Inner Ear Effects of Middle Ear Surgery

Abstract

Introduction Hearing loss following middle ear surgery is an important issue because it is common, is detrimental to patients, and may be preventable. Patients are often told the risk of inner ear hearing loss following middle ear surgery is low, however, not all publications qualify this loss in the same way, and some use more sensitive indicators than others. Most of these losses are permanent and compound other hearing losses, such as from aging. In addition to hearing, balance is often also affected. This harm caused by surgery is poorly understood, but is likely to be due to a combination of noise- and force-related factors. Strategies to minimise the noise and force trauma of middle ear surgery offer hope to decrease the morbidity of these operations. Aims 1. To review the incidence of postoperative sensorineural hearing loss (POSNHL) locally 2. To examine the significance of this inner ear harm on patients’ quality of life (QoL) 3. To prospectively investigate the effects of middle ear surgery on inner ear hearing and balance function 4. To measure the key forces of middle ear surgery Methodology A retrospective review of sensorineural function in patients undergoing middle ear surgery from 1998 to 2009 in Christchurch was undertaken with a >10 dB at 4 kHz bone conduction marker of POSNHL. The Glasgow Benefit Inventory was sent to all patients identified in the retrospective review who had a complete sensorineural assessment. Patients having middle ear surgery were enrolled in a study to measure extended high frequency (EHF) audiometry, and vestibular-evoked myogenic potentials (VEMP) perioperatively.

A miniature sensor was incorporated into modified microscope instruments to measure the forces required for ossicular palpation, prosthesis placement and destructive procedures which may be part of a patient’s surgery, the forces of which are transmitted to the inner ear. Results 834 (36.5%) patients had complete sensorineural function tests perioperatively, and sixty nine (8.3%) sustained a POSNHL. Lower rates were found in revision surgery, higher rates were seen with trainee surgeons. 303 (34.9%) QoL questionnaires were returned and there was a very low correlation between POSNHL and QoL (p=0.09). There was, however, a significant association with air-conduction audiometry and QoL (p<0.0001) and this was echoed in patients’ comments which noted hearing outcome to be the most important predictor of QoL. Fourteen patients had complete EHF audiometry, and five (31.3%) had a POSNHL >10 dB. Only two cases out of sixteen were detected with a 4 kHz POSNHL criterion. VEMP was not useful for noting vestibular harm following surgery. Force measurements were made on six cadaveric temporal bones and nineteen live patients. In general, less force was required the closer palpation was to the stapes, and more force was required for cadaveric bones. Trainees used more force than consultant surgeons. Significance Postoperative inner ear harm exists and is much more common than is generally quoted. Hearing is the most important outcome for patients having middle ear surgery, and so efforts to optimise this outcome and decrease complications should be encouraged.