Intraoperative Monitoring for Hearing Preservation and Restoration in Acoustic Neuroma Surgery

Abstract

Su rgeryHearing preservation during AN surgery is one of the most intriguing and interesting aspects of the otoneurosurgeon's work.Advances in diagnostic testing enabling audiologists and neuro-otologists to diagnose a higher proportion of patients with small ANs are probably the most important factors underlying the progressive increase in hearing preservation rates. The application of neurophysiological intraoperative monitoring methods and the consequent refinement of surgical techniques are additional important factors that have increased hearing preservation rates.The challenge facing the neuro-otologist today is all the more stimulating as a result of the incredible progress achieved in hearing restoration in the only hearing ear in patients with AN or in patients with NF2. Most of these patients cannot be rehabilitated using a traditional cochlear implant when the auditory nerves are no longer intact after surgery. The multichannel ABI electrically stimulates the auditory system at the level of the cochlear nuclei, providing partial restoration of auditory function. 1-6 An additional theoretical indication for ABI is total deafness in patients with head trauma or cochlear nerve aplasia. A critical role in the decision to 187 Skull

Audiologic Outcomes With the Penetrating Electrode Auditory Brainstem Implant

“…This was intended to place the stimulating surfaces of the microelectrodes within the VCN. Electrically evoked auditory brainstem responses (EABRs) were recorded during electrode placement to guide the surgeon (23,24). Generally, it was not possible to record EABRs from scalp electrodes when stimulating with penetrating electrodes.…”

Intraoperative neuromonitoring techniques in the surgical management of acoustic neuromas

“…5,12,16,36,49,52,62,75,88,94,99,103,112,115,116,120,130,132,139,147 Although this discrepancy may highlight the need for improvement in IONM of CN VIII, 99 it may also reflect the inherent difficulty in preserving auditory function, as large tumors are more highly associated with postoperative deficits, 1,11,20,23,88,89,103,116 and tumors with extensive infiltration into the cerebellopontine angle render acoustic preservation an arduous task. 23,89,147 Operative damage to the vestibulocochlear nerve can be induced in various ways.…”

“…54 The quick response time in conjunction with larger amplitudes than BAEPs 19,48,79,129 has strengthened the reputation of measuring CNAPs as the most preferred monitoring method of choice. 14,16,17,19,20,48,99,146 When comparing direct CNAPs with ECOG, direct CNAPs possess higher predictive value of postoperative functionality, with lower false-positive and higher true-positive rates. 18,146 Electrocochleography and direct CNAPs have unique disadvantages.…”

“…64,81,129 The recording electrode is placed directly on the acoustic nerve, the negative electrode is attached to the mastoid of the contralateral ear, and a reference electrode is placed on the scalp. 16,54,79,99,108,148 It is common practice to place the recording electrode proximal to the tumor being resected, 14,17,79,99,129 with adhesive such as Gelfoam applied between the electrode and nerve to reinforce the placement. 54,99,148 Like the BAEP and ECOG, a click stimulus is applied through an earphone, and the resulting compound action potential is measured.…”

“…59,64,79,97,129,149 The electrical pulse rate is set at a range of 20-50 clicks per second. 16,54,79,97,99,148 Before commencing with the operation, the stimulus intensity, as measured in decibels, is adjusted until the patient can hear the click; the stimulus is eventually delivered at several decibels higher than the measured threshold. 71,97 Upon delivery of the stimulus, the ears are stimulated bilaterally so white noise is applied at an intensity several decibels lower to obscure the response of the contralateral ear.…”