Mastoiditis is a bacterial infection of the mastoid air cells (small, air-filled cavities located in the mastoid process, which is the bulge in the skull behind the ear).

Mastoiditis, a bacterial infection within the honeycomb-like mastoid process, in most cases results when an ear infection spreads to the mucus membrane surrounding the mastoid process and eventually reaches the walls of the bone itself.

If the infection persists, it may destroy the delicate structures of the mastoid. This can...