Vestibular Schwannoma

Retrosigmoid (Suboccipital)

-30% Hearing preservation -IAC cant be fully accessed with this approach and place at risk for reoccurrence

Classifications

1. Intracanalicular 2. Extracanalicular

Observation: Advantages

Avoid surgery and radiation

ABR Hallmark Characteristics

-Absolute wave V latency -Waves l-lll and l-V Interwave latencies prolonged -Interaural latency difference of Wave V

Stereotactic Radiation Therapy

-Also called gamma knife, CyberKnife, Linac, and "radiosurgery" -Highly focused beams of radiation to the outlined treatment area that follows the tumor while avoiding the surrounding bone or brain -Nonsurgical -Tumor doesn't disappear but it stops growth (>90% of cases) -Hearing preservation accomplished in 44 to 66% of cases and only about 2 to 4% require additional treatment.

Vestibular Schwannoma

-Also known as an acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma -A vestibular schwannoma is a slow growing, benign tumor that arises from the proliferation of the myelin-producing Schwann cells encasing the vestibular portion of CN VIII -Schwann cells produce myelin that insulates the nerve fibers that serve the hearing and balance systems. -Arise in the internal auditory canal (IAC) and may grow medially into the cerebellopontine angle (CPA)

Surgical Removal: Risks

-Cerebrospinal fluid leak (10%) -Prolonged headaches -Vertigo -Meningitis -Loss of other cranial nerve function (V, VI, VII) -Stroke -Serious neurologic problems -Death (<1%)

Audiological Management

-Dependent on otologic management -Monitoring -Amplification (BAHA or CROS, traditional amplifications) -Counseling -Vestibular rehabilitation -Surgical removal -Stereotactic radiation therapy -Observation

Middle Cranial Fossa

-For tumors that are small and limited to IAC -80-90% Hearing preservation

Etiology & Pathophysiology: NF2

-Genetic disorder resulting in bilateral vestibular schwannomas -Autosomal dominance with incomplete penetrance -Symptoms typically develop in teens or early adulthood. -Multiple brain and spinal cord related tumors that affect surround nerves -More complicated than unilateral vestibular schwannoma ->95% vestibular schwannomas are sporadic in nature; only 2-5% occur due to Neurofibromatosis Type 2

Other Signs & Symptoms

-Greater decrease in word recognition than to be expected -General imbalance (No true vertigo) -Abnormal gait and ataxia -VII: Facial nerve damage -Other symptoms may occur due to pressure against adjacent cranial nerves, brainstem, and cerebellum -Headaches -Drowsiness -Loss of consciousness: due to obstruction to the flow of cerebrospinal fluid (CSF): Very urgent

Translabyrinthe

-Hearing is always lost -Most aggressive approach -Most common

Extracanalicular

-Leans upon the outer boundary of the internal acoustic opening -Extends to the CPA -Looks like a "mushroom cap" or "ice cream cone" to fill space between temporal bone and brain

Growth Patterns

-Mean growth rate: 1 to 4mm per year -Up to 75% showing no appreciable growth rate -Some exceptions of over 18mm per year -Path of least resistance -Tumors greater than 2cm in diameter are likely to eventually contact and compress the brainstem and cerebellum causing more severe symptoms

OAEs

-Most DPOAE's & TPOAEs are "normal" or consistent with hearing function -Absent OAEs: consistent with a cochlear HL -OAEs are better than audiometric thresholds- consistent with 8th nerve involvement -May give insight into hearing preservation

Incidence & Prevalence

-Most common occurring tumors of the CPA (75-90%) -8% of all intracranial tumors -1-2 in 100,000 individuals -3,000 new cases a year in U.S. -Typically unilateral with only approximately 5% occurring bilaterally -Average ages 40 to 60 -Both female and male equally

ABR Results

-Neurological ABR is as effective as MRI with large tumors (> 1cm) but not as sensitive for smaller ones -Stacked ABR will be useful for identification of tumors >1cm -Considered at risk: Behavioral pure-tone thresholds are better than ABR thresholds -Abnormal results in "unaffected ear" - Interwave III-V

Speech Testing

-Positive PI-PB Rollover -Greater decrease in word recognition more than to be expected based on PTA -Asymmetry in word recognition between ears

Balance Testing

-Results will point towards unilateral paresis on affected side. -Positive Romberg may be seen -Dynamic Gait Index (DGI) may be useful -Central findings are possible depending on size and location -Tracking abnormalities may be observed -Amplitude decreased on side of involvement with VEMP testing

Intracanalicular

-Situated or occurring within a canal -Often result in widening of IAC

Observation

-The patient is observed for hearing, balance, tinnitus, and facial nerve function. -MRI is performed yearly or every 6 months depending on the rate of tumor growth -This approach is ideal for a patient with a small, non-growing tumor, those who are asymptomatic, those who are older and whose health precludes surgery

Etiology & Pathophysiology

-The tumor comes from an overproduction of Schwann cells. -The gene responsible for the development of a vestibular schwannoma is chromosome 22q12, which codes for the tumor suppressor merlin or schwannomin. -A variety of mutations may occur in this gene and the type of mutation present has been linked to the severity of the disease. -Loss of myelin function results in Schwann cell mutations and tumor development. -Arise in the internal auditory canal (IAC) and grow medially into the CPA

Observation: Disadvantages

-Tumor is still there and does not disappear -MRI must be done at least once every 1-2 years -Hearing loss and dizziness may develop or worsen, even if the tumor is not growing -May be more difficult to perform hearing preservation surgery later on

Acoustic Reflexes

-Typically elevated or absent (95% patients) -Diagonal: Unilateral VIII disorder -Inverted L: Combined VII and VIII nerve disorder -Rapid decay indicative of retrocochlear involvement

Pure-tone Testing

-Unilateral or asymmetrical sensorineural high frequency hearing loss -Possible hearing within normal limits or a minimal asymmetry -Criteria: Two adjacent frequencies have a 15dB or more difference and the better ear has a 30dB PTA. If PTA is more than 30dB than the criteria changes to 20dB difference between adjacent frequencies.

Hallmark Symptoms

-Unilateral tinnitus -Unilateral progressive high frequency SNHL hearing loss on the side of tumor -Typically high frequency due to tumor pressing on outer boundary of the auditory portion of the VIII nerve -Degree and rate of progression doesn't correlate with tumor size or growth -Can have sudden onset HL, but it is rare.

Surgical Removal Techniques

1. Translabyrinthe 2. Retrosigmoid (Suboccipital) 3. Middle Cranial Fossa

Classifications & Growth Patterns

1. Unilateral HL and tinnitus 2. Cranial nerve affection, 5th is the earliest then 7th and lately 9th, 10th, 11th, and 12th 3. Cerebellar compression, nystagmus, ataxia, and incoordination

What does choice of treatment depend upon?

Choice of treatment will depend on the size of the tumor, patient age, general health, hearing status, and patient input

MRI

Loss of sensation to light touch around the posterior edge of the external auditory meatus is an early sign of a schwannoma - Called "Hitselberger's sign"

Otologic Test: Gold Standard

MRI w/ gadolinium

Tymps

Type A

Surgical Removal

Type is chosen based on size, desire to preserve hearing, and surgeon's preference

Otoscopy

normal