Acoustic neuroma overview: Difference between revisions
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==Overview== | ==Overview== | ||
Acoustic | 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 [[Deafness|deaf]], [[Blindness|blind]], with uncontrollable [[Nausea and vomiting|vomiting]], [[Headache|headaches]], and [[Twitching|facial jerking]]. He died at 21 years of age. Sir Charles Bell provided the first known report of a case of [[Meckel's cave|Meckel cave]] neuroma in 1833, demonstrating the relationship of the [[tumor]] to the [[Cerebellum|cerebellopontine angle]]. Sir Charles Ballance successfully removed an acoustic neuroma in 1894, although the [[patient]] had right side [[Facial nerve paralysis|facial paralysis]] and [[Trigeminal nerve|trigeminal]] [[anesthesia]]. Since then, tremendous efforts of many [[Surgeon|surgeons]] have been continuing to provide [[Surgery|surgical]] approaches to improve outcomes of treatments and decrease [[Adverse effect (medicine)|side effects]] of interventions. Acoustic neuroma may be [[Classification|classified]] according to the findings on [[magnetic resonance imaging]] ([[Magnetic resonance imaging|MRI]]) or it can also be [[Classification|classified]] based on [[microscopic]] [[histopathology]], and whether or not they are associated with [[Neurofibromatosis type II|neurofibromatosis type 2]]. Based on [[microscopic]] [[histopathology]], acoustic neuroma may be [[Classification|classified]] into four subtypes: conventional [[schwannoma]], cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. While acoustic neuromas are benign [[Tumor|tumors]], there is no established system for the [[Cancer staging|staging]] of acoustic neuromas. Koos [[Grading (tumors)|grading]] scale provides four [[Grading (tumors)|grades]] based on extrameatal extension and compression of the [[brain stem]] , a reliable method for [[tumor]] [[classification]] which is used in practice. Acoustic neuroma arises from [[Schwann cells]], which are the [[Cell (biology)|cells]] involved in the conduction of [[Nervous system|nervous]] impulses along [[axons]], [[nerve]] development and [[Nerve regeneration|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 [[Cell (biology)|cells]] with [[Cytoplasm|cytoplasmic]] processes arranged in [[Fascicle|fascicles]], little [[stromal]] [[matrix]] and verocay bodies. Antoni type B growth pattern is composed of loose meshwork of [[Cell (biology)|cells]], less dense [[Cell (biology)|cellular]] [[matrix]], microcysts and myxoid change. Numerous studies show the correlation between [[Neurofibromatosis type II|Neurofibromatosis type 2 (NF2)]] and acoustic neuroma. Other causes can include exposure to occupational noise and cellular telephone use. 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]]. 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. Common [[Risk factor|risk factors]] in the development of acoustic neuroma are [[neurofibromatosis type 2]] and [[radiation]] exposure. Less common [[Risk factor|risk factors]] include sporadic defects in [[Tumor suppressor gene|tumor suppressor genes]], exposure to loud noise, history of [[parathyroid adenoma]], and the use of cellular phones. According to the U.S. Preventive Services Task Force (USPTF), [[Screening (medicine)|screening]] for [[acoustic neuroma]] is not recommended. Evaluation for [[Neurofibromatosis type II|NF-2]] should be done in individuals with an apparently sporadic [[Acoustic neuroma|vestibular schwannoma]] occurring before the age of 30, or a [[spinal tumor]] or [[meningioma]] occurring at less than 20 years of age. 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 [[Patient|patients]]. The [[tumor]] does not [[Metastasis|metastasize]] to other parts of the [[Human body|body]]. [[Hearing impairment|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 [[Visual system|vision]] problems and difficulty [[breathing]] and [[swallowing]]. [[Complication (medicine)|Complications]] of acoustic neuroma include [[Hearing impairment|hearing loss]], [[Hydrocephalus]], and recurrence of the [[tumor]]. Small, slow-growing [[Tumor|tumors]] may not need treatment. [[Patient|Patients]] experience similar [[quality of life]] whether treatment is [[observation]], [[radiation]], or [[surgery]]. [[Gadolinium]]-enhanced [[Magnetic resonance imaging|MRI scan]] is the definitive [[diagnostic test]] for acoustic neuroma and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]]. On [[brain]] [[Magnetic resonance imaging|MRI]], acoustic neuroma characterized by hypointense mass on T1-weighted [[Magnetic resonance imaging|MRI]], and hyperintense mass on T2-weighted [[Magnetic resonance imaging|MRI]]. Chronic gradual unilateral [[hearing impairment]] is the most common complaint present in 95% of the [[Patient|patients]]. Common [[Symptom|symptoms]] include chronic gradual unilateral [[Hearing impairment|hearing loss]], ringing in the [[ear]], [[Disequilibrium]], [[Face|facial]] [[Paresthesia|numbness]], [[Face|facial]] [[pain]], and [[Headache]]. Less common [[Symptom|symptoms]] include [[Face|facial]] [[muscle weakness]], [[Taste alteration|taste disturbances]], [[Xerophthalmia|dryness of the eyes]], sudden [[Tears|lacrimation]], [[Dysarthria|speech problem]], [[Dysphagia|difficulty swallowing]], [[Aspiration (medicine)|aspiration]], [[Dysphonia|hoarseness]], and [[Otalgia|ear pain]]. [[Patient|Patients]] with acoustic neuroma usually appear normal. [[Physical examination]] of [[Patient|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]], [[Face|facial]] [[twitching]] or [[hypesthesia]], [[Drooling]], [[Facial paralysis|drooping on one side of the face]], loss of taste, and [[ataxia]]. There are no [[Diagnosis|diagnostic]] [[Medical laboratory|laboratory]] findings associated with acoustic neuroma. There are no [[electrocardiogram]] findings associated with acoustic neuroma. There are no [[X-rays|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 [[Diagnosis|diagnostic]] of acoustic neuroma. Findings on [[Computed tomography|CT scan]] diagnostic of acoustic neuroma include erosion and widening of the [[Internal auditory meatus|internal acoustic canal]]. [[Gadolinium]]-enhanced [[Magnetic resonance imaging|MRI scan]] is the definitive [[diagnostic test]] for acoustic neuroma and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]]. On [[brain]] [[Magnetic resonance imaging|MRI]], acoustic neuroma characterized by hypointense mass on T1-weighted [[Magnetic resonance imaging|MRI]], and hyperintense mass on T2-weighted [[Magnetic resonance imaging|MRI]]. There are no other [[imaging]] findings associated with acoustic neuroma. [[Audiometry]] as the best initial [[Screening (medicine)|screening]] [[test]] for the [[diagnosis]] of acoustic neuroma. It can detect asymmetric [[Sensorineural hearing loss|sensorineural hearing impairment]] in about 95% of the [[Patient|patients]]. Brain stem-evoked response audiometry (ABR, BAER, or BSER) may be done in some cases with unexplained asymmetries in standard [[Audiometry|audiometric testing]] as a further [[screening]] measure and an abnormal [[Hearing (sense)|auditory]] [[brain stem]] response [[test]] should be followed by an [[MRI]]. The mainstay of [[therapy]] for acoustic neuroma is [[surgery]] and [[radiation therapy]]. Since acoustic neuroma tends to be slow-growing and is a [[benign]] tumor, careful observation with follow-up [[Magnetic resonance imaging|MRI scans]] every 6 to 12 months may be appropriate for elderly [[Patient|patients]], [[Patient|patients]] with small [[Tumor|tumors]], [[Patient|patients]] with significant [[medical conditions]], and [[Patient|patients]] who refuse treatment. [[Surgery]] is the mainstay of treatment for acoustic neuroma. [[Patient|Patients]] with age under 65 years, medium to large-grade [[Tumor|tumors]], significant [[Hearing impairment|hearing loss]], or higher [[headache]] severity scores will have more satisfying outcomes from [[surgery]] in comparison with [[observation]]. There are three main [[Surgery|surgical approaches]] for the removal of an acoustic neuroma: [[Translabyrinthine approach|translabyrinthine]], retrosigmoid or [[Occipital|sub-occipital]], and middle [[fossa]]. Selection of a particular approach is based on several factors including the size and location of the [[tumor]] and whether or not preservation of [[Hearing (sense)|hearing]] is a goal. There are no established measures for the [[Prevention (medical)|primary prevention]] of acoustic neuroma. [[Prevention (medical)|Secondary prevention]] strategies following acoustic neuroma treatment include follow-up [[Magnetic resonance imaging|MRI scans]]. | ||
==Historical Perspective== | ==Historical Perspective== | ||
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 [[Nausea and vomiting|vomiting]] | 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 [[Deafness|deaf]], [[Blindness|blind]], with uncontrollable [[Nausea and vomiting|vomiting]], [[Headache|headaches]], and [[Twitching|facial jerking]]. He died at 21 years of age. Sir Charles Bell provided the first known report of a case of [[Meckel's cave|Meckel cave]] neuroma in 1833, demonstrating the relationship of the [[tumor]] to the [[Cerebellum|cerebellopontine angle]]. Sir Charles Ballance successfully removed an acoustic neuroma in 1894, although the [[patient]] had right side [[Facial nerve paralysis|facial paralysis]] and [[Trigeminal nerve|trigeminal]] [[anesthesia]]. Since then, tremendous efforts of many [[Surgeon|surgeons]] have been continuing to provide [[Surgery|surgical]] approaches to improve outcomes of treatments and decrease [[Adverse effect (medicine)|side effects]] of interventions. | ||
==Classification== | ==Classification== | ||
Acoustic neuroma may be classified according to findings on [[magnetic resonance imaging]] ([[Magnetic resonance imaging|MRI]]) or classified based on microscopic [[histopathology]], and whether or not they are associated with [[neurofibromatosis]] | Acoustic neuroma may be [[Classification|classified]] according to the findings on [[magnetic resonance imaging]] ([[Magnetic resonance imaging|MRI]]) or it can also be [[Classification|classified]] based on [[microscopic]] [[histopathology]], and whether or not they are associated with [[Neurofibromatosis type II|neurofibromatosis type 2]]. Based on [[microscopic]] [[histopathology]], acoustic neuroma may be [[Classification|classified]] into four subtypes: conventional [[schwannoma]], cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. While acoustic neuromas are benign [[Tumor|tumors]], there is no established system for the [[Cancer staging|staging]] of acoustic neuromas. Koos [[Grading (tumors)|grading]] scale provides four [[Grading (tumors)|grades]] based on extrameatal extension and compression of the [[brain stem]] , a reliable method for [[tumor]] [[classification]] which is used in practice. | ||
==Pathophysiology== | ==Pathophysiology== | ||
Acoustic neuroma arises from [[Schwann cells]], which are the cells | Acoustic neuroma arises from [[Schwann cells]], which are the [[Cell (biology)|cells]] involved in the conduction of [[Nervous system|nervous]] impulses along [[axons]], [[nerve]] development and [[Nerve regeneration|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 [[Cell (biology)|cells]] with [[Cytoplasm|cytoplasmic]] processes arranged in [[Fascicle|fascicles]], little [[stromal]] [[matrix]] and verocay bodies. Antoni type B growth pattern is composed of loose meshwork of [[Cell (biology)|cells]], less dense [[Cell (biology)|cellular]] [[matrix]], microcysts and myxoid change. | ||
==Causes== | ==Causes== | ||
Numerous studies show the correlation between [[Neurofibromatosis type II|Neurofibromatosis type 2 (NF2)]] and acoustic neuroma. Other causes can include exposure to occupational noise and cellular telephone use. | |||
==Differential Diagnosis== | ==Differential Diagnosis== | ||
Acoustic neuroma must be differentiated from [[meningioma]], epidermoid, [[facial]] | 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]]. | ||
==Epidemiology | ==Epidemiology and Demographics== | ||
The [[incidence]] of acoustic neuroma | 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. | ||
==Risk Factors== | ==Risk Factors== | ||
Common risk factors in the development of acoustic neuroma are [[neurofibromatosis type 2]] | Common [[Risk factor|risk factors]] in the development of acoustic neuroma are [[neurofibromatosis type 2]] and [[radiation]] exposure. Less common [[Risk factor|risk factors]] include sporadic defects in [[Tumor suppressor gene|tumor suppressor genes]], exposure to loud noise, history of [[parathyroid adenoma]], and the use of cellular phones. | ||
==Screening== | ==Screening== | ||
According to the U.S. Preventive Services Task Force (USPTF), screening for [[acoustic neuroma]] is not recommended. Evaluation for [[Neurofibromatosis type II|NF-2]] | According to the U.S. Preventive Services Task Force (USPTF), [[Screening (medicine)|screening]] for [[acoustic neuroma]] is not recommended. Evaluation for [[Neurofibromatosis type II|NF-2]] should be done in individuals with an apparently sporadic [[Acoustic neuroma|vestibular schwannoma]] occurring before the age of 30, or a [[spinal tumor]] or [[meningioma]] occurring at less than 20 years of age. | ||
==Natural History, Complications and Prognosis== | ==Natural History, Complications and Prognosis== | ||
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. | 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 [[Patient|patients]]. The [[tumor]] does not [[Metastasis|metastasize]] to other parts of the [[Human body|body]]. [[Hearing impairment|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 [[Visual system|vision]] problems and difficulty [[breathing]] and [[swallowing]]. [[Complication (medicine)|Complications]] of acoustic neuroma include [[Hearing impairment|hearing loss]], [[Hydrocephalus]], and recurrence of the [[tumor]]. Small, slow-growing [[Tumor|tumors]] may not need treatment. [[Patient|Patients]] experience similar [[quality of life]] whether treatment is [[observation]], [[radiation]], or [[surgery]]. | ||
== | ==Diagnostic Study of Choice== | ||
[[Gadolinium]]-enhanced [[Magnetic resonance imaging|MRI scan]] is the definitive [[diagnostic test]] for acoustic neuroma and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]]. On [[brain]] [[Magnetic resonance imaging|MRI]], acoustic neuroma characterized by hypointense mass on T1-weighted [[Magnetic resonance imaging|MRI]], and hyperintense mass on T2-weighted [[Magnetic resonance imaging|MRI]]. | |||
==History and Symptoms== | ==History and Symptoms== | ||
Chronic gradual unilateral [[hearing impairment]] is the most common complaint present in 95% of the [[Patient|patients]]. Common [[Symptom|symptoms]] include chronic gradual unilateral [[Hearing impairment|hearing loss]], ringing in the [[ear]], [[Disequilibrium]], [[Face|facial]] [[Paresthesia|numbness]], [[Face|facial]] [[pain]], and [[Headache]]. Less common [[Symptom|symptoms]] include [[Face|facial]] [[muscle weakness]], [[Taste alteration|taste disturbances]], [[Xerophthalmia|dryness of the eyes]], sudden [[Tears|lacrimation]], [[Dysarthria|speech problem]], [[Dysphagia|difficulty swallowing]], [[Aspiration (medicine)|aspiration]], [[Dysphonia|hoarseness]], and [[Otalgia|ear pain]]. | |||
==Physical Examination== | ==Physical Examination== | ||
[[Patient|Patients]] with acoustic neuroma usually appear normal. [[Physical examination]] of [[Patient|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]], [[Face|facial]] [[twitching]] or [[hypesthesia]], [[Drooling]], [[Facial paralysis|drooping on one side of the face]], loss of taste, and [[ataxia]]. | |||
==Laboratory Findings== | ==Laboratory Findings== | ||
There are no diagnostic laboratory findings associated with acoustic neuroma. | There are no [[Diagnosis|diagnostic]] [[Medical laboratory|laboratory]] findings associated with acoustic neuroma. | ||
==Electrocardiogram== | ==Electrocardiogram== | ||
There are no electrocardiogram findings associated with acoustic neuroma. | There are no [[electrocardiogram]] findings associated with acoustic neuroma. | ||
== | ==X Ray== | ||
There are no | There are no [[X-rays|x-ray]] findings associated with acoustic neuroma. | ||
==Echocardiography/Ultrasound== | |||
There are no [[echocardiography]] or [[ultrasound]] findings associated with acoustic neuroma. | |||
==CT== | |||
[[CT scan]] of the [[head]] may be [[Diagnosis|diagnostic]] of acoustic neuroma. Findings on [[Computed tomography|CT scan]] diagnostic of acoustic neuroma include erosion and widening of the [[Internal auditory meatus|internal acoustic canal]]. | |||
==MRI== | ==MRI== | ||
[[Gadolinium]]-enhanced [[MRI scan]] is diagnostic | [[Gadolinium]]-enhanced [[Magnetic resonance imaging|MRI scan]] is the definitive [[diagnostic test]] for acoustic neuroma and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]]. On [[brain]] [[Magnetic resonance imaging|MRI]], acoustic neuroma characterized by hypointense mass on T1-weighted [[Magnetic resonance imaging|MRI]], and hyperintense mass on T2-weighted [[Magnetic resonance imaging|MRI]]. | ||
==Other Imaging Findings== | ==Other Imaging Findings== | ||
There are no other imaging findings associated with acoustic neuroma. | There are no other [[imaging]] findings associated with acoustic neuroma. | ||
==Other Diagnostic Studies== | ==Other Diagnostic Studies== | ||
[[Audiometry]] as the best initial [[Screening (medicine)|screening]] | [[Audiometry]] as the best initial [[Screening (medicine)|screening]] [[test]] for the [[diagnosis]] of acoustic neuroma. It can detect asymmetric [[Sensorineural hearing loss|sensorineural hearing impairment]] in about 95% of the [[Patient|patients]]. Brain stem-evoked response audiometry (ABR, BAER, or BSER) may be done in some cases with unexplained asymmetries in standard [[Audiometry|audiometric testing]] as a further [[screening]] measure and an abnormal [[Hearing (sense)|auditory]] [[brain stem]] response [[test]] should be followed by an [[MRI]]. | ||
==Medical Therapy== | ==Medical Therapy== | ||
The mainstay of therapy for acoustic neuroma is [[surgery]] and [[radiation therapy]]. Since acoustic neuroma tends to be slow-growing and is [[benign]] | The mainstay of [[therapy]] for acoustic neuroma is [[surgery]] and [[radiation therapy]]. Since acoustic neuroma tends to be slow-growing and is a [[benign]] tumor, careful observation with follow-up [[Magnetic resonance imaging|MRI scans]] every 6 to 12 months may be appropriate for elderly [[Patient|patients]], [[Patient|patients]] with small [[Tumor|tumors]], [[Patient|patients]] with significant [[medical conditions]], and [[Patient|patients]] who refuse treatment. | ||
==Surgery== | ==Surgery== | ||
[[Surgery]] is the mainstay of treatment for acoustic neuroma. Patient with age under 65 years | [[Surgery]] is the mainstay of treatment for acoustic neuroma. [[Patient|Patients]] with age under 65 years, medium to large-grade [[Tumor|tumors]], significant [[Hearing impairment|hearing loss]], or higher [[headache]] severity scores will have more satisfying outcomes from [[surgery]] in comparison with [[observation]]. There are three main [[Surgery|surgical approaches]] for the removal of an acoustic neuroma: [[Translabyrinthine approach|translabyrinthine]], retrosigmoid or [[Occipital|sub-occipital]], and middle [[fossa]]. Selection of a particular approach is based on several factors including the size and location of the [[tumor]] and whether or not preservation of [[Hearing (sense)|hearing]] is a goal. | ||
==Primary Prevention== | ==Primary Prevention== | ||
There are no | There are no established measures for the [[Prevention (medical)|primary prevention]] of acoustic neuroma. | ||
==Secondary Prevention== | ==Secondary Prevention== | ||
Secondary prevention strategies following acoustic neuroma treatment include follow-up [[MRI scans]]. | [[Prevention (medical)|Secondary prevention]] strategies following acoustic neuroma treatment include follow-up [[Magnetic resonance imaging|MRI scans]]. | ||
==References== | ==References== | ||
<references /> | <references /> | ||
Revision as of 20:16, 26 April 2019
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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]
Overview
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 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. 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. 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. 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. 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. 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. 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. 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 similar quality of life whether treatment is observation, radiation, or surgery. Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter. On brain MRI, acoustic neuroma characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI. Chronic gradual unilateral hearing impairment is the most common complaint present in 95% of the patients. Common symptoms include chronic gradual unilateral hearing loss, ringing in 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. 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. Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter. On brain MRI, acoustic neuroma characterized by hypointense 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. The mainstay of therapy for acoustic neuroma is surgery and radiation therapy. Since acoustic neuroma tends to be slow-growing and is a benign tumor, careful observation with follow-up MRI scans every 6 to 12 months may be appropriate for elderly patients, patients with small tumors, patients with significant medical conditions, and patients who refuse treatment. Surgery is the mainstay of treatment for acoustic neuroma. Patients with age under 65 years, medium to large-grade tumors, significant hearing loss, or higher headache severity scores will have more satisfying outcomes from surgery in comparison with observation. There are three main surgical approaches for the removal of an acoustic neuroma: translabyrinthine, retrosigmoid or sub-occipital, and middle fossa. Selection of a particular approach is based on several factors including the size and location of the tumor and whether or not preservation of hearing is a goal. There are no established measures for the primary prevention of acoustic neuroma. Secondary prevention strategies following acoustic neuroma treatment include follow-up MRI scans.
Historical Perspective
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.
Classification
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.
Pathophysiology
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.
Causes
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.
Differential Diagnosis
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.
Epidemiology and Demographics
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.
Risk Factors
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.
Screening
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.
Natural History, Complications and Prognosis
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 similar quality of life whether treatment is observation, radiation, or surgery.
Diagnostic Study of Choice
Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter. On brain MRI, acoustic neuroma characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.
History and Symptoms
Chronic gradual unilateral hearing impairment is the most common complaint present in 95% of the patients. Common symptoms include chronic gradual unilateral hearing loss, ringing in 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.
Physical Examination
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.
Laboratory Findings
There are no diagnostic laboratory findings associated with acoustic neuroma.
Electrocardiogram
There are no electrocardiogram findings associated with acoustic neuroma.
X Ray
There are no x-ray findings associated with acoustic neuroma.
Echocardiography/Ultrasound
There are no echocardiography or ultrasound findings associated with acoustic neuroma.
CT
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.
MRI
Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter. On brain MRI, acoustic neuroma characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.
Other Imaging Findings
There are no other imaging findings associated with acoustic neuroma.
Other Diagnostic Studies
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.
Medical Therapy
The mainstay of therapy for acoustic neuroma is surgery and radiation therapy. Since acoustic neuroma tends to be slow-growing and is a benign tumor, careful observation with follow-up MRI scans every 6 to 12 months may be appropriate for elderly patients, patients with small tumors, patients with significant medical conditions, and patients who refuse treatment.
Surgery
Surgery is the mainstay of treatment for acoustic neuroma. Patients with age under 65 years, medium to large-grade tumors, significant hearing loss, or higher headache severity scores will have more satisfying outcomes from surgery in comparison with observation. There are three main surgical approaches for the removal of an acoustic neuroma: translabyrinthine, retrosigmoid or sub-occipital, and middle fossa. Selection of a particular approach is based on several factors including the size and location of the tumor and whether or not preservation of hearing is a goal.
Primary Prevention
There are no established measures for the primary prevention of acoustic neuroma.
Secondary Prevention
Secondary prevention strategies following acoustic neuroma treatment include follow-up MRI scans.