Journal of Otology & RhinologyISSN: 2324-8785

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Research Article, J Otol Rhinol Vol: 3 Issue: 3

Single-sided Deafness with a Vestibular Schwannoma in the only Hearing Ear: Role of Cochlear Implantation

Robert S Hong1,2*, Jack M Kartush1, Aaron J Parkinson3 and Michael J LaRouere1
1Michigan Ear Institute, Farmington Hills, Michigan, USA
2Department of Otolaryngology, Wayne State University, Detroit, USA
3Cochlear Americas, Centennial, Colorado, USA
Corresponding author : Robert S Hong
Michigan Ear Institute, 30055 Northwestern Hwy, #101; Farmington Hills, MI 48334, USA
Tel: 248-865-4444; Fax: 248-865-6161;
E-mail: [email protected]
Received: February 15, 2014 Accepted: May 27, 2014 Published: June 05, 2014
Citation: Hong RS, Kartush JM, Parkinson AJ, LaRouere MJ (2014) Single-sided Deafness with a Vestibular Schwannoma in the only Hearing Ear: Role of Cochlear Implantation. J Otol Rhinol 3:3. doi:10.4172/2324-8785.1000157

Keywords: Cochlear implant; BAHA; CROS; Single-sided deafness; Vestibular schwannoma

Keywords

Cochlear implant; BAHA; CROS; Single-sided deafness; Vestibular schwannoma

Abbreviations

BAHA: Bone Anchored Hearing Appliance; CNC: Consonant- Nucleus-Consonant; CROS: Contralateral Routing of Signals; RMS: Root Mean Square; SNR: Signal-To-Noise Ratio; SSQ: Speech, Spatial and Qualities of Hearing Scale.

Introduction

Vestibular schwannomas are benign, slow-growing tumors of the vestibular division of the eighth cranial nerve. They are most commonly found in the context of an asymmetric sensorineural hearing loss, with imaging obtained as part of the workup revealing such a tumor in 1 to 7.5% of cases [1,2]. Expansion of the tumor within the narrow confines of the internal auditory canal leads to compression of the adjacent cochlear nerve and hearing loss early in the course of tumor growth. However, occasionally, a workup for asymmetric sensorineural hearing loss can reveal a tumor not on the side with hearing impairment, but on the opposite, normal hearing ear. The incidental finding of a lesion in the internal auditory canal in an only hearing ear is rare, with isolated cases reported in the literature [3-5].
Recently, we have encountered another case of a patient with a vestibular schwannoma in an only hearing ear. In determining how best to care for this patient, we found the literature lacking with respect to management of our patient’s overall hearing. In the largest case series of 7 patients with a tumor in the only hearing ear, [7] suggested that observation of tumor was warranted in the majority of such cases, with hearing-conservation surgery reserved for select cases where the lack of intervention results in a high risk of deafness. However, the best course of treatment for the contralateral deaf side if observation of the tumor was selected was not addressed.
The purpose of this article is multi-fold. We would like to highlight a number of important considerations that come into play in the decision-making process for treatment of single-sided deafness in the context of a vestibular schwannoma in the contralateral only hearing ear. Issues that will be addressed include whether such hearing loss should be treated at all, and if so, which modality is preferable: BAHA vs. CROS hearing aid vs. cochlear implant. In the case of our patient, the decision was ultimately made to perform cochlear implantation in the deaf (non-tumor) ear. As such, this provided us with the relatively uncommon opportunity to study cochlear implantation in the context of single-sided deafness. Over the past several years, a number of studies have suggested that cochlear implantation in the context of single-sided deafness may result in significant benefits for both sound localization and speech perception in background noise [6-8]. This study serves to add to the small but growing body of literature on cochlear implantation for single-sided deafness.
A MRI scan of the brain with gadolinium obtained at that time was normal, with no evidence of a tumor in the internal auditory canal or cerebello-pontineangle. The patient presented for the first time to our clinic about 1 year ago with symptoms of worsening imbalance and tinnitus. Audiometric testing revealed the patient to have left severe-to-profound hearing loss and right normal hearing. Video nystagmography showed no evidence of peripheral vestibular weakness. Given the patient’s worsening symptoms, a MRI scan was repeated, demonstrating a 3 mm intracanalicular tumor on the right, normal hearing side (Figure 1). No lesion was seen on the left, deaf side.
Figure 1: Vestibular schwannoma. MRI scan with gadolinium (axial view) demonstrates an intracanalicular tumor (white arrow) on the right, which is the only-hearing side.
With respect to management of the tumor in the only hearing ear, the different treatment options of observation, hearing preservation surgery and stereotactic radio surgery were discussed with the patient. Given the small size of the tumor and the completely normal hearing in that ear, the decision was made to observe with serial MRI scans, as we did not want an active intervention to lead to profound deafness in an only hearing ear, particularly without evidence of tumor growth.
With respect to management of the single-sided deafness, our recommendation was cochlear implantation of the left ear. Our rationale was that this would provide the patient time to become accustomed to using a cochlear implant should he lose all of his hearing in the ear with the vestibular schwannoma. Other potential options to rehabilitate single-sided deafness were also explored with the patient. Both the BAHA and CROS hearing devices were discussed as reasonable alternatives to provide the patient with a sensation of hearing on his deaf side. However, as both devices rely on at least some serviceable hearing in the good ear, these options were presented as potentially temporary solutions for single-sided deafness. If the patient has complete hearing loss in the only hearing ear, such as from tumor growth, these devices would become useless. Nevertheless, the patient was interested in trialing these devices, and with approval from the Institutional Review Board at Providence Hospital in Southfield, MI (IRB #226688-11), we proceeded to set up a trial to allow us to assess patient performance on sound localization and speech perception in noise in the following conditions: (1) untreated (normal hearing in one ear and profound deafness in the opposite), (2) after 3 weeks of using the CROS hearing aid (Phonak, Warrenville, IL, USA), (3) after 3 weeks of using the Cochlear BAHA (soft band) device, and (4) after cochlear implantation with a Nucleus CI24RE Freedom Implant (Cochlear Ltd., Lane Cove, Australia) at 3 months and 6 months post-activation.

Tests

Unaided hearing thresholds
Audiometric thresholds, including bone and air conduction thresholds, were obtained for each ear using insert earphones at each study visit. This allowed for monitoring of hearing status particularly in the normal hearing ear, which was at risk of hearing loss throughout the study secondary to tumor growth.
Speech perception in quiet
The Consonant-Nucleus-Consonant (CNC) word recognition test [9] consists of 10 recorded lists of 50 monosyllabic words in CD format. Two lists were randomly chosen and administered in quiet at a level equal to 60 dBA in the sound field at each study visit in the best-aided condition. With the cochlear implant, multiple conditions were tested, including cochlear implant alone, better hearing ear alone, and bimodal.
Speech perception in noise
The AzBio test [10] is a test consisting of 15 lists of 20 sentences each. Each list includes 5 sentences from each of 4 different male and female speakers. For this study, the target signal (sentence material) was presented at 60 dBA and always presented from a loudspeaker situated directly in front of the listener (0 degrees). The competing signal used is composed of 10-talker babble, presented at a +5 dB signal-to-noise ratio (SNR), and tested from the front, 90 degrees to the subject’s left, and 90 degrees to the subject’s right. Results were obtained in the best-aided condition at each study visit. With the cochlear implant, only the better hearing ear alone and bimodal conditions were tested.
Sound localization
For the localization testing (in the horizontal plane) a loudspeaker array consisting of eight, evenly spaced (15° apart), loudspeakers arranged in a 105° arc centered directly in front of the listener was constructed. The delivery of the stimuli, including the number repetitions per loudspeaker and randomization, were controlled by custom software. Common, everyday sounds were used as stimuli all with different spectral contents and intensity levels. This test was similar to that used by Dunn et al. [8]. Listeners were asked to identify the speaker from which the sound originated. Performance was determined by calculating the average root-mean-square (RMS) error in degrees as previously described [11], with smaller values corresponding to better localization ability, and perfect performance equating to a RMS error of 0 degrees. Individual responses for each stimulus presentation were also recorded such that response patterns could be graphically represented.
Speech, Spatial and Qualities of Hearing (SSQ) questionnaire
The standardized Speech, Spatial and Qualities of Hearing questionnaire was used to assess participant perceptions of hearing in 3 domains: (1) speech-hearing, corresponding to the ability to understand speech in different listening situations, (2) spatial hearing, corresponding to the ability to assess direction and distance of sound, and (3) qualities of hearing, corresponding to the naturalness of perceived sound and ability to segregate sounds [12]. The questionnaire consists of 49 total items, with respondents indicating on a scale of 0 to 10 their response to each item, with a higher number representing greater ability. An alternative form (SSQ-B) was used to allow for relative comparisons between the subject’s perception of hearing with the device of interest and that prior to any hearing intervention [13]. The scale on the SSQ-B ranged from -5 to +5, where -5 indicated “much worse,” 0 indicated “unchanged” and +5 indicated “much better” hearing ability than without the hearing device.

Results

The subject was tested on CNC word recognition in quiet, speech perception in noise, sound localization, and the SSQ questionnaire for the following conditions: (1) prior to any hearing intervention, (2) after trailing the CROS hearing aid on the left for 3 weeks, (3) after trailing the BAHA softband on the left for 3 weeks, and after cochlear implantation in the left (deaf) ear at (4) three months post-activation and (5) six months post-activation. Throughout the course of the study, the participant’s hearing remained normal in the ear with the vestibular schwannoma (right ear), as assessed by audiometry at each study visit.
With respect to performance on CNC word recognition in quiet, excellent performance (>99% correct) was obtained for the bilateral condition prior to any hearing intervention, with the CROS, and with the BAHA. When the left ear was tested alone after receiving the cochlear implant, CNC word recognition was 53% correct at 3 months and 82% correct at 6 months post-activation. CNC word recognition in the contralateral normal hearing (right) ear remained excellent at all testing intervals.
The results for AzBio speech perception in noise are shown in Figure 2. In all cases, speech is presented from the front, with the location of the noise varying from the front, 90 degrees to the subject’s left (to the impaired and subsequently implanted ear), and 90 degrees to the right (to the normal hearing ear). Figure 2a shows performance prior to any hearing intervention (one normal ear), with the CROS, and with the BAHA. In all cases, performance is excellent (>90% correct) when speech is presented from the front and noise is presented to the impaired ear, as the patient is presumably able to use the contralateral normal-hearing ear to understand the target speech. A small decline in performance is found in all cases when the noise is moved from the impaired ear to the front, as having the speech and noise originate from the same location makes speech perception more difficult. Nevertheless, performance remains good (70 to 90% correct) in all cases. Finally, the condition where noise is presented to the normal-hearing ear results in the poorest performance in all cases.
Figure 2: AzBio sentences in noise. Performance on this task is shown for (A) the best-aided condition preoperatively prior to any hearing intervention (normal ear), with the CROS, and with the BAHA. Performance on this task after cochlear implantation is performed is demonstrated at (B) 3 months postactivation and (C) 6 months post-activation, comparing the normal-hearing ear alone to the bimodal condition. In all cases, speech is presented from the front, and the location of the noise varies from the front, to the normal-hearing side, and to the impaired/implanted side.
Figure 2b and 2c show performance on speech perception in noise following cochlear implantation at 3 months and 6 months post-activation, respectively. Data for the normal ear alone and the bimodal (cochlear implant + normal ear) conditions are presented separately. In both modalities, similar trends to those seen in Figure 2a are observed, with declining performance as the noise is moved from the implanted ear to the front to the normal ear. Interestingly, this subject appears to show significant learning effects when noise is presented to the normal ear. The preoperative normal ear condition shown in Figure 2a and postoperative normal ear condition (6 months post-activation) shown in Figure 2c both test the performance of the right normal-hearing ear by itself. In the preoperative condition, the left ear has a profound hearing loss and in the postoperative condition, the cochlear implant in the left ear is turned off. However, the normal ear at 6 months shows better speech perception in noise when the noise is presented to the normal ear (~55% correct) compared to preoperatively (~15% correct). This suggests that over the course of using the different devices, the subject has learned to become a better listener when noise is presented to the normal hearing side. Given the observation of this learning effect, it is difficult to make any meaningful conclusion comparing the CROS, BAHA, and cochlear implant with respect to speech perception in noise.
Figure 3 shows the results for sound localization. The best performance, corresponding to the lowest RMS error, is obtained in the bimodal conditions combining the cochlear implant and normal-hearing ears, with performance continuing to improve from 3 months to 6 months post-activation. These observations are highlighted by Figure 4, with the data re-plotted using bubble plots. Hypothetical perfect performance on sound localization, with each response correctly matching each stimulus location, corresponds to the bubbles forming a perfectly diagonal line, as shown in the bottom right corner of the figure. When the subject was tested prior to any hearing intervention (preoperative better ear only) or with the CROS device, all responses were skewed toward the better hearing side, with no demonstrable sound localization ability. Data demonstrating increased responses along the hypothetical diagonal line are seen with the BAHA and bimodal plots and most strongly with the bimodal condition at 6 months post-activation. This suggests that the addition of the cochlear implant provides the patient with an increased ability to localize sound, with improvements continuing to be seen over the first 6 months of usage.
Figure 3: Sound localization. Performance on this task comparing perceived with actual stimulus location is shown for the better-hearing ear alone (solid black circles) compared to with the different devices tested (inverted white triangles). Comparisons are made for the CROS, BAHA, and cochlear implant. The cochlear implant is assessed at both 3 and 6 months postactivation. Values for root mean square (RMS) error are also shown above each plot, with a smaller value indicating better performance. Error bars represent standard deviation.
Figure 4: Sound localization. Performance on this task is shown prior to cochlear implantation (preoperative), following the CROS and BAHA trials, and both 3 months and 6 months after activation of the cochlear implant in the bimodal condition. For comparison, the hypothetical results of a normalhearing individual with perfect sound localization are shown in the bottom right corner, with all of the bubbles falling along the diagonal line.
The SSQ questionnaire was administered prior to any hearing intervention and the subject responded with average values of 3.4 out of 10 in the speech-hearing domain, 4.3 out of 10 in the spatial hearing domain, and 8.1 out of 10 in the qualities of hearing domain, with 10 out of 10 being the ideal score. An alternative version of the SSQ (SSQ-B) allowing for patient comparisons to the initial preoperative hearing were used for the subsequent study visits, and the results are shown in Figure 5. The results following the BAHA trials are not shown, as the responses from that visit were mistakenly performed relative to the preceding CROS trial as opposed to the initial preintervention hearing. In all cases, the subject indicates improvement in speech perception, spatial hearing, and the qualities of hearing compared to the initial visit.
Figure 5: Speech, spatial and qualities of hearing (SSQ-B) questionnaire. Ratings in the three domains of this scale are provided for the CROS and cochlear implant devices compared to prior to any hearing intervention, with a positive value indicating improvement in a particular domain with addition of the device. Data for the BAHA are not available.

Discussion

This study demonstrates the viability of cochlear implantation in the management of single-sided deafness when an acoustic neuroma is present in the contralateral only-hearing ear. The role of the cochlear implant is two-fold. The first role is to guard against the possibility that the tumor leads to significant hearing loss in the only hearing side, leaving the patient with bilateral deafness for an extended period of time. The second role is to enhance the patient’s current hearing ability; while usable hearing is present in the ear with the tumor.
In considering the importance of cochlear implantation for the former, prophylactic role, one must determine how likely such a patient is to lose the hearing on the only hearing side. Overall, it has been reported that about 40-60% of tumors that are observed will lose serviceable hearing over 5 years [14-21]. In one large metaanalysis of 982 patients with sporadic vestibular schwannomas who underwent observation (tumors < 2.5 cm in size) over a period of 2 to 5 years, Sughrue et al. [22] reported that initial tumor size did not affect likelihood of hearing loss. In contrast, the rate of tumor growth was a significant predictor of hearing loss, with tumors that grew faster than 2.5 mm per year having significantly higher rates of hearing loss than those that grew more slowly, though even 25% of tumors in the little to no growth category (<2.5 mm per year) lost hearing preservation [16]. The findings above suggest that patients undergoing observation for vestibular schwannoma have a significant risk of hearing loss. If this hearing loss is slow and gradual, the patient may have time to adapt with increasingly more powerful hearing aids over this time period, and perhaps ultimately, a cochlear implant. However, if the hearing loss is sudden, as occurs in 10% of patients with vestibular schwannomas [20], such a patient may be forced to endure an extended period of time (months) with no hearing at all, until a cochlear implant can be placed and activated. This would adversely affect the patient’s ability to work and function on a daily basis, leading to significant short-term handicap. Furthermore, since post-lingually deafened adults continue to experience improvement in hearing outcomes with a cochlear implant over the first 1-2 years, it would likely be even longer before the patient would be optimally functioning from a hearing standpoint if suddenly rendered profoundly deaf. Thus, it appears prudent to implant patients undergoing observation of vestibular schwannomas in an only hearing ear sooner rather than later.
An alternative approach to a patient with a tumor in an only hearing ear is to consider active intervention for the tumor, such as with microsurgery or stereotactic radiotherapy, in an attempt to save the hearing in that ear while treating the tumor. Rates of hearing preservation for smaller tumors following microsurgery and stereotactic radiotherapy are variable, most often being reported to be from 40% to 70% [17-19]. However, we would argue that even with the most favorable statistics, the patient still has a significant chance of losing hearing in the only hearing ear, such that it would be prudent to perform cochlear implantation on the contralateral deaf side before treatment of tumor. We did not choose this alternative approach in our patient as we did not want to risk an active intervention leading directly to deafness in the patient’s only hearing ear, especially with no evidence of tumor growth.
The alternatives of using a CROS hearing aid or a BAHA for hearing rehabilitation were also explored with the patient. From a decision-making standpoint, we counseled the patient that a cochlear implant would be a better treatment for his single-sided deafness than either of these other devices. Both the CROS and BAHA devices rely on relatively normal sensori-neural hearing in the contralateral ear. In the case of our patient, if the tumor in the normal hearing ear was to grow, this could lead to a significant sensori-neural hearing loss and render both the CROS and BAHA devices useless. In contrast, a cochlear implant would maintain its utility regardless of what happened to the normal hearing ear, as it would continue to provide useful electric hearing to the other side.
In addition to the prophylactic benefits of cochlear implantation, our subject has also enjoyed the auditory advantages of having a cochlear implant in one ear combined with normal hearing in the opposite ear. The addition of a cochlear implant resulted in improvements in sound localization, as well as subjective improvements with speech perception in challenging listening situations, spatial hearing, and the quality of hearing. Benefits for speech perception in noise as tested in a sound field were unclear, as the subject showed learning effects, which confounded interpretation of the data. Additionally, there was no evidence that the cochlear implant interfered significantly with hearing on the normal side. The patient has remarked that over several months, the integration of the acoustic and electric hearing has become better and better, and that he consistently uses his cochlear implant on a daily basis.
The improvements in hearing from a cochlear implant used to treat single-sided deafness that we observed are consistent with that described in the literature. Others have demonstrated that a cochlear implant in the context of single-sided deafness leads to improved sound localization ability [6-8] and improved ratings on the SSQ questionnaire [21] compared to with a single normal hearing ear alone. Improvements in speech perception in noise with the addition of a cochlear implant to a contralateral normal hearing ear have been mixed, depending on the individual subject and spatial configuration of the target speech relative to the noise. Some have shown significant improvements [6,8,21] and others have shown little difference [7,22]. All of the studies have suggested that the cochlear implant does not interfere with overall hearing performance compared to the normal hearing ear alone.
One additional important consideration in cochlear implantation of a patient with a vestibular schwannoma is the issue of MRI compatibility of the cochlear implant. A patient with an intracanalicular tumor in the only hearing ear will need routine surveillance MRIs into the indefinite future to assess for tumor growth. A number of studies have suggested that a 1.5 Tesla MRI scan can be performed with the internal magnet left in place if a reinforcing bandage is placed over the implant, though rare complications of significant patient discomfort, magnet displacement, and reversal of magnet polarity have been described [23-26]. However, currently the Food and Drug Administration has approved such MRI scans only if the internal magnet is removed, which requires minor surgical procedures to remove and then later replace the magnet. Given that our patient will need multiple MRI scans for tumor surveillance, the decision was made to perform cochlear implantation with the magnet left out of the device. Instead of a magnet, our recipient uses an adhesive to hold the external component of the implant in place, facilitated by keeping the hair in this area extremely short.
To our knowledge, cochlear implantation has not been explicitly described in the literature as a management option for single-sided deafness in patients with a vestibular schwannoma in the contralateral only-hearing ear. Interestingly, a close reading of the study by Firszt et al. [10] did find that one of the three subjects in that study was implanted under the same circumstances as our patient, with a tumor in an only hearing ear. However, the reasoning behind the decisionmaking process for cochlear implantation was not described. We believe that cochlear implantation in the unusual circumstances described in this study is an excellent option both to guard against a period of prolonged hearing disability should the patient suddenly lose hearing in the good (tumor) ear and to provide rehabilitation of single-sided deafness for improved sound localization and speech understanding in challenging listening environment.

Acknowledgments

We would like to Sandra Porps for help with data collection, Marianne Lahey and Jennifer Monitz for help in study coordination and George Cire for technical advice. The authors would also like to thank Rich Tyler, PhD from the University of Iowa for permitting the use of the localization software used for this study. This study was sponsored by Cochlear Americas (Centennial, CO).

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