Acellular mastoid along with surrounding tissue destroyed occurs in Sclerotic mastoid Mastoid Cancellous bone: consist of air cells( "honeycomb" ) Largest air cell is mastoid antrum 3 types of mastoid are :- Pneumatized:Mastoid cells are well developed and intervening septa are thin Diploetic: Mastoid consists of marrow spaces and a few air cells Sclerotic or acellular:No air cells mastoid air cells before and after sclerosis