Acoustic neuroma overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Acoustic schwannomas, also known as vestibular schwannomas, are relatively common tumours that arise from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses.[1] It is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (8th cranial nerve). A type of schwannoma, this tumor arises from the Schwann cells responsible for the myelin sheath that helps keep peripheral nerves insulated.[2] Bilateral acoustic schwannomas are strongly suggestive of neurofibromatosis type 2 (NF2).These tumours classically present on imaging as a solid nodular mass with an intracanalicular component which often result in widening of the porus acusticus. They usually have vivid contrast enhancement and, when larger, cystic degeneration can be present. Haemorrhagic areas may also be seen, but calcification is typically not present. The tumour is also sometimes called an acoustic neuroma, but the term "acoustic" is a misnomer, as the tumor rarely arises from the acoustic division of the vestibulocochlear nerve. The term "neuroma" is also a misnomer, since it means "nerve tumor" but an acoustic neuroma is a Schwannoma. Acoustic neuroma may be classified into three subtypes based MRI, and into four subtypes based on microscopic histopathology. On microscopic histopathological analysis, acoustic neuroma is characterized into two types, Antoni A and Antoni B, based on growth patterns. 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 the ages of 30 and 60.
Classification
Acoustic neuroma may be classified into three subtypes based MRI, and into four subtypes based on microscopic histopathology.
Pathophysiology
On microscopic histopathological analysis, acoustic neuroma is characterized into two types, Antoni A and Antoni B, based on growth patterns.
Causes
Majority of the cases of acoustic neuroma are idiopathic. Less common causes include defect in tumor suppressor genes and high-dose ionizing radiation.
Acoustic neuroma 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.
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 the ages of 30 and 60.
Risk Factors
Common risk factors in the development of Acoustic neuroma are Neurofibromatosis type 2 and low dose radiation.
Natural History
Common complications of acoustic neuroma include hearing loss, facial numbness and weakness, difficulty with balance, ringing in the ear, hydrocephalus and recurrence of tumor. Due to improved surgical techniques and early diagnosis, the morbidity associated with surgical removal of these lesions is reduced. Acoustic neuroma patients have a very good prognosis with minimal complications if treated.
History and Symptoms
Symptoms of acoustic neuroma include hearing loss, tinnitus, vertigo, unsteadiness, pressure in the ears, headaches and facial pain.
Physical Examination
Common physical examination findings of acoustic neuroma include abnormal weber test, decreased or absent ipsilateral corneal reflex, facial twitching or hypesthesia and abnormal caloric stimulation test.
MRI
Gadolinium-enhanced MRI scan is diagnostic of Acoutic neuroma. On brain MRI, glioblastoma is characterized by hypointense mass on T1-weighted MRI and hyperintense mass on T2-weighted MRI
CT
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.
Other Diagnostic Studies
Other diagnostic studies for Acoustic neuroma include audiometry, auditory brainstem response test, and electronystagmography.
Medical Therapy
Optimal therapy for acoustic neuroma includes Observation, Surgery, and Radiation therapy.
Surgery
Surgery is the mainstay of treatment for Acoustic neuroma.