A Study of Drill Induced Hearing Loss in the Contralateral Ear Following Mastoid Surgery.

Abstract

Background: Mastoidectomy is the mainstay of COM treatment . Usage of the micro motor drill has an effect on the contralateral ear due to the noise induced by the drill and the sound-conducting characteristic of the intact skull. Aims And Objectives: 1. To identify the drill induced hearing loss in the contralateral ear, by transient evoked otoacoustic emissions following mastoidectomy. 2. To identify the relation between the type of burr tip used and the amount of hearing loss. Methodology: This study consisted of 63 patients that underwent mastoidectomy. A pre-operative PTA and TEOAE was done. PTA was repeated on POD-1 and POD-7. TEOAE was done on POD-1,3 and 7. Intraoperatively, the type of burr tip used and the individual drilling time for each type of drill bit was recorded. Results: 37 patients developed transient SNHL by POD-3. All patients recovered by POD-30. Higher frequencies of 3000 Hz and 4000 Hz were commonly affected. No change was detected on PTA. Conclusion: The drill is not only a source of noise but is also a strong vibration generator. These strong oscillations are transmitted into the cochlea. Thus surgeons should select appropriate burrs and drills to minimize the temporal bone vibrations.