mastoiditis /mas′toidī″tis/ [Gk, mastos + eidos, form, itis, inflammation] , an infection of one of the mastoid bones, usually an extension of a middle ear infection. It is characterized by earache, fever, headache, and malaise. Swelling of the mastoid process often displaces the pinna anteriorly and inferiorly. The infection is difficult to treat, often requiring antibiotic administered intravenously for several days. Children are most often affected. Residual hearing loss may follow the infection.