MONITORING OPERATIONS IN THE SKULL BASE CHAPTER VI

Monitoring of cranial nerves in skull base operations: what to monitor? 1. Extraocular muscles 2. Facial muscles 3. Masseter muscle 4. Tongue 5. CNIX pharynx 6. CNX larynx 7. ABR 8. CAP from CNVIII and cochlear nucleus

Monitoring other cranial motor nerves Extraocular muscles CN III CN IV CN VI Lower cranial nerves CN IX CN X CN XI CN XII

Monitoring other cranial motor nerves Monitoring the facial nerve is a model for monitoring other cranial motor nerves

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

How to record the response? Recording of electromyographic (EMG) potentials Mechanical recordings of muscle contractions Recording of motor nerve CAP

Recording of EMG potentials

Recording muscle responses Muscle relaxants cannot be used

MONITORING OTHER CRANIAL MOTOR NERVES EXTRAOCULAR MUSCLES CN III CNVI CNIV LOWER CRANIAL NERVES CNIX CNX CNXI CNXII

Monitoring nerves that innervate extraocular muscles CN III, CN IV, CN VI

Recording EMG potentials from extraocular muscles Using needle electrodes

Recording 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

EMG potentials recorded from extraocular muscles in response to electrical stimulation of respective cranial nerves intracranially

Recording EMG potentials from extraocular muscles Using non-invasive electrodes

Electrical stimulation of the oculomotor nerve (CN III) Middle rectus Lateral rectus Masseter

Monitoring multiple systems simultaneously Extraocular muscles Facial muscles Masseter muscle Tongue Neck muscles BAEP VEP

Typical placements of recording electrodes used in skull base operations Recording 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

Monitoring other cranial motor nerves Lower cranial motor nerves CN IX, CN X, CN XI, CN XII

FROM YINGLING

Monitoring CN X can be done by placing recording electrodes in the vocal folds

FROM YINGLING Monitoring CNX

FROM YINGLING

Auditory neuromonitoring Recording of auditory evoked potentials in operations in the posterior fossa

Monitoring of ABR can detect manipulations of the brainstem before cardiovascular signs change

Waveform analysis of the ABR provides information about the anatomical location of an injury

Different conventions for display of BAEP

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

Waveform analysis of the BAEP provides information about the anatomical location of an injury PEAK III PEAK V Ipsilateral stimulation

Contralateral stimulation Waveform analysis of the BAEP provides information about the anatomical location of an injury PEAK III PEAK V