Schwannoma overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief:  Maneesha Nandimandalam, M.B.B.S.[2]

## Overview

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Schwannoma may be classified according to pathology into 4 subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. Based on location it is classified into intracranial schwannoma,Acoustic neuroma (most common),trigeminal schwannoma, facial nerve schwannoma. Schwannomas are composed of spindle cells which demonstrate two growth patterns Antoni type A and Antoni type B. Antoni type A patternin which elongated cells are densely packed and arranged in fascicles. Palisades are sometimes seen, when prominent these form verocay bodies. Antoni type B pattern cells are less compact and are prone to cystic degeneration. Schwannoma variants include ancient schwannoma, cellular schwannoma, melanotic schwannoma, plexiform schwannoma. The incidence vestibular schwannoma is approximately 1 per 100,000 individuals. People of all age groups may develop vestibular schwannoma. The incidence is more common between the 3rd and 5th decades of life. The median age at diagnosis is 5th decade.Symptoms of intracranial schwannoma include hearing loss, tinnitus, dysphagia, ataxia, Vertigo, Facial weakness, Dizziness, spinal schwannomas present with Back pain, Urinary incontinence, Urinary retention, Clumsiness, Weakness, Paresthesias. Surgery is the mainstay of treatment for schwannoma. There are three main approaches like translybyrinthine, retrosigmoid, middle fossa. The common complications of surgery include vertigo, hearing loss is another important complication associated with the operation, post-operative headache, cerebrospinal fluid (CSF) leakage, facial paralysis

## Historical perspective

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## Classification

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Schwannoma may be classified according to pathology into 4 subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. Based on location it is classified into intracranial schwannoma,Acoustic neuroma (most common),trigeminal schwannoma, facial nerve schwannoma, jugular foramen schwannoma, hypoglossal schwannomas, spinal schwannoma, intercostal nerve schwannoma, intramuscular schwannoma, posterior mediastinum schwannoma, retroperitoneum schwannoma, intracerebral schwannoma.

## Pathophysiology

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Schwannomas may arise sporadically or in association with Neurofibromatosis type 2 as a result of mutations involving merlin protein. Loss of function of a tumor suppressor gene called merlin gene is noted commonly. Schwannomas are composed of spindle cells which demonstrate two growth patterns Antoni type A and Antoni type B. Antoni type A patternin which elongated cells are densely packed and arranged in fascicles. Palisades are sometimes seen, when prominent these form verocay bodies. Antoni type B pattern cells are less compact and are prone to cystic degeneration. Schwannoma variants include ancient schwannoma, cellular schwannoma, melanotic schwannoma, plexiform schwannoma. Immunohistochemistry positive for S100, collagen IV, CD34, neurofilament protein, podoplanin, calretinin, Sox10. Associated conditions include neurofibromatosis type 2, schwannomatosis, carney's complex.

## Causes

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## Epidemiology and Demographics

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The incidence vestibular schwannoma is approximately 1 per 100,000 individuals. People of all age groups may develop vestibular schwannoma. The incidence is more common between the 3rd and 5th decades of life. The median age at diagnosis is 5th decade. The incidence seems to be higher in Asian population and lower in Hispanics and African-Americans. Vestibular schwannoma affects men and women equally with a slight predilection towards female population.

## Risk Factors

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## Screening

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## Differentiating Schwannoma from other Diseases

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On the basis of seizure, visual disturbance, and constitutional symptoms, schwannoma must be differentiated from oligodendroglioma, meningioma, hemangioblastoma, pituitary adenoma, astrocytoma, primary CNS lymphoma, medulloblastoma, ependymoma, craniopharyngioma, pinealoma, AV malformation, brain aneurysm, bacterial brain abscess, tuberculosis, toxoplasmosis, hydatid cyst, CNS cryptococcosis, CNS aspergillosis, and brain metastasis.

## Natural History, Complications and Prognosis

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## Diagnosis

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### History and Symptoms

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Symptoms of intracranial schwannoma include hearing loss, tinnitus, dysphagia, ataxia, Vertigo, Facial weakness, Dizziness, spinal schwannomas present with Back pain, Urinary incontinence, Urinary retention, Clumsiness, Weakness, Paresthesias

### Physical Examination

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### X-Ray

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There are no X-ray findings associated with schwannoma.

### CT

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CT findings of schwannoma include low to intermediate attenuation, intense contrast enhancement, small tumors typically demonstrate homogeneous enhancement and larger tumors may show heterogeneous enhancement, adjacent bone remodelling with smooth corticated edges

### MRI

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Schwannomas appear on T1 as isointense or hypointense, T1 C+ (Gd) intense enhancement,T2- heterogeneously hyperintense (Antoni A: relatively low, Antoni B: high), cystic degenerative areas may be present, especially in larger tumors, T2- larger tumors often have areas of hemosiderin. Signs can also be useful in diagnosing such as split-fat sign: thin peripheral rim of fat best seen on planes along long axis of the lesion in non-fat-suppressed sequences, target sign: peripheral high T2 signal, central low signal rarely seen intracranially, fascicular sign: multiple small ring-like structures.

### Ultrasound

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### Other Imaging Findings

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### Other Diagnostic Studies

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## Treatment

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### Medical Therapy

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### Surgery

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The feasibility of surgery depends on the stage of schwannoma at diagnosis. Surgery is the mainstay of treatment for schwannoma. There are three main approaches like translybyrinthine, retrosigmoid, middle fossa. The common complications of surgery include vertigo, hearing loss is another important complication associated with the operation, post-operative headache, cerebrospinal fluid (CSF) leakage, facial paralysis

### Primary Prevention

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There are no primary preventive methods available for schwannoma.

### Secondary Prevention

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## References

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