Jason Rusnak M.S. CNIM Biotronic NeuroNetwork Tuesday, May 31, Motor Cortical Mapping

Transcription

1 Jason Rusnak M.S. CNIM Biotronic NeuroNetwork Tuesday, May 31, 2016 Motor Cortical Mapping

2 Motor Cortical Mapping

3 Cortical Mapping Success Cortical Mapping Success Depends on: Knowing General Anatomy Where is the tumor? What structures are at risk? What can we monitor? Knowing Modalities Which are appropriate How to perform each optimally Anesthetic Cooperation If cooperation is limited, know how to optimize Monitoring Paradigm (stimulation/recording) Stimulation Type (Ojemann or Tanaguchi) Probe Type (handheld probe or cortical grid) Stimulation Configuration (bipolar, monopolar) Monitoring Execution (stimulation/recording) Mapping generally moves very quickly Need clear plan & troubleshooting techniques Need cooperation from trainee and hospital staff

4 Anatomy

5 Cerebral Cortex Sulcus (plural: Sulci) a depression or fissure in the surface of the brain. Fissure (plural: Fissures) Large furrows (sulci) that divide the brain into lobes Gyrus (plural: Gyri) Is a ridge on the cerebral cortex Generally surrounded by one or more sulci

6 Cortical Landmarks Central Sulcus: (aka: RolandicFissure, Fissure of Rolando) prominent brain landmark Divides parietal lobe from frontal lobe; primary motor cortex from primary somatosensorycortex. Medial Longitudinal Fissure: (aka: Great longitudinal Fissure, Interhemispheric Fissure) Deep groove separates the cerebral hemispheres Lateral Sulcus: (aka: Sylvian Fissure, Lateral Fissure) prominent brain landmark Divides frontal/parietal lobes from temporal lobe

7 Homunculus Homunculus: Latin for little human Topographic layout of Sensory and Motor Cortices Very similar for sensory vs. motor, with slight differences

8 Homunculus cont.

9 Speech and Language Broca s area Speech Motor: Aphasia Wernicke s Language Comprehension: Anomia

10 Phase Reversal Phase Reversal (PR) of Somatosensory responses In addition to post-rolandic cortical responses recorded from somatosensory cortex from stimulation of MN (or UN) and PTN Pre-rolandic cortical responses of reversed polarity also exist, referred to as: Phase Reversal These reversed polarity responses may have the same latency (P20), or slightly increased (P25)

11 Phase Reversal cont. Phase Reversal (PR) of Somatosensory responses Stimulating MN (or UN) or PTN Record directly from contralateral cortex (for MN) or midline between cortical hemispheres (for PTN) using a 1x4 or 1x5 cortical grid electrode Grid contacts (active) will be referenced to Fpz

12 Phase Reversal Example

13 Phase Reversal Success Setting-up for Success TIPs: Baseline SSEP response Set up erb s for positional issues Acquire a normal scalp potential prior to mapping to confirm morphology, latency and overall presence of a response Be sure to confirm correct stimulator programmed in the software!! Ex. Left crani = RMN Confirm silver contacts of grid centrally located between gold pegs of cortical grid cable plug

14 Phase Reversal Success cont. Largest PR Response Closest to the generator Closest to the central sulcus Note: despite relatively large responses, excessive noise can still be observed from cortical recordings, preoperative baseline responses will assist in analysis of difficult data

15 Motor Cortical Mapping Can be performed with 2 types of stimulation: Ojemann Classic bipolar biphasic pulses Tanaguchi pulse trains (monopolar or bipolar) Can be performed with 2 types of stimulators: Ojemann handheld probe Cortical Grid Electrode

16 Ojemann Stimulator Penfield OjemannTechnique (classic method) Stimulus Parameters Stimulus Type: continuous biphasic pulses Pulse Duration: ms(default 1.0mS) Pulse Frequency: Hz (default 60Hz) Stimulus Intensity: 2-20 ma(peak-to-peak) * Technique:4secs on/4secs off; non-sequenced repetitions *Note: the Ojemann stimulation dial ranges from 1-10mA, however since the pulses are biphasic the range may be referred to as 2-20mA pp (peak-to-peak). If a surgeon states a threshold, be sure to confirm the terminology being used.

17 Ojemann Stimulator

18 Tanaguchi Method TanaguchiPulse Train Method (ie.tcmeps*) Stimulus Parameters Stimulus Type: single monophasicpulse trains Pulses per train: 5-7 Pulse Duration: 0.5 ms Pulse Frequency: Hz (default 400 Hz) Stimulus Intensity: 5-25 ma * Note: Tanaguchi stimulus parameters are identical to those used for TCMEPs except for the stimulus level, since bone and dura impedence are no longer being traversed

19 Ojemann versus Tanaguchi Ojemann PRO: Ojeman CON: Ease of eliciting seizure activity (upto 27% incidence) More involved technique (increased time) More involved interpretation Bipolar only Tanaguchi PRO: Well-known Believed to distribute lower ion residue (biphasic pulses) Ideal for Language Mapping Ease of use Ease of evaluation and quantification Ease of documentation Increased effectiveness Low incidence of seizure activation (<1% incidence) Less over-all charge distributed to brain More compatible with general anesthesia Continuous stimulation during tumor resection possible and recommended Ideal for Motor Mapping Tanaguchi CON: Less well-known Need to use caution in discerning facial responses

20 MCM Recording Both Ojemann &Tanaguchi Stim will require recording CONTRALATERAL muscles from an EP machine Face: orbicularis oculi, orbicularis oris Referential (oculi-oris) or bipolar (oculi, oris) Referential saves an EP channel and is more sensitive, but also has increased stim artifact Bipolar is preferred, to decrease stim artifact If more sensitivity needed for face: add other facial muscles (ex.masseter) per surgeon pref. Shoulder: Trapezius-Deltoid Upper Arm: Biceps-Triceps Lower Arm: Brachioradialis-Flexor Carpi Ulnaris Upper Leg: Vastus Lateralis-Biceps Femoris Lower Leg: Tibialis Anterior-Gastrocnemius Foot: Abductor Hallucis Brevis-Flexor Digitorum Brevis Recording channels may be adjusted per surgeon request dependent on the location of concern, however it should be kept in mind that areas of concern at the cortical surface may differ from areas of concern under the cortex if resection continues onto white matter tract areas where fibers converge

21 Motor Cortical Mapping Paradigm Penfield OjemannTechnique 4 secson/4 secsoff Stimulate in circular pattern, incrementally increasing stimulus level with each circular pass until responses acquired, or after-discharge epileptiformactivity observed Stimulus should be run 1mA lower than level producing after-discharge activity EEG recording grid placed in close proximity to record after-discharge activity Caution: To avoid over-activation of cortex and possible seizures: Avoid stimulating longer than 4 secs/trial Do not stimulate same location consecutively Tanaguchi Pulse Train Technique Stimulation can be increased incrementally in location of choice Using monopolaror/bipolar stimulation Continuous stimulation during tumor resection possible and recommended EEG recording grid recommended but may not be necessary None Caution:

22 Ojemann Data Since Ojemann stimulator is a separate machine NOT hooked up to our monitoring equipment: Watch Free-Run EMG for responses Responses generally look like spike trains Responses will generally be time-linked to the stimulus artifact, but NOT the window Need to be careful to not interpret stimulus artifact as a response Stimulus artifact will be most prominent in facial channels Activity should stop shortly after stimulation ceases If activity continues, or worse increases, irrigate the brain with icecold irrigation immediately: this is the start of a seizure

23 MCM Ojeman Example Responses: Hand, lower arm, small in shoulder?, Uleg At 14mA pp

24 Tanaguchi Data Since Tanaguchi data is analogous to TCMEP data from our monitoring equipment: Triggered-EMG is automatically saved per trial Responses will be time-linked to the stimulus, and therefore observed just like TCMEPs Need to be careful to not interpret stimulus artifact as a response Stimulus artifact will be most prominent in facial channels Activity should only occur at the expected latency, if response latency not appropriate or keeps changing, verify in Live EMG Window, this is likely spontaneous EMG activity! If activity continues, or worse increases, irrigate the brain with ice-cold irrigation immediately: this is the start of a seizure

25 Tanaguchi Example Responses: Hand, lower arm At 20mA, bipolar Ojeeman probe

26 Tanaguchi Example cont. Facial responses are the most difficult to discern due to the proximity of the recording to the stimulus Facial response latency ~15-20mS! Stimulus artifact train can obscure a response Stimulus artifact may be misinterpreted as a response Facial TCMEP papers suggest using only 3 pulses to avoid contaminating facial recordings with stim artifact, but this might also diminish ability to evoke a response We often use 5 pulses, which have latency about ~13mS

27 Tanaguchi Example cont. Responses: Artifact or a response? Neurologist observed eye blinking (ie. eyelid) Recall: good to have someone observe the patient for responses, especially from face Note: timebase is 20ms/div

28 Subcortical Motor Mapping Same stimulus technique used for motor cortical mapping (ojemann or Tanaguchi; bipolar or monopolar) can be used for subcortical mapping using handheld probe

29