Prognostic value of ABR-ECochG intraoperative morphology changes in term of hearing preservation in patients with Vestibular Schwannoma
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Background: A vestibular schwannoma (VS) is a benign tumor that arises from the Schwann cells. Prompt diagnosis and the use of intraoperative monitoring of hearing (IM) during the removal of the tumor increases the probability ofhearing preservation. During the operation, various IM can be used: auditory brainstem responses (ABR), transtympanal electrocochleography (TT-ECochG) and distortion product otoacoustic emissions (DPOAE). Objective: The aim of this study was to determine the usefulness of IM during the VS removal operation and to analyze the changes in morphology of auditory potentials records in relation to hearing after the operation. Material and Methods: Retrospective analysis was done of the audiological tests results and the records of IM performed with 15 patients with vestibular schwannoma. Analyzed were: threshold of hearing, speech intelligibility, ABR wave V latency, action potential (AP) amplitude and latency measured pre- and postoperatively. Results: The preoperative hearing thresholds ranged from 10 to 25 dB HL, while postoperative from 25 to 65 dB HL at the whole frequency band 0,125 –8 kHz. In the postoperative speech audiometry the speech understanding reached 65%. The median value for ABR wave V latency prolongation was 1,38 ms while for the AP latency 0,23 ms. AP amplitude has been reduced by 1.43 μV. Conclusion: The analyzed material presents significant correlation between hearing threshold and the parameters characterizing the hearing physiology of the ABR wave V latency, the amplitude reduction and the AP latency prolongation. The above proves the usefulness of IM in VS removal surgeries.
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