Subperiosteal abscess of the mastoid is one of the more frequent complications of acute otomastoiditis and results in coalescent mastoiditis extending through the external cortex of the mastoid sinus. This can occur in any direction:
- postauricular: common as the bone is particularly thin ("Macewen triangle")
- inferomedial: medial to the attachment of sternocleidomastoid can result in a Bezold abscess