Liang, Jianning; (2002) A study of the epidermoid formation and its relation to cholesteatoma. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A special technique was devised to study the incidence, location and origin of the epidermoid formation (EF) in sections of temporal bones of fetuses and young children. In the search for EFs a strategy of screening selected sections of EDTA-decalcified paraffin wax-embedded and serially sectioned bones was used to conserve unstained sections for later immunohistochemical staining. Epithelial structures suspected in the screening as EFs were characterized as epidermoid by using immunohistochemistry. The technique employed a novel method of antigen retrieval by heating sections in a 70°C water bath. Since the expression of antigens characteristic of epidermoid tissue varies with age of development it was necessary to use different antibodies at different ages. Thirty-six paraffin- embedded temporal bones from 19 cases aged from six gestational weeks to 15 months post partum formed the core of this study, which was augmented by use of step sections of celloidin-embedded archival temporal bones. Each temporal bone after 16 weeks gestation, but none before this time, contained one or more, often multiple, confirmed EFs. EF sizes increased significantly with increasing age. EFs were absent after 8 months postpartum. Maps of the position of EFs in relation to the eardrum showed most to be sited in the annular region, in all four quadrants, although the majority was in the anterosuperior quadrant. A study of the interface between annular external canal epidermis and middle ear epithelium between 14 and 18 gestational weeks suggested that EFs arise from external canal epidermis at that time. The findings indicate that epidermoid tissue, often in substantial amounts, enters the middle ear from the 16th gestational week in all fetuses and provides support for the EF as a possible origin of cholesteatoma.

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