Detailed insight into transtympanic electrocochleography (TT-ECochG) and direct cochlear nerve action potential (CNAP) for intraoperative hearing monitoring in patients with vestibular schwannoma – methodology of measurements and interpretation of results

Abstract

<b>Background:</b> The aim was to present the methodology and interpretation of intraoperative hearing monitoring with simultaneous Transtympanic Electrocochleography (TT-ECochG) and direct Cochlear Nerve Action Potential (CNAP) measurements during vestibular schwannoma removal. <br><b>Materials and Methods:</b> Detailed methodology of measurements and interpretation of results are presented in three exemplary patients who underwent tumor removal via middle fossa approach (MFA) with the use of intraoperative monitoring of hearing with TT-ECochG and direct CNAP performed in real time. In addition, all responses were automatically recorded and stored along with surgical information and subjected to detailed analyses and calculation after surgery. <br><b>Results:</b> The following changes in TT-ECochG and direct CNAP responses were observed: Patient #1 – TT-ECochG and CNAP responses with minor, but transient, morphology changes (hearing was preserved); Patient #2 – CNAP responses changed significantly but, temporarily, from triphasic into biphasic responses later, with marked but partially reversible desynchronization of CNAP; changes in TT-ECochG responses were also observed but, at the end, returned to baseline (surgery-related deterioration of hearing); Patient #3 – irreversible changes of TT-ECochG and direct CNAP (complete loss of hearing). <br><b>Conclusions:</b> A combination of TT-ECochG and direct CNAP allows for real-time monitoring of auditory function during vestibular schwannoma resection and surgical manipulation which contribute to the risk of hearing loss. Therefore, the surgeon can be instantly informed about changes which could increase the possibility of preserving the patient’s hearing

Intra-Operative Cochlear Nerve Function Monitoring in Hearing Preservation Surgery: A Systematic Review of the Literature

“…Pobożny et al (2020) described their PAMR cochlear nerve monitoring technique, stating pros and cons on a total of 10 patients [ 1 ].…”

“…Regarding its major limitations, compared to other techniques, such as cochlear monitoring, a large number of samples (up to several hundred repetitions) are needed to achieve optimal nerve monitoring with a clear identification of wave alterations at a given stimulus level [ 1 , 8 ]. Moreover, the poor signal-to-noise ratio of ABR necessitates a long data acquisition time to achieve an adequate signal-to-noise ratio, and it cannot provide real time results [ 1 , 5 ].…”

“…The VS is a benign tumour originating from the Schwan’s sheath, with a slow pattern of growth [ 1 ]. It is a clinical concern because of its mass effect on the surrounding delicate anatomical structures, sometimes resulting in initial clinical presentations of tinnitus and hearing loss, or even deafness [ 2 ].…”

“…The surgical approach in acoustic neuroma has gained increasing consensus since 1991, the year of the recommendations of the National Institutes of Health Consensus Development Conference on Acoustic Neuroma. Since then, microsurgery has been considered the best modality to treat this condition: the goals of this surgery have become progressively more advanced, with the aim to obtain both complete tumour removal and preserve neurological function of adjacent structures, including both facial and cochlear nerve function [ 1 ]. It is not surprising, then, that in experienced centres, more and more authors have chosen this therapeutic option.…”

Analysis of tympanic sinus shape for purposes of intraoperative hearing monitoring: a microCT study

“…According to our knowledge, in the literature there are no descriptions of a specific design of the electrode, which could be used for intraoperative hearing monitoring during middle ear or cochlea surgery through posterior tympanotomy approach [ 8 , 25 ].…”