INTRODUCTION — Vestibular schwannomas (also known as acoustic neuromas, acoustic schwannomas, acoustic neurinomas, or vestibular neurilemomas) are Schwann cell-derived tumors that commonly arise from the vestibular portion of the eighth cranial nerve (figure 1).
Vestibular schwannomas account for approximately 8 percent of intracranial tumors in adults and 80 to 90 percent of tumors of the cerebellopontine angle (CPA). In comparison, they are rare in children, except for patients with neurofibromatosis type 2 (NF2). (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)".)
The epidemiology, pathogenesis, clinical presentation, diagnosis, and management of patients with vestibular schwannomas will be reviewed here.
EPIDEMIOLOGY — The overall incidence of vestibular schwannomas is approximately 1 per 100,000 person-years in the United States [1]. The incidence is higher in Taiwan (2.66 per 100,000 person-years) and Asian Pacific Islanders (1.37 per 100,000 person-years) and lower in Hispanics (0.69 per 100,000 person-years) and African Americans (0.36 per 100,000 person-years) [1,2].
The incidence appears to be increasing, due at least in part to the incidental diagnosis of asymptomatic lesions with the widespread use of magnetic resonance imaging (MRI) and computed tomography (CT) [3,4]. A retrospective analysis of 46,000 MRI scans done for other reasons identified eight unsuspected vestibular schwannomas (0.02 percent) [3], and autopsy studies suggest that the prevalence may be even higher [5,6].
The median age at diagnosis is approximately 50 years [4]. The tumors are unilateral in more than 90 percent of cases [7], affecting the right and left sides with equal frequency. They occur equally in both genders [1]. Bilateral vestibular schwannomas are primarily observed in patients with neurofibromatosis type 2 (NF2) [6]. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)", section on 'Vestibular schwannomas'.)
PATHOGENESIS AND RISK FACTORS — Bilateral vestibular schwannomas are one of the characteristic clinical features of neurofibromatosis type 2 (NF2). Studies in NF2 patients led to the identification of the neurofibromin 2 gene, which is located on chromosome 22. The NF2 gene produces merlin, also known as schwannomin, a cell membrane-related protein that acts as a tumor suppressor. Biallelic inactivation of the NF2 gene is found in most sporadic vestibular schwannomas [8]. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)" and "Risk factors for brain tumors", section on 'Neurofibromatosis type 2'.)
In addition to NF2, other risk factors that have been associated with the development of vestibular schwannomas in epidemiologic studies include the following:
●Childhood exposure to low-dose radiation for benign conditions of the head and neck has been associated with an increased risk of vestibular schwannoma [9,10]. In a series of 2311 children irradiated between 1939 and 1962, 41 vestibular schwannomas were identified with a latent period of 20 to 55 years [10]. The increase in risk was proportional to the dose of radiation to the cerebellopontine angle (CPA; relative risk per Gy 1.14). (See "Risk factors for brain tumors", section on 'Ionizing radiation'.)
●Some but not all studies have shown an increased incidence of various brain tumors, including vestibular schwannomas, associated with the use of cellular telephones. Meta-analyses of case-control studies have found a possible slight increase in risk of brain tumors associated with cell phone use in higher-quality studies, with an induction period of 10 years or longer [11,12]. Subsequent studies have cast doubt on this association, however, as the incidence of cell phone use has markedly increased without a complementary increase in vestibular schwannoma incidence [13,14].
●There are conflicting data on noise exposure as a risk factor for vestibular schwannomas [7,15-18], despite experimental studies supporting biological plausibility [19,20]. Most studies finding a positive association have relied on self-reported measures of noise exposure [7,16,17], making it difficult to exclude recall bias as an alternative explanation for the findings. In two population-based case-control studies that used a job exposure matrix to assign noise exposure levels, occupational noise exposure was not associated with an increased risk of vestibular schwannoma [1,21]. Other studies, however, have found a positive association between vestibular schwannoma and self-reported exposure to loud noise in leisure activities without hearing protection (odds ratio [OR] 1.5) [1,22].
HISTOPATHOLOGY — Vestibular schwannomas arise from perineural elements of the Schwann cell and are similar pathologically to peripheral schwannomas found in other parts of the body. They occur with equal frequency on the superior and inferior branches of the vestibular nerve (figure 1); only rarely are they derived from the cochlear portion of the VIII nerve.
Microscopically, zones of alternately dense and sparse cellularity, called Antoni A and B areas, respectively, are characteristic of vestibular schwannomas (picture 1). Malignant degeneration is extremely rare, with only six cases having been reported. Immunohistochemical staining for S100 protein is usually positive in both the benign and the rare malignant forms of this tumor [23].
CLINICAL PRESENTATION — Symptoms associated with vestibular schwannoma can be due to cranial nerve involvement, cerebellar compression, or tumor progression.
The clinical presentations of these tumors are illustrated by a series of 1000 vestibular schwannomas treated at a single institution [24]. Clinical manifestations in this series included the following:
●Cochlear nerve – Symptomatic cochlear nerve involvement occurred in 95 percent of patients [24]. The two major symptoms were hearing loss and tinnitus. Hearing loss was present in 95 percent, but only two-thirds of these patients were aware of this limitation. The hearing loss was usually chronic, with an average duration of approximately four years. Occasionally, vestibular schwannomas can present with sudden sensorineural hearing loss. (See "Sudden sensorineural hearing loss in adults: Evaluation and management".)
Tinnitus was present in 63 percent, with an average duration of three years [24]. The incidence of tinnitus was higher in hearing than in deaf patients but was also present in 46 percent of deaf patients.
●Vestibular nerve – Involvement of the vestibular nerve occurred in 61 percent of patients [24]. Affected patients frequently acknowledged having unsteadiness while walking, which was typically mild to moderate in nature and frequently fluctuated in severity. True spinning vertigo was uncommon because these slow-growing tumors cause gradual rather than acute asymmetries in vestibular function. In this setting, the central vestibular system can often compensate for the gradual loss of input from one side.
The most nondescript vertiginous sensations, such as brief tilting or veering, can suggest the presence of a vestibular schwannoma. The decision whether to obtain a magnetic resonance image (MRI) for a patient with these symptoms depends upon clinical judgment, with no good data in the literature about the likelihood that someone with such symptoms harbors a schwannoma. (See "Causes of vertigo".)
●Trigeminal nerve – Trigeminal nerve disturbances occurred in 17 percent of patients [24]. The most common symptoms were facial numbness (paresthesia), hypesthesia, and pain. The average duration of symptoms was 1.3 years; the symptoms usually occurred after hearing loss had been present for more than two years and vestibular symptoms for more than one year. (See "Trigeminal neuralgia".)
●Facial nerve – The facial nerve was involved in 6 percent of patients [24]. The primary symptoms were facial paresis and, less often, taste disturbances (due to nervus intermedius impairment). Xerophthalmia, paroxysmal lacrimation, and xerostomia can also be seen [25].
●Tumor progression – Other presenting signs can be the result of tumor progression, leading to pressure on adjacent posterior fossa structures. Very large tumors can press on the cerebellum or brainstem and result in ataxia. Brainstem compression, cerebellar tonsil herniation, hydrocephalus, and death can occur in untreated cases. The functions of the lower cranial nerves can also become impaired, leading to dysarthria, dysphagia, aspiration, and hoarseness.
DIAGNOSIS — The diagnosis of vestibular schwannoma is generally suggested by the presence of asymmetric sensorineural hearing loss (which should be confirmed by audiometry) or other cranial nerve deficits. Such symptoms may lead to imaging with magnetic resonance imaging (MRI) or computed tomography (CT). Vestibular schwannomas account for 80 to 90 percent of posterior fossa lesions that are identified in this way.
The differential diagnosis includes meningioma, which accounts for 4 to 10 percent of cases. Other less common causes of such lesions include facial nerve schwannomas, gliomas, cholesterol cysts, cholesteatomas, hemangiomas, aneurysms, arachnoid cysts, lipomas, and metastatic tumor.
Physical examination — Hearing tests are typically abnormal due to involvement of the acoustic nerve. The Weber and Rinne tests may be useful in suggesting asymmetric sensorineural hearing impairment. (See "Evaluation of hearing loss in adults", section on 'Examination'.)
Further neurologic examination may reveal other cranial nerve deficits. A decreased or absent ipsilateral corneal reflex and facial twitching or hypesthesia may occur as cranial nerves V and VII become affected. Other cranial nerve deficits are uncommon unless the tumor is large. Romberg, Hall-Pike, and other common office balance tests are typically normal.
Audiometry — Audiometry is the best initial screening laboratory test for the diagnosis of vestibular schwannoma, since only 5 percent of patients will have a normal test. Pure tone and speech audiometry should be performed in an acoustically shielded area. Test results typically show an asymmetric sensorineural hearing loss, usually more prominent in the higher frequencies. Hearing loss does not necessarily correlate with tumor size. The speech discrimination score is usually markedly reduced in the affected ear and out of proportion to the measured hearing loss. (See "Evaluation of hearing loss in adults", section on 'Formal audiologic assessment'.)
Many other auditory tests have been used historically to try to diagnose vestibular schwannomas. These include acoustic reflex testing, impedance audiometry, and Bekesy audiometry. They have limited accuracy and diagnostic value, and their utility has diminished with the advent of brainstem-evoked response audiometry (AER/ABR).
Brainstem-evoked response audiometry can be used as a further screening measure in patients with unexplained asymmetries in standard audiometric testing. Test results show a delay in nerve conduction time on the affected side, reflecting the probable presence of a tumor. Prior to MRI, ABR was the most accurate screening modality. In centers experienced with its use, the test shows abnormalities in 90 to 95 percent of patients with tumors less than 1 cm. However, the false-negative rate can be as high as 30 percent with small vestibular schwannomas, and there is a 10 percent false-positive rate [26]. It is still a useful test when financial resources are limited and when conservative management is the expected course of a positive screen [27].
Vestibular testing — Vestibular testing has limited utility as a screening test for the diagnosis of vestibular schwannoma because of the accuracy of evoked response audiometry. When testing is performed, a decreased or absent caloric response on the affected side may be seen. When the tumor is small, though, a normal response is often seen.
Imaging — The procedure of choice is MRI, which can detect tumors as small as 1 to 2 mm in diameter (image 1) [28]. When brainstem testing is abnormal or the suspicion for a vestibular schwannoma is high for another reason, MRI scanning with gadolinium contrast should be performed, including millimeter sections through the internal auditory meatus. If a patient cannot tolerate MRI, high-resolution CT scanning with and without contrast is an alternative.
Vestibular schwannomas are seen on MRI and CT scans as enhancing lesions in the region of the internal auditory canal with variable extension into the cerebellopontine angle (CPA). CT scans with bone windows can also be of prognostic significance as the extent of widening of the internal auditory canal (IAC) and the extent of tumor growth anterior and caudal to the IAC are predictive of postoperative hearing loss [29].
Fast spin echo MRI may be useful as a screening test due to its low cost compared with gadolinium MRI, noninvasiveness, and high sensitivity and specificity. In one study of 25 patients and 50 ears, there were 11 true positives and 39 true negatives on gadolinium MRI. There were no false positives or false negatives with fast spin echo MRI [30]. This test is useful when performed specifically for evaluation for a vestibular schwannoma, not as a general screen.
TREATMENT — The three major treatment options for patients with a vestibular schwannoma are surgery, radiation therapy, and observation. Management decisions take into account the size of the tumor, signs and symptoms, patient age and comorbidities, and patient preferences [31]. Where available, patients may benefit from multidisciplinary specialty review with input from neurosurgery, otolaryngology, and radiation oncology.
Surgery — Surgery generally results in satisfactory long-term control of vestibular schwannomas; however, one group has reported a 10-year recurrence rate of approximately 20 percent for both completely and partially resected schwannomas [32].
Surgical techniques — There are three standard operative approaches. Selection of a particular approach is determined by a number of factors, including the size of the tumor and whether or not preservation of hearing is a consideration.
●Retromastoid suboccipital (retrosigmoid) – The suboccipital approach can be used for any size tumor with or without attempted hearing preservation.
●Translabyrinthine – The translabyrinthine approach has been recommended for acoustic tumors larger than 3 cm and for smaller tumors when hearing preservation is not an issue [33].
●Middle fossa – The middle fossa approach is suitable for small (<1.5 cm) tumors when hearing preservation is a goal.
In many institutions, a team consisting of a neurosurgeon and an otologist perform the procedure. The experience of both the surgeon and the hospital are important in optimizing the surgical outcome and minimizing the risk of complications [34].
Outcomes — Complete tumor removal is feasible in almost all patients and there are few if any recurrences when tumor removal is complete [35-38]. However, the outcome is less favorable in patients who undergo subtotal removal in an attempt to preserve anatomic continuity of the facial or acoustic nerves. Regrowth and/or recurrence, which is usually asymptomatic, occurs in up to 15 to 20 percent of cases when initial resection is incomplete [39,40].
The likelihood of surgical morbidity, which includes hearing loss, facial weakness, and vestibular disturbances, depends upon tumor size. Facial nerve function can be preserved in most patients even with large tumors [38,41,42], and serviceable hearing can be preserved in many patients. However, only rarely does hearing improve after vestibular schwannoma surgery. Intraoperative facial nerve and auditory monitoring have alerted surgeons to potential injury, thereby improving the final outcome [41].
The outcomes that are achievable with an experienced team can be illustrated by the following observations:
●In one series of 179 patients, 97 to 99 percent of patients had complete tumor removal without evidence of recurrence at a mean follow-up duration of 70 months [35]. Normal or near normal facial movement was present in 94 to 97 percent of patients with small tumors and 28 to 57 percent with large tumors; in addition, 45 to 82 percent of patients with good hearing and small tumors retained their hearing. Treatment complications consisted mainly of cerebrospinal fluid leakage, which occurred in 15 percent of patients; there were two deaths (1 percent).
●Similar results were noted in another report of 1000 tumors treated at a single institution [36]. Ninety-eight percent of tumors were completely removed; in the other 21 patients, deliberate partial removal was performed in severely ill patients for decompression of the brainstem or in an attempt to preserve hearing in the last hearing ear. Anatomic preservation of the facial nerve and the cochlear nerve was achieved in 93 and 68 percent, respectively. Major neurologic complications included tetraparesis in one patient, hemiparesis in 1 percent, lower cranial nerve palsies in 5.5 percent, and cerebrospinal fluid fistulas in 9.2 percent. There were 11 deaths (1.1 percent) occurring at 2 to 69 days postoperatively.
Persistent headaches are another significant complication following surgery [43,44]. In a quality-of-life analysis of 1657 patients treated surgically, 46 percent reported headaches occurring more than once a day, and these were often severe enough to cause disability [43]. The headaches eventually resolved in approximately one-half. Postoperative headaches were more commonly associated with the retrosigmoid surgical approach, and tended to be more frequent and severe in women.
Other complications — A number of complications in addition to damage to cranial nerves VII and VIII are associated with microsurgery. These were analyzed in a literature review that included over 32,000 patients who underwent surgical resection of a vestibular schwannoma [45]:
●The overall mortality rate was 0.2 percent.
●Cerebrospinal fluid leaks were observed in 8.5 percent, of which one-third resolved with conservative treatment. This complication was significantly more frequent in patients who underwent a translabyrinthine approach, although at least one report has suggested that technical modifications can decrease this complication with this approach [37]. The frequency of cerebrospinal fluid leaks was not related to tumor size.
●Non-audiofacial neurologic complications were seen in 9 percent of cases.
●Vascular complications, primarily hemorrhage, were observed in 1 percent of cases.
●Infections were reported in 4 percent of cases, most of which were meningitis.
Compared with younger adults, older adults undergoing surgery for vestibular schwannoma may be at substantially higher risk for in-hospital complications [46,47]. In a retrospective study using the National Inpatient Sample database in the United States for vestibular schwannoma surgeries from the years 2002 to 2010 (n = 4147), adults ≥65 years of age were at increased risk for medical complications such as acute cardiac events, renal failure, and infection (adjusted odds ratio [OR] 1.8) as well as in-hospital mortality (OR 13) [46].
Radiation therapy — Radiation therapy approaches that have been used in patients with vestibular schwannoma include stereotactic radiosurgery (SRS), stereotactic radiotherapy (SRT), and proton beam therapy, as well as conventional fractionated radiation therapy.
There are no randomized trials comparing different radiation therapy approaches, and data are only available from observational studies [48]. A critical review of the literature concluded that equivalent local control can be achieved with each of these approaches and that treatment decisions could be based upon the availability of expertise and technology, as well as patient-specific factors [49].
Stereotactic radiosurgery — SRS is a technique that utilizes multiple convergent beams to deliver a high single dose of radiation to a radiographically discrete treatment volume, thereby minimizing injury to adjacent structures. This can be accomplished with either the gamma knife or a linear accelerator. Radiosurgery is a viable treatment option for selected patients with smaller tumors (<3 cm) or for enlarging tumors in patients who are not candidates for surgery. (See "Stereotactic cranial radiosurgery".)
Early single-center experience indicated that marginal treatment doses of up to 22 Gy yielded excellent local control rates (>95 percent) with up to 10 years of follow-up; however, cranial nerve toxicities, including hearing preservation rates as low as 40 percent at two years and trigeminal or facial nerve palsies in up to one-third of patients, indicated a need for dose reduction [50-53].
Subsequent single-center studies using a marginal dose of 12 to 13 Gy to treat tumors up to 3 cm in diameter have reported local control rates of 91 to 100 percent at 10 years and trigeminal or facial nerve complication rates below 5 percent [49]. Although hearing preservation rates of 60 to 70 percent were initially described [54], longer-term follow-up studies indicate that rates of functional hearing preservation decline to approximately 25 to 50 percent at 10 years, even with contemporary treatment doses of 12 to 13 Gy [55-58].
Risk factors for worse hearing outcomes include older age, larger tumor volume, and greater degree of baseline hearing loss [57,59,60]. The impact of cochlear radiation dose alone as a predictive parameter for hearing outcomes remains controversial. While several retrospective studies have reported improved hearing preservation with maximum cochlear dose <4 Gy [61], or central cochlear dose <4.2 Gy [62], others have not found cochlear dose to be a significant factor on multivariate analysis [63].
Other potential complications include:
●Cystic degeneration – Delayed cyst formation has been reported in 2 percent of patients, occurring at a median of six years after SRS and requiring craniotomy for symptomatic management in a small minority [56].
●Postradiation tumor expansion – An increase in tumor diameter of >2 mm (with median tumor volume increase of 75 percent) has been reported in 14 percent of patients at a median of nine months following radiosurgery, of which one-third remain enlarged with no sequential growth [64]. A decrease in central enhancement was observed in 93 percent of patients. Postradiation expansion may be more likely in tumors with greater preradiation growth rates [65].
●Malignant transformation – Malignant transformation has been described in case reports [66-68]. Two separate large, single-center retrospective series have estimated a malignant transformation rate of 0.3 percent after SRS [56,69].
●Local tissue scarring – There is a concern that scarring following SRS may complicate subsequent microsurgery should the tumor recur. In a series of 20 cases in which surgical salvage was performed following recurrence after radiosurgery, approximately one-half were determined to have greater difficulty for resection or facial nerve preservation [70].
Vestibular schwannomas in patients with neurofibromatosis type 2 (NF2) present a particular challenge because lesions are frequently bilateral, and patients may be at increased risk for secondary malignancies. Reports on the use of SRS in patients with NF2 have shown variable results, and long-term follow-up is lacking. Treatment of vestibular schwannomas in patients with NF2 is discussed in more detail separately. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)", section on 'Treatment of vestibular schwannomas'.)
Stereotactic radiotherapy — Fractionated SRT utilizes focused doses of radiation given over a series of treatment sessions. The intent is to reduce radiation injury to critical neural structures while preserving tumor control. (See "Stereotactic cranial radiosurgery".)
Multiple series have demonstrated the general safety and efficacy of this approach [49,71-76].
●In one retrospective study, 200 patients with 202 vestibular schwannomas were treated with SRT (n = 172) or SRS (n = 30) [71]. For patients treated with SRT, the median dose was 57.6 Gy, given in 1.8 Gy fractions. At a median follow-up of 75 months, the 5- and 10-year local control rates were both 96 percent and there was no significant difference between the two treatment techniques. In patients with serviceable hearing prior to SRT, the hearing preservation rate was 78 percent at five years.
●In another single institution series using a different schedule, 496 patients were treated between 1995 and 2007 [75]. A dose of 25 Gy in five fractions or 30 Gy in 10 fractions was used (89 and 11 percent of cases, respectively). Analysis of the 385 patients with imaging follow-up at least 18 months after diagnosis found a therapeutic failure rate of 3 percent, as defined by progressive tumor growth requiring surgical intervention. However, 30 percent of these patients experienced some tumor growth, and 9 percent had a long-term twofold or greater increase in tumor volume after treatment. Patients with a small tumor (volume less than 1 cm3) were more likely to experience tumor growth than those with larger tumors.
Proton beam therapy — Proton beam therapy may provide maximal local tumor control while minimizing cranial nerve injuries. The physical characteristics of the beam result in the majority of the energy being deposited at the end of a linear track (the Bragg peak), with the dose falling rapidly to zero beyond the Bragg peak. Thus, the use of proton beam therapy permits the delivery of high doses of radiation therapy to the target volume while limiting the "scatter" dose received by surrounding tissues.
In one report of 88 patients who were treated with fractionated proton beam therapy, the two- and five-year local control rates were 95 and 94 percent, respectively [77]. Salvage therapy was necessary in five (radiosurgery in one, craniotomy in one, and shunting for hydrocephalus in three). Seven of 21 patients with functional hearing retained serviceable hearing ability, while facial and trigeminal nerve function was preserved in 91 and 89 percent of patients, respectively.
Observation — Since vestibular schwannomas are typically slow growing, observation with follow-up magnetic resonance imaging (MRI) scans every 6 to 12 months may be warranted in carefully selected patients [31].
The growth rate of untreated tumors during observation was illustrated by a single-institution series of 386 patients who were initially managed with observation between 1990 and 2005 [78]. Patients were reimaged at one year and subsequently followed based upon rate of growth. Indications for conservative management varied but included age >60 years, significant comorbidity, small tumor size, lack of symptoms, risk of further hearing loss, or patient preference. Overall, 59 percent of patients had an annual tumor growth rate <1 mm/year, although 39 patients (12 percent) had tumor growth ≥3 mm at one year.
A review of the literature identified 21 studies that included 1345 patients who were managed conservatively [79]. With an average follow-up of 3.2 years, 43 percent of tumors showed evidence of growth, 51 percent remained stable, while 6 percent had evidence of regression without treatment. Hearing loss occurred in one-half of the 347 individuals in whom it was assessed longitudinally. In 15 of the studies, 20 percent of 1001 individuals eventually required treatment with either surgery or radiation, due to either tumor growth on imaging or symptom progression.
Observation may be particularly appropriate in older adult patients who are poor candidates for immediate intervention. However, if there are signs or symptoms of tumor progression, age should not be considered an absolute contraindication to either surgery or radiation [80,81]. While several series have found that neurologic complications and surgical outcomes are comparable to those in younger patients undergoing surgery, older patients are at increased risk for medical complications, including in-hospital mortality [46]. (See 'Other complications' above.)
Observation is associated with a risk of progressive hearing loss. If hearing preservation is an important consideration, early treatment should be encouraged [82]. Hearing preservation outcomes after radiation therapy are generally better in patients with serviceable hearing (Gardner-Robertson [GR] class I or II) than in those with higher degrees of hearing loss at the time of treatment [62,74].
Studies on the natural history of small vestibular schwannomas have helped to define the risk factors for further hearing loss. A review of the literature identified 34 studies that included 982 patients with vestibular schwannomas <25 mm in diameter, who had functional hearing and were managed with observation [83]. Those patients with a tumor growth rate ≤2.5 mm/year had a significantly higher rate of hearing preservation compared with those with a higher tumor growth rate (75 versus 32 percent) [83].
A single-institution prospective study identified 59 patients over a 22-year period who had vestibular schwannomas with serviceable hearing and were managed with serial observation from presentation until hearing loss developed [84]. None of these patients underwent either surgery or radiation therapy during the period of observation. For patients whose tumors exhibited rapid growth (ie, >2.5 mm/year) at any time during the observation period, the median time to hearing loss was seven years, and all of these patients had lost hearing in less than 10 years. Hearing loss generally developed within one to two years of the onset of rapid tumor growth. By contrast, the median time to hearing loss was 15 years in those with tumors that never exhibited rapid growth.
For patients with vestibular schwannomas in whom preservation of residual functional hearing on the involved side is important, these data suggest that careful serial imaging is needed, and therapeutic intervention is indicated if there is evidence of rapid tumor growth (ie, >2.5 mm/year), regardless of tumor size.
HEARING REHABILITATION — Unfortunately, many patients with vestibular schwannoma lose some or all of their hearing either from the tumor or from intervention to remove or control the tumor (either surgery or radiation therapy). This loss can be immediate or delayed over years.
Loss of hearing in one ear poses three major problems in hearing:
●Inability to localize the direction sound is coming from
●Loss of understanding in background noise
●Loss of ability to hear sounds coming from the deaf side (head-shadow effect)
Treatment options — While the focus tends to be on the diagnosis and treatment of vestibular schwannomas, options for rehabilitation of the hearing deficit are slowly increasing [85]. If surgery is planned, preoperative discussion of these options is important, as a titanium screw or a cochlear implant can be placed at the time of surgery when hearing is gone or expected to be lost. Rehabilitation can then begin much earlier in the postoperative course without requiring a second operation.
Therapies range from supportive, compensatory strategies to hearing aids and implantable devices.
●Get used to the loss. Individuals can function with only one hearing ear. Positioning oneself so that the good ear is always toward the action and having important conversations in quiet settings can minimize the impact of only having one hearing ear.
●Use a hearing aid in the ear if any serviceable hearing is left or consider a contralateral routing of signal (CROS) hearing aid if it is not. A CROS aid sends the sound from the bad ear to the good ear. This eliminates the head-shadow effect, but since all the sound is still going through one ear it does not eliminate the other two problems.
●A bone-anchored hearing aid (BAHA) is a device where a titanium screw is placed in the skull on the deafened side. A percutaneous hearing aid is attached to the screw. Sound is then sent through the skull to the good side by bone vibration. This option eliminates the head-shadow effect and may do a little for sound localization because of the sensation of the skull vibration, but it does not help in background noise. All of the sound is still going through one ear.
●Cochlear implants are devices where an electrode array is threaded into the cochlea to stimulate the auditory nerve directly. This requires that the auditory nerve is still intact. This is the case for patients undergoing observation for growth, for patients that have had radiation, and for postsurgical patients where the auditory nerve was left intact no matter what the approach. Some case reports show that the nerve can still be stimulated to help restore some of the lost hearing.
Questions remain as to how much hearing can be restored; however, limited data now show it is a viable option. The advantage of this option is that it can potentially improve all three of the problems caused by the hearing loss. New implants are now magnetic resonance imaging (MRI) compatible, so that continued monitoring of the posterior fossa and internal auditory canal is possible without risk of damage to the implant or injury to the patient [86-89].
●Brainstem implants have been available for many years. Electrodes can be placed next to the cochlear nucleus to stimulate the area directly and bypass the inner ear and cochlear nerve directly. The success of these implants is limited because of the small number of electrodes available and the placement and contact of the electrodes with the cochlear nucleus. They are usually done when the patient has loss of hearing in both ears and no auditory nerve to stimulate [90].
POST-TREATMENT FOLLOW-UP — The optimal approach for follow-up studies after diagnosis and treatment is uncertain, and there are no data to support specific recommendations. Because of the potentially slow growth of these tumors, prolonged follow-up is necessary. The following represents an empiric approach:
●For patients being managed with observation, yearly scans for 10 years, with scans subsequently every three to five years if there has been no growth. Audiometry should also be performed on a regular basis, if preservation of hearing is an important consideration.
●For patients who underwent surgery, yearly scans for 8 to 10 years, and less frequently thereafter if no residual tumor is present.
●For patients treated with radiation therapy, yearly scans for 10 years and then every two years if no growth seen.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Primary brain tumors".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Vestibular schwannoma (acoustic neuroma) (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Clinical presentation – Vestibular schwannomas (acoustic neuromas) account for 80 to 90 percent of cerebellopontine angle (CPA) tumors in adults. The most common clinical manifestations of vestibular schwannomas are unilateral sensorineural hearing loss, often in association with tinnitus. Symptoms may also be due to involvement of other cranial nerves. (See 'Clinical presentation' above.)
●Diagnosis – Diagnosis of a CPA tumor is based upon magnetic resonance imaging (MRI) or computed tomography (CT) imaging. (See 'Diagnosis' above.)
●Management
•Timing of intervention – For patients with large tumors, young age, and/or significant hearing impairment, we suggest early rather than delayed therapeutic intervention (Grade 2C). Observation is associated with a risk of progressive hearing loss. If hearing preservation is an important consideration, early treatment should be encouraged. (See 'Treatment' above.)
•Treatment modality – Both surgery and various radiation therapy techniques represent acceptable options for patients undergoing treatment. The choice of therapy should be based upon the availability of teams with appropriate expertise in treating vestibular schwannomas, as well as patient-specific factors. (See 'Surgery' above and 'Radiation therapy' above.)
•Role of observation – For older patients with small tumors and limited hearing loss, we suggest observation with serial imaging and audiometry (Grade 2C). However, such patients should be monitored at least annually for evidence of tumor progression. Rapid tumor growth (>2.5 mm/year), rather than the absolute size of the tumor, may serve as a useful indicator for therapy. (See 'Observation' above and 'Post-treatment follow-up' above.)
●Hearing rehabilitation – Options for rehabilitation of hearing deficits are slowly increasing. If surgery is planned, preoperative discussion of these options is important, as a titanium screw or a cochlear implant can be placed at the time of surgery when hearing is gone or expected to be lost. (See 'Hearing rehabilitation' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Peter Black, MD, PhD, who contributed to an earlier version of this topic review.
