Bu Saad, Ibrahim; (2022) The effect of surgical approach on hearing preservation in cochlear implant patients. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background Preservation of residual hearing (RH) in cochlear implantation is important for speech perception, hearing in noise, and music quality. In addition, preserving intra-cochlear structures may allow patients to benefit from future therapeutic advances. Successful hearing preservation (HP) is multifactorial, and the effects of certain surgical techniques remain subject to debate. Objectives i. To review the literature on the effect of electrode array insertion surgery on hearing preservation (HP). ii. Compare the round window (RW) approach to cochleostomy (CY) in terms of HP, speech perception, electrode array dislocations, and insertion depth. iii. Investigate the relationship between electrode dislocation, insertion depth, HP, and speech perception. iv. Evaluate current surgical practice of HP in the United Kingdom. Methods The thesis aims were addressed by; i. completing a comprehensive evaluation of the current evidence on the influence of surgical electrode placement on HP; ii. a retrospective study that examined surgical approach, cochlear size, electrode array placement, insertion depth, and HP; iii. a web-based survey that evaluated current surgical practise of HP CI; and iv. a randomised controlled trial (RCT) with double-blinding that compared radiological and audiological outcomes of both approaches and investigated the correlation between insertion accuracy and insertion depth. Results The literature showed achievable HP with both approaches, heterogeneity in the inclusion criteria, and quantifying methods of HP. Most CI surgeons in the UK use RW for standard and HP patients, CY as an alternative, use intra-operative corticosteroids and antibiotics. However, there is disagreement on medical regimens and indications for HP protocols. CY approach had superior HP, which was significant at 1 and 3 months. Speech perception, accuracy of insertion, and insertion depth are not significantly different between approaches. Insertion accuracy significantly correlates with depth. Insertion depth, HP, and speech perception scores did not correlate. Conclusion This thesis examined HP surgery. Cochlear implant procedures have changed over time. Recent medical literature reports few CY cases, making comparisons difficult. Most surgeons in the UK use RW as the normal treatment and CY as an alternative, which limits retrospective studies. The RCT study overcame previous controversies and limitations in the literature. The RCT provided in this thesis shows that the CY has better HP only in the short term and there is no significant difference between both approaches after that. This allows surgeons to abandon a difficult RW operation and switch to CY. When protecting hearing, insertion depth shouldn't be a priority. Resistance during insertion may suggest trauma. HP surgeries need national and international guidelines to improve surgical outcomes.

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