Coalescent mastoiditis is simply the term given to acute otomastoiditis when mucoperiosteal disease extends to involve the bone. The septae which normally separate one mastoid air cell from another are resorbed. This change is only easily appreciated on thin section bone-algorithm through the temporal bones. Comparison to the contralateral mastoid may be useful in detecting early changes, although normal asymmetry should be taken into account.
Complications (see acute otomastoiditis article) are much more likely once infection spreads to the bone, and include periauricular cellulitis and intracranial extension.