Untreated, the infection can spread to surrounding structures, including the brain, causing serious complications.

Drainage from the ear occurs in more serious cases often manifests as brown discharge on the pillowcase upon waking.

Organisms that are rarely found are Pseudomonas aeruginosa and other Gram-negative aerobic bacilli, and anaerobic bacteria.

[7] P. aeruginosa, Enterobacteriaceae, S. aureus and anaerobic bacteria (Prevotella, Bacteroides, Fusobacterium, and Peptostreptococcus spp.)

Some mastoiditis is caused by cholesteatoma, which is a sac of keratinizing squamous epithelium in the middle ear that usually results from repeated middle-ear infections.

Most ear infections occur in infants as the eustachian tubes are not fully developed and don't drain readily.

[citation needed] In all developed countries with up-to-date modern healthcare the primary treatment for mastoiditis is administration of intravenous antibiotics.

As culture results become available, treatment can be switched to more specific antibiotics directed at the eradication of the recovered aerobic and anaerobic bacteria.

If there are complications, or the mastoiditis does not respond to the above treatments, it may be necessary to perform a mastoidectomy: a procedure in which a portion of the bone is removed and the infection drained.

However, it is difficult for antibiotics to penetrate to the interior of the mastoid process and so it may not be easy to cure the infection; it also may recur.