Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach

Abstract

The retrosigmoid approach using auditory monitoring for a small AN can accomplish total tumour removal with an excellent hearing preservation rate. CNAP provides reliable auditory monitoring more frequently than ABR, reflects the intraoperative auditory function almost in real-time, predicts postoperative hearing with excellent sensitivity and specificity, and is more useful for monitoring in the removal of small AN with hearing preservation.

Intraoperative neuromonitoring techniques in the surgical management of acoustic neuromas

“…As a result of advances in microneurosurgery and facial nerve IONM, many patients with smaller tumors have minimal functional loss of the nerve, as indicated by low House-Brackmann grades. [3][4][5][6][7]12,27,36,46,62,110,115,117,124,130,146 In patients with larger tumors, the outcomes are not as optimistic, as these patients are at an increased risk of postoperative facial nerve deficits. 4,27,36,56,60,62,117,125 …”

“…Between peak latencies and interpeak latencies, the latter is the more clinically useful marker because peak latencies are more susceptible to influence from external factors such as age, thus rendering them less reliable. 71 However, the majority of these parameters are, at best, warning signs that alert the surgeon; among them, only maintenance of Waves I and V has been consistently shown to correlate with better postoperative hearing preservation rates, 34,50,88,91,98,121,136,141,146 although others have found poor hearing outcomes despite wave preservation. 30,59 The prognostic power of BAEPs is based solely on the preservation of the waves; in other words, when actual changes are seen on BAEPs, the severity or presence of postoperative deficits cannot be predicted reliably.…”

“…81,108,142,149 Because ECOG involves peripheral nerve stimulation, the N1 waveform seen on ECOG is congruent with Wave I on BAEP monitoring. 8,42,64,71,79,113,120,129 The absolute loss of N1 on ECOG 48,88,96,114,120,139,149 or on direct recording 8,108,129,132,145,146,149 is frequently associated with postoperative hearing deficiency. Changes to the latency or amplitude of N1 on either ECOG or direct recording are also electrophysiological signs suggestive of injury.…”

“…Changes to the latency or amplitude of N1 on either ECOG or direct recording are also electrophysiological signs suggestive of injury. 8,14,17,19,48,54,79,120,131,142,145,146 Further electrical waveforms are seen in ECOG, thus differentiating it from a direct CNAP reading. The cochlear microphonics and summation potential are both electrical responses generated from the organ of Corti, 54,94,113,120 and lower cochlear microphonic detection thresholds may be involved in prognosticating postoperative hearing function.…”

“…Among these methods, the most frequently Intraoperative neuromonitoring techniques in the surgical management of acoustic neuromas used are EMG for the facial nerve and BAEP monitoring for the vestibulocochlear nerve. 41,42,79,142,146,148 Here, we assess the fundamental characteristics underlying the major techniques available in IONM, emphasizing specific advantages and limitations of their utilization for optimal patient management.…”