Binaural hearing aid intervention for a patient with nonserviceable hearing loss after surgery for vestibular schwannoma: A case report

Abstract

A vestibular schwannoma is a benign tumor; however, the schwannoma itself and interventions can cause sensorineural hearing loss. Most vestibular schwannomas are unilateral tumors that affect hearing only on one side. Attention has focused on improving the quality of life for patients with unilateral hearing loss and therapeutic interventions to address this issue have been emphasized. Herein, we encountered a patient who was a candidate for hearing preservation surgery based on preoperative findings and had nonserviceable hearing after the surgery, according to the Gardner–Robertson classification. Postoperatively, the patient had decreased listening comprehension and ability to localize sound sources. He was fitted with bilateral hearing aids, and his ability to localize sound sources improved. Although the patient had postoperative nonserviceable hearing on the affected side and age-related hearing loss on the unaffected side, hearing aids in both ears were useful for his daily life. Therefore, the patient was able to maintain a binaural hearing effect and the ability to localize the sound source improved. This report emphasizes the importance of hearing preservation with vestibular schwannomas, and the demand for hearing loss rehabilitation as a postoperative complication can increase, even if hearing loss is nonserviceable.

Introduction

Vestibular schwannomas are clinically benign schwannomas that arise from the vestibulocochlear nerve and cause sensorineural hearing loss. ¹ This type of tumor is clinically and oncologically regarded as benign as does not metastasize or invade the surrounding tissues. Despite being benign, vestibular schwannomas cause symptoms such as hearing impairment, dizziness, vertigo attack, tinnitus, peripheral facial palsy, and headache. Furthermore, as the tumor grows, it can compress the brainstem, which can be life-threatening. ² Since most of these tumors are unilateral, except for neurofibromatosis, they cause unilateral hearing loss. Sensorineural hearing loss caused by vestibular schwannomas is not always severe or permanent. Approximately 10% to 30% of patients diagnosed with a vestibular schwannoma will develop sudden sensorineural hearing loss,^3–5 and 3% of patients diagnosed with sudden sensorineural hearing loss will be diagnosed with vestibular schwannoma. ⁶ Magnetic resonance imaging (MRI) or brainstem audiometry are useful for diagnosing a vestibular schwannoma from other differential diagnoses, such as sudden sensorineural hearing loss and Ménière's disease.

There are several management methods for vestibular schwannomas and treatment methods should be carefully selected. This is because both the tumor as well as the intervention can cause serious complications, including dizziness, hearing loss, and, in the worst situation, mortality. A “wait-and-scan” policy, in which patient tumors are observed once or twice using MRI annually, is well applied for nongrowing tumors. Interventions should be considered for tumor growth and worsening clinical symptoms, which can sometimes severely affect patient quality of life.^7,8

Treatment options for growing vestibular schwannomas include radiation therapy and surgery. The possibility of preserving hearing is important when determining how to approach the tumor. To some extent, the degree of preoperative hearing loss can predict whether hearing preservation is possible. The Gardner–Robertson classification is often used as an indicator, and serviceable hearing is defined as hearing loss of 50 dB or less and best speech intelligibility of 50% or better using pure-tone and speech audiometry. ⁹ If these conditions are worse, hearing is defined as “nonserviceable hearing.” If hearing is determined as nonserviceable before surgery, the patient is generally not eligible for hearing preservation surgery. ¹⁰

Postoperative hearing loss can be considered a candidate for interventions such as hearing aids. However, there are few reports on interventions for postoperative hearing loss ¹¹ ; therefore, the effectiveness of interventions such as hearing aids, especially for patients with nonserviceable hearing after the vestibular schwannoma surgery, remains unclear. Herein, we report a patient with nonserviceable hearing after hearing preservation surgery. The patients’ ability to localize sound sources improved with the use of bilateral hearing aids.

Case report

A 73-year-old man had complaints of right-sided hearing loss, tinnitus, and dizziness. Facial palsy and headache were not observed. MRI showed a cerebellopontine angle tumor, and the patient was referred to our department. Brain MRI performed at our hospital revealed a tumor with a major axis of 18 mm, suggesting a vestibular schwannoma (Figure 1). The tumor compressed the brainstem, and surgical intervention was recommended.

Figure 1.

Preoperative and postoperative magnetic resonance imaging findings, pure-tone and speech audiometry, and auditory brainstem response. Preoperative magnetic resonance imaging (MRI) shows an approximate 18 mm vestibular schwannoma located in the right inner ear canal and cistern with an enlarged inner ear canal. The tumor has slightly compressed the brainstem (A: fast spoiled gradient echo (FSPGR), B: fast imaging employing steady-state acquisition (FIESTA)). Postoperative contrast-enhanced MRI was performed 3 days after surgery. This indicated that the tumor had been completely removed. Both images are coronal sections (C: FSPGR, D: gadolinium contrast-enhanced FSPGR). Preoperative hearing was 50 dB HL on the right and 40 dB HL on the left; postoperative hearing was 68.8 dB HL on the right and 36.3 dB HL on the left, with a decrease in hearing mainly in the high frequencies (E: 1 month before surgery, F: 1 month after surgery, R-operated ear, Scale-out: no response at the equipment's maximum output limitations). High-frequency hearing loss was present on the left side, indicating age-related hearing loss. The best preoperative percentages of speech audiograms were 75% (90 dB) on the right and 90% (80 dB) on the left. Postoperative percentages were 30% (80 dB) lower on the right and 95% (80 dB) lower on the left. (H: 2 weeks before surgery, I: 2 years after surgery, R-operated ear). Hearing level on the right side has been maintained during 5 years postoperatively (J: 5 years after surgery).

The preoperative pure tone hearing test demonstrated 50 dB HL (50 dB HL in 500 Hz, 45 dB HL in 1000 Hz, 50 dB HL in 2000 Hz, and 55 dB HL in 3000 Hz) on the right, in contrast 40 dB HL (35 dB HL in 500 Hz, 40 dB HL in 1000 Hz, 35 dB HL in 2000 Hz, and 50 dB HL in 3000 Hz) on the left (Figure 1). The best word recognition score was significantly reduced to 75% (90 dB) on the right, in contrast to 90% (80 dB) on the left (Figure 1). Distortion product otoacoustic emissions, measured for predicting possibilities for hearing preservation after surgery, ¹² showed no reaction on both sides. A small wave V was observed in the auditory brainstem response (ABR) evoked with 90 dB sound stimulation, whereas no obvious wave V was detected with less than 80 dB. Wave V latencies were 6.18 and 4.47 ms on the right and left sides, respectively. Therefore, we performed tumor removal surgery using a retrolabyrinthine approach to preserve hearing.

Tumor resection with the retrolabyrinthine approach was performed as previously reported. ¹³ In brief, nerve monitoring by dorsal cochlear nucleus action potentials (DNAP) and facial nerve root-elicited muscle action potentials (FREMAP) was performed during surgery. ¹² FREMAP was maintained above 80% for orbicularis oculi and oris, with no final decline. DNAP temporarily decreased to 20% during tumor removal; however, the operation was suspended for a while, and there was a tendency to recover. The final DNAP amplitude was 45% of the initial amplitude. The surgery was completed with no evident complications, and the resected tumor was diagnosed as a vestibular schwannoma by pathohistological examination. MRI was performed on the second postoperative day, and no residual tumor was evident, suggesting complete tumor removal (Figure 1).

One month postoperatively, a pure tone audiogram revealed worsening for right sensorineural hearing loss with 68.8 dB HL on the right side, and approximately the same hearing level was observed on the left side (36.3 dB HL) (Figure 1F). The best word recognition score also worsened to 20% (80 dB) on the right side (Figure 1I). Six months after surgery, the patient started wearing bilateral air conduction hearing aids. After wearing the hearing aids, the best speech intelligibility improved to 40% (90 dB) on the right and 100% (70 dB) on the left (Figure 2 A–C). In addition, using bilateral hearing aids improved his sense of directionality compared to without hearing aids in either ear (Figure 2 D–F). We performed a sound source localization test using multiple speakers ¹⁴ to evaluate sound source localization ability. When the hearing aid was worn only on the unaffected (left) side, his sense of direction was worse than when he did not wear the hearing aids, and he misidentified the source of the sound to the left. Directional perception markedly improved by wearing hearing aids bilaterally; wearing hearing aids on the surgical side significantly benefited the patient. Therefore, the patient continued to use hearing aids daily in both ears.

Figure 2.

Speech audiogram and sound source localization test. Hearing rehabilitation began with hearing aids 1 year after surgery. The left side had age-related hearing loss and the patient was fitted with a bilateral hearing aids. The best speech intelligibility on the right was 30% (80 dB), which improved slightly to 40% (90 dB) after wearing the hearing aids. The left was 90% (80 dB) and improved to 100% (70 dB) after wearing the hearing aids. (A: right ear, B: left ear, and C: binaural ear). A sound source localization test was conducted 1 year after wearing the hearing aids. Without hearing aids, the frontal sound source was difficult to discern and was biased toward either the left or right. With the hearing aid on the left, sounds from all directions were perceived as coming from the left. The ability to localize sound sources improved significantly when hearing aids were worn in both ears (D: before fitting hearing aids, E: fitting hearing aids to the left ear, and F: fitting hearing aids to the binaural ear).

Currently 5 years have passed since the surgery. MRI has revealed no tumor regrowth, and the hearing level on the right side has been maintained (Figure 1 J).

Ethics approval to report this case was obtained from the Ethics Committee of Keio University School of Medicine (approval number [20200033]). Written informed consent was obtained from the patients for the publication of anonymized information in this study.

Discussion

Herein, we presented the case of a patient with vestibular schwannoma who underwent hearing preservation surgery. Although the patient had lost some extent of hearing and had “nonserviceable hearing” after surgery according to the Robertson–Gardner classification, wearing bilateral hearing aids, including on the postoperative deteriorated side, significantly improved his hearing quality. This case suggests the usefulness of hearing aid intervention for patients with a vestibular schwannoma, even if postoperative hearing is determined nonserviceable.

Considering sound localization ability, it is difficult to evaluate the possibility of preserving the sound source localization ability before surgery. In patients with posterior labyrinthine damage, the ability to localize sound sources and speech intelligibility is reduced compared with hearing ability. Therefore, hearing preservation does not necessarily indicate that the ability to localize sound sources is preserved, especially in cases of vestibular schwannomas. There are two main types of orientation testing: sound source localization testing using multiple speakers and sound image localization testing using headphones. We used a sound source localization test with multiple speakers for evaluation. ¹⁴ Since this test is performed under sound-field conditions, it can evaluate the ability to localize sound sources before and after wearing a hearing aid. In addition, it may be useful to evaluate and compare an index of sound source localization ability before and after vestibular schwannoma surgery, hearing aids, and other therapeutic interventions. Examinations of more cases are needed to determine which assessments are useful for predicting the preservation of the ability to localize the sound source, especially in cases of vestibular schwannoma.

Vestibular schwannomas are typically unilateral. As aforementioned, disease progression can result in hearing loss and also occur as a treatment complication. Unilateral hearing loss is considered an obstacle in daily life. However, preservation of hearing is not a priority in the treatment of vestibular schwannomas; surgical approaches that do not aim for hearing preservation, such as the translabyrinthine approach, have often been employed for tumor resection in cases with residual hearing, especially those with nonserviceable hearing according to Gardner–Robertson classification.

In recent years, therapeutic interventions for unilateral hearing loss have become increasingly important. The advantages of binaural hearing include binaural summation, sound source localization, and binaural unmasking (improvement of hearing in noise) are well known. ¹¹ A loss of these functions reduces hearing under directional and noisy conditions, resulting in a reduced quality of life. Hearing preservation surgery for vestibular schwannomas and auditory rehabilitation for postoperative hearing loss is increasingly important.

Tumor size and localization should be considered when determining indications for surgery. In addition, preoperative hearing is important for determining indications of hearing preservation surgery; it predicts whether hearing preservation is possible. As previously mentioned, the Gardner–Robertson classification is generally used. In this classification, grade I [good: pure tone average (PTA) ≤ 30 dB with speech discrimination score (SDS) ≤ 70%] and grade II (serviceable: PTA of 30–50 dB with SDS ≤ 50%) are considered “useful hearing.” ⁹ Relatively good hearing preservation is possible if the tumor size is up to approximately 2 cm and preoperative hearing is grade I or II. ¹⁰ Therefore, in this case, hearing preservation surgery was performed. Unfortunately, the patient's postoperative hearing was classified as nonserviceable.

As mentioned previously, more emphasis has been placed on postoperative auditory rehabilitation. ¹¹ Interventions for unilateral hearing loss include using devices such as the Bone-Anchored hearing aid (BAHA®) and contralateral routing of signal hearing aids for severe cases of hearing loss when hearing aids are ineffective. However, these are designed to be heard by the better-hearing ear, and binaural hearing effects, such as a sense of direction, cannot be expected. In this case, the patient had postoperative residual hearing, which made it possible to wear a hearing aid even though hearing was classified as nonserviceable. This improved the patient's sense of direction owing to the binaural hearing effect. Word intelligibility also improved, albeit only slightly. Therefore, we believe that the most reliable way to maintain binaural hearing effectiveness is to preserve hearing to the extent that hearing aid use can be expected to improve hearing.

Notably, a successful rate of hearing preservation surgery for vestibular schwannomas is 50%–80%, ¹³ which means patients can have “nonserviceable hearing” levels after hearing preservation surgery. This case suggests that even if hearing loss is nonserviceable, it can be effectively managed through interventions such as hearing aids. This might imply that even if preoperative hearing loss is worse than grade Ⅲ, hearing preservation surgery might be a choice for maintaining a chance of postoperative hearing support with hearing aids. Previously, in our department, ABR/OAE was performed to determine the indications for hearing preservation surgery. ¹² We also reported a better hearing preservation rate than previously reported by continuous monitoring using ABR/DNAP, even in cases where hearing preservation is expected to be difficult. In the future, it is expected that the application of hearing preservation surgery will expand to include the maintenance of sound source localization ability.

This study has the limitation of including only one case. Therefore, further studies, such as larger case studies, are needed to determine the usefulness of binaural hearing aid interventions to improve a patient's ability to localize sound sources for postoperative hearing loss resulting from vestibular schwannoma surgery.

Conclusion

We encountered a case in which a patient with a vestibular schwannoma underwent hearing preservation surgery and had nonserviceable hearing according to the Gardner–Robertson classification. The bilateral hearing aid intervention improved the patient's ability to localize sound sources. This finding suggests that postoperative auditory rehabilitation and hearing conservation surgery may be beneficial for patients with nonserviceable hearing.