Cortical Mapping in the ORisetonline.org/yahoo_site_admin/assets/docs/Cortical_Mapping.9616… ·...

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Cortical Mapping in the OR

Jason Coleman, CNIM

March 16th, 2019

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Introduction

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I am an employee of Nuvasive Clinical Services, a provider of intraoperative monitoring including cortical mapping.

Disclosures

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Today’s discussion will include:

• Goals and capabilities of cortical mapping

• Short anatomical review

• Mapping Concepts

• Mapping applications

Overview

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Goals and Capabilities

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Overall Goal: Identify eloquent functional area of the cortex, in order to avoid or minimize damage during cortical procedures such as tumor resections and vascular procedures.

• Proactively identify critical areas prior to manipulation

• Continually test for eloquent proximity throughout resection

• Continuous complimentary assessment between periods of mapping

Goals and capabilities

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Pros:

• Proactive location of eloquent tissue

• Proximity detection through tissue

• Able to continually perform neuro exams (awake)

• Little to no anesthetic suppression (awake)

Cortical Mapping: Pros and Cons

Cons:• Anesthetically challenging

• Awake patients have little airway management

• Possible to elicit seizures during stimulation

• Awake cases require cooperative patient and proper field access

• Requires a physician in-room for interpretation, as well as an interpreter for multilingual patients

• Require intact patient function preoperatively

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Anatomy Review

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Anatomy Review

First described in detail by Korbinian Brodmann in 1909

Based on cytoarchitecture, later associated with function

Often still associated with corresponding functions (e.g. Broca’s area described as Brodmann 44 and 45).

Multiple areas/tissue types may participate in the same function: e.g., areas 3, 1, and 2 all comprise the sensory cortex (post-central gyrus).

Brodmann Areas

Felten, D., O’Banion, M., Maida, M., (2015) Netter’s Atlas of Neuroscience, 3rd Edition. Elsevier Health Sciences

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Anatomy Review

Pre-central gyrus of the frontal lobe (Brodmann area 4, in red) comprises the main motor control area of the brain

Post-central gyrus of the parietal lobe (Brodmann areas 3,1,2, in blue) comprise the main somatosensory areas

Topographical map of the gyrus with respect to affected area

Derived from stimulating awake patients during epilepsy surgery by Wilder Penfield

Cortical Homunculus

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Anatomy Review

Pyramidal axons originating from the primary motor cortex

Descend through the internal capsule to the red nucleus

Surgical encroachment can result in complete and permanent hemiplegia

Stimulation can suggest proximity

Motor Tracts

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Anatomy Review

Language mapping involves a complex number of inputs, including:

• Broca’s area (Brodmann 44 and 45): word generation, motor speech generation

• Wernicke's Area (Brodmann 22): interpretation of written and spoken language

• Angular Gyrus (Brodmann 39): interpretation of visual and written language

• Supramarginal Gyrus (Brodmann 40): phonological interpretation and verbal articulation

Language Generators

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Cortical Mapping: Concepts

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Cortical mapping is generally a process of ACTIVE STIMULATION to either EVOKE a response, or DISRUPT a function (with exception to passive electrocorticography)

• Evoked responses: an electrically readable response from a distal stimulus, such as phase reversal from limb stimulation, or evoked EMG from motor cortex stimulation. These generally can be performed on (properly) anesthetized patients.

• Disruption (pseudo-lesion) response: intentional disruption of localized function, such as language errors from Wernicke's stimulation, visual field disruptions from optic radiation stimulation. Disruption-type responses are generally used for more complex processes and, as such, require and awake patient to properly examine for effect.

• Passive response: non-stimulated responses generally caused by existing disease, e.g. epileptiform potentials in electrocorticography. Can be observed in both awake and asleep patients with proper anesthetic.

Response Types


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Penfield Stimulation

• Slower biphasic stimulation (~60 Hz)

• Longer duration stimulus (~4 seconds)

• Optimal for language and cognitive testing

• Higher risk for stimulation-associated seizure (Szelényi 2007)

Tanaguchi Stimulation

• Short, high frequency pulse train (“train of five”)

• Duration ~15 mS

• Good motor mapping, poor language disruption duration (Axelson, 2009)

• Less risk for stimulation-associated seizure

Cortical Stimulation Types


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Proper response titration is necessary for localization

Increased stimulation spreads in three dimensions (in particular for monopolar stimulation)

Stimulus far above activation thresholds will activate distal tissues

Stimulation below thresholds will yield false negatives even on direct contact

Localization of Responses

Gray, Henry, Anatomy of the human body, 20th ed. Philadelphia: Lea & Febiger, 1918

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Proper anesthetic management is critical to successful cortical mapping. In growing order of sensitivity:

• Phase reversal: not disturbed by NMB, halogens less than 0.5 MAC

• Motor cortical mapping: eliminated by NMB, thresholds significantly affected by halogens and even TIVA (Simon et al 2010). Care must also be taken with dexmedetomidine, which demonstrates significantly increased motor thresholds. (Mahmoud et. al 2010)

• Language mapping: due to possibly complex tasks, any agent altering cognitive function may interfere with monitoring

Anesthetic Management


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Cortical Mapping: Applications

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Direct cortical SSEP response to locate the central sulcus

Often first mapping modality employed in a procedure (espunder GA)

Grid oriented A/P, crossing the suspected CC, and over SSEP generator site (generally MN or PTN)

Requires cortical contact and ability to elicit SSEP

Absence of SSEPs at baseline, or meningioma, are poor indicator for PR

Phase reversal ≠ complete cortical mapping!

Phase Reversal

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Cortical Mapping: ApplicationsPhase reversal

Response appearance: Responses from sensory cortex appear as normal cortical SSEP responses. Larger responses note closer proximity to the generator.

Responses from the pre-central gyrus typically demonstrate an inverted morphology, often with slightly delayed onset vs sensory responses (~1-2mS).

In this example, contact 1 suggests motor cortex, 2 is the largest SSEP response. This is the “dual radial” model response.

Caution should be taken when recording away from the response generator. This may lead to an error in sulcus location.

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Cortical Mapping: ApplicationsPhase reversal

Closer “on axis” verification of PR involves locating a triphasic response, adding an additional radial P25 peak.

In this image, strongest PR is located between contacts 6 and 7.

This response suggests a more precise location of generator location, verified by typically lower motor activation thresholds of indicated pre-central gyrus (Jahangiri et. al, 2011)

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One of the most frequent mapping modalities, utilized to identify

functional primary motor control areas of the brain.

Motor responses are elicited by direct stimulation of the surface

of the motor cortex.

Motor mapping can be performed in both awake and

anesthetized patients (with compatible agents) with varying

degrees of sensitivity.

May either Penfield stimulation or pulse-train. Typically Penfield

responses are visually or tactilely identified, while pulse-train

responses are recorded via triggered EMG window.

Motor Cortical Mapping

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Tanaguchi stimulation:

Similar stimulus to modern TcMEP stimulation. A short pulse train is delivered using a monopolar ball-tip probe, bipolar probe, monopolar grid, or bipolar grid contact.

Responses are recorded similar to TcMEP. Due to the short response length, these are recorded in triggered EMG trials.

Responses are poorly evaluated in live-EMG windows. Some responses may be directly visible.


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Penfield stimulation:

Extended, biphasic cortical stimulation from a device such as an Ojemann cortical stimulator.

Reponses may be visible as discernable involuntary patient movement, or disruption of motor tasks (such as holding up the arm). May also attempt to record in a live EMG window.

Note: awake stimulation of related structures (e.g. supplemental motor area) may also cause disruptions in motor tasks.

Be aware of risk of stimulation-related seizure.


Ai-Lien, Chang "He went through brain surgery - awake" The Straits Times [Singapore] 22 March, 2018

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Subcortical white matter mapping:

Stimulation for tracts below gray matter below the surface, often to determine proximity

Generally monopolar pulse-train stimulation

Subcortical motor thresholds <4 mA are considered “danger close”, but lower thresholds may be sustainable under specific criteria (Seidel et al, 2013)

IMPORTANT TO NOTE: Anesthetic agents may raise tract thresholds, causing higher thresholds and potential false negatives.


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Sensory Mapping:

• Requires an awake patient

• Typically uses Penfield stimulation

• Completely relies on subjective reporting of the patient

• On positive stimulation patients often report feelings of tingling, warmth, or movement even when the area is not moving

Sensory Cortical Mapping

Penfield, W, Boldrey, E. “Somatic Motor and Sensory Representation in the Cerebral Cortex of Man as Studied by Electrical Stimulation” Brain, Volume 60, Issue 4, 1 December 1937, Pages 389–443, https://doi.org/10.1093/brain/60.4.389

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Language mapping utilizes cortical stimulation to mimic a lesion in the affected area.

Longer duration stimulation for arrest detection. Generally Penfield, but continuous pulse-trains are being evaluated in some facilities (Riva et al 2016)

Positive stimulation generally results in expressive or receptive aphasias:

• Expressive: ability to form and speak words is interrupted. Comprehension generally intact.

• Receptive: difficulty comprehending verbal or visual inputs with intact or semi-intact fluency.

Language Mapping

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Disruption of Broca’s area generally presents as:

• Slow, heavily labored speech, or none at all

• Difficulty making sentences, esp longer than 3-4 words

• Anterior portion may leave speech partially intact but interfere with generation of words (esp verbs)

• Writing is severely impaired

• Comprehension remains generally intact

• Patient is generally aware of errors

NOTE: When mapping Broca’s, it is important to differentiate Broca’s speech arrest from disruption of the adjacent motor cortex

Language Mapping: Broca’s Area

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Disruption of Wernicke's area generally presents as:

• Poor ability to name presented object

• Reading impaired or impossible

• Profound comprehension disruption to verbal or visual cues

• Intact grammatic fluency with marked situational errors (does not make sense)

• Recurrent perseveration

• Patients are usually completely unaware of errors

Language Mapping: Wernicke's Area

Shape/color board for receptive aphasia

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Disruption of Wernicke's area and the angular gyrus (sometimes considered part of WA) are often similar, however some outstanding characteristics are:

• Anomia/word finding issues (similar to WA)

• Intact auditory comprehension

• Difficulty reading

• Intact repetition

• Generally “sensible” sentences with expanded descriptions of object the patient cannot name (i.e. “the furry thing that barks” for “dog”)

Angular Gyrus

Reading test for language mapping

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Supramarginal gyrus disruption generally presents as conduction aphasia:

• Repetition is severely impaired

• Reading is typically difficult

• Literal paraphasias are frequent, and the patient is aware

• Speech is unlabored

• Otherwise intact fluency and comprehension

Supramarginal Gyrus/Auditory Cortex

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Question and Answer

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Thank You!

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Szelényi, Andrea; Joksimovic, Boban; Seifert, Volker. "Intraoperative Risk of Seizures Associated With Transient Direct Cortical Stimulation in Patients With Symptomatic Epilepsy." Journal of Clinical Neurophysiology, Vol 24, no. 1, pp. 39-43, Feb 2007

Hans W.Axelson, Göran Hesselager, Roland Flinka. "Successful localization of the Broca area with short-train pulses instead of ‘Penfield’ stimulation" SeizureVolume 18, Issue 5, June 2009, Pages 374-375

Simon MV, Michaelides C, Wang S, Chiappa KH, Eskandar EN. "The effects of EEG suppression and anesthetics on stimulation thresholds in functional cortical motor mapping." Clin Neurophysiol. 2010; 121(5):784-92.

Mahmoud M, Sadhasivam S, Salisbury S, Nick TG, Schnell B, Sestokas AK, Wiggins C, Samuels P, Kabalin T, McAuliffe J. "Susceptibility of transcranial electric motor-evoked potentials to varying targeted blood levels of dexmedetomidine during spine surgery." Anesthesiology. 2010 Jun;112(6):1364-73. doi: 10.1097/ALN.0b013e3181d74f55.

Gray, Henry, 1825–1861. "Anatomy of the human body, by Henry Gray. 20th ed., thoroughly rev. and re-edited by Warren H. Lewis." Philadelphia: Lea & Febiger, 1918.

Kathleen Seidel, Jürgen Beck, Lennart Stieglitz, Philippe Schucht, and Andreas Ra. "The warning-sign hierarchy between quantitative subcortical motor mapping and continuous motor evoked potential monitoring during resection of supratentorial brain tumors" Journal of Neurosurgery Volume 118 (2013): Issue 2 (Feb 2013): Pages 215-488

Ai-Lien, Chang "He went through brain surgery - awake" The Straits Times [Singapore] 22 March, 2018

Marco Riva, Enrica Fava, Marcello Gallucci, Alessandro Comi, Alessandra Casarotti, Tommaso Alfiero, Fabio A. Raneri, Federico Pessina and Lorenzo Bello, "Monopolar high-frequency language mapping: can it help in the surgical management of gliomas? A comparative clinical study Journal of Neurosurgery Volume 124, Issue 5, May 2016: Pp 1211-1547

Penfield, W, Boldrey, E. “Somatic Motor and Sensory Representation in the Cerebral Cortex of Man as Studied by Electrical Stimulation” Brain, Volume 60, Issue 4, 1 December 1937, Pages 389–443, https://doi.org/10.1093/brain/60.4.389

Jahangiri F., Sherman J., Sheehan J., Shaffrey M., Dumont A., Vengrow M., Vega-Bermudez F., “Limiting the Current Density During Localization of the Primary Motor Cortex by Using a Tangential-Radial Cortical Somatosensory Evoked Potentials Model, Direct Electrical Cortical Stimulation, and Electrocorticography.” Neurosurgery. (2011) 69. 893-8. 10.1227//NEU.0b013e3182230ac3

References

https://doi.org/10.1093/brain/60.4.389

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