Acoustic neuroma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Mohsen Basiri M.D. Simrat Sarai, M.D. [2]

vestibular schwannoma is the most common tumor of the cerebellopontine angle in adults. It is approximately 8-9% of all intracranial tumors. The term “vestibular schwannoma” is preferred over acoustic neuroma which is a misnomer. Acoustic neuroma is a noncancerous tumor. In 1777, Eduard Sandifort first described Acoustic neuroma. In 1822, Wishart described Bilateral acoustic neuroma for the first time. It grows slowly from an overproduction of Schwann cells and is additionally called a vestibular schwannoma. The tumor then presses on the hearing and balance nerves within the internal ear. Schwann cells normally encircle and support nerve fibers. An outsized tumor can compress the facial nerve, which controls facial muscles and sensation or it can compress brain structures. Acoustic neuroma may be classified according to the findings on magnetic resonance imaging (MRI), microscopic histopathology, association with neurofibromatosis type 2 or not. On microscopic histopathological analysis, an acoustic neuroma may display two types of growth patterns: Antoni type A and Antoni type B. Screening for acoustic neuroma is not recommended at any age. Approximately 50% of all acoustic neuromas grow slowly 1 – 2 mm in one year. The growth rate is more rapid (greater than 2 mm/year) in about 20% of the patients. The tumor does not metastasize to other parts of the body. Widespread access to sensitive neuro-diagnostic imaging has led to a remarkable rise in the detection of vestibular schwannomas. Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeters in diameter. Acoustic neuroma characterized by hypointense lesion on T1-weighted MRI, and hyperintense lesion on T2-weighted MRI of brain. Treatment strategies are often divided into an observational wait-and-scan approach, irradiation, microsurgery, and a mixture of these methods. Each strategy features a set of benefits and limitations. Complication include long-term facial-nerve paralysis, bilateral hearing loss, or chronic dizziness or imbalance and these may require rehabilitative intervention.

• In 1777, Eduard Sandifort first described Acoustic neuroma.

• In 1822, Wishart described Bilateral acoustic neuroma for the first time. The patient under study became progressively deaf, blind, had uncontrollable vomiting, headaches, and facial jerking and died at 21 years of age. Wishart found numerous tumors in the skull at autopsy. He described the following: “The seventh cranial nerve pair was diseased in the same manner; a tumor of the size of a small nut, and very hard, being attached to each of them, just where they enter the meatus auditorius internus.”

• In 1833, Charles Bell provided the first known report of a case of the neuroma, demonstrating the relationship of the tumor to the cerebellopontine angle.

• In 1894, Charles Ballance successfully removed an acoustic neuroma surgically. Since then, tremendous efforts of many surgeons have been continuing to provide surgical approaches to improve outcomes of treatments and decrease side effects of interventions.
• Early in 1925, Dandy reported, operative mortality in acoustic neuroma was ranging from 67% to 84%. Harvey Cushing, through increased experience and partial, intracapsular removal of the tumor, was able to reduce the mortality rate to 11%.
• Because of the concern of tumor regrowth, Walter Dandy suggested total removal of the tumor by intracapsular enucleation followed by “deliberate, painstaking dissection of the capsule” from the brainstem through a suboccipital approach, which became the standard technique for removing acoustic neuromas for the next many years. Although there were improvements in diagnosis and treatment, mortality rate was still high.
• Dr William House had developed the middle cranial fossa approach for decompensation of the internal auditory canal in 1960. He performed a series of cadaver sections to find a method to expose the cerebellopontine angle through mastoid to preserve the facial nerve, the tympanic membrane, and posterior canal wall which leads to development of translabyrinthine approach.
• In 1965, when the first international symposium on acoustic neuroma was organized, leading neurosurgeons, otologists, neurologists, and audiologists attended the meeting and covered an expanded range of subjects.
• Over the years, the recognized approaches include: retrosigmoid, middle fossa, and translabyrithine. The approach had to be selected depending on the size and location of the tumor as well as patient’s general condition and preoperative hearing condition

Acoustic neuroma may be classified according to the findings on

• magnetic resonance imaging (MRI)

• microscopic histopathology; Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes:

microscopic histopathology
Conventional schwannoma,
Cellular schwannoma,
Plexiform schwannoma,
Melanotic schwannoma

• Associated with neurofibromatosis type 2 or not.

• Koos grading scale provides four grades based on extra meatal extension and compression of the brain stem , a reliable method for tumor classification which is used in practice now a days.
• In addition, several disease variants, including macrocytic and hemorrhagic vestibular schwannomas, may have a more aggressive course.

• Acoustic neuroma arises from Schwann cells of the vestibulocochlear (eighth cranial) nerve, which are the cells involved in the conduction of nervous impulses along axons, nerve development, and regeneration. On microscopic histopathological analysis, an acoustic neuroma may display two types of growth patterns: Antoni type A and Antoni type B.
• Antoni type A growth pattern is composed of elongated cells with cytoplasmic processes arranged in fascicles, little stromal matrix, and verocay bodies. Antoni type B growth pattern is composed of a loose meshwork of cells, less dense cellular matrix, microcysts, and myxoid change.

• Depending on size, tumors may be fully confined to the internal auditory canal or may extend to varying degrees into the cerebellopontine angle. As a tumor grows, it expands within the confines of the internal auditory canal and exerts pressure on adjacent nerves before growing medially into the cerebellopontine angle.
• Larger tumors that extend into the cerebellopontine angle may compress the trigeminal nerve located cranially, the lower cranial nerves located caudally, and the brain stem and cerebellum medially.
• Progressive medial effacement of the pons may result in obstruction of the fourth ventricle and subsequent obstructive hydrocephalus leading to severe heading and vomiting.

• Neurofibromatosis type 2 is a rare autosomal dominant disorder caused by pathogenic variants within the NF2 gene; nearly half of affected people have a positive family history, and the remaining cases result from new variants.

• As acoustic neuromas are benign tumors in nature, there is no well established criteria for the staging of acoustic neuromas.

• Numerous studies show the correlation between Neurofibromatosis type 2 (NF2) and acoustic neuroma. Other causes can include Constant or continuous exposure to loud noise (such as music or work-related noise) Neck or face radiation can lead to acoustic neuroma many years later and cellular telephone use. Bilateral acoustic neuromas affect both ears and are inherited (genetic mutations in neurofibromatosis-2/NF-2 genes).

• Vestibular schwannoma must be differentiated from Schwannomas originating from other nerves (e.g., facial-nerve schwannoma), meningiomas (In contrast to vestibular schwannomas, posterior fossa meningiomas involve the internal auditory canal less frequently and typically grow eccentrically to the medial canal opening), metastases from primary tumors at other sites, or malignant peripheral nerve sheath tumors that develop new or secondarily within preexisting schwannomas, either spontaneously or after radiation treatment. Acoustic neuroma must also be differentiated from the intracranial epidermoid cyst ( Epidermoid are the third most common tumor of the cerebellopontine angle and are isointense to surrounding cerebrospinal fluid on T1­ and T2­ weighted imaging), facial nerve schwannoma, trigeminal schwannoma, ependymoma, leiomyoma, intranodal palisaded myo-fibro-blastoma, malignant peripheral nerve sheath tumor (MPNST), gastrointestinal stromal tumor, neurofibroma, Meniere’s disease, and Bell’s palsy.

• Enhanced diagnostics leading to increase detection has lead to rising in the incidence of vestibular schwannoma. It is approximately 8-9% of all intracranial tumors.
• From the 1900s the incidence of vestibular schwannomas remained static since patients presented with large tumors causing symptoms that had grown over a period of years without being detected.
• The incidence of acoustic neuroma ranges from 0.3 to 1 per 100, 000 individuals in 1970, current incidence rates range from 3 to 5 cases per 100,000 person-years.
• 20 cases per 100,000 person-years in patients aged 70 years.
• A lifetime prevalence is exceeding 1 case among 500 persons.
• Sporadic unilateral vestibular schwannomas, which account for more than 95% of cases. Women are more commonly affected by acoustic neuroma than men. Most cases of acoustic neuroma develop in individuals between 30 and 60 years of age.
• Denmark’s national registry showed the average age at diagnosis increased from 49 to 60 years, the mean tumor size decreased from 2.8 cm to 0.7 cm.
• Developed countries with widespread access to MRI, population-based data suggest that up to 25% of all new cases are diagnosed incidentally during imaging that was obtained for unrelated indications like severe headache or imbalance problem.

Common risk factors in the development of acoustic neuroma are

• neurofibromatosis type 2
• radiation exposure
• Less common risk factors include sporadic defects in tumor suppressor genes
• Exposure to loud noise
• History of parathyroid adenoma
• The use of cellular phones
• Several groups have suggested that environmental exposures, such as cell phone use or long-term noise exposure may increase the risk of tumorigenesis but this relation is still under study.

• According to the U.S. Preventive Services Task Force (USPTF), screening for acoustic neuroma is not recommended. Evaluation for NF-2 should be done in individuals with an apparently sporadic vestibular schwannoma occurring before the age of 30, or a spinal tumor or meningioma occurring at less than 20 years of age.

• Indications for screening MRI study include sudden or asymmetric sensorineural hearing loss detected through pure-tone and speech audiometry.

• Patients with an isolated, unilateral vestibular schwannoma who do not have other signs of neurofibromatosis type 2 and have no affected relatives generally do not need to undergo genetic testing, nor do their family members.
• The average age at diagnosis increased from 49 to 60 years, the mean tumor size decreased from 2.8 cm to 0.7 cm because of early detection of the tumor via advanced technology.

• Approximately 50% of all acoustic neuromas grow slowly (1 – 2 mm/year). The growth rate is more rapid (greater than 2 mm/year) in about 20% of the patients. The tumor does not metastasize to other parts of the body. Hearing loss, when occurs, is irreversible. If left untreated, an acoustic neuroma can block the flow of cerebrospinal fluid and cause hydrocephalus, which may lead to severe vision problems and difficulty breathing and swallowing.
• Complications of acoustic neuroma include hearing loss, Hydrocephalus, and recurrence of the tumor. Small, slow-growing tumors may not need treatment. Patients experience a similar quality of life whether treatment is observation, radiation, or surgery.
• Large tumors associated with symptomatic brain-stem compression, hydrocephalus, trigeminal neuralgia or neuropathy, or a combination of these complications.
• Although many of the stigmata of facial-nerve injury can be electively managed, incomplete eye closure must be aggressively treated to reduce the risk of exposure keratopathy, commonly manifested as blurred vision, ocular pain, and redness.

• An important ramification of increased disease detection is a potential for overtreatment, which could result in unnecessary complications and health care expenditures. Many patients, who just decades ago would have lived out their lives without having their tumors detected, are now receiving treatment.

• Population-based data showed that 334 of 636 patients had a useful hearing at diagnosis, with a speech discrimination score of more than 70% (indicating that 70% percent of words were repeated back correctly by the patient), but after 10 years of observation, only 31% retained hearing above this threshold. Notably, 88% of patients who started with a speech discrimination score of 100% still had a score of more than 70% at 10 years, suggesting that excellent speech comprehension at diagnosis portends favorable long-term hearing outcomes.
• Unfortunately, since symptom progression is not strongly correlated with tumor growth and since the growth rate is highly variable, patients who are lost to follow-up are at increased risk for the development of a large tumor, with an associated increase in the risk of a poor outcome with eventual treatment.
• The risk of secondary cancer from radiosurgery approaches 0.02%.

Widespread access to sensitive neuro-diagnostic imaging has led to a remarkable rise in the detection of vestibular schwannomas. Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeters in diameter. On brain MRI, acoustic neuroma is characterized by a hypo-intense lesion on T1-weighted MRI, and hyperintense lesion on T2-weighted MRI.

Chronic gradual unilateral hearing impairment is that the commonest complaint resent in 95% of the patients. Common symptoms include chronic gradual unilateral hearing loss, ringing within the ear, Disequilibrium, facial numbness, facial pain, and Headache. Less common symptoms include facial muscle weakness, taste disturbances, dryness of the eyes, sudden lacrimation, speech problem, difficulty swallowing, aspiration, hoarseness, and ear pain, ipsilateral sensorineural hearing loss in more than 90% of patients.

Hearing loss is usually subtle initially and should first become apparent when the patient is employing a telephone or lying in bed with the contralateral ear covered.

Symptoms of dizziness or imbalance in up to 61% of patients, and complaint of asymmetric tinnitus in 55%. Tinnitus is assumed to result from cochlear deafferentation and cortical maladaptation — a mechanism akin to deafferentation pain, as seen in the phantom limb syndrome, tinnitus may persist even after surgery.

There is an increasing difficulty with sound localization and speech comprehension in the presence of background noise, which results from the loss of binaural hearing. Similarly, symptoms of vertigo and continuous dizziness occur in only about 8% and 3% of cases, respectively.

Patients with large tumors that compress the brain stem and cerebellum may have hypoesthesia during a trigeminal distribution, secondary tic douloureux, cerebellar dysmetria, and ataxia, or slowly progressive hydrocephalus without alteration of consciousness.

Symptom progression isn’t strongly correlated with tumor growth. The sensorineural deafness and vestibular hypofunction aren’t reversed even with tumor treatment.

Patients with acoustic neuroma usually appear normal. Physical examination of patients with acoustic neuroma is usually remarkable for Sensorineural hearing loss in the affected ear, positive Rinne test, abnormal Weber test, Papilledema, Nystagmus, Diplopia on lateral gaze, decreased or absent ipsilateral corneal reflex, facial twitching or hypesthesia, Drooling, drooping on one side of the face, loss of taste, and ataxia.

There are no diagnostic laboratory findings associated with acoustic neuroma.

There are no electrocardiogram findings associated with acoustic neuroma.

There are no x-ray findings associated with acoustic neuroma.

There are no echocardiography or ultrasound findings associated with acoustic neuroma.

CT scan of the head may be diagnostic of acoustic neuroma. Findings on CT scan diagnostic of acoustic neuroma include erosion and widening of the internal acoustic canal.

25% of all new cases are diagnosed incidentally during imaging that was obtained for unrelated indications (e.g., headache). Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter highly sensitive and specific accurate radiologic diagnosis in most cases, without the need for a confirmatory biopsy. On brain MRI, acoustic neuroma characterized by hypo intense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.

There are no other imaging findings associated with acoustic neuroma.

Audiometry as the best initial screening test for the diagnosis of acoustic neuroma. It can detect asymmetric sensorineural hearing impairment in about 95% of the patients. Brain stem-evoked response audiometry (ABR, BAER, or BSER) may be done in some cases with unexplained asymmetries in standard audiometric testing as a further screening measure and an abnormal auditory brain stem response test should be followed by an MRI.

Treatment strategies are often divided into an observational wait-and-scan approach, irradiation, microsurgery, and a mixture of those methods. each strategy features a set of benefits and limitations. As such, patient preference plays a serious role in shared decision-making. Tumor size chiefly drives treatment recommendations; however, deciding is additionally guided by the subtle patient- and provider-related factors. Several new drug therapies that aim to halt tumor growth, including aspirin and monoclonal antibodies, have recently been explored but remain investigational. The foremost consistent predictor of future growth during an observational strategy is larger tumor size at diagnosis.

Typically, tumors that have a maximal diameter of but 1.5 cm within the cerebellopontine angle are considered for a wait-and-scan approach. The wait-and-scan approach has gained popularity for a minimum of two reasons: many tumors are now discovered as small masses in older people with mild symptoms; furthermore, reports over the past 15 years have documented radiographically that only 22 to 48% of tumors have shown growth (most commonly defined as an increase of ≥2 mm in diameter). The mainstay of therapy for acoustic neuroma is surgery and radiotherapy. Since acoustic neuroma tends to be slow-growing and should be a benign tumor, careful observation with follow-up MRI scans every 6 to 12 months could even be appropriate for elderly patients, patients with small tumors, patients with significant medical conditions, and patients who refuse treatment.

Surgery is that the mainstay of treatment for acoustic neuroma. If growth is definitively confirmed, most patients receive a recommendation to undergo radiosurgery or microsurgery. Patients with age under 65 years, medium to large-grade tumors, significant deafness , or higher headache severity scores will have more satisfying outcomes from surgery as compared with observation. There are three main surgical approaches for the removal of an acoustic neuroma: translabyrinthine, retro sigmoid or sub-occipital, and middle fossa approach. The choice of a specific approach is predicated on several factors including the dimensions and site of the tumor and whether or not the preservation of hearing may be a goal. Active monitoring of the tumor with serial imaging, signifying a transition in clinical care from up-front microsurgical resection, which epitomized treatment in earlier eras, to management of the chronic disease.

It is performed in an outpatient setting, with no activity restrictions for the patient after radiosurgery. It prevents tumor growth but doesn’t cure. The diameter of but 3.0 cm within the cerebellopontine angle is typically considered to be candidates for radiosurgery. the utilization of highly conformal radiation, defined as radiation delivered in 1 to five fractions to an image-defined target, with maximal sparing of the encompassing tissue. Gamma-knife radiosurgery is one sort of conformal radiation. Gamma knife treatment consists of 192 cobalt-60 sources arranged concentrically to deliver an ovoid isocenter of radiation performed under local anesthesia the dose prescribed is typically 12 to 14 Gy at the five hundred isodose lines, delivered during a single fraction. Treatment typically incorporates a stereotactic head frame and thin-slice, non–contrast-enhanced computerized tomography, and contrast-enhanced axial MRI to stereotactically target the tumor in three-dimensional space. Linear accelerator–based platforms also are employed by many centers. Most of those systems involve one, collimated radiation beam with a gantry that rotates around the patient, creating a focused arc of radiation that stereotactically targets the lesion of interest. Transient tumor enlargement within the primary 3 years after radiosurgery is common, although variable tumor shrinkage eventually occurs in additional than half treated cases. tumor control is reported in additional than 90% of cases of vestibular schwannoma at 10 years of follow-up. Radiosurgical treatment failure is usually defined by tumor growth that persists for quite 3 years, the event of signs or symptoms related to progressive mass effect, and rapid tumor enlargement. Salvage microsurgery is usually recommended after failure.

Cyber knife involves frameless, LINAC-based radiation delivered by means of a highly maneuverable robotic arm with 6 df for movement, with real-time image guidance. This treatment plan prescribes hypo fractionated radiation, at a dose of 25 Gy delivered in 5 fractions to the 80% isodose line.

The linear accelerator (LINAC)–based systems use one , collimated radiation beam with a mobile gantry to make a focused arc of radiation, with frameless stereotaxis; the patient is usually immobilized with the utilization of a customized, soft, plastic mask . The treatment plan prescribes a dose of 12.5 Gy delivered to the 80% isodose line during a single fraction.

It causes radiation-induced brainstem edema, trigeminal neuropathy or neuralgia, and hydrocephalus, also as diminished long-term tumor control. the danger of secondary cancer from radiosurgery approaches 0.02%

Microsurgery is usually preferred for the treatment of tumors that are larger than 3 cm in diameter. the treatment of choice for giant tumors related to symptomatic brain-stem compression, hydrocephalus, tic douloureux or neuropathy, or a mixture of those complications and enormous tumor size. All procedures are performed while the patient is under general anaesthesia and need the utilization of an binocular microscope with intraoperative neural monitoring. There are three primary microsurgical approaches wont to remove vestibular schwannomas are the center fossa, translabyrinthine, and retro sigmoid approaches.

primary microsurgical approaches	Description	Benefits	Risks
Translabyrinthine approach	This surgical approach incorporates a postauricular incision, elimination of bone between the ear canal and sigmoid sinus, and extraction of the semicircular canals to reach the internal auditory canal and cerebellopontine angle (CPA).	Complete exposure of the IAC and fundus Early identification of CN VII A clear view of lateral brain stem facing tumor	The only approach that inherently sacrifices hearing function, since it involves drilling through the internal ear. So hearing sacrifice is unavoidable Autologous fat graft is required
Retrosigmoid approach	The surgery involves a curvilinear, vertically oriented occipital incision and a craniotomy positioned just posterior and inferior to the sigmoid and transverse sinuses. Once the dura is opened, the posterior lip of the internal auditory canal is removed to show the extension of the tumor into this bony canal. Drilling is usually limited by the posterior semicircular canal and vestibule, which can’t be breached if the hearing is to be preserved.	Wide-field visualization of posterior fossa Possible hearing conservation or protection	It may be difficult to visualize the lateral-most aspect of the internal auditory canal It may require cerebellar retraction during procedure
Middle cranial fossa approach	This approach is employed just for small tumors limited to the internal auditory canal or those with but 1 cm of medial extension into the CPA when hearing protection may be a primary purpose. The procedure entails a temporal incision and a craniotomy centered just over the basis of the zygoma. Extradural dissection is then performed under the temporal dura, and therefore the bone covering the internal auditory canal is removed to supply the trail to the tumor.	Usually offers access to full length of the internal auditory canal Possible hearing conservation or preservation	It requires temporal lobe retraction There’s limited CPA access for larger tumors via this approach

The goal is maximal tumor extraction with the protection of neurologic function. Intraoperative facial-nerve monitoring with electromyography is routinely used. Cochlear-nerve monitoring is usually used when hearing conservation is attempted, and monitoring of other regional cranial nerves could also be included for giant tumors. The patient is hospitalized for two to 4 days after the procedure and is ambulatory at the time of discharge. The danger of tumor recurrence after gross total resection is 0 to twenty. Fortunately, the prospect of other major neurovascular complications, like permanent injury to other regional cranial nerves or perioperative stroke, is rare, even with large tumors. The prevalence of postoperative spinal fluid leak is 9 to 13%, aseptic meningitis 2 to 4%, and culture-positive bacterial meningitis 1%.

There’s a risk of eye dryness due to damage to the facial and incomplete eye closure must be aggressively treated to scale back the danger of exposure keratopathy, commonly manifested as blurred vision, ocular pain, and redness.

There are no established measures for the primary prevention of acoustic neuroma.

Secondary prevention strategies following acoustic neuroma treatment include follow-up MRI scans. Imaging and audiological evaluation are commonly performed 6 months after the diagnostic MRI so as to spot a fast-growing tumor or a more aggressive process mimicking a vestibular schwannoma. If there’s no growth at 6 months, imaging and hearing assessments are performed annually thereafter until year 5, when many specialists advocate every other year assessments. lifelong follow-up is suggested, to attenuate the value of ongoing tumor surveillance and therefore the risk of adverse events associated with contrast medium, several groups have transitioned to the utilization of thin-slice, heavily T2-weighted resonance cisternography without contrast medium, which features a high degree of accuracy and interrater reliability. Research showed that excellent speech comprehension at diagnosis portends favorable long-term hearing outcomes. After radiosurgery, patients undergo audiometric evaluation and MRI studies annually for the primary 3 years, then every other year until 10 years, then every 5 years indefinitely.

Those with long-term facial-nerve paralysis, bilateral hearing loss, or chronic dizziness or imbalance may require rehabilitative intervention.

For patients in whom serviceable hearing is maintained within the ipsilateral ear, observation (i.e., no additional hearing rehabilitation) or use of a standard hearing aid is usually adequate. surgical means (i.e., bone-conduction implants) or nonsurgical means (e.g., contralateral routing of signals [CROS] hearing aids. Research showed that excellent speech comprehension at diagnosis portends favorable long-term hearing outcomes.

Facial-nerve paralysis is rare overall, but the danger approaches 50% among patients with large tumors. nervous disorder and eye dryness are primary concerns within the early postoperative period. Eye lubricants and moisture chambers generally provide adequate protection. Usually, referral to an ophthalmologist for upper eyelid weight placement, punctal plugs, or tarsorrhaphy should be considered if longer-term paralysis is anticipated or ophthalmologic complications appear. Improvement is usually greatest within 6 months after the onset of paralysis, but continued recovery is often seen for up to 18 months.

People who report substantial dizziness or imbalance should undergo a comprehensive balance assessment to accurately identify any coexisting disorders and to assess and mitigate the danger of falling. Common conditions which will exacerbate dizziness include peripheral neuropathy, age-related loss of contralateral vestibular function, vision loss, and vestibular migraine. The mammalian peripheral vestibular apparatus has limited regenerative capacity. Thus, balance therapy is that the therapeutic mainstay for people that have troublesome symptoms associated with chronic vestibular hypofunction.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D.

Acoustic neuroma was first described by Eduard Sandifort , a professor of anatomy in the Netherlands, in 1777. Bilateral acoustic neuroma was first described by Wishart in 1822. He described a patient who became progressively deaf, blind, with uncontrollable vomiting, headaches, and facial jerking. He died at 21 years of age. Sir Charles Bell provided the first known report of a case of Meckel cave neuroma in 1833, demonstrating the relationship of the tumor to the cerebellopontine angle. Sir Charles Ballance successfully removed an acoustic neuroma in 1894, although the patient had right side facial paralysis and trigeminal anesthesia. Since then, tremendous efforts of many surgeons have been continuing to provide surgical approaches to improve outcomes of treatments and decrease side effects of interventions.

• Acoustic neuroma was first described by Eduard Sandifort, a professor of anatomy in the Netherlands, in 1777.^[1]
• Bilateral acoustic neuroma was first reported by Wishart in 1822, in a patient who became progressively deaf, blind, had uncontrollable vomiting, headaches, and facial jerking. The patient died at 21 years of age. Wishart found numerous tumors in the skull at autopsy. He described the following: “The seventh cranial nerve pair was diseased in the same manner; a tumor of the size of a small nut, and very hard, being attached to each of them, just where they enter the meatus auditorius internus.” ^[2]
• In most of the 18th century any surgery within the dura resulted in patient’s death, until understanding the role of bacteria, sepsis and the development of anesthesia was made in late 1800s. Sir Charles Ballance successfully removed an acoustic neuroma in 1894, although the patient had right side facial paralysis and trigeminal anesthesia.
• Early in 1925, Dandy reported, operative mortality in acoustic neuroma was ranging from 67% to 84%. Harvey Cushing, through increased experience and partial, intracapsular removal of the tumor, was able to reduce the mortality rate to 11%.
• Because of the concern of tumor regrowth, Walter Dandy suggested total removal of the tumor by intracapsular enucleation followed by “deliberate, painstaking dissection of the capsule” from the brainstem through a suboccipital approach, which became the standard technique for removing acoustic neuromas for the next 40 years. Although there were improvements in diagnosis and treatment, mortality rate was still high.^[3]
• Dr William House had developed the middle cranial fossa approach for decompensation of the internal auditory canal in 1960. He performed a series of cadaver sections to find a method to expose the cerebellopontine angle through mastoid to preserve the facial nerve, the tympanic membrane, and posterior canal wall which leads to development of translabyrinthine approach.^[4]
• In 1965, when the first international symposium on acoustic neuroma was organized, leading neurosurgeons, otologists, neurologists, and audiologists attended the meeting and covered an expanded range of subjects.
• Over the years, the recognized approaches include: retrosigmoid, middle fossa, and translabyrithine. The approach had to be selected depending on the size and location of the tumor as well as patient’s general condition and preoperative hearing condition.^[5]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D.

Acoustic neuroma may be classified according to the findings on magnetic resonance imaging (MRI) or it can also be classified based on microscopic histopathology, and whether or not they are associated with neurofibromatosis type 2. Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. While acoustic neuromas are benign tumors, there is no established system for the staging of acoustic neuromas. Koos grading scale provides four grades based on extrameatal extension and compression of the brain stem , a reliable method for tumor classification which is used in practice.

Not associated/Sporadic

• The vast majority are the sporadic form. 95% of all the cases of acoustic neuroma are sporadic. The cause of sporadic form is unclear

Associated with Neurofibromatosis type II (NF2)^[1]

• NF2 is a rare disorder and it accounts for 5% of acoustic neuromas
• Acoustic neuroma associated with neurofibromatosis type II are typically bilateral and cause gradually progressive hearing loss, tinnitus, and balance dysfunction

• Entirely intracanalicular: The entire tumor is completely within the bony canal
• Intracranial extension without brain stem distortion: Intracranial portion of the tumor is 1.5 – 2.5 cm. (Some references mentioned 1 – 2 cm)
• Intracranial extension with brain stem distortion: Intracranial portion of the tumor is greater than 2.5 cm. (Some references mentioned more than 2 cm)

• Conventional schwannoma: It is the most common schwannoma
• Cellular schwannoma: It may mimic malignant peripheral nerve sheath tumor
• Plexiform schwannoma: It may mimic malignant peripheral nerve sheath tumor if cellular, especially in childhood
• Melanotic schwannoma

Acoustic neuromas are benign tumors (WHO grade 1), but there is no established system for the staging of acoustic neuromas. Numerous stage grading systems have been reported according to tumor size. Tumor size is more important and can be measured by measuring the maximum diameter of the tumor.^[4][5][6]

According to the Koos grading scale, there are 4 grades of acoustic neuroma based on the findings on magnetic resonance imaging (MRI), extrameatal extension and compression of the brain stem:^[7]

Koos Classification for Acoustic Neuroma
Grade	Definition
I	Tumor involves only the internal auditory canal
II	Tumor extends into the cerebellopontine angle, but does not encroach on the brain stem.
III	Tumor fills the entire cerebellopontine angle
IV	Tumor displaces the brain stem and adjacent cranial nerves

Below table summarizes the current grading systems used in practice:

Main grading systems for acoustic neuromas
Tumor size (CPA Maximum diameter)	Sterker	House	Koos	Samii	Tumor Description
0 (intracanalicular)	Tube type	Intracanalicular	Grade I	T1	Confining to internal acoustic canal
≤ 10 mm	Small	Grade 1 (Small)	Grade II	T2	Superpassing internal acoustic canal
≤ 15 mm		Grade 2 (Medium)		T3a	Tumor occupying CPA
≤ 20 mm	Mild
≤ 30 mm		Grade 3 (Moderately Large)	Grade III	T3b	Tumor occupying CPA and contacting the brainstem without compression
≤ 40 mm	Large	Grade 4 (Large)	Grade IV	T4a	Tumor compressing the brainstem
> 40 mm	Huge	Grade 5 (Giant)		T4b	Severe brainstem displacement and deformation of fourth ventricle under tumor compression
Main grading systems for acoustic neuromas. The classifications on the left side (blue area) are mainly based on tumor size, while those on the right side (yellow area) are based on the anatomical relationship around the tumor. Koos classification (green area) combines the tumor size and anatomical relationship for larger tumors.

^[8]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D. Sabawoon Mirwais, M.B.B.S, M.D.[3]

Acoustic neuroma arises from Schwann cells, which are the cells involved in the conduction of nervous impulses along axons, nerve development and regeneration. On microscopic histopathological analysis, acoustic neuroma may display two types of growth patterns: Antoni type A and Antoni type B. Antoni type A growth pattern is composed of elongated cells with cytoplasmic processes arranged in fascicles, little stromal matrix and verocay bodies. Antoni type B growth pattern is composed of loose meshwork of cells, less dense cellular matrix, microcysts and myxoid change.

• Acoustic neuromas are benign tumors (WHO grade 1), usually arising from the intracanalicular segment of the vestibular portion of the vestibulocochlear nerve (CN VIII), near the transition point between glial and Schwann cells (Obersteiner-Redlich zone).
• An acoustic neuroma arises from a type of cell known as the Schwann cell. These cells form an insulating layer over all nerves of the peripheral nervous system (i.e., nerves outside of the central nervous system) including the eighth cranial nerve.
• Most acoustic neuromas are found along the vestibular portion of the eighth cranial nerve.
• As these tumors are made up of Schwann cells, and usually located along the vestibular portion of the eighth cranial nerve, many physicians prefer to use the term, “vestibular schwannoma“. However, the term acoustic neuroma is still used more often in the medical literature.^[1]
• Acoustic neuromas are well circumscribed encapsulated masses, which unlike neuromas, arise from but are separate from nerve fibers.

• One the most common causes of acoustic neuroma is neurofibromatosis type 2 (NF2), an autosomal dominant disease caused by loss of function mutation.
• Genetic studies have linked both sporadic and NF2-associated acoustic neuromas to a single gene, the NF2 gene, located on chromosome 22 band q11–13.1.

• Acoustic neuroma is strongly associated with neurofibromatosis type 2 (NF2).^[2]

On gross pathology, following are the characteristic findings of acoustic neuroma:

• Rubbery-firm with a pale, gray color^[3]
• Well-defined capsule
• Different degrees of vascularity

• Pale gray and firm^[4]
• Fine trabeculated appearance
• Cystic degeneration
• Hemorrhage
• Calcification
• Xanthomatous changes

• The tumor is made up of spindle cells with elongated nuclei and fibrillary cytoplasm.^[5]
• The spindle cells are arranged in two ways:

1. Antoni A

• Antoni A tissue is small with organized and interwoven course of elongated bipolar cells.^[6]
• The spiral framework, formed by the arrangement of the nuclei and fibers, can resemble a meningioma.
• Verocay bodies can also be seen.^[7]

2. Antoni B

• It is represented by a random grouping of cells around foci of necrosis, cystic change, hemorrhage, and blood vessels.^[8]
• This tissue can also have a variable amount of lymphocytic infiltration.

The following findings on electron microscopy are characteristic of an acoustic neuroma:

• Characteristic basement membrane of the schwann cells.^[9][10]
• Wide-spaced collagen.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]Sabawoon Mirwais, M.B.B.S, M.D.[3]

Numerous studies show the correlation between Neurofibromatosis type 2 (NF2) and acoustic neuroma. Other causes can include exposure to occupational noise and cellular telephone use. 

• Genetic studies have linked both sporadic and NF2-associated acoustic neuromas to a single gene, the NF2 gene, located on chromosome 22 band q11–13.1.^[1][2]

• Exposure to radiation in childhood can lead to the development of acoustic neuroma.
• Acoustic neuroma, in this case, can occur after a long latency period.^[3]

Cellular Telephone Use

• It is suspected that the long term use of cellular phones can also lead to the development of acoustic neuroma but this suspicion is not backed by any significant data.

Occupational noise exposure

• A small number of epidemiologic studies of occupational noise exposure, based on self-report, have suggested an association with acoustic neuroma.^[4]

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Acoustic neuroma must be differentiated from meningioma, intracranial epidermoid cyst, facial nerve schwannoma, trigeminal schwannoma, ependymoma, leiomyoma, intranodal palisaded myofibroblastoma, malignant peripheral nerve sheath tumour (MPNST), gastrointestinal stromal tumor, neurofibroma, Meniere’s disease, and Bell’s palsy.

Acoustic neuroma must be differentiated from:^[1]

• Meningioma
• Intracranial epidermoid cyst
• Facial nerve schwannoma
• Trigeminal schwannoma
• Ependymoma
• Metastasis
• Leiomyoma
• Intranodal palisaded myofibroblastoma
• Gastrointestinal stromal tumor
• MPNST – schwannoma with ancient change has no significant mitotic activity^[2]
• Neurofibroma
• Meniere’s disease
• Bell’s palsy

Differentiating features of common differential diagnoses are:^[3]

Differentiating features of common differential diagnosis
Disease/Condition	Differentiating Signs/Symptoms	Findings on CT or MRI
Meningioma	Hearing loss is less common	Usually more homogeneous in appearance: significant signal heterogeneity with cystic or hemorrhagic areas is more typical of vestibular schwannoma than meningiomas (although cystic meningiomas do occur) Meningiomas tend to have a broad dural base Usually lack trumpeted internal acoustic meatus sign Calcification is more common
Intracranial epidermoid cyst	Hearing loss is less common	No enhancing component Very high signal on DWI (Diffusion weighted imaging) Does not widen the internal auditory canal
Facial nerve schwannoma	Facial weakness is common and occurs early Sometimes associated with neurofibromatosis	CT and MRI imaging results are similar to acoustic neuroma but enhancement extends into the geniculate ganglion of the facial nerve and facial canal
Trigeminal schwannoma	Clinically associated with facial numbness Hearing loss is less common	CT and MRI imaging display a dumbbell-shaped mass over the petrous apex affecting Meckel cave. The trigeminal nerve enhancement extends proximal to the tumor and does not extend into the internal acoustic meatus

Since the most common outcome of acoustic aeuroma is hearing loss, the differential diagnoses for SSNHL (Sudden Sensorineural Hearing Loss ) are listed below.^[4]

Identifiable Causes of Sudden Sensorineural Hearing Loss
Autoimmune	Autoimmune inner ear disease	Neurologic	Migraine
	Behcet’s disease		Multiple sclerosis
	Cogan syndrome		Pontine ischemia
	Systemic lupus erythematosis	Otologic	Fluctuating hearing loss
Infectious	Bacterial Meningitis		Meniere’s disease
	Cryptococcal meningitis		Otosclerosis
	HIV AIDS		Enlarged vestibular aqueduct
	Lassa fever	Toxic	Aminoglycosides
	Lyme disease		Chemotherapeutic agents
	Mumps		Non-steroidal anti-inflammatory drugs
	Mycoplasma infection		Salicylates
	Syphilis	Traumatic	Inner ear concussion
	Toxoplasmosis		Iatrogenic trauma/surgery
Vascular	Cardiovascular bypass		Perilymphatic fistula
	Temporal bone fracture		Cerebrovascular accident/stroke
	Sickle cell disease	Metabolic	Diabetes mellitus
Neoplastic	Acoustic neuroma		Hypothyroidism
	Cerebellopontine angle or petrous meningiomas	Functional	Conversion disorder
	Cerebellopontine angle or petrous apex metastases		Malingering
	Cerebellopontine angle myeloma

The most important differential diagnosis of acoustic neuroma is meningioma of the pontine angle. Below given diagram demonstrates the difference between acoustic neuroma and meningioma of the pontine angle based on CT scan findings:^[5]

<13cm3

Volume

>35cm3

No

Increased attenuation

Yes

No

Marked calcification

Yes

No

Oval shape

Yes

Yes

Round shape

Mostly No

Acoustic Neuroma

No

Tumor reaches dorsum sellae anteriorly

Yes

Meningioma

Mostly No

Apparently broad attachment to bone

Yes

No

Center of tumor anterior to porus

Sometimes Yes

No

Tumor reaches > 2 cm above dorsum

Mostly Yes

Sometimes

Peripheral edema

No

Mostly Yes

Widening of porus or other bone changes

No

Diseases	Clinical manifestations					Para-clinical findings		Gold standard	Additional findings
	Symptoms				Physical examination
						Lab Findings	Imaging
	Acute onset	Recurrency	Nystagmus	Hearing problems
Peripheral
BPPV [6][7][8]	+	+	+/−	−	+ Dix-Hallpike maneuver	−	−	Dix-Hallpike maneuver	May be associated with nausea, vomiting, and gait instability
Vestibular neuritis [9]	+	+/−	+ /− (unilateral)	−	+ Head thrust test	−	−	History/ Physical exam	May be associated with nausea, vomiting, gait instability and previous upper respiratory infection
HSV oticus [10][11][12][13]	+	+/−	−	+/−	Taste loss in the front two-thirds of the tongue Acute facial nerve paralysis Vesicles in the ear canal, the tongue, and/or hard palate	+ VZV antibody titres	In MRI with gadolinium dye we may have enhancement of the facial nerve and cranial nerve VIII	History/ Physical exam	May be associated with otalgia, dry mouth, and dry eyes
Meniere disease [14][15]	+/−	+	+/−	+ (Progressive)	Sensorineural hearing loss	−	In CT scan we may see small or invisible vestibular aqueduct	History/ Physical exam/ Rulling out other diagnoses	May be associated with nausea, vomiting, and tinnitus
Labyrinthine concussion [16][17]	+	−	−	+	high frequency hearing loss	−	We may see other evidences of head trauma or temporal bone fracture	History/ Physical exam	It happens following blunt head trauma May be associated with dizziness or tinnitus
Perilymphatic fistula [18][19][20]	+/−	+	−	+	Tullio phenomenon	−	CT scan may show fluid around the round window recess	History/ Physical exam/Imaging	Can be a complication of a stapedectomy, head injury, or heavy lifting It may be provoked by sneezing, lifting, straining, coughing, and loud sounds
Semicircular canal dehiscence syndrome [21][22]	+/−	+	−	+ (air-bone gaps on audiometry)	Tullio phenomenon	−	CT scan may show defect in the arcuate eminence of the superior semicircular canal	History/ Physical exam/Imaging	It may be provoked by Valsalva maneuver, coughing, and sneezing
Vestibular paroxysmia [23][24][25]	+	+	+/− (Induced by hyperventilation)	−	Impaired caloric testing	−	We may see evidence of vestibulocochlear nerve compression on MRI	History/ Physical exam/Imaging	It may be provoked by head turn or other action They respond well to treatment with carbamazepine or oxcarbazepine
Cogan syndrome [26][27][28]	−	+	+/−	+	Interstitial keratitis Oscillopsia Absent vestibular function on caloric test Systemic vasculitis (Aortitis)	Increased ESR and cryoglobulins	In CT scan we may see calcification or soft tissue attenuation obliterating the intralabyrinthine fluid spaces	History/ Physical exam	It may cause Ménière-like attacks
Vestibular schwannoma [29][30]	−	+	+/−	+	Sensorineural hearing loss + Rinne test Lateralization of Weber test to the normal ear	−	In CT scan we may see erosion, and widening of the internal acoustic meatus Hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI	Imaging	Gadolinium-enhanced MRI scan is definitive diagnostic test of acoutic neuroma
Otitis media [31][32]	+	−	−	+/−	Fever Presence of effusion in the middle ear	Increased acute phase reactants	Opacification of the middle ear	History/ Physical exam	Patient may show other signs and symptoms of upper respiratory infection such az cough, nasal discharge, and fever
Aminoglycoside toxicity [33]	+	−	−	+	Oscillopsia	−	−	History/ Physical exam	May be associated with nausea, vomiting, and ataxia It may be irreversible Gentamicin is the most common one
Recurrent vestibulopathy [34][35]	+	−	−	−	−	−	−	History/ Physical exam	The underlying pathophysiology is unknown It may happen infrequently, every one to two years It may be associated with nausea and vomiting It may overlap with vestibular migraine
Central
Vestibular migrain [36][37]	–	+	+/−	+/−	History of migraine headaches	−	They may have white-matter hyperintensities (WMHs) on MRI	ICHD-3 criteria	It may be associated with anxiety and depression
Epileptic vertigo [38]	−	+	+/−	−	They may experience loss of consciousness and motor/sensory problems	−	−	EEG	They response well to anti-seizure drugs
Multiple sclerosis [39][40][41]	−	+	+/−	−	Lhermitte’s sign Spasticity Increased reflexes Internuclear ophthalmoplegia Optic neuritis Gait disturbance	Elevated concentration of CSF oligoclonal bands	Brain atrophy and some contrast enhancing plaques on CT scan Cerebral plaques disseminating in space and time on MRI	History and physical examination Imaging CSF analysis	MS is at least two times more common among women than men The onset of symptoms is mostly between the age of fifteen to forty years, rarely before age fifteen or after age sixty
Brain tumors [42]	+/−	+	+	+	Papilledema Focal neurological deficits	Cerebral spinal fluid (CSF) may show cancerous cells	On CT scan most of the brain tumors appears as a hypodense mass lesions On MRI most of the brain tumors appears as a hypointense or isointense on T1-weighted scans, or hyperintense on T2-weighted MRI.	Imaging Biopsy	Patieny may experience headache, seizures, visual changes and changes in personality, mood and concentration
Cerebellar infarction/hemorrhage	+	−	++/−	−	Limb ataxia Gait disturbance Dysarthria	−	Based on the time interval between stroke and imaging we may have different presentations	Imaging	Posterior inferior cerebellar artery is the most common artery that causes vertigo
Brain stem ischemia	+	−	+/−	−	Contralateral body weakness Visual field deficits Oculomotor abnormalities Bulbar findings	−	Based on the time interval between stroke and imaging we may have different presentations For more information click here	Imaging	It may be associated with subclavian steal syndrome
Chiari malformation [43][44]	−	+	+	−	Tachycardia Pupillary dilatation Impaired gag reflex Impaired coordination	−	In CT scan we may see hydrocephalus, herniated cerebellar tonsils, and a flattened spinal cord In MRI we may see cerebellar tonsillar herniation, wedge shaped tonsils, syringohydromyelia, small posterior fossa, obstructive hydrocephalus, and brainstem anomalies	Imaging	Patient may experience ringing in the ears
Parkinson [45][46][47]	−	+	−	−	Hypomimia Cogwheel rigidity Resting tremor Gait problems Bradykinesia	−	On brain CT scan, Parkinson disease is characterized by cortical and subcortical atrophy MRI findings in Parkinson disease are reduction in T2 relaxation time and reduced iron content in putamen and GPe	History and physical examination	Patients may present with slowness of movement (bradykinesia), shaking hands while they are at rest (resting tremor) and muscle stiffness (rigidity).

ABBREVIATIONS

VZV= Varicella zoster virus, MRI= Magnetic resonance imaging, ESR= Erythrocyte sedimentation rate, EEG= Electroencephalogram, CSF= Cerebrospinal fluid, GPe= Globus pallidus externa, ICHD= International Classification of Headache Disorders

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D.Sabawoon Mirwais, M.B.B.S, M.D.[3]

The incidence of acoustic neuroma ranges from 0.3 to 1 per 100, 000 individuals. The prevalence of acoustic neuroma is approximately 0.2 per 100,000 individuals. Women are more commonly affected by acoustic neuroma than men. Most cases of acoustic neuroma develop in individuals between 30 and 60 years of age.

Acoustic neuroma accounts for 7 – 8% of all primary intracranial tumors and 75 – 90% of cerebellopontine angle masses. Bilateral vestibular schwannomas are highly suggestive of neurofibromatosis type 2 (NF2), although bilateral tumors are encountered in the familial form of acoustic schwannomas in the absence of other stigmata of NF2.^[1][2][3]

Age-adjusted incidence rates across demographic variables
demographic variables		Rate (per 100,000)
Gender	Male	1.1
	Female	1.0
Race	White	1.1
	Black	0.4
	Other	1.3
Age (yrs), all	<20	0.1
	20-39	0.6
	40-49	1.5
	50-64	2.7
	65+	2.0
Age (yrs), Male	<20	0
	20-39	0.5
	40-49	1.6
	50-64	2.6
	65+	2.4
Age (yrs), Female	<20	0.1
	20-39	0.7
	40-49	1.3
	50-64	2.8
	65+	1.7

The incidence of acoustic neuroma ranges from 0.3 to 1 per 100, 000 individuals.^[4][5][6][7]

The prevalence of acoustic neuroma is approximately 0.2 per 100,000 individuals.^[8]

The in-hospital mortality rate of surgery for acoustic neuroma in the United States is 0.5%.^[9]

• Most cases of acoustic neuroma develop in individuals between the ages of 30 and 60.
• Although quite rare, they can also develop in children.^[10]

Acoustic neuroma can affect women more often than men.^[11]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D.

Common risk factors in the development of acoustic neuroma are neurofibromatosis type 2 and radiation exposure. Less common risk factors include sporadic defects in tumor suppressor genes, exposure to loud noise, history of parathyroid adenoma, and the use of cellular phones.

• Neurofibromatosis type 2^[1][2]
• Childhood exposure to radiation of the head and neck^[3][4]
• Exposure to high-dose ionizing radiation^[5][6]

• Sporadic defects in tumor suppressor genes in some individuals
• Exposure to loud noise on a consistent basis^[7]
• A concomitant history of having had a parathyroid adenoma^[8]
• The use of cellular phones^{[9][10][11][12][13]}

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According to the U.S. Preventive Services Task Force (USPTF), screening for acoustic neuroma is not recommended. Evaluation for NF-2 should be done in individuals with an apparently sporadic vestibular schwannoma occurring before the age of 30, or a spinal tumor or meningioma occurring at less than 20 years of age.

• According to U.S. Preventive Services Task Force (USPTF), screening for acoustic neuroma is not recommended.
• Annual hearing screening with BAER (Brain stem auditory evoked response test), with referral to an audiologist for amplification, or speech therapy is recommended in patients with NF-2.
• Evaluation for NF-2 should be done in individuals with an apparently sporadic vestibular schwannoma occurring before the age of 30, or a spinal tumor or meningioma occurring at less than 20 years of age.^[1][2]

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