What can vestibular-evoked myogenic potentials tell us about vestibular schwannomas?

Roza Ucar; Feray Güleç-Uyaroğlu; Neşe Çelebisoy

doi:10.4103/NSN.NSN_68_20

CASE REPORT

Year : 2020 | Volume : 37 | Issue : 4 | Page : 228-230

What can vestibular-evoked myogenic potentials tell us about vestibular schwannomas?

Roza Ucar¹, Feray Güleç-Uyaroğlu¹, Neşe Çelebisoy²
¹ Department of Neurology, Izmir Tepecik Education and Research Hospital, Izmir, Turkey
² Department of Neurology and Clinical Neurophysiology, Medical School, Ege University, Izmir, Turkey

Date of Submission	20-May-2020
Date of Decision	30-May-2020
Date of Acceptance	05-Jun-2020
Date of Web Publication	29-Dec-2020

Correspondence Address:
Feray Güleç-Uyaroğlu
Associate Professor of Neurology, Department of Neurology, Izmir Tepecik Education and Research Hospital, Konak 35170, Izmir
Turkey

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/NSN.NSN_68_20

Abstract

A 27-year-old female presented with complaints of dizziness and tinnitus in the right ear. The neurological examination and the audiometry were completely normal. Ocular vestibular-evoked myogenic potential (oVEMP) obtained by the stimulation of the right ear was absent, whereas bilateral cervical VEMPs and left-sided oVEMP response were normal. With the absence of hearing loss and absent oVEMP on the affected side, the superior vestibular nerve involvement was decided. Magnetic resonance imaging revealed a vestibular schwannoma (VS) in the right cerebellopontine angle 32 mm × 31 mm in size. The patient was presented to show the contribution of cheap vestibular tests in the diagnosis of VSs as well as the prediction of the involved nerve. It was also interesting to see a tumor with a diameter exceeding 3 cm not causing hearing loss.

Keywords: Cervical vestibular evoked myogenic potentials, magnetic resonance imaging, ocular vestibular evoked myogenic potentials, vestibular schwannoma

How to cite this article:
Ucar R, Güleç-Uyaroğlu F, Çelebisoy N. What can vestibular-evoked myogenic potentials tell us about vestibular schwannomas?. Neurol Sci Neurophysiol 2020;37:228-30

How to cite this URL:
Ucar R, Güleç-Uyaroğlu F, Çelebisoy N. What can vestibular-evoked myogenic potentials tell us about vestibular schwannomas?. Neurol Sci Neurophysiol [serial online] 2020 [cited 2023 Mar 27];37:228-30. Available from: http://www.nsnjournal.org/text.asp?2020/37/4/228/305392

Introduction

Vestibular schwannoma (VS) is a benign tumor originating from Schwann cells.

It commonly occurs in the vestibular part of the vestibulocochlear nerve. Cochlear nerve and facial nerves can also be involved. In approximately 90% of patients with VS, the tumor has been reported to originate from the inferior vestibular nerve (IVN).^[1]

Vestibular-evoked myogenic potentials (VEMPs) are generated by the stimulation of the otolith organs. Cervical VEMPs (cVEMPs) are thought to derive from the saccule proceed along the IVN and by descending vestibulo-collic pathways reach the neck muscles. Ocular VEMPs (oVEMPs) are considered as a test of the utriculus and the superior vestibular nerve (SVN) and reflect the ascending projections to the extraocular muscles.^[2]

There are several studies on VEMPs in patients with VS^{[3],[4],[5],[6],[7],[8]} with conflicting results on their eligibility in distinguishing the nerve of origin in VS. We herein report a patient with VS who had tinnitus but normal hearing that presented with an absent oVEMP response, whereas the cVEMP response was normal.

Case Report

A 27-year-old female applied with complaints of dizziness and tinnitus in the right ear, that started 5 months ago. The neurological examination was completely normal. The laboratory examination was insignificant. Pure-tone audiometry was normal. VEMPs were recorded using a Synergy device (Medelec; Oxford Instruments Medical Inc., Old Woking, UK). Clicks at an intensity of 110 dBnHL (normal hearing level) of 0.1-ms duration were the acoustic stimuli, given at a frequency of 5 Hz through a headphone to each ear unilaterally. The electromyogram signal was bandpass filtered from 10 to 1000 Hz and the average time was 100 ms. cVEMPs were recorded by an active electrode placed on the upper half of the sternocleidomastoid muscle on the side of the stimulation and the reference electrode was placed on the upper third of the sternum. oVEMPs were recorded with the active electrode placed 0.5 cm below the lower eyelid and the reference electrode placed 2 cm below it contralateral to the ear stimulated.

Mean cVEMP p13, n23 latencies and p13-n23 amplitudes were 12.0 ms, 18.7 ms, and 270.7 μV, for the right and 11.7 ms, 18.6 ms, and 292.5 μV for the left side, respectively [Figure 1]. In the oVEMP, on stimulation of the left side p1, n1 latencies and amplitude were normal (8.5 ms, 13.5 ms, and 29.6 μV, respectively), but no response was obtained on stimulation of the right ear [Figure 2].

Figure 1: Normal cervical vestibular evoked myogenic potential recordings from right (a) end left (b) sternocleidomastoid muscles

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Figure 2: Absent ocular vestibular evoked myogenic potential response in the stimulation of the right ear (a), normal ocular vestibular evoked myogenic potential response in stimulation the left ear (b)

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On cranial magnetic resonance imaging, a round mass lesion 32 mm × 31 mm in size was observed at the right cerebellopontine angle, extending from the internal acoustic canal. It was hypoisointense on T1-weighted images, hyperintense on T2-weighted images, and showing homogeneous contrast enhancement on T1-contrast enhanced images [Figure 3]. The patient was operated on and the pathology was compatible with schwannoma.

Figure 3: Cranial magnetic resonance imaging showed, a round mass lesion 32 mm × 31 mm in size was observed at the right cerebellopontine angle, extending from the internal acoustic canal. It was hyperintense on T2-images (a), hypo-isointense on T1-images (b), showing homogeneous contrast enhancement on T1-contrast enhanced images (c)

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Discussion

VS can affect a single branch of the vestibular nerve, and according to the literature, this is usually the IVN that goes with cVEMP pathology.^[4] In our case, there was pure SVN involvement and oVEMP response was absent on the affected side. Since the IVN is more anatomically related to the acoustic nerve, accompanying hearing loss is often present,^[9] and the clinical picture becomes more difficult to overlook.

In recent studies, researchers focused on the prediction of vestibular tests in determining the nerve of origin of the VS.^{[3],[4],[5],[6],[7],[8],[10]} Chiarovano et al .^[3] reported that the sensitivity of all VEMP tests in diagnosing VS was 85% and in some patients, the only abnormal test was oVEMPs. Iwasaki et al .^[5] observed an abnormal oVEMP response in 80% of patients with VS similar with the caloric test. Ushio et al .^[10] and Patko et al .^[7] reported a sensitivity of around 80% for VEMPs in patients with VS. In a study with 130 VS patients, it was proposed that no significant difference in terms of VEMP responses was present between tumors arising from the SVN and the IVN.^[6] Similarly, Tsutsumi et al .^[8] have suggested that the VEMP was not a useful test in demonstrating the nerve origin in VS patients.

In our case, while the cVEMPs were normal bilaterally unilateral absent oVEMP response suggested the involvement of the SVN on that side. This could explain normal hearing, but the tumor diameter was more than 1 cm exceeding into the pontocerebellar angle which is then accepted as the diameter to cause hearing loss.^[9] Therefore, it was interesting for this patient to have normal audiometry.

Depending on this case, we can say VS affecting the SVN even with diameters over 3 cm can be skipped easily in the absence of imaging despite careful neurological examination. In these patients, electrophysiological tests such as VEMPs which are cheap and quick to perform can be very helpful.

The limitation of this case report is the absence of caloric tests estimating the function of the SVN, which innervates the horizontal semicircular canal and the video head impulse test that assesses each semicircular canal individually. What we would expect was caloric weakness and decreased gain with overt and covert saccades on testing in the plane of superior and horizontal canals of the affected side innervated by the SVN.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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