|Year : 2020 | Volume
| Issue : 2 | Page : 375-380
Effect of cochlear implantation on the cervical vestibular evoked myogenic potentials
Abdel-Latif El-Rasheedy1, Ahmed Khashaba2, Waled Ezzat3, Yasser Nafie2, Ahmed Elshafai1
1 Department of Otorhinolaryngology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Otorhinolaryngology, Military Medical Academy, Cairo, Egypt
3 Department of Otorhinolaryngology, Faculty of Medicine, Ain Shams University, Cairo, Egypt
|Date of Submission||09-Jan-2015|
|Date of Decision||06-Mar-2015|
|Date of Acceptance||07-Mar-2015|
|Date of Web Publication||25-Jun-2020|
Department of Otorhinolaryngology, Faculty of Medicine, Menoufia University, Menoufia
Source of Support: None, Conflict of Interest: None
The aim was to evaluate the effect of cochlear implantation (CI) on the cervical vestibular-evoked myogenic potentials (cVEMP), and to examine the correlation between the different approaches of CI and vestibular insult.
The function of the CI is to bypass the damaged or missing cochlear structures by exciting neurons in the auditory nerve directly with electrical stimuli. Although studies have shown that CI is effective and safe, the potential effects on vestibular function are of clinical concern.
Patients and methods
Twenty patients with bilateral sensorineural hearing loss subjected to CI surgery by two different surgical techniques (11 with posterior tympanotomy approach, nine with transcanal approach) were enrolled in the study. The patients were subjected to preoperative evaluation of the vestibular function with cVEMP. Revaluation of the vestibular function with the same test was done 2–3 months postoperatively.
cVEMP results revealed that 7/20 (35%) had abnormal responses preoperatively. There was significant difference between cVEMP results preoperatively and postoperatively where nine patients out of 13 patients (69%) lost cVEMP response postoperatively (P = 0.004). There was no significant difference between the two different surgical approaches used during the study. cVEMP was normal postoperatively when the round window insertion technique was used (80%), while there was loss of cVEMP response postoperatively in all patients (100%) with bony cochleostomy insertion.
Vestibular system function deficit was found in 69% of CI children as measured by cVEMP postoperatively. There was no significant difference between the classic posterior tympanotomy approach and the transcanal approach regarding the vestibular deficit. Insertion of electrodes through the round window carries less harmful effects to the vestibular system (20%), than insertion through cochleostomy (100%).
Keywords: cervical vestibular-evoked myogenic potential test, cochlear implant, cochleostomy, posterior tympanotomy approach, transcanal approach
|How to cite this article:|
El-Rasheedy AL, Khashaba A, Ezzat W, Nafie Y, Elshafai A. Effect of cochlear implantation on the cervical vestibular evoked myogenic potentials. Menoufia Med J 2020;33:375-80
|How to cite this URL:|
El-Rasheedy AL, Khashaba A, Ezzat W, Nafie Y, Elshafai A. Effect of cochlear implantation on the cervical vestibular evoked myogenic potentials. Menoufia Med J [serial online] 2020 [cited 2020 Oct 22];33:375-80. Available from: http://www.mmj.eg.net/text.asp?2020/33/2/375/287807
| Introduction|| |
Cochlear implant (CI) is an electronic device that is implanted under the skin with electrodes positioned in the cochlea to stimulate the auditory nerve. Electrical current induces action potentials in the auditory nerve fibers which are transmitted to the brain. CI bypasses damaged or missing hair cells within the cochlea that would normally code sound. Although this surgery is considered to be safe, balance disorder is a very frequent postoperative complaint in cochlear recipients. In 2013, Katsiari and colleagues found that about one-third of implantees could experience a significant vestibular disturbance after surgery, independent of their age, cause, or preoperative caloric result. Different etiologies are suggested to explain vertigo after this surgery: perilymphatic fistula induced by cochlear fenestration or a disruption of endolymphatic flow caused by the electrode itself and mechanical irritation of the membranous labyrinth or the labyrinthitis triggered by a foreign body in the cochlea. Vestibular evoked myogenic potential (VEMP) is defined as muscle reflexes following strong acoustic stimulation. VEMP is the use of sound as stimulus to initiate a vestibular influence on the postural muscles. The saccule which is the lower of the two otolithic organs in erect position has a slight sound sensitivity and its stimulation provokes contraction of the neck and postural muscles. The purpose of the VEMP test is to determine if the saccule as well as the inferior vestibular nerve and their central connections are intact and working normally or not. Among the complementary tests in an otoneurologic evaluation, advantages of VEMP are that it is an objective, reliable, noninvasive, inexpensive, easy to perform, and rapid test that causes the patient no discomfort.
Although hearing functions have been investigated in CI patients, few studies have investigated the vestibular function preimplantation and postimplantation. This work was designed to investigate the effect(s) of the CI on cervical vestibular evoked myogenic potentials (cVEMPs) and to correlate these findings (if any) to different approaches of CI surgery in children.
| Patients and Methods|| |
The ethical Committee of the faculty of medicine Menoufia university accepted the study and patients gave an informed consent. This is a prospective, randomized study, where 20 patients were included from October 2013 to September 2015. The parents of these patients gave their informed written consent to participate in the study. All patients suffered from bilateral profound sensorineural hearing loss. Children with preoperative neurological and visual disorders were included in the study.
All patients were assessed by history taking including personal history, history of hearing loss and vestibular symptoms such as dizziness, visual acuity problems especially with head movements, poor spatial relationships, difficulty navigating in the dark, motion sickness or sensitivity, nausea and abnormal movement patterns (unsteady gait, clumsiness, and poor posture), and developmental motor milestones and family history. Physical examination was performed including general and otological examination which entails possible presence of congenital anomalies and assessment for vestibular dysfunction. Investigations included routine investigations for CI and assessment of vestibular function by cVEMP using the two channel-evoked potential system Audera, model 091090 (Grason Stadler 10395 West 70th St. Eden Prairie, MN 55344, USA).
cVEMP was recorded from the sternocleidomastoid muscle. Impedance should be less than 5 kohm. The band-pass filter was 5–1500 Hz. Sound stimuli were 500 Hz tone burst of 95 dB nHL with a repetition rate of three pulses per se cond delivered through earphones. Responses were averaged over 200 sweeps and the recorded time per response ranged from 1 to 2 min. Analysis time (window) was 50 ms and sensitivity was 50 μV. Two traces from each side were obtained in order to assess reproducibility. The child was encouraged to rotate his neck to the contralateral side of stimulation to activate the sternomastoid muscle. cVEMP testing took an average of 20 min. Most of the children required continuous motivation from the examiner to comply with the testing instruction. In each trace, the latency and amplitude of the two positive–negative waves P13–N23 were labeled and measured.
The posterior tympanotomy approach
A 8–10 cm-long skin incision, 'inverted S-shaped incision,' was performed postauricularly ended at the mastoid tip. Anterior flap of the skin and subcutaneous tissues were elevated until the retroauricular sulcus, and 3–5 cm posteriorly. A rectangular-shaped incision of the exposed periosteum was done in a plane 0.5 cm anterior to the skin incision. Cortical mastoidectomy with thinning of the posterior external auditory canal was done. Following cortical mastoidectomy, the descending or mastoid portion of the facial nerve was identified and skeletonized until it could be seen through a thin layer of bone. Bone in the facial recess, between the chorda tympani laterally, the facial nerve medially, and the incus bar superiorly, was then carefully removed till the base of the pyramid could be seen. The round window membrane was usually 1–1.5-mm inferior to the stapes tendon. The round window niche was removed using a 1–1.5 mm burr to identify the round window membrane. Meticulous drilling at the anteroinferior margin of the round window niche with a 1-mm diamond burr was then used and continued until the 'blue' lining of the endosteum was visible.
Then drilling a bed for the receiver/stimulator (R/S) device was done in the posterosuperior direction in relation to mastoidectomy. We usually drilled a tunnel in the temporal bone and then drilled a canal to deliver the electrode array into the mastoid cavity. Receiver/stimulator was then placed and secured in its bed beneath the elevated periosteal flab 'sub-periosteal pocket.' At this point, a slightly curved needle was used to open the round window membrane and the electrode was inserted [Figure 1]. Cochleostomy site was tucked with temporalis fascia, then the posterior tympanotomy and mastoid bowel was packed with Gelfoam. The incisions were closed in layers. The skin incisions were closed subcutaneously with 3.0 Vicryl.
|Figure 1: Posterior tympanotomy approach of the right ear showing: (A) the electrode; (B) passing through the round window.|
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The transcanal technique
The incision was a small postauricular incision. The incision was deepened into the periosteum. A strip of conchal cartilage 1 cm long and 2 mm wide was harvested. The periosteal pocket for the receiver package was developed and the bed was drilled at an adequate location depending on the brand of the implant used. The site was determined so that the electrode runs more or less in a gentle curve from the bed to the trough without kinks. A tympanomeatal flap was elevated through 210° (on the right side from 1 to 6 through 9 around the posterior meatal wall), the round window niche and promontory and incudostapedial joint were exposed. When the round window niche was not adequately exposed, a limited canalplasty could be performed. A trough was fashioned along the junction of the posterior and superior meatal walls parallel to the axis of the long process of the incus. The trough runs straight from inside out and is 2 mm deep. It must have straight walls with no bevel to prevent movement of the electrode. A small bridge of bone was maintained at the medial end. It had a dual purpose: protection of the chorda and fixation of the electrode in place. The round window approach was used for electrode insertion. The niche overhang was drilled until the round window membrane is exposed. The round window niche was filled with hyaluronic acid and dexamethasone which helped lubricate the electrode and prevents air bubbles from forming during the advancement of the electrode. The electrode tip was positioned and the membrane was gently punctured. Afterwards the electrode was gently advanced in a superior to inferior direction and it was the direction of the cochlea which guided it. The round window was then sealed with muscle [Figure 2].
|Figure 2: Transcanal approach showing the electrode passing through the tunnel (A), past the bridge (B), and into round window (C).|
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Immediately postoperatively evaluation of the vestibular symptoms were done. Two to three months after the surgery of CI, revaluation of the vestibular symptoms were done and all patients were subjected again to cVEMP test.
Primary outcome measures
The occurrence of vestibular symptoms post-CI and the presence or absence of cVEMP after CI.
Secondary outcome measures
Comparison between classical and transcanal approaches and between insertion through cochleostomy or through round window regarding postoperative cVEMP.
Data were collected, tabulated, and statistically analyzed using SPSS (the Statistical Package for the Social Sciences) program version 16 for windows (SPSS Inc., Chicago, Illinois, USA) and for all the analysis a P value less than 0.05 was considered statistically significant. Data were shown as mean, range, or value with frequency and percentage. A 95% confidence interval was considered. Mann–Whitney test was done for quantitative variables which are not normally distributed. Pearson's χ2-test was done for qualitative variables with the use of Fischer's exact test if the expected frequencies were not suitable for χ2-test. The Wilcoxon test was done to detect mean and SD of non-normally distributed pre- and post-values of the same variable of the same group of patients. McNemar's test was performed to differentiate changes in different follow-up results of dichotomous qualitative studied variables. All data are tested with Kolmogorov–Smirnov Z-test and most of them were found not normally distributed and so presented with mean ± SD and using nonparametric tests to test association.
| Results|| |
The current study included 20 patients (2–19 years) with a mean age of 5.3 ± 4.1 years; all underwent CI surgery, and 11 patients with the classic posterior tympanotomy approach while nine of them with the transcanal approach. The most common etiology of hearing loss in the study group was heredofamilial (35%), of unknown etiology (35%) followed by neonatal insult (10%). All cases had complete electrode insertions. Implantation was right-sided in 19/20 (95%), only one case was implanted in the left ear.
Three patients were complaining of vestibular symptoms preoperatively while 15 (75%) patients were complaining of these symptoms early postoperatively, χ2-test disclosed that the prevalence of vertiginous symptoms was significantly higher (P < 0.001) only in the early postoperative period compared with either preoperative or late postoperative periods [Table 1].
|Table 1: Comparison between pre- and early- and late-postoperative vestibular symptoms in the implanted ear group|
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Preoperatively, out of 20 ears, seven (35%) ears showed absent cVEMP while 13 (65%) ears had normal cVEMP. Postoperatively, only four (20%) ears continued to show normal cVEMP. χ2-Test revealed this difference to be significant (P = 0.004) [Table 2].
|Table 2: Comparison between preoperative and postoperative vestibular evoked myogenic potential in implanted and nonimplanted ears among the studied patients (n=20)|
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In this study, normal cVEMP was registered in 13 ears before implantation. Seven of these ears were implanted using the classical approach while six were implanted using the transcanal approach. Postoperatively, the normal cVEMP was registered from only two (29%) ears in the classical approach group (P = 0.08) and another two (33%) ears in the transcanal group (P = 0.15). This difference was found to be insignificant [Table 3]. The CI electrodes were introduced into the cochlea either through cochleostomy technique (eight cases) or through round window technique (five cases). All the cases with cochleostomy technique disclosed abnormal cVEMP postimplantation, while four cases with the round window technique disclosed normal cVEMP postimplantation; these differences were found to be significant (P = 0.004) [Table 3].
|Table 3: Correlation between the classical approach of cochlear implant and vestibular insult|
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| Discussion|| |
Numerous studies have attempted to characterize the effects of CI on the vestibular system. Unlike adult patients, few vestibular tests are well tolerated by children; for example, the caloric testing, although very useful for the evaluation of peripheral vestibular system, is not really accepted by children, while the cVEMP testing is easily applicable to children.
In our study, cVEMP results revealed that 7/20 (35%) had abnormal responses preoperatively. This matches to a great extent the results of previous studies which found a high percentage of abnormality in cVEMP among hearing impaired children. Jin et al. demonstrated that cVEMP response was abnormal or absent in 50% of cases. Shall found that 21% of children demonstrated absent cVEMP response unilaterally, while 67% of children showed bilateral absent response. Furthermore, Zhou et al. found more abnormality in cVEMP representing 91% of cases. Nordfalk et al. found that 11 patients out of 33 patients (33%) showed abnormal cVEMP responses before CI surgery.
The high prevalence of vestibular impairments in hearing impaired pediatric patients was explained by the close anatomical and phylogenetic relation between the cochlea and the saccule, where they are closely related in terms of innervation and vascular supply. They share the continuous membranous labyrinth of the inner ear and function by means of similar receptor cells.
In our study, nine patients out of 13 patients (69%) lost cVEMP response postoperatively. The prevalence of postoperative vestibular hypofunction reported by previous studies ranged from 20 to 76%. Studies as those of Ernst et al. reported postoperative lost cVEMP responses in 42% of adult cases, where absence of cVEMP response changed from 36% preoperatively to 78% postoperatively. Bogle et al. demonstrated a change in the presence of cVEMP response in children from 100% prior to implantation to 53% following surgery. Nordfalk et al. found that 11 out of 21 patients (52%) lost their cVEMP responses after surgery.
Other studies have reported less percentage of abnormality as Todt et al. who found that 21% of cases lost their normal responses postoperatively. Licameli et al. showed postoperative absent response in 20% of cases. On the other hand, there are authors who believed the CI may improve balance as Buchman et al., Cushing et al., and Szirmai et al. who found that 26% had vestibular response improvement postoperatively, whose explanation was not clear for the author.
Katsiari et al. demonstrated that direct trauma from insertion caused by the electrode, intraoperative loss of perilymph, acute serous labyrinthitis due to cochleostomy, foreign body reaction with labyrinthitis, endolymphatic hydrops, and electrical stimulation by the implant could be plausible mechanisms of this impairment.
The results of our study revealed that nine patients out of 13 patients (69%) lost cVEMP response postoperatively. There was no significant difference between the two different surgical approaches used during the study. The results also showed that cVEMP was normal postoperatively when round window insertion technique was used (80%) while there was loss of cVEMP response postoperatively in all patients when insertion of the electrodes was done through bony cochleostomy.
Rossi et al. found a rate of 3.1% of patients with postoperative dizziness after transmembrane electrode insertion. In contrast to this, a similar study done by Enticott et al. with an anterior cochleostomy described rates of 32%. Todt et al. investigated the impact of different cochleostomy techniques on vestibular receptor integrity and vertigo after CI where 62 adult patients underwent implantation via an anterior or round window insertion approach. Results showed significant differences of postoperative VEMP responses (50 vs 13%) and the electronystagmography results (42.9 vs 9.4%) were found with respect to the two different insertion techniques.
Tien and Linthicum demonstrated that temporal bone studies have shown that an electrode insertion into the scala vestibuli involves a damage of the osseous spiral lamina, basilar membrane, and vestibular receptors. The saccule was the most frequently damaged vestibular receptor, followed by the utricle and the semicircular canals. However, when the electrode was inserted into the scala tympani, no vestibular damage was found.
From an anatomic point of view, there is a high variability between the bony promontorial lip (the major landmark for the cochleostomy approach) and the RW itself; and the RW rim and the position of the basilar membrane. The latter distance is between 0.2 and 0.7 or 0.5 mm from the center of the RW. Thus, the risk of inserting the electrode into the scala vestibuli to possibly damage the basilar membrane or hook region is greater with the cochleostomy approach.
| Conclusion|| |
Vestibular system function deficit was found in 69% of CI children as measured by cVEMP postoperatively. There is no significant difference between the classic posterior tympanotomy approach and the transcanal approach regarding the vestibular deficit. Insertion of electrodes through the round window carries less harmful effects to the vestibular system (20%) than insertion through cochleostomy (100%).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]