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Heterotopic brain tissue usually involves extracranial midline structures of the head and neck such as nose, nasopharynx, and oral cavity. Its occurrence in the non-mid-line structures, including middle ear, is rare. We described a 50-yr-old-man with het-erotopic glial tissue in the middle ear and mastoid bone. The patient presented with progressive hearing loss for 8 yr. There was no history of congenital anomalies, trau-ma, or ear surgery. Computed tomography revealed a mass-like lesion with soft tis-sue density occupying the middle ear cavity and mastoid antrum. At the operation, a graywhite fibrotic mass was detected in the epitympanic area. Mesotympanum and ossicles were intact. The patient underwent left simple mastoidectomy with type I tympanoplasty. During operation, definite cranial bone defect or cerebrospinal fluid leakage was not found. Histologically, the lesion was composed of exclusively mature, disorganized glial tissue with fibrovascular elements in a rather loose fibrillary back-ground. Glial tissue showed diffuse positive reaction for glial fibrillar acidic protein and S100 protein on immunohistochemical study.
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