The infection may also spread lateral to produce a subperiosteal abscess. The spread of pus medially to the petrous air cells causes petrositis. Masked mastoiditis has an insidious course, owing to the use of broad spectrum antibiotics to treat middle ear disease. The presence of pathology may only be apparent on careful neurologic examination. Diagnosis is usually made on CT of the temporal bones which demonstrates temporal bone pathology in conjunction with the accompanying intracranial complication.
Acute mastoiditis can also occur in conjunction with chronic ear disease.
It has been the teaching in the past that acute mastoiditis only occurred in well pneumatized mastoids in which the thin bony trabeculae are easily broken down. However, several studies note the presence of cholesteatoma in patients with acute mastoiditis. Antibiotic therapy is guided by the patients history. If the history is otherwise uncomplicated by ear disease or protracted episode of otitis media, the infecting organism is probably S. pneumo or S. pyogenes which is best treated by ampicillin. If the patient has a protracted course of otitis media then coverage for S. Aureus and gram negative organisms is necessary with a penicillinase resistant penicillin and an aminoglycoside or single antibiotic coverage with a cephalosporin.