Acoustic neuroma overview

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Overview

Historical Perspective

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Epidemiology and Demographics

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Natural History, Complications and Prognosis

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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.

References


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