Effect of Mastoid Drilling on Hearing of the Contralateral Normal Ear in Mastoidectomy.

To evaluate hearing of the contralateral normal ear before and after mastoidectomy in a longitudinal manner and to assess whether the hearing loss is transient or permanent and to find out the duration of temporary hearing loss. This was a clinical longitudinal observational study involving 50 patients with unilateral chronic suppurative otitis media requiring mastoidectomy operation over a period of 18 months after satisfying the inclusion criteria. During the part of the mastoidectomy surgery involving drilling of the mastoid bone, noise levels were recorded at multiple points in the surgery using a digital sound level meter. Postoperatively, beginning from Day 1 to Day 7, PTA and OAE of the contralateral ear were recorded for all patients. The patients were then followed up at 1, 3 and 6 months postoperatively, at which times PTA and OAE were repeated. There is an increase in the absence of High Frequency DPOAEs on the first and second postoperative days, but this increase is higher than that of Low Frequency DPOAEs and gradually returns to normal by 72 h. OAEs were found to be more sensitive at diagnosing and tracking the progress of affected patients. All affected ears only had a temporary postoperative hearing loss, primarily affecting the higher frequencies and returning to normal within 72 h. Drill-generated noise and vibration during mastoidectomy operation is associated with a significant temporary shift in hearing thresholds of the contralateral normal ear in susceptible individuals, affecting the higher frequencies, and is best evaluated using DPOAEs.