MONITORING OPERATIONS IN THE SKULL BASE CHAPTER VI.
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Transcript of MONITORING OPERATIONS IN THE SKULL BASE CHAPTER VI.
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MONITORING OPERATIONS IN THE SKULL BASE
CHAPTER VI
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Monitoring of cranial nerves in skull base operations:
what to monitor?1. Extraocular muscles 2. Facial muscles3. Masseter muscle4. Tongue5. CNIX pharynx6. CNX larynx7. ABR8. CAP from CNVIII and cochlear nucleus
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Monitoring other cranial motor nerves
Extraocular muscles• CN III• CN IV• CN VILower cranial nerves• CN IX• CN X• CN XI• CN XII
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Monitoring other cranial motor nerves
• Monitoring the facial nerve is a model for monitoring other cranial motor nerves
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How to activate the motor system?
• Electrical stimulation of motor nerves• Magnetic stimulation of motor nerves• Electrical stimulation of the motor cortex• Magnetic stimulation of the motor cortex
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How to record the response?
• Recording of electromyographic (EMG) potentials
• Mechanical recordings of muscle contractions
• Recording of motor nerve CAP
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Recording of EMG potentials
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Recording muscle responses
• Muscle relaxants cannot be used
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MONITORING OTHER CRANIAL MOTOR NERVES
EXTRAOCULAR MUSCLES• CN III• CNVI• CNIVLOWER CRANIAL NERVES• CNIX• CNX• CNXI• CNXII
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Monitoring nerves that innervate extraocular muscles
CN III, CN IV, CN VI
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Recording EMG potentials from extraocular muscles
• Using needle electrodes
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Recording from extraocular muscles:Place needle electrodes percutaneously so they come close to respective musclesMedial rectus for CNIIILateral rectus for CNVISuperior oblique for CNIV
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EMG potentials recorded from extraocular muscles in response to electrical stimulation of respective cranial nerves intracranially
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Recording EMG potentials from extraocular muscles
• Using non-invasive electrodes
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Electrical stimulation of the oculomotor nerve (CN III)
Middle rectus
Lateral rectus
Masseter
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Monitoring multiple systems simultaneously
• Extraocular muscles• Facial muscles• Masseter muscle• Tongue• Neck muscles• BAEP• VEP
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Typical placements of recording electrodes used in skull base operationsRecording from extraocular muscles: Place needle electrodes percutaneously so they come close to respective muscles Medial rectus for CNIII Lateral rectus for CNVI Superior oblique for CNIV
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Monitoring other cranial motor nerves
Lower cranial motor nerves
CN IX, CN X, CN XI, CN XII
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FROM YINGLING
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Monitoring CN X can be done by placing recording
electrodes in the vocal folds
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FROM YINGLING
Monitoring CNX
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FROM YINGLING
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Auditory neuromonitoring
Recording of auditory evoked potentials in operations in the
posterior fossa
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Monitoring of ABR can detect manipulations of the
brainstem before cardiovascular signs change
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Waveform analysis of the ABR provides information about the
anatomical location of an injury
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Different conventions for display of BAEP
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NEURAL GENERATORS OF THE ABR:
• Peak I: distal auditory nerve• Peak II: central auditory nerve• Peak III: mainly cochlear nucleus• Peak IV: unknown• Peak V: termination of the lateral lemniscus in the contralateral inferior colliculus
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Waveform analysis of the BAEP provides information about the anatomical location of an injury
PEAK III
PEAK VIpsilateralstimulation
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Contralateral stimulation
Waveform analysis of the BAEP provides information about the anatomical location of an injury
PEAK III
PEAK V
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