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
Historical perspective
Classification
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
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
Epidemiology and Demographics
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
Screening
Differentiating Schwannoma from other Diseases
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
Diagnosis
History and Symptoms
Physical Examination
X-Ray
CT
MRI
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.