Petrositis usually refers to infection of the temporal bone, the bone in the skull that surrounds the ear. This infection goes deep to the inner ear. It is sometimes associated with otitis media (a middle ear infection).
Chole RA, Sudhoff HH. Chronic otitis media, mastoiditis, and petrositis. In: Flint PW, Haughey BH, Lund VJ, Niparko JK, Richardson MA, Robbins KT, Thomas JR, eds. Cummings Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2010:chap 139.