['Case report.', 'A tertiary care pediatric hospital.', 'A 7-year-old boy complained of retroauricular pain 3.5 years after cochlear implantation. Temporal bone computed tomographic scan revealed a soft tissue density filling the mastoid and middle ear space. There was extensive osseous erosion involving the cochlear promontory that resulted in lateral displacement electrode array into the middle ear space.', 'Mastoidectomy with removal of cochlear implant.', 'Pathologic examination of the soft tissue filling the mastoid cavity was consistent with a cholesterol granuloma. The cultures of the mastoid cavity demonstrated no growth. Examination of the explanted device revealed a cell layer covering the length of the electrode. The stylet tract was filled with cells that grew out through the silicone component. No birefringent cholesterol crystals were detected in the tissue surrounding the electrode. Biofilms were not identified.'] Do cochlear implant device failure secondary to cholesterol granuloma-mediated cochlear erosion?