Mastoiditis refers to the inflammation of the mastoid bone, specifically its air cells. The mastoid bone is located at the temporal portion of the skull, which is a paired bone.
Infection of the mastoid air cells is closely related to the occurrence of otitis media due to its proximity to the middle ear. There may be redness of the lining of the air cells, pus formation within the air cells, loss of mastoid bone structure and extension into the adjacent structures the most important of which is the brain.