A rare case of mastoiditis caused by botryomycosis is reported. The patient was an 11-year-old boy with swelling in the right retroaural region. He was affected with acute otitis media in April 1998. At that time, he was treated with antibiotics at another hospital. In July 1998, right retroaural swelling recurred, and he was diagnosed as having acute mastoiditis.
For further examination of the recurrent acute mastoiditis, he was referred to our hospital. Computed tomography (CT) indicated granulation in the mastoid cavity, a cortical bone defect, and an abscess in the right retroaural region. Because the lesion was only in the mastoid air cells, we initially treated him with an intravenous injection of antibiotics. However, the postaural swelling did not disappear completely, and a mastoidectomy was performed on August 20, 1998. There was granulation tissue with purulent discharge in the mastoid process, but not in the antrum or tympanic cavity. The route between the air cells and the antrum was blocked by the granulation in the mastoid process. The histological diagnosis of the granulation was botryomycosis based on the findings of specific granules shown in the granulation tissue. Botryomycosis is rarely observed in the head and neck region, and the exact mechanism of botryomycosis remain unclear, though several hypotheses have been proposed.
