A vestibular schwannoma (also known as acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma) is a benign, usually slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear. The tumor comes from an overproduction of Schwann cells.
Vestibular schwannomas (VSs) are the most common cerebellopontine angle tumors, accounting for 75% of all lesions in this location.
The overall incidence of vestibular schwannomas is about one per 100,000 person-years.
However, 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.
The median age at diagnosis is approximately 50 years. The tumors are unilateral in more than 90 percent of cases, affecting the right and left sides with equal frequency.
Approximately 3,000 cases are diagnosed each year in the United States.
Most recent publications suggest that the incidence of acoustic neuromas is rising because of advances in MRI scanning. Studies in Denmark published in 2004 show the incidence is 17.4 per million. Most acoustic neuromas are diagnosed in patients between the ages of 30 and 60, and men and women appear to be affected equally 1).
There have been no definite risk factors identified. An increased risk of VS has been shown to positively correlate with mobile phone use of at least 5 years’ duration, but this finding is still controversial.
There was little evidence of an increase in the risk of meningioma, VS, or parotid gland tumors in relation to mobile phone use 2).
There have been no definite risk factors identified. An increased risk of VS has been shown to positively correlate with mobile phone use of at least 5 years’ duration, but this finding is still controversial.
There was little evidence of an increase in the risk of meningioma, VS, or parotid gland tumors in relation to mobile phone use 3).
see the Koos grading scale.
Classification of Samii (Hannover System)
Tumors are typically described as small (less than 1.5 cm)
Medium (1.5 cm to 2.5 cm)
Large (2.5 cm to 4 cm)
Giant (greater than 4 cm).
Tumors are described by a combination of their location and size.
An intracanalicular tumor is small and in the internal auditory canal.
A cisternal tumor extends outside the auditory canal. A compressive tumor infringes upon the cerebellum or brainstem. Very large tumors may obstruct cerebrospinal fluid drainage.
The tumor may develop within the auditory canal, where the vestibulocochlear nerve which supplies the inner ear penetrates the skull (intracanalicular neuroma) or outside the canal (extra-canalicular neuroma).
A progressive decline in unilateral hearing is the most common symptom that leads to the diagnosis of a vestibular schwannoma.
The tumor can produce hearing loss through either direct progressive injury to the cochlear nerve (slowly progressive sensorineural hearing loss) or interruption of cochlear blood supply (sudden and fluctuating hearing losses).
A significant number of individuals with vestibular schwannomas have a reduction in speech discrimination disproportionate to the reduction in the hearing threshold (pure-tone average). This is consistent with direct injury to the cranial nerve. However, many patients with smaller vestibular schwannomas have normal or near-normal hearing based on speech discrimination scores. There is no strict relationship between the size of the tumor and the quality of the residual hearing. Hearing loss associated with vestibular schwannoma can be sudden or fluctuating in 5–15% of patients. Such hearing loss, usually referred to as “sudden deafness”, may improve spontaneously or in response to corticosteroid therapy.
Three to five percent of patients with vestibular schwannoma have normal hearing at the time of diagnosis. The presence of unilateral tinnitus alone is a sufficient reason to evaluate an individual for a vestibular schwannoma.
Vertigo and disequilibrium are uncommon presenting symptoms among patients with these tumors. Rotational vertigo (the illusion of movement or falling) is more common when tumors are small. On the other hand, dysequilibrium (a sense of unsteadiness or imbalance) appears to be more common in larger tumors. Overall, approximately 40–50% of patients with vestibular schwannomas report some balance disturbance. However, such disturbance is the presenting symptom in less than 10% of patients. The gradual reduction of vestibular function in general is well compensated for by central mechanisms. Headaches are present in 50–60% of patients at the time of diagnosis, but fewer than 10% of patients have headache as their presenting symptom. Headache appears to become more common as tumor size increases and is a prominent feature in patients who develop hydrocephalus associated with a large tumor. Facial numbness occurs in about 25% of patients and isphenomenon occurring in 5–10% of patients, the development of facial weakness associated with a small or medium-size tumor should raise suspicion that the diagnosis is not compatible with a vestibular schwannoma. Other diagnoses, such as facial neuroma, meningioma, epidermoid tumor, arteriovenous malformation (AVM) or lipoma should be excluded. Larger tumors can obstruct the flow of cerebrospinal fluid through the ventricular system. In the early decades of the 20th century, 75% of patients presented with hydrocephalus. Clinical study of the nervus intermedius component often shows dysfunction. If specifically asked, the patient will often notice a change in lacrimation with an eye dryness that can be documented by a Schirmer test. Patients may report dysguesia with a feeling of a metallic taste.
Dizziness is a frequent complaint in patients with vestibular schwannoma (VS). An abnormal vestibulo-ocular reflex (VOR) can explain this dizziness in patients with VS. The video Head impulse test (vHIT) offers a chance to describe specifically the VOR findings in such patients. : Fifty consecutive patients with VS were classified in accordance with the morphology of the VOR; gain, covert saccade, and overt saccade were analyzed both in the affected side and in the healthy side. For all patients, caloric tests were performed. All patients were tested before surgery.
Caloric response was normal in 31 of 50 patients. The video Head impulse test was abnormal in 45 of 50 patients. For the affected side, low horizontal VOR gain was found in 27 of 50 patients, covert saccade was observed in 37 of 50, and overt saccade was observed in 26 of 50. In the healthy side, vHIT was abnormal in 29 of 50 patients, with a low gain in four of 50, covert saccade in seven of 50, and overt saccade in 23 of 50. In VS, gain for the affected side is not associated with caloric response, but gain for the affected side is associated with gain in the healthy side. Covert and overt saccade for the affected side is associated with gain for the affected side. In the healthy side, overt saccade is associated with low gain for the affected side.
Video head impulse test improves the vestibular testing before surgery in patients with VS and should be included in the usual clinical tests for these patients 4).
In the 1980s tests for cerebrospinal fluid protein, vestibular testing, and arteriography have been supplanted by modern audiometry with acoustic reflex testing, brain stem evoked responses, and computed tomography (CT). The various types of plain radiography are confirmed as an extremely useful screening modality. CT is insufficiently sensitive to serve as a primary screening procedure, but is a valuable confirmatory test 5).
The most common chief complaint in patients diagnosed with CPA tumors was asymmetrical hearing loss, with most frequent accompanying symptoms being tinnitus in patients with vestibular schwannoma (VS) and dizziness in those with other types of CPA tumor. The most frequent patterns of hearing loss were the descending type in patients with VS and the flat type in patients with non-VS tumors (p < 0.05). Pure tone thresholds tended to increase more in patients with VS than non-VS tumors according to tumor size, and pure tone averages were significantly higher in patients with VS than non-VS tumors of 11-25 mm in size (p < 0.05) 7).
Trigeminal nerve, and facial nerve dysfunction are common preoperative findings.
Examination may show hypoesthesia in the most superficial part of the external auditory canal. In a population of 46 patients tested by a Schirmer test before radiosurgery, Tamura et al found that 41% of patients experienced some lacrimal deficit on the side of the tumor. more common at the time of presentation than facial weakness (about 10% of patients). A decrease in the corneal reflex generally occurs earlier and more commonly than documented facial hypoesthesia. Even though approximately 50–70% of individuals with large tumors have facial hypoesthesia on neurological examination, they are often unaware of it, and it is rarely the presenting symptom.
The HBS produced comparable results between different observers in patients with normal or only mildly impaired facial nerve function. Interobserver variability increased depending on the severity of facial nerve paresis. The results suggest that the HBS does not promote uniformity of reporting and comparison of outcomes in patients with moderate or severe facial nerve paresis 8).
May show erosion and widening of the internal acoustic meatus. The density of these tumours on non-contrast imaging is variable, and often they are hard to see, especially on account of beam hardening and streak artefact form the adjacent petrous temporal bone.
Contrast enhancement is present, but can be underwhelming, especially in larger lesions with cystic components.
In the management of patients with vestibular schwannoma it is essential to reliably assess tumor size. In respect to volumetric and linear measurements of these tumors we evaluated a) the inter-rater reliability, b) the intra-rater variability, c) the concordance of volume measurements derived from axial versus those from coronal MRI datasets, and d) the correlation of one-dimensional and volumetric measurements.
A strict MRI protocol for follow-up investigations should be adhered to in order to minimize measuring errors 9).
slightly hypointense cf. adjacent brain (63%)
isointense cf. adjacent brain (37%)
may contain hypointense cystic areas
heterogeneously hyperintense cf. to adjacent brain
cystic areas fluid intensity
may have associated peritumoural arachnoid cysts
T1 C+ (Gd) contrast enhancement is vivid but heterogeneous in larger tumours Post-op MRI
Linear enhancement may not indicate tumour, but if there is nodular enhancement suspect tumour recurrence (needs follow up MRI).
Gao S et al., reported a cerebellar glioblastoma multiforme patient, with his clinical presentations and imaging characteristics mimicking a vestibular schwannoma. To the best of authors knowledge, this is the first reported patient with cGBM mimicking a vestibular schwannoma 10).
Further examination of how patients with VS perceive their disease, cope with illness and use social support networks may also help to inform future practice and the creation of decision analytical models 11).
Postoperative improvements in hearing in patients with vestibular schwannoma are extremely rare.
In large/compressive, trigeminal nerve deficit has to be sought to avoid corneal complications in particular. Trigeminal hypoesthesia occurs preoperatively in about half of the cases. It remains relatively stable after tumor removal, but there appears to be an increased rate of absent corneal reflex and neurotrophic keratitis postoperatively. Karkas et al. were able to correlate pre/postoperative trigeminal hypoesthesia with pre/postoperative MRI findings 13).
At a mean of almost 8 years following treatment, approximately half of patients with VS experience headaches of varying frequency and severity. Patient-driven factors including age, sex, mental health, and preexisting headache syndrome are the strongest predictors of long-term severe headache disability. Tumor size and treatment modality have less impact. These data may assist with patient counseling regarding long-term expectations following diagnosis and treatment 14).
Case-control study of 37 patients who underwent surgical resection of sporadic VS following prior SRS at two tertiary academic referral centers between 2003 and 2015. A cohort of nonirradiated control subjects, matched according to tumor size, age, and treatment center, were used as comparison.
Thirty-seven patients were included. The median time from radiation to surgical salvage was 36 months (range 9.6-153 months). Following tumor progression after SRS, 18 (49%) patients underwent gross total resection, 10 (27%) underwent near-total resection, and nine (24%) underwent subtotal resection. Postoperative complications following salvage surgery included one (3%) case of stroke, four (11%) cases of cerebrospinal fluid leak, and two (5%) cases of meningitis. Twenty-seven (73%) patients had good postoperative facial nerve outcome (House-Brackmann Score I-II) at long-term follow-up. There were no cases of tumor recurrence or regrowth after a median length of 26 months following microsurgical salvage (range 3-114 months). The rate of satisfactory postoperative facial nerve function was not different between study and control subjects (73% vs. 76%; P = 0.8); however, less-than-complete resection was utilized more frequently among previously radiated patients (P = 0.01).
Microsurgical salvage of VS following primary radiation therapy is challenging. Less-than-complete resection is required in a greater percentage of patients to preserve facial nerve integrity and prevent neurological complications. Long-term follow-up is needed to determine the risk of delayed progression following incomplete tumor removal 15).
A total of 106 patients with unilateral VS were enrolled in this study prospectively. Each patient received a caloric reflex test, vestibular evoked myogenic potential (VEMP) test, and cochlear nerve function test (hearing) before the operation and 1 week, 3, and 6 months, postoperatively. All patients underwent surgical removal of the VS using the suboccipital approach. During the operation, the nerve of tumor origin (SVN or IVN) was identified by the surgeon. Tumor size was measured by preoperative magnetic resonance imaging.
The nerve of tumor origin could not be unequivocally identified in 38 patients (38/106, 35.80%). These patients were not subsequently evaluated. In 26 patients (nine females, seventeen males), tumors arose from the SVN and in 42 patients (18 females, 24 males), tumors arose from the IVN. Comparing with the nerve of origins (SVN and IVN) of tumors, the results of the caloric tests and VEMP tests were significantly different in tumors originating from the SVN and the IVN in our study. Hearing was preserved in 16 of 26 patients (61.54%) with SVN-originating tumors, whereas hearing was preserved in only seven of 42 patients (16.67%) with IVN-originating tumors.
The data suggest that caloric and VEMP tests might help to identify whether VS tumors originate from the SVN or IVN. These tests could also be used to evaluate the residual function of the nerves after surgery. Using this information, we might better predict the preservation of hearing for patients 16).
A retrospective cohort study of 489 patients who underwent vestibular schwannoma resection at the Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota between 2000 and 2014. Delayed facial palsy was defined as deterioration in facial function of at least 2 House-Brackmann (HB) grades between postoperative days 5 to 30. Only patients with a HB grade of I to III by postoperative day 5 were eligible for study inclusion.
One hundred twenty-one patients with HB grade IV to VI facial weakness at postoperative day 5 were excluded from analysis. Of the remaining 368, 60 (16%) patients developed DFP (mean 12 days postoperatively, range: 5-25 days). All patients recovered function to HB grade I to II by a mean of 33 days (range: 7-86 days). Patients that developed DFP had higher rates of gross total resections (83% vs 71%, P = .05) and retrosigmoid approaches (72% vs 52%, P < .01). There was no difference in recovery time between patients who received treatment with steroids, steroids with antivirals, or no treatment at all (P = .530).
Patients with a gross total tumor resection or undergoing a retrosigmoid approach may be at higher risk of DFP. The prognosis is favorable, with patients likely recovering to normal or near-normal facial function within 1 month of onset 17).
Thirty-two patients diagnosed with acoustic neuroma received contrast-enhanced magnetic resonance imaging of brain were recruited. The volume was calculated by the ABC/2 equation and planimetry method (defined as exact volume) at the same time. The 32 patients were divided into three groups by tumor volume to avoid volume-dependent overestimation (<3 ml, 3-6 ml and >6 ml).
The tumor volume by ABC/2 method was highly correlated to that calculated by planimetry method using linear regression analysis (R2=0.985). Pearson correlation coefficient (r=0.993, p<0.001) demonstrates nearly perfect association between two methods.
The ABC/2 formula is an easy method in estimating the tumor volume of acoustic neuromas that is not inferior to planimetry method 18).
Thirty-eight VS patients were split in three groups according to caloric vestibular test results before surgery; nine had a symmetrical vestibular response (vestibular normoreflexy), 19 with a decreased response of more than 20% of the affected side (vestibular hyporeflexy) and 10 with an absent caloric response on the side of the affected labyrinth (vestibular areflexy). They underwent pendular rotary vestibular testing (RVT), allowing to evaluate gain and directional preponderance of the vestibulo-ocular reflex, and a sensory organisation test (SOT), evaluating balance control in six conditions (C1 to C6). These tests were performed shortly before, and 8 and 90 days after surgery. Directional preponderance performances of patients with vestibular normoreflexy or hyporeflexy followed a classical time-course with a huge asymmetry just after surgery and a recovery to pre-operative performances at 90 days; patients with vestibular areflexy were relatively stable in time. Variation in SOT performances of patients with vestibular normoreflexy, especially in the more complex C4 to C6, followed a classical time-course with an important postural degradation just after surgery and a recovery to pre-operative performances at 90 days. Patients with vestibular areflexy showed no balance degradation just after surgery and a marked increase in performances at 90 days after surgery, especially in C5 and C6. Performances of patients with vestibular hyporeflexy were intermediate, close to performances of patients with vestibular normoreflexy before surgery and close to performances of patients with vestibular areflexy at 8 and 90 days after surgery. Pre-operative vestibular function alteration triggers an adaptive process, characterized by a restoration of the symmetry of the vestibular nuclei activity and by sensory substitution and new behavioural strategies, allowing the anticipation of unilateral vestibular deafferentation effects 19).
Seventy-six patients underwent the primary removal of an acoustic neurinoma at the Mayo Clinic from 1978 through 1980. Hearing loss was present in 97% of the patients, and tinnitus and dysequilibrium occurred in 70% of the patients. The most common signs were a decreased corneal reflex, nystagmus, and facial hypesthesia. In these patients, pure tone and speech audiometry are used to define the hearing loss. When hearing is still present, the speech discrimination is often disproportionately low. Acoustic reflex testing and brain stem evoked response are used to determine whether the hearing loss is cochlear or retrocochlear. When these tests could be performed in this series of patients, they were accurate in 85 to 95%. The vestibular response to caloric testing is expected to be decreased or absent in about 90% of patients, and this was so in 86% of our patients. Radiographic studies are the most important tests currently used for the diagnosis of acoustic neurinoma. Tomography of the internal auditory canal shows abnormalities in 80% of patients. Computed tomography with contrast enhancement demonstrates abnormalities in 90% of patients. The computed tomographic (CT) scan may reveal the location, the size, and often the consistency of the tumor. In cases still questionable after CT scanning, positive contrast rhombencephalography is used for clarification. In this series, no single symptom, sign, abnormal audiometric test result, or abnormal radiographic finding was present in all patients; therefore, the most important factor in diagnosis is an alert physician 20).
126 tumors have been operated by Sterkers from 1966 to 1978. The surgery was done either by the middle fossa, or the translabyrinthine, or the retrosigmoid approach. The perservation of the Facial nerve is obtained in 93%, the facial function is normal in 70%. The hearing is preserved after removal of the tumor in 50% of the intracanalar neuromas, and in 35% after removal of tumors expanded in the angle 21)
Temporal bone invasion by VS is extremely rare. A 51-year-old man who revealed temporal bone destruction beyond IAC by unilateral VS. The bony destruction extended anteriorly to the carotid canal and inferiorly to the jugular foramen. On histopathologic examination, the tumor showed typical benign schwannoma and did not show any unusual vascularity or malignant feature. Facial nerve was severely compressed and distorted by tumor, which unevenly eroded temporal bone in surgical field. Vestibular schwannoma with atypical invasion of temporal bone can be successfully treated with combined translabyrinthine and lateral suboccipiral approach without facial nerve dysfunction. Early detection and careful dissection of facial nerve with intraoperative monitoring should be considered during operation due to severe adhesion and distortion of facial nerve by tumor and eroded temporal bone 22)
A 15-year-old male who presented with hearing loss due to a small left-sided vestibular schwannoma (VS) not associated with neurofibromatosis type 2 (NF2), which had been apparent for six months. Magnetic resonance imaging with gadolinium diethylenetriamine penta-acetic acid revealed a mass, 10 mm in diameter, located in the left inner auditory canal. The patient had no family history of NF2 and gene mutation analysis showed no signs of the condition. Small sporadic or non-NF2 VS is extremely rare and the treatment decision-making process is complicated in children when considering the implications for the impairment of childhood development and lifelong disability. Following careful consideration, the patient in the present study underwent treatment with stereotactic radiosurgery. The five-year post-operative follow-up examination showed tumor stability without additional neurological deficits and at the time of writing the patient was alive and well 23).