Unusually large mastoid antrum ('mega antrum').

Patients who present with a unilateral non-tender bony swelling in the mastoid region without any clinical evidence of middle ear infection could be diagnosed as having a fibrous or bony lesion affecting the temporal bone. In such cases, if there is radiological evidence of large lucent area in the mastoid antrum without any bony dehiscence one should keep in mind in the differential diagnosis a mega antrum in addition to congenital cholesteatoma and eosinophilic granuloma. A large lytic lesion in the mastoid segment of the temporal bone with an intact tympanic membrane therefore presents a diagnostic dilemma. A case of an unusually large mastoid antrum in an young adult with no middle ear suppuration and a cosmetically unacceptable swelling behind the ear is presented.