Learning Objectives: The committee on Nomenclature of the Japan Otological Society (JOS) was appointed in 2004 to create a cholesteatoma staging system widely applicable in Japan and as simple as possible to use in a clinical practice. After the initial proposal of the principal staging system for attic cholesteatoma in 2008, we proposed 2010 staging system for two main types of acquired cholesteatoma, pars flaccida and pars tensa types. Since then, this system has been widely used in Japan, allowing for more meaningful communication between outcome studies based on surgical methods used for a respective type and stage of cholesteatoma. We have recently added two more types, congenital cholesteatoma and cholesteatoma secondary to a pars tensa perforation, as 2015 JOS cholesteatoma staging and classification system. Briefly, the principal JOS staging system defines four stages: stage I, cholesteatoma confined to the primary site; stage II, involving two or more sites; stage III, with intratemporal complications; stage IV, with intracranial complications. This system is applicable to pars flaccida, pars tensa, congenital cholesteatomas and cholesteatoma secondary to a tensa perforation.

A nationwide survey was conducted by the Committee of JOS in order to promote the use of this system and to capture the prevalence of cholesteatoma types and stages in Japan in 2015. The operative methods employed in each case were also included. Medical information of the patients were anonymized and registered through the JOS website voluntarily between 1 January and 29 February 2016.

As of 2016/02/27, 1480 cases from 59 hospitals have been registered, with stage I 25%, stage II 57%, stage III 14% and stage IV 0.5%. 64% of the cases were assigned to pars flaccida type, 13% to pars tensa type, 12% to congenital cholesteatoma and 5% to cholesteatoma secondary to a tensa perforation. The final registry data and the detailed breakdowns of cholesteatoma classification and staging will be presented.