Acoustic neuroma overview
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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]
Overview
Acoustic neuroma, also known as vestibular schwannoma, is a tumor that arises from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses.[1] Acoustic neuroma is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (8th cranial nerve).[2] Acoustic neuroma may be classified into several subtypes based on MRI scan, microscopic histopathology, and whether or not they are associated with neurofibromatosis type 2. Acoustic neuroma may be classified based on MRI scan into three subtypes: entirely canalicular, intracranial extension without brainstem distortion, and intracranial extension with brain stem distortion. Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma.[3] Acoustic neuroma arises from Schwann cells, which are the cells that are normally 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.[2] Antoni type A growth pattern is composed of elongated cells with cytoplasmic process arranged in fascicles, little stromal matrix and verocay bodies. Antoni type B growth pattern is composed of loose meshwork of cells, less densely cellular matrix, microcysts and myxoid change. The majority of cases of acoustic neuroma are idiopathic.[1] Common risk factors in the development of acoustic neuroma are neurofibromatosis type 2, radiation, exposure to loud noise, history of parathyroid adenoma, and the use of cellular phones.[1] Symptoms of acoustic neuroma include hearing loss, tinnitus, vertigo, headaches, facial weakness, facial numbness and tingling, dizziness, taste changes, difficulty swallowing and hoarseness and, confusion.[1] Gadolinium-enhanced MRI scan is diagnostic of acoutic neuroma. On brain MRI, acoustic neuroma is characterized by hypointense mass on T1-weighted MRI and hyperintense mass on T2-weighted MRI.[1]Head CT scan may be diagnostic of acoustic neuroma. Findings on CT scan diagnostic of acoustic neuroma include erosion and widening of the internal acoustic canal.[2] Other diagnostic studies for acoustic neuroma include audiometry, auditory brainstem response test, and electronystagmography.[1] The predominant therapy for acoustic neuroma is surgical resection. Adjunctive radiation and radiosurgery may be required. Since acoustic neuromas tend to be slow-growing and are benign tumors, careful observation over a period of time may be appropriate for some patients.[1] Surgery is the mainstay of treatment for acoustic neuroma.[1]
Historical Perspective
Bilateral acoustic neuroma was first discovered by Wishart in 1922.[4]
Classification
Acoustic neuroma may be classified into several subtypes based on MRI scan, microscopic histopathology, and whether or not they are associated with neurofibromatosis type 2. Acoustic neuroma may be classified based on MRI scan into three subtypes: entirely canalicular, intracranial extension without brainstem distortion, and intracranial extension with brain stem distortion. Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma.[3]
Pathophysiology
Acoustic neuroma arises from Schwann cells, which are the cells that are normally 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.[1] Antoni type A growth pattern is composed of elongated cells with cytoplasmic process arranged in fascicles, little stromal matrix and verocay bodies. Antoni type B growth pattern is composed of loose meshwork of cells, less densely cellular matrix, microcysts and myxoid change.
Causes
The majority of cases of acoustic neuroma are idiopathic.[1]
Differential Diagnosis
Acoustic neuroma must be differentiated from meningioma, epidermoid, facial nerve schwannoma, trigeminal schwannoma, ependymoma, leiomymoma, intranodal palisaded myofibroblastoma, malignant peripheral nerve sheath tumour (MPNST), gastrointestinal stromal tumor, neurofibroma, Meniere's disease, and Bell's palsy.[2]
Epidemiology And Demographics
The incidence of acoustic neuroma is approximately 1 per 100,000 individuals worldwide. The prevalence of acoustic neuroma is approximately 2,500 new cases per 100,000 individuals. Women are more commonly affected with acoustic neuroma than men. Most cases of acoustic neuroma develop in individuals between 30 and 60 years of age.[5]
Risk Factors
Common risk factors in the development of acoustic neuroma are neurofibromatosis type 2, radiation, exposure to loud noise, history of parathyroid adenoma, and the use of cellular phones.[1]
Screening
According to the USPTF, screening for acoustic neuroma is not recommended. Evaluation for NF-2 should be done in individuals with an apparently sporadic acoustic neuroma occurring at less than 30 years of age, or a spinal tumor or meningioma occurring at less than 20 years of age.[6]
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. Acoustic neuroma patients have a very good prognosis with minimal complications if treated.[7]
Staging
Acoustic neuroma may be classified into three subtypes based on tumor size and into six subtypes based on tumor location.
History and Symptoms
Symptoms of acoustic neuroma include hearing loss, tinnitus, vertigo, headaches, facial weakness, facial numbness and tingling, dizziness, taste changes, difficulty swallowing and hoarseness and confusion.[1]
Physical Examination
Common physical examination findings of acoustic neuroma include abnormal Weber test, decreased or absent ipsilateral corneal reflex, and facial twitching or hypesthesia.[5]
Laboratory Findings
There are no diagnostic laboratory findings associated with acoustic neuroma.
Electrocardiogram
There are no electrocardiogram findings associated with acoustic neuroma.
Chest X Ray
There are no chest x ray findings associated with acoustic neuroma.
MRI
Gadolinium-enhanced MRI scan is diagnostic of acoutic neuroma. On brain MRI, acoustic neuroma is characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.[1]
CT
Findings on CT scan diagnostic of acoustic neuroma include erosion and widening of the internal acoustic canal.[2]
Echocardiography or Ultrasound
There are no echocardiography or ultrasound findings associated with acoustic neuroma.
Other Imaging Findings
There are no other imaging findings associated with acoustic neuroma.
Other Diagnostic Studies
Other diagnostic studies for acoustic neuroma include audiometry, auditory brainstem response test, and electronystagmography.[1]
Medical Therapy
The predominant therapy for acoustic neuroma is surgical resection. Adjunctive radiation and radiosurgery may be required. Since acoustic neuromas tend to be slow-growing and are benign tumors, careful observation over a period of time may be appropriate for some patients.[1]
Surgery
Surgery is the mainstay of treatment for acoustic neuroma.[1]
Primary Prevention
There are no primary preventive measures available for acoustic neuroma.
Secondary Prevention
Secondary prevention strategies following acoustic neuroma treatment include follow-up MRI scans.
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 Vestibular Schwannoma. Wikipedia(2015) https://en.wikipedia.org/wiki/Vestibular_schwannoma Accessed on October 2 2015
- ↑ 2.0 2.1 2.2 2.3 2.4 Acoustic Schwannoma. Radiopedia(2015) http://radiopaedia.org/articles/acoustic-schwannoma Accessed on October 2 2015
- ↑ 3.0 3.1 Schwannoma. Librepathology(2015) http://librepathology.org/wiki/index.php/Schwannoma Accessed on October 2 2015
- ↑ Welling DB (1998). "Clinical manifestations of mutations in the neurofibromatosis type 2 gene in vestibular schwannomas (acoustic neuromas)". Laryngoscope. 108 (2): 178–89. PMID 9473065.
- ↑ 5.0 5.1 Acoustic neuroma. Medline Plus(2015) https://www.nlm.nih.gov/medlineplus/ency/article/000778.htm Accessed on October 2 2015
- ↑ Evans DG, Ramsden RT, Gokhale C, Bowers N, Huson SM, Wallace A (2007). "Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma?". Clin Genet. 71 (4): 354–8. doi:10.1111/j.1399-0004.2007.00778.x. PMID 17470137.
- ↑ Acoustic neuroma. NHS(2014) http://www.nhs.uk/Conditions/Acoustic-neuroma/Pages/Complications.aspx Accessed on October 2 2015