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Vestibular schwannoma (acoustic neuroma)

Vestibular schwannoma (acoustic neuroma)
Literature review current through: Jan 2024.
This topic last updated: Dec 12, 2023.

INTRODUCTION — Vestibular schwannomas (previously known as acoustic neuromas) are Schwann cell-derived, histologically benign tumors of the eighth cranial nerve, most commonly arising from the vestibular portion of the nerve (figure 1). They account for approximately 8 percent of all intracranial tumors in adults and 80 to 90 percent of tumors in the cerebellopontine angle.

Vestibular schwannomas commonly cause morbidity related to hearing loss, dizziness, and vestibular dysfunction, and large tumors pose risk of facial nerve dysfunction as well as symptoms due to mass effect on the adjacent brainstem. Both surgery and radiation therapy are used to treat schwannomas, and treatment decisions are optimally made with multidisciplinary input from neurosurgery, otolaryngology, and radiation oncology.

The epidemiology, pathogenesis, clinical presentation, diagnosis, and management of patients with sporadic vestibular schwannomas will be reviewed here. Bilateral vestibular schwannomas in patients with NF2-related schwannomatosis are reviewed separately. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)".)

EPIDEMIOLOGY — The overall incidence of vestibular schwannoma is approximately 3 to 5 per 100,000 person-years [1,2]. The incidence rises with advancing age. For patients over 70 years of age, the incidence may be as high as 21 per 100,000 person-years [1].

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 males and females [8]. Bilateral vestibular schwannomas are primarily observed in patients with NF2-related schwannomatosis (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 NF2-related schwannomatosis (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 [9]. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)" and "Risk factors for brain tumors".)

Aside from NF2, which accounts for a very small proportion of all patients with vestibular schwannoma, other risk factors that have been associated with the development of vestibular schwannomas in epidemiologic studies include the following:

Ionizing radiation – Childhood exposure to low-dose radiation for benign conditions of the head and neck has been associated with an increased risk of vestibular schwannoma [10,11]. 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 [11]. 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'.)

Cellular phones and radiofrequency fields – Evidence supporting a possible association between cellular telephone use and brain tumors, including vestibular schwannomas, is mixed, as reviewed in detail separately. (See "Risk factors for brain tumors", section on 'Cellular phones and radiofrequency fields'.)

Noise exposure – There are conflicting data on noise exposure as a risk factor for vestibular schwannomas [7,12-15], despite experimental studies supporting biologic plausibility [16,17]. Most studies finding a positive association have relied on self-reported measures of noise exposure [7,13,14,18], 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 [8,19]. 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) [8,20].

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 [21]. There are no pathologic markers that predict recurrent or clinically aggressive behavior [22].

CLINICAL PRESENTATION — Symptoms associated with vestibular schwannoma can be due to vestibulocochlear nerve dysfunction, compression of nearby cranial nerves, and, for larger tumors, mass effect on adjacent structures like the brainstem and cerebellum. Based on a series of 1000 patients with vestibular schwannoma presenting to a single institution, the most common presenting signs and symptoms are as follows [23]:

Cochlear nerve – Symptomatic cochlear nerve involvement occurred in 95 percent of patients [23]. 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 [23]. The incidence of tinnitus was higher in hearing than in deaf patients but was also present in 46 percent of deaf patients. In another single-institution series of 478 patients, male sex and moderate hearing impairment were positive predictors of preoperative tinnitus, while large tumors and complete hearing loss were negative predictors [24].

Vestibular nerve – Involvement of the vestibular nerve occurred in 61 percent of patients [23]. 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 an 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 [23]. 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 [23]. 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].

Progressive mass effect – Other presenting signs can be the result of mass effect, 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 — Vestibular schwannoma should be suspected in patients presenting with unexplained unilateral sensorineural hearing loss on audiometry. Although definitive diagnosis requires histologic confirmation, a confident clinical diagnosis can be made radiographically in most cases based on the characteristic appearance of an enhancing, nodular tumor along the eighth cranial nerve on high resolution contrast-enhanced brain MRI.

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 — Audiometric testing should be obtained in all patients with a suspected vestibular schwannoma. 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. (See "Evaluation of hearing loss in adults", section on 'Formal audiologic assessment'.)

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, auditory brainstem response (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 >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].

Vestibular testing has limited utility in the evaluation of patients with vestibular schwannoma. 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 — Contrast-enhanced MRI with millimeter sections through the internal auditory meatus can detect tumors as small as 1 to 2 mm in diameter (image 1) [27]. 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 nodular enhancing lesions in the region of the internal auditory canal with variable extension into the CPA. CT scans with bone windows may show widening of the internal auditory canal.

The radiographic differential diagnosis includes meningioma, which accounts for 4 to 10 percent of enhancing masses in the CPA. Other less common causes of such lesions include facial nerve schwannomas, gliomas, cholesterol cysts, cholesteatomas, hemangiomas, aneurysms, arachnoid cysts, lipomas, and metastatic tumor.

Recommended MRI sequences for vestibular schwannoma include high-resolution T2-weighted and contrast-enhanced T1-weighted images, in addition to standard T1, T2, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI) sequences in axial, coronal, and sagittal planes [28]. Growth should be monitored with postcontrast three-dimensional T1 magnetization-prepared rapid gradient-echo (MP-RAGE) or high-resolution T2 (including Constructive Interference in Steady State [CISS] or fast imaging employing steady-state acquisition [FIESTA] sequences).

The Koos grading system is commonly used to describe vestibular schwannoma size and location on MRI [29]:

Grade I – Small intracanalicular tumors

Grade II – Small tumor with protrusion into the CPA; no contact with the brainstem

Grade III – Tumor occupying the cerebellopontine cistern with no brainstem displacement

Grade IV – Large tumor with brainstem and cranial nerve displacement

Whom to refer for genetic evaluation — In adults, the majority of vestibular schwannomas are unilateral and sporadic, and genetic evaluation is not indicated.

All patients with bilateral vestibular schwannomas and all patients younger than 30 years of age with a unilateral vestibular schwannoma should be referred for comprehensive evaluation for NF2-related schwannomatosis (NF2) and other schwannomatoses. The likelihood that a unilateral vestibular schwannoma is the first manifestation of NF2 or other schwannomatoses is inversely correlated with age. Beyond the age of 30 years, the risk that a unilateral vestibular schwannoma is related to NF2 is minimal. (See "NF2-related schwannomatosis (formerly neurofibromatosis type 2)", section on 'Diagnosis'.)

MANAGEMENT

Our approach — Initial management decisions for vestibular schwannoma depend primarily on symptoms/signs and tumor size (particularly the cisternal component, as reflected in the Koos grade). Hearing preservation is an important goal, although it is not always possible, and all treatment options carry risk of hearing loss. Patient preferences weigh heavily in treatment decisions for smaller tumors since both surgery and radiation therapy are effective treatments, few comparative studies have been performed, and risk profiles vary by treatment modality as well as patient characteristics. Where available, patients should undergo multidisciplinary specialty review with input from neurosurgery, otolaryngology, and radiation oncology.

Koos grade I and II tumors — Koos grade I and II vestibular schwannomas occupy the internal auditory canal and do not protrude into the cerebellopontine cistern (grade I, intracanalicular) or protrude into the cistern but do not contact the brainstem (grade II). Such tumors may be identified incidentally or in association with unilateral hearing loss, tinnitus, or vestibular symptoms.

Asymptomatic — For most patients with asymptomatic Koos grade I or II tumors, we suggest observation rather than immediate intervention [30,31]. Patients should be followed with serial MRI scans and audiometry at least annually and offered definitive treatment if the tumor enlarges or hearing deteriorates. Longitudinal studies indicate that the rate of growth is a better predictor of risk for future hearing loss than absolute tumor size. (See 'Watchful waiting' below.)

If early intervention is desired for a small, asymptomatic tumor, radiation therapy (stereotactic radiosurgery [SRS] or stereotactic radiotherapy [SRT]) is often favored because it is noninvasive and avoids operative risks, which include hearing loss and facial nerve injury [30,32]. SRS/SRT for small tumors is associated with high rates of long-term tumor control and hearing preservation, although the risk of hearing loss rises with long-term follow-up. SRS and SRT are both used, and selection is at the discretion of the radiation oncologist. (See 'Radiation therapy' below.)

Partial hearing loss or vestibular symptoms — Treatment decisions for patients with small tumors who have reduced but serviceable hearing when the tumor is discovered should be individualized and based on shared decision-making. There are two components of treatment to consider: the timing of treatment (early versus watchful waiting) and treatment modality (SRS/SRT versus surgery).

Timing – There is no consensus on whether to treat early or wait until the tumor progresses further (either by size or symptoms) before treating. It is important for clinicians and patients to understand that treatment of symptomatic tumors does not typically reverse existing symptoms, and clinical characteristics at the time of diagnosis do not reliably predict progression. Across various studies, approximately 50 percent of patients who are observed will progress to treatment within five years. (See 'Watchful waiting' below.)

Although early treatment with SRS achieves better tumor size control in the short term compared with watchful waiting, there is evidence from a single randomized trial that hearing and quality-of-life outcomes are similar at four years [33], and there is no prospective comparative evidence on hearing preservation outcomes beyond four years. Long-term retrospective data in small and medium-sized tumors are mixed, with some studies finding an association between SRS and better hearing outcomes and others finding no association [34-37]. On the other hand, the risk of treatment-related hearing loss and other complications increases with increasing tumor size, which provides some rationale for treating early, particularly if adherence with monitoring cannot be ensured or in patients who place a high value on control of tumor growth. (See 'Radiation therapy' below.)

In the Vestibular Schwannoma, Radiosurgery or Expectation (V-REX) trial, 100 patients with newly diagnosed unilateral vestibular schwannoma with a maximal tumor diameter <2 cm in the cerebellopontine angle (CPA) were randomly assigned to upfront SRS or a watchful waiting strategy, with treatment only given when tumor growth was documented radiographically [33]. Mean age was 54 years, and the vast majority of patients were symptomatic with hearing loss (89 percent), tinnitus (81 percent), dizziness (54 percent), and/or balance problems (47 percent). Thirty-five percent of tumors were intracanalicular (Koos grade I), and the median tumor volume was 350 mm3 (0.35 cm3). At four years, 94 percent of patients in the upfront SRS group had received no further treatment; among three patients who progressed, two underwent surgical resection and one received repeat SRS. In the watchful waiting group, 56 percent of patients had stable tumors at four years and received no active treatment; among 44 percent who progressed, all but one received SRS (14 patients after year 1, six after year 2, and three after year 3). Geometric mean tumor volume at four years relative to baseline was reduced in the upfront SRS group (0.87) and increased in the watchful waiting group (1.51). However, there were no statistically significant differences in nearly all secondary outcomes, including all objective and patient-reported measures of hearing, vestibular function, balance, and quality of life. Hearing acuity (mean pure-tone average) declined in both groups by approximately 20 decibels at four years, and mean word recognition scores also declined by approximately 30 percentage points in both groups.

Overall, the trial was underpowered for secondary outcomes, and the quality of the evidence for the question of timing remains low. Nonetheless, these results argue weakly against upfront treatment as a uniform approach in all patients, since, at least at four years, over half of patients in the watchful waiting group were spared the risks of treatment (even if relatively low for SRS) without sacrificing symptom control. (See 'Watchful waiting' below.)

Treatment modality – For most patients with small symptomatic tumors who are selected for therapy, we suggest SRS/SRT rather than surgery. Particularly for Koos grade I (intracanalicular) tumors, there is a general consensus that SRS/SRT offers excellent tumor control and acceptable hearing preservation rates with a lower complication rate than surgery. (See 'Radiation therapy' below.)

Complete hearing loss — For patients with Koos grade I or II tumors who already have complete hearing loss, the goals of treatment are tumor control and preservation of nearby cranial nerve function (eg, facial nerve, trigeminal nerve). Observation is usually preferred for such patients, since facial nerve function is not endangered until the tumor is much larger, and some patients will not progress to require any intervention in their lifetime. For those who progress and require treatment, SRS/SRT is often favored over surgery in terms of risk profile, but treatment decisions are individualized.

Koos grade III tumors — Most patients with Koos grade III tumors present with vestibular or cochlear nerve symptoms; facial paresis is rare. Treatment is generally indicated, since further tumor enlargement threatens brainstem compression and nearby cranial nerve function, and the risks of treatment also rise with increasing tumor size. The goals of treatment are tumor control and preservation of facial nerve function and hearing, if still present.

Both surgery and SRS/SRT should be discussed, and treatment selection is individualized based on tumor size, cranial nerve function, patient age and comorbidities, fitness for surgery, and patient preferences. With larger tumors, the size of the cisternal component of the tumor is a key consideration for radiation eligibility and planning, since swelling and local mass effect can increase transiently after radiation. SRS/SRT carries lower immediate risks of cranial nerve dysfunction, but surgery can be more definitive if a gross total resection is achieved. Facial nerve preservation is a key surgical consideration, and when gross total resection is not possible, residual tumor may be observed or treated with adjuvant SRS/SRT, depending on size and patient preferences.

Koos grade IV tumors — Koos grade IV tumors have large cisternal components causing compression of the brainstem and displacement of cranial nerves. Maximum tumor diameter is typically >3 cm. The primary goal of treatment is decompression of the brainstem and cranial nerves, which can only be achieved with surgery. Complete resection carries considerable risk for loss or further deterioration of cranial nerve function, and subtotal resection followed by observation or SRS/SRT is also an option.

Bilateral tumors — Vestibular schwannomas in patients with NF2-related schwannomatosis (NF2) present a particular challenge because lesions are frequently bilateral, and patients may be at increased risk for secondary malignancies with radiation therapy. 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'.)

Watchful waiting — The goals of observation are to monitor tumor growth and hearing function over time to guide decisions about definitive treatment.

Surveillance interval — Patients with an untreated vestibular schwannoma selected for watchful waiting should be followed regularly with both brain MRI and audiometry (for those with serviceable hearing) [30]. There are no data to support a specific surveillance interval, and decisions may be individualized based on patient and tumor characteristics [31]. A common practice is to follow patients annually for the first ten years with both brain MRI and audiometry. Some clinicians may choose a shorter interval (eg, every six months) in the first one to two years after discovery of the tumor to establish short-term stability before moving to yearly assessments. Beyond ten years, assessments may be spaced out to every three to five years for tumors that remain stable.

Contrast-enhanced MRI of the brain should include high-resolution, triplanar T1 postcontrast and T2-weighted images through the internal auditory canal for optimal visualization (see 'Imaging' above). Maximum tumor diameter is usually along the axis of the internal auditory canal and should be compared serially on comparable cuts. Volumetric tumor size assessments are increasingly available but may need to be requested from neuroradiology. Such measurements are more sensitive to small changes in size, particularly for tumors with an irregular shape. However, thresholds for relative change in volume over time are not well studied prospectively.

Risk factors for progression — Rates of progression in patients under observation vary widely in published studies, which include heterogeneous patient populations with a range of baseline characteristics (age, symptoms, tumor size) and length of follow-up. On average, approximately 50 percent of patients who are observed will progress to treatment within five years due to tumor growth, symptomatic progression, or both [33,38-40]. In the only randomized trial with a watchful waiting group, 46 percent of the patients under observation progressed to treatment at four years [33]. (See 'Partial hearing loss or vestibular symptoms' above.)

Multiple risk factors for progression have been identified in individual studies but variably reproduced. The most consistently implicated predictors are [31,41]:

Larger baseline tumor size (eg, ≥2 cm)

Tumor extending into the cerebellopontine cistern (ie, Koos grade II or higher)

Cystic tumors

Tumor growth within the first year of follow-up

Tinnitus or dysequilibrium at baseline

An additional factor that may be more important than absolute tumor size is the rate of change [42,43]. 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 [42]. Those patients with a tumor growth rate >2.5 mm/year were at higher risk for hearing loss compared with those with a lower tumor growth rate (68 versus 25 percent).

Criteria for treatment — Criteria for initiating treatment in patients who are being monitored serially are not well defined. Vestibular schwannomas may enlarge slowly over many years, and defining the appropriate time to intervene can be difficult.

Most experts consider year-over-year growth rate more heavily than absolute size when following smaller tumors. For patients in whom preservation of residual functional hearing on the involved side is important, either rapid tumor growth (eg, >2.5 mm in one year) or a year-over-year decline in objective hearing by audiometry are considered indications for treatment based on their association with risk for further loss of hearing (see 'Risk factors for progression' above). Selection of treatment (radiation versus surgery) is governed by size and patient preferences, as discussed above. (See 'Our approach' above.)

Patient age, comorbidities, baseline tumor size, and risks of intervention also affect treatment decisions. For Koos grade II tumors, the size of the cisternal portion of the tumor affects radiation safety and treatment planning related to the adjacent brainstem, and the threshold to initiate treatment may be lower for patients who wish to avoid surgery.

Advanced age should not be considered an absolute contraindication to either surgery or radiation [44,45]. 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 'Surgical risks and complications' below.)

Radiation therapy

Conformal techniques — Image-guided conformal radiation therapy techniques used to treat vestibular schwannoma include SRS, SRT, and proton radiotherapy. Use of these techniques reduces collateral radiation dose to the normal brain compared with older standard radiation techniques such as three-dimensional conformal radiotherapy. This is particularly important for the delivery of radiation to vestibular schwannomas, which are near critical structures such as the brainstem and lower cranial nerves.

There are no randomized trials comparing different radiation therapy approaches, and data are only available from observational studies [47]. Evidence-based guidelines from the Congress of Neurological Surgeons (CNS) and European Association of Neuro-Oncology (EANO) have 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 [30,31,48].

Stereotactic radiosurgery (SRS) – SRS 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. SRS is an appropriate technique for tumors up to approximately 3 cm in diameter. (See "Stereotactic cranial radiosurgery".)

For vestibular schwannomas, a single-fraction SRS dose ≤13 Gy should be used to facilitate hearing preservation and minimize risk of cranial nerve deficits [30,31]. There is no difference in radiographic control with different doses, and historical studies using higher marginal treatment doses (up to 22 Gy) found unacceptably high rates of cranial nerve toxicity with long-term follow-up [49-52].

Stereotactic radiotherapy (SRT) – SRT utilizes the same technique as SRS (multiple convergent beams), but the total dose is given over a series of treatment sessions (fractionated). The intent of fractionation is to reduce radiation injury to critical neural structures while preserving tumor control. SRT is a commonly used alternative to single-fraction SRS for larger tumors. (See "Stereotactic cranial radiosurgery".)

The usual total dose of SRT for vestibular schwannomas depends on the fractionation schedule. The dose can be delivered using conventional fractionation (daily doses of 1.8 to 2 Gy to a total dose of 50 to 54 Gy) or hypofractionation (3 to 7 Gy per fraction to a total dose of 21 to 35 Gy).

Proton radiotherapy – Proton radiotherapy is a form of heavy particle radiation used at a limited number of specialized centers around the world. Protons achieve greater avoidance of normal tissue radiation dose than photon-based techniques based on the physical characteristics of the proton beam, which deposits energy at the end of a linear track (the Bragg peak), beyond which there is a rapid fall-off in dose to zero. Centers may use either passive scatter or pencil beam technology to deliver protons; existing data for vestibular schwannomas are based on patients treated with passive scatter technology.

For vestibular schwannomas, proton radiotherapy can be delivered in a single fraction or divided over multiple sessions. A common single-fraction passive scatter dose is 12 CGE (cobalt Gray equivalents) [53]. The usual total dose used for fractionated passive scatter proton radiotherapy is 50.4 to 54 CGE [54,55].

Local control and hearing preservation — With contemporary techniques and dosing, radiation therapy for vestibular schwannomas achieves local control rates ≥90 percent at ten years [31,47,48,54-58]. The primary risk factor for local failure after radiation therapy is large baseline tumor size (>3 cm).

As histologically benign tumors with a low mitotic rate, vestibular schwannomas typically shrink modestly or not at all with radiation therapy, and the primary goal is to halt further growth. Transient tumor enlargement can be seen within the first year after radiation and should not be confused with treatment failure. (See 'Radiation risks and complications' below.)

Rates of hearing preservation after radiation therapy for vestibular schwannoma vary across individual studies and with length of follow-up. Hearing preservation is also variably defined; most commonly, it is defined as retention of serviceable hearing (pure tone average [PTA] score ≤50 dB and speech discrimination score ≥50 percent) in patients who had serviceable hearing at the time of treatment. A 2023 meta-analysis of long-term hearing outcomes after SRS for small to medium-sized vestibular schwannomas (median tumor volume 1.6 to 1.9 cm3) included 16 observational studies with ≥5 years of audiometric follow-up in a total of 1409 patients [59]. With a median follow-up of 6.7 years, the overall hearing preservation rate was 59.4 percent. Predictors of hearing preservation included younger age, good pretreatment hearing status (Gardner-Robertson class 1), small tumor volume (<1.2 cm3), Koos I grade, treatment within two years of diagnosis, and lower marginal and cochlear dose. Longer-term follow-up studies indicate that rates of functional hearing preservation may decline to approximately 25 to 50 percent at 10 years, even with contemporary treatment doses of 12 to 13 Gy [56,60-62].

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 [63], or central cochlear dose <4.2 Gy [64], others have not found cochlear dose to be a significant factor on multivariate analysis [65]. While unequivocal evidence for the impact of cochlear dose on hearing outcomes remains to be determined, as prior studies have used variable cochlear dosimetric assessments and criteria for hearing preservation, a mean cochlear dose of <4 to 6 Gy while maintaining tumor coverage may be prudent for clinical practice [66].

Radiation risks and complications — Radiation therapy for vestibular schwannoma is generally well tolerated. Risks of acute treatment-related side effects such as nausea, fatigue, and skin irritation are generally low. (See "Acute complications of cranial irradiation", section on 'Stereotactic radiosurgery'.)

Long-term risks and complications include the following:

Delayed hearing loss – Hearing preservation rates decline with long-term follow-up after radiation therapy in the absence of tumor regrowth, indicating that radiation itself may be associated with delayed injury to the cochlear nerve. Chronic injury to the nerve due to the tumor may also contribute. (See 'Local control and hearing preservation' above.)

Other cranial neuropathies – New or worsening facial nerve deficit after SRS occurs in 1.3 percent of patients with long-term follow-up (median 6.7 years) [59]. The risk of new trigeminal neuropathy is approximately 3 percent.

Posttreatment dizziness – Following SRS, approximately 17 percent of patients develop transient dizziness, and 3 percent develop chronic dizziness [67]. A retrospective study of 53 patients treated with 12 Gy SRS showed on multivariate analysis that minimum dose >5 Gy to the vestibular apparatus resulted in significant worsening dizziness post-SRS [68].

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 [61].

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 [69]. 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 [70].

Malignant transformation – Malignant transformation has been described in case reports [71-73]. Two separate large, single-center retrospective series have estimated a malignant transformation rate of 0.3 percent after SRS [61,74]. Patients should be informed that there is minimal risk of malignant transformation after SRS [31].

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 [75].

Surgery — The goals of vestibular schwannoma surgery are maximal resection and cranial nerve preservation [32]. Success depends on a variety of factors including the surgical approach, hearing status of the patient at baseline, and tumor size and location.

Surgical techniques — There are three standard operative approaches for vestibular schwannoma resection. Selection of an approach is determined by multiple factors, including the size of the tumor and whether preservation of hearing is a consideration.

When hearing preservation is a goal, surgeons most often use a retrosigmoid or middle fossa approach [32]. When hearing has already been lost, either a retrosigmoid or translabyrinthine can be used.

Surgery at a high-volume institution is recommended whenever possible. 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 [76].

Intraoperative facial nerve monitoring is used routinely during vestibular schwannoma surgery to help preserve facial nerve function [77].

Outcomes — Complete tumor removal is feasible in almost all patients, and there are few if any recurrences when tumor removal is complete [78-81]. 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 [82,83].

The probability of incomplete resection and risk of hearing and facial nerve dysfunction begin to increase for tumors with >14 to 20 mm extension into the CPA [84]. Facial nerve function can be preserved in most patients even with large tumors [81,85,86], 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 [85].

A 2018 systematic review by the Congress of Neurological Surgeons (CNS) identified eight observational series on middle fossa or retrosigmoid vestibular schwannoma resections that included sufficient data on preoperative and postoperative hearing status and at least 12 months of clinical follow-up [32]. Hearing preservation rates for patients with serviceable hearing at baseline ranged from 19 to 77 percent for middle fossa resections and 11 to 68 percent for retrosigmoid resections. In the same studies, rates of facial nerve preservation ranged from 50 to 86 percent for middle fossa resections and 59 to 99 percent for retrosigmoid resections. Factors associated with increased likelihood of hearing preservation were smaller tumor size and better baseline hearing.

Surgical risks and complications — All attempts at surgical resection of a vestibular schwannoma carry some risk of injury to the vestibulocochlear nerve and nearby cranial nerves, such as the facial nerve. Risk is largely determined by tumor size, as discussed above. (See 'Outcomes' above.)

Other early surgical risks include the following [87]:

Cerebrospinal fluid (CSF) leak – CSF leak complicates approximately 10 percent of vestibular schwannoma surgeries [87]. The risk varies primarily based on surgical approach rather than tumor size. Leaks may be most common after translabyrinthine resections, although technical modifications may reduce risk [80]. Approximately one-third of CSF leaks resolve with conservative management, and two-thirds require repair.

Other neurologic deficits – Postoperative neurologic complications other than audiofacial dysfunction occurred in 9 percent of cases [87]. Acute balance problems were most common and resolved within three months in 60 percent of patients.

Postoperative infection – The risk of postoperative infection, primarily meningitis, was 4 percent.

Vascular complications – Vascular complications, primarily hemorrhage, were observed in 1 percent of cases.

Mortality – Surgical mortality rates for vestibular schwannoma resection are 0.2 to 0.5 percent [30,87].

Compared with younger adults, older adults undergoing surgery for vestibular schwannoma may be at substantially higher risk for in-hospital complications [46,88]. 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 OR 1.8) as well as in-hospital mortality (OR 13) [46].

Persistent headaches appear to be common after surgery for vestibular schwannoma [89,90]. 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 [89]. 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 females.

Posttreatment 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 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.

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)

While the focus tends to be on the diagnosis and treatment of vestibular schwannomas, options for rehabilitation of the hearing deficit are slowly increasing [91]. 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.

Compensatory strategies – 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.

Hearing aids – 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 with background noise. All of the sound is still going through one ear.

Cochlear implants – 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 who have had radiation, and for postsurgical patients in whom 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 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 [92-95].

Brainstem implants – 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 the number of electrodes used is small and contact of the electrodes with the cochlear nucleus may be suboptimal. They are usually done when the patient has loss of hearing in both ears and no auditory nerve to stimulate [96].

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. Larger tumors may cause facial and trigeminal nerve palsies as well as brainstem compression. (See 'Clinical presentation' above.)

Diagnosis – Vestibular schwannoma should be suspected in patients presenting with unexplained unilateral sensorineural hearing loss on audiometry. A confident clinical diagnosis can be made radiographically in most cases based on the characteristic appearance of an enhancing, nodular tumor along the eighth cranial nerve (image 1). (See 'Diagnosis' above.)

All patients with bilateral vestibular schwannomas and all patients younger than 30 years of age with a unilateral vestibular schwannoma should be referred for comprehensive evaluation for NF2-related schwannomatosis (NF2) and other schwannomatoses. Genetic evaluation is not indicated in older adults with unilateral tumors. (See 'Whom to refer for genetic evaluation' above.)

Management – Initial management decisions depend primarily on symptoms/signs and tumor size (particularly the cisternal component, as reflected in the Koos grade). Multidisciplinary review with input from neurosurgery, otolaryngology, and radiation oncology is encouraged. (See 'Our approach' above.)

Koos grade I (small intracanalicular) and II (small tumor with protrusion into CPA; no contact with brainstem) tumors

-For most patients with Koos grade I or II tumors, we suggest watchful waiting rather than immediate intervention (Grade 2C). Those with larger tumors and/or partial haring loss may reasonably choose early intervention, which is associated with improved tumor control but similar hearing and quality-of-life outcomes at four years compared with watchful waiting. (See 'Koos grade I and II tumors' above.)

-Patients selected for watchful waiting should be followed with serial contrast-enhanced brain MRI and audiometry at least annually. The threshold for treatment is individualized; rapid year-over-year growth (eg, >2.5 mm) appears to be more predictive of deterioration in hearing than absolute size. (See 'Risk factors for progression' above and 'Criteria for treatment' above.)

-For most patients with Koos grade I or II tumors who are selected for treatment, we suggest radiation (stereotactic radiosurgery [SRS] or stereotactic radiotherapy [SRT]) rather than surgery (Grade 2C). Radiation offers excellent tumor control and acceptable hearing preservation rates with a lower complication rate than surgery. (See 'Partial hearing loss or vestibular symptoms' above and 'Radiation therapy' above.)

Koos grade III tumors (occupying the cerebellopontine cistern with no brainstem displacement)

-For most patients with Koos grade III tumors, we suggest definitive treatment rather than watchful waiting (Grade 2C). Further tumor enlargement threatens brainstem compression and nearby cranial nerve function, and the risks of treatment also rise with increasing tumor size. The goals of treatment are tumor control and preservation of facial nerve function and hearing, if still present. Both surgery and SRS/SRT should be discussed, and treatment selection is individualized based on tumor size, cranial nerve function, patient age and comorbidities, and patient preferences. (See 'Koos grade III tumors' above.)

Koos grade IV tumors (large tumor with brainstem and cranial nerve displacement)

-Koos grade IV tumors have large cisternal components causing compression of the brainstem and displacement of cranial nerves. The primary goal of treatment is decompression of the brainstem and cranial nerves, which can only be achieved with surgery. Complete resection is generally curative but carries considerable risk; subtotal resection may be followed by SRS/SRT when needed for tumor control. (See 'Koos grade IV tumors' above.)

Hearing rehabilitation – Many patients with vestibular schwannoma lose some or all of their hearing either from the tumor or from its treatment. This loss can be immediate or delayed over years. Therapies for hearing loss range from supportive, compensatory strategies to hearing aids and implantable devices. (See 'Hearing rehabilitation' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Peter Black, MD, PhD, who contributed to an earlier version of this topic review.

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References

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