal layer. Focal expression of CK7 and CK8 was detected in over 50 % of samples. No difference in cytokeratin expression was seen in cases requiring reoperation or with malignant transformation. Ki67 index did not differ in cases requiring reoperation (p = 0.55). Discussion and conclusion: The cytokeratin profile of CPA ECs corresponds with stratified epithelium of ectodermal origin. CPA EC cytokeratin expression pattern differs from previously reported cytokeratin expression of middle ear cholesteatoma, which suggests a different origin. Cytokeratin profile or Ki67 index were not predictive of consequent reoperation or malignant transformation in this cohort.

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