Pathogenesis of sinus cholesteatoma.

Unlabelled: The aim of the present study was to provide evidence for the establishment of sinus cholesteatoma, defined as postero-superior pars tensa retraction extending into the posterior tympanum and tympanic sinuses.

Background: There is clinical evidence for formation of a retraction, but there is a lack of explanation for the transition from a retraction pocket to an active and expanding sinus cholesteatoma. Epidemiological studies on incidence of postero-superior retractions of pars tensa and follow-up studies on patients with similar pars tensa retractions were performed. Additionally, expression of proliferation marker and analysis of basement membrane were studied in samples of sinus cholesteatoma. The prevalence of pars tensa pathology was between 9.2 and 24% of investigated ears. In children with manifest secretory otitis there were some sinus cholesteatomas and 5-6% severe retractions, some of those became pre-cholesteatomas, requiring treatment and controls. Immunohistochemistry of sinus cholesteatomas showed that proliferating keratinocytes were very often found within epithelial cones growing towards the underlying stroma. These growth cones exhibit focal discontinuities of the basement membrane especially in areas of intense subepithelial inflammation. As a possible explanation based on clinical and immunohistochemical findings, we propose a four-step concept for pathogenesis of sinus cholesteatoma combining the retraction and proliferation theory: (1) The retraction pocket stage. (2) The proliferation stage of the retraction pocket, subdivided in (a) Cone formation, (b) Cone fusion. (3) Expansion stage of attic cholesteatoma. (4) Bone resorption.