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25 Cards in this Set
- Front
- Back
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Name 4 of the 7 types of intracranial neoplasms (tumors)?
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1. Medulloblastomas
2. Astrocytomas 3. Craniopharyngiomas 4. Ependymomas 5. Pinealomas 6. Gliomas 7. Meningiomas |
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Impact of tumor depends on (4 things)?
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Invasiveness
size location rate of growth |
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Do patients with brain tumors usually have auditory complaints?
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Rarely
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What are the 3 major types of 8th nerve tumors?
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Schwannomas
neurofibromas meningiomas |
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Which type of 8th nerve tumor is most common?
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Schwannomas
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Where do neurofibromas originate?
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From Schwann cells
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What is the rate of growth of meningiomas?
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Slow growing
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What is the diagnostic parameter of ABR for tumors?
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Interwave latency
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What are the 4 latency criteria for normal vs. abnormal retrocochlear pathology?
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1). Absolute latency of wave V exceeds clinical normal limits
2). Abnormal interaural wave V latency 3). Abnormal (prolonged) wave I-V latency 4). Abnormal interaural latency difference for I-V |
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Describe the 2 ways a tumor can interfere with generation of ABR-physically, not the waveforms
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1. Compressing or stretching of 8th nerve fibers by expanding tumor mass resulting in decreased synchrony of 8th nerve fibers or increased resistance in nerve conduction velocity
2. Compromised blood supply to 8th nerve and cochlea |
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What does obtaining symmetrical ABR abnormalities for both ears suggest?
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Bilateral 8th nerve tumors, or MS
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Stimulus rates affect what component of the ABR?
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Both latency and amplitude
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What are 3 things that must be included in case report?
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Copies of waveforms
Test parameters Latency values-both numerical and marked on the waveforms |
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What does ECochG consist of?
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Cochlear Microphonic
Summating Potential Action Potential |
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Where does the cochlear microphonic come from?
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OHCs
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What is the cochlear microphonic?
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Alternating current potential that follows the waveform of the stimulus
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The cochlear microphonic is best evoked by what stimulus?
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Single polarity stimulus, because an alternating polarity stimulus will cancel it out
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What is the SP?
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A shift in baseline of recording, following a continuous tone or transient acoustic stimulus. It usually occurs in the same direction, and just prior to compound AP of the 8th nerve
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What is the AP?
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A far-field representation of compound AP of the 8th cranial nerve. The same as ABR wave I
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AP amplitude is largest for what type of stimulus?
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Transient stimulus with abrupt and rapid rise times
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What components of ECoG are affected by stimulus frequency?
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CM- because it closely follows the waveform of the stimulus
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What components of the ECoG are affected by stimulus duration?
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Summating potential
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How is ECoG affected by an increase in stimulus intensity?
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AP latency decreases slightly and amplitude increased as stimulus increases. SP is not seen at lower intensity levels. CM is only present with monophasic stimulus polarity.
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What is the normal pattern for ECoG?
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Robust AP preceded by distinct but small amplitude SP
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What are 2 general types of abnormal ECochG?
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Little or no response of AP.
Large SP & small AP – associated with Menieres |
