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General information & Epidemiology?
- -Histologically benign schwann-cell sheath tumor that usually arises from of the inferior division of the vestibular nerve (not the cochlear portion)
- -Arise as a result of the loss of a tumor-suppressor gene on the long arm of chromosome 22
- -In neurofibromatosis Type 2 (NF2) this is either inherited or represents a new mutation that may then be transmitted to o spring)
- -common intracranial tumors, comprising 8–10% of tumors in most series
- -VSs typically become symptomatic after age 30. At least 95% are unilateral-The incidence of vestibular schwannomas (VS) is increased in neurofibromatosis (NFT), with bilateral VS being pathognomonic of neurofibromatosis Type 2 (NFT2)
- -Patient <40 yrs old with unilateral VS should also be evaluated for NFT2
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Pathology?
- -Tumors are composed of Antoni A fibers (narrow elongated bipolar cells) and Antoni B fibers (loose reticulated)
- -Verocay bodies are also seen
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Clinical Symptoms?
- Triad of ipsilateral sensorineural hearing loss, tinnitus and balance diffculties
- -symptoms are closely correlated with tumor size
- -Larger tumors can cause facial numbness, weakness or twitching,possibly brainstem symptoms & rarely hydrocephalus.
- Symptoms
- hearing loss 98%
- tinnitus 70%
- dysequilibrium 67%
- H/A 32%
- facial numbness 29%
- facial weakness 10%
- diplopia 10%
- N/V 9%
- otalgia 9%
- change of taste 6%
- Symptoms from 8th nerve compression
- -Unilateral sensorineural hearing loss, tinnitus and dysequilibrium are related to pressure on the eighth nerve complex in the IAC
- -Hearing loss is insidious and progressive in most.10% report sudden hearing loss. 70% have a high frequency loss pattern and word discrimination is usually affected (especially noticeable in telephone conversation)
- -Tinnitus is usually high pitched
- -Unsteadiness manifests primarily as difficulty with balance
- Sudden hearing loss (SHL) with VS is presumably due to an infarction of the acoustic nerve, or acute occlusion of the cochlear artery.Treatment options for SHL include:
- 1. steroids: e.g. prednisone 60 mg PO q d ×10 d then tapered
- 2. famciclovir 500 mg po TID×10 d
- 3. ?conservative treatment: rest, restriction of salt alcohol and tobacco
- Symptoms from 5th and 7th nerve compression
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Otalgia, facial numbness and weakness, and taste changes occur as the tumor enlarges and compresses the fifth and seventh nerves (do not occur until the tumor is >2 cm) - -facial weakness is a rare even though
- the 7th nerve is almost always distorted early; whereas facial numbness occurs sooner once trigeminal compression occurs. This may be due to the resiliency of motor nerves relative to sensory nerves
- Symptoms from compression of brainstem and other cranial nerves-Larger tumors cause brainstem compression (with ataxia, H/A, N/V, diplopia, cerebellar signs, and if unchecked, coma, respiratory depression and death) and lower cranial nerve (IX, X, XII) palsies (hoarseness, dysphagia…)
- -Obstruction of CSF circulation by larger tumors (usually > 4 cm) may produce hydrocephalus with increased ICP
- -Rarely, 6th nerve involvement may cause diplopia
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Signs?
- -Hearing loss due to VIII involvement is the earliest cranial nerve finding
- -Since hearing loss is sensorineural, Weber test will lateralize to the uninvolved side, and if there is enough preserved hearing, Rinne test will be positive (normal: air conduction>bone conduction) on both sides
- -Vestibular involvement causes nystagmus (may be central or peripheral)
- -Facial nerve (VII) dysfunction is uncommon before treatment. When present, it is usually graded clinically on the House and Brackmann scale
- Sign
- abnormal corneal reflex 33%
- nystagmus 26%
- facial hypoesthesia 26%
- facial weakness (palsy) 12%
- abnormal eye movement 11%
- papilledema 10%
- Babinski sign 5%
- Clinical grading of facial nerve function(House and Brackmann)1 normal normal facial function in all areas
- 2 mild dysfunction 1. gross: slight weakness noticeable on close inspection; may have
- very slight synkinesis
- 2. at rest: normal symmetry and tone
- 3. motion:
- a) forehead: slight to moderate movement
- b) eye: complete closure with effort
- c) mouth: slight asymmetry
- 3 moderate dysfunction 1. gross: obvious but not disfiguring asymmetry: noticeable but
- not severe synkinesis
- 2. motion:
- a) forehead: slight to moderate movement
- b) eye: complete closure with effort
- c) mouth: slightly weak with maximal effort
- 4 moderate to severe dysfunction 1. gross: obvious weakness and/or disfiguring asymmetry
- 2. motion:
- a) forehead: none
- b) eye: incomplete closure
- c) mouth: asymmetry with maximum effort
- 5 severe dysfunction 1. gross: only barely perceptible motion
- 2. at rest: asymmetry
- 3. motion:
- a) forehead: none
- b) eye: incomplete closure
- 6 total paralysis no movement
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Differential diagnosis?
- 1. Meningioma
- 2. Metastases
- 3. Neuroma from cranial nerves other than VIII (trigeminal neuroma, facial nerve neuroma)
- 4. Arachnoid cyst
- 5. Cholesterol granuloma
- 6. lipoma
- 7. Aneurysm: PICA, AICA, vertebrobasilar
- 8. Glomus tumor (glomus jugulare/glomus tympanicum)
- 9. Primary tumors of temporal bone (e.g. sarcoma or carcinoma)
- 10. Ectodermal inclusion tumors (e.g.epidermoid (cholesteatoma)
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Evaluation?
General information
- 1. Brain MRI without and with contrast. FIESTA MRI if available. If MRI is contraindicated, then a CT scan without and with contrast
- 2. Temporal bone CT for detailed bony anatomy if surgery is contemplated
- 3. Audiometric evaluation:
- a) pure tone audiogram
- b) speech discrimination evaluation
- c) patients with small VSs (≤ 15 mm dia) also get:
- ● ENG: assesses superior vestibular nerve
- ● VEMP: assesses inferior vestibular nerve
- ● ABR: prognosticates chance of hearing preservation
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