“Surgery of the lateral skull base: 50 years of endeavour” Section 2. Advances and open issues PETROUS BONE CHOLESTEATOMA Diego Zanetti*, Giorgio Conte°, Laura Magnoni *, Federica Di Berardino* *Unit of Audiology, Dept. of Clinical Sciences and Community Health, University of Milano; Dept. of Surgery, Fondazione IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milano °Dept. of Neuroradiology, University of Milano, Fondazione IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milano