Neurosurgery notes/Procedures/Cranial procedures/Tumor cranial procedures/Awake surgery

Awake surgery

View Details
logo
Parent item
Tumor cranial procedures

General

  • The key to a successful awake procedure is patient preparation.
  • Not for
    • Poor patient cooperation
      • Careful patient selection is needed to ensure the patient fully understands what will happen during surgery.
    • High weight and body habitus
  • Arguments for awake surgery
    • Individual variability and pathway distortion from intrinsic brain tumours makes neuronavigation less reliable.
      • Speech arrest, anomia, and alexia are often located far outside the anatomic boundaries of Broca’s area (Sanai et al., 2008).
    • Direct stimulation mapping is the gold standard for identification and preservation of functional areas.
  • 2 types
    • Fully awake surgery
      • Performed after the infiltration of local anaesthetic into the scalp or following regional nerve block of the scalp.
      • Dexmedetomidine
        • Highly selective a2-receptor agonist
        • Acts as a
          • Mild sedative
          • Analgesic
          • Anxiolytic
        • Rarely induces cardiorespiratory suppression
    • Asleep- awake- asleep (AAA) technique
      • General anaesthesia, with or without the use of an airway, during the opening and closing portions with emergence of patients from anaesthesia in the interim.
        • However, the more commonly advocated anaesthesia technique for the opening and closing portions is termed monitored anaesthesia care (also called conscious sedation).
      • The same medications used in the AAA technique are given (propofol and fentanyl) but they are given in pulses and at lower doses with the goal of providing a smooth transition to alertness and obviating the difficulties of airway intervention
  • After skin incision and removal of the bone flap, all sedatives are stopped, after which the patient is asked to take multiple deep breaths to decrease hypercapnia before dural opening

Cortical mapping including awake craniotomy

  • Aims
    • Mapping to find safe entry zones, and continuously monitoring
    • Motor pathways and locating corticospinal tracts subcortically can be of value both to guide surgery and detect spasm of perforating vessels.
  • General
    • When testing a positive response is sought first, giving a threshold before trusting ‘negative’ stimulation sites.
    • EEG should be assessed to detect after discharges and detect seizures early
      • If mapping performed with too high a current there is increased risk of seizures, and the stimulus spread may result in excessive caution and incomplete tumour removal.
    • The seizure risk overall is 4.9%,
      • Treatment of intraop seizure
        • Irrigation with cold saline on the seizing cortex
        • A dedicated intravenous line is filled with a 1 mg per kg bolus of propofol
    • Excessive chemical seizure control from the anaesthetist can render the awake patient too drowsy to cooperate with the awake procedure.
    • The tumour surgeon must balance the goal of maximal resection with preservation of motor and language functional sites.
  • Mapping motor area
      • First (somatosensorry phase reversal)
      • Localized by SSEPs showing the Rolandic sulcus (phase reversal, usually from contralateral median stimuli)
      • Further mapping can be performed with stimuli from a probe where appropriate.
      • The strip is left in this area and a contact over the motor cortex is stimulated repeatedly to give monitoring of motor tracts throughout.
      • Neuloh et al. 2007
        • Developed by
        • Gave excellent results in insular tumours — where vascular spasm may compromise motor pathways.
          • Some 44% of his cases showed deterioration in MEP responses.
          • If these were lost rest, irrigation, and papaverine, restored responses in 29%, but if they did not return, a neurological deficit occurred.
      • Tech (Somatosensory-Phase reversal)
        • Muengtaweepongsa 2024
        • Stimulation from nerve and sense in cortex:
          • Stimulate median nerve or post tibial nerve
          • Sense at primary sensory cortex.
        • Positioning on the cortex
            • Recorded by a strip electrode (a row of five or six electrodes embedded in silicon) placed on the cortex
            • Median nerve SEP-PRs
              • The electrode must be placed in a cortical area between 3 and 8 cm from the midline.
              • The largeness of this area is due to the large cortical representation area of the hand.
            • Tibial nerve SEP-PR
              • Cortical area is limited to 0–3 cm from the midline.
            • Positioning the strip in the interhemispheric space is not recommended as this is technically very difficult and the correct position cannot be verified.
            ntral su Recording -strip Fig. I. Grid electrode for recording somatosensory evoked potential phase reversal (SEP-PR). The black line indicates the central sulcus.
            Grid electrode for recording somatosensory evoked potential phase reversal (SEP-PR). The black line indicates the central sulcus.
          • Care must be taken for the placement of the recording electrodes.
              • Electrodes must cross the central sulcus,
              • Electrodes must cover the hand or leg area of the sensorimotor gyri
              • Electrodes must make an angle of 15° with the sagittal direction, and
              • Electrodes must not cover the centre of the lesion but instead lie adjacent to the visible margins of the tumor mass
               
              Fig. 2. Diagram showing the correct positioning of the recording grid. Optimal position must have a 150 angle to the central sulcus.
              Diagram showing the correct positioning of the recording grid. Optimal position must have a 15° angle to the central sulcus.
        • Mechanism
              • notion image
            • Stimulation of median nerve at the wrist
            • Wait 19ms
            • The sensory cortex generate a point of highest potential eg -100microV
              • While the areas around it generate slightly lower potential -80, -60, -30 etc
            • The strip electrode over the sensory and motor cortex has 6 electrodes one would imagine each electrode having the following values if the 4th electrode has the highest potential
                  • Electrode
                  Voltage (microV)
                  1
                  -10
                  2
                  -50
                  3
                  -80
                  4
                  -100
                  5
                  -80
                  6
                  -50
                • These readings are using the mastoid as a reference
            • When one compares (A-B electrode) between electrode you would get the following
              • Electrode comparison will show that between the 3/4 and 3/5 electrode there is a phase reversal happening
                  • Bipolar electrode
                  Voltage (microV)
                  1-2
                  -10-(-50)=+40
                  2-3
                  -50-(-80)=+30
                  3-4
                  -80-(-100)=+20
                  4-5
                  -100-(-80)=-20
                  5-6
                  -80-(-50)=-30
                • This phase reversal can also occur at any other gyri away from the sensory cortex. So to understand that it is the motor cortex a MEP needs to be done at one end of the electrode strip to confirm that there is motor cortex.
        • The location of the electrode must be adjusted to obtain maximum peak amplitudes by moving it in a mediolateral and frontolateral direction or by rotating it at angles of 15°
            • 25 ev 12.spv 0 FACE 3-4 2-3 60 FACE 5 6 HAND. 25 60 Fig. 2. SSEP recorded in a bipolar (top left) or referential (bottom left) manner, using a scalp muscle reference (M). The orientation of electrodes is shown (bottom right), as it would be seen by the surgical team. The more detailed diagram of electrode locations (top right) allows one to compare locations where direct cortical stimulation produced sensations (closed circles). This patient was conscious during the operation. In one location, direct cor- tical stimulation also produced the patient's typical epileptic aura. At other locations, no sensation was caused by direct cortical stimulation (open circles). Higher intensity stimula- tion probably would have caused motor responses from some of the anterior locations tested. At 25 ms an N20 negative potential was seen maximally around electrode 4. Just prior to that, at about 22 ms, a series of small negative potentials was seen, also maximal around electrode 4. 'Ihese results confirm that electrode 4 lay in the primary sensory cortex, allow- ing us to deduce that electrodes 2 and 3 lay on the motor cortex. (From Nuwer 1987)
            SSEP recorded in a bipolar (top left) or referential (bottom left) manner, using a scalp muscle reference (M). The orientation of electrodes is shown (bottom right), as it would be seen by the surgical team. The more detailed diagram of electrode locations (top right) allows one to compare locations where direct cortical stimulation produced sensations (closed circles). This patient was conscious during the operation. In one location, direct cortical stimulation also produced the patient’s typical epileptic aura. At other locations, no sensation was caused by direct cortical stimulation (open circles). Higher intensity stimulation probably would have caused motor responses from some of the anterior locations tested. At 25 ms an N₂₀ negative potential was seen maximally around electrode 4. Just prior to that, at about 22 ms, a series of small negative potentials was seen, also maximal around electrode 4. These results confirm that electrode 4 lay in the primary sensory cortex, allowing us to deduce that electrodes 2 and 3 lay on the motor cortex. (From Nuwer 1987)
        • Phase reversal of somatosensory evoked potentials is based on the fact that the dipole of the afferent volley changes from the postcentral to the precentral gyrus
        • SEP-PR feasibility in most of the series 95%.
        • SEP-PR Failure:
          • Tumor-related shifting of the central sulcus
          • Misplacement of the recording electrodes in relation to the anatomical location of the sensorimotor
          • Influence of narcotic agents and brain edema.
        • SEP-PR not recordable:
          • The tumor desynchronizes the propagated afferent electrical volleys along the thalamocortical pathway
          • The mass effect of the lesion distorts the spatiotemporal projection of cortical electrical dipoles to the brain surface
      Second
      • Direct stimulation: Motor area localization confirmation.
      • Cortical mapping
        • Tech
          • Newer (Tanaguchi and Schramm 1993) ‘train of 5’ method
            • Motor cortex stimulation normally uses five anodal pulses at 500 Hz.
            • Anode
              • A probe with 2 mm ball
              • Held on cortex
            • Cathode
              • As a separate electrode such as a needle inserted into the forehead, or vertex
                • Does not usually cause distress if the cathode is placed in an anaesthetised area (e.g. vertex).
              • If patient is awake do not need train of 5
              • If patient is asleep a train of 5 is needed
            • Recording of stimulus:
              • With paired steel needles inserted into a ‘homunculus’ of muscles contralaterally and the best responses are commonly seen from muscles with largest cortical representation, that is,
                • Abductor pollicis brevis
                • Abductor digit minimi (or first dorsal interosseous)
                • Mentalis
                • Deltoid or biceps
                • Extensor digitorum communis
                • Vastus medialis
                • Tibialis anterior
                • Abductor hallucis
            • This short high frequency train appears less likely to induce seizures, and a lower charge is required, than the 50 Hz method
              • Irrigation with cold saline/ ringer on the cortex
            • Positive and negative mapping
              • Positive mapping
                • Early mapping techniques utilized large craniotomies with the goal of identifying positive functional sites;
              • Negative mapping
                • Use smaller exposures with reliance on negative mapping (Sanai et al., 2008).
                • Negative mapping strategies represent a shift in mapping techniques, keeping eloquent areas untouched and free from exposure.
          • Older (Penfield and Jasper (1954))
      • Subcortical (including spinal) dissection
        • Tech
          • A probe is used to give cathodal stimulation
            • With other electrode as anode, for direct stimulation of corticospinal tracts
          • Cathodal stimuli can also be used to localize corticospinal tracts from within spinal tumours
      Outcome of mapping
      • Sacko et al., 2011
        • Significantly better outcomes in awake surgery when tumours are in eloquent areas with more complete excision and with fewer deficits.
      Associate motor area mapping
      • SMA
        • Damage gives profound weakness which in general resolves spontaneously over a period of days or weeks.
        • Damage to SMA can be detected by inability to perform planned motor tasks for example, opposing specific digits:
          • This can affect ipsilateral as well as contralateral hands.
        • In theory, if the motor responses are intact from cortical stimulation recording directly from contralateral muscles, and voluntary activation fades, the SMA is being excised.
          • Motor recovery should occur in about a month.
      • Premotor motor area surgery
        • Can leave permanent deficit
        • Cortical and subcortical stimulation in awake subjects can again minimize deficit
  • Speech mapping in the temporal lobe,
      • Technique
      • Awake
        • Continuous electrocorticography is used to improve mapping accuracy, monitor for subclinical seizure activity, and detect after- discharge potentials.
          • A recording electrode strip is placed on the brain surface
        • Cortex stimulated using a bipolar cortical stimulator.
          • To give a smaller area of stimulation
          • Train of five stimuli give fewer seizures, and are more effective in most situations
            • Speech arrest with 50 Hz stimuli is the simplest test
          • Stimulation duration for speech is 2-4s which is longer than motor which is 16ms this makes it higher likely to generate seizures in speech marking
        • The stimulating current is increased in small 2 mA increments, up to a maximum of 10 mA, while observing for any after discharges (akin to focal seizures).
        • Once the patient’s threshold for after discharges has been established,
          • Patients are asked to name objects shown on picture cards while the cortex continues to be stimulated and any paraphasic errors or speech arrest are noted.
          • The aforementioned steps are then repeated so that the patient’s speech area may be mapped out on the brain’s surface.
        • All language testing is repeated at least three times per cortical site, and a positive site is defined as the inability to count, name objects, or read words during stimulation at least two out of three times.
      • Asleep
        • Some speech pathways may be detected in asleep patients by ‘train of 5’ stimuli eliciting long latency responses in cricothyroid and similar responses may be seen in the palate and tongue.
      Test
      • Identify, via direct stimulation sites responsible for
        • Speech arrest
          • Speech arrest is defined as discontinuation in number counting without simultaneous motor response.
          • Dysarthria can be distinguished from speech arrest by an absence of involuntary muscle contractions affecting speech (Sanai et al., 2008).
        • Anomia
        • Alexia
      • Areas relevant for speech
      • Picture recognition
      • Verb generation test
  • Visual pathways mapping
    • Visual pathway can be located in awake subjects by stimulation eliciting flashes, colours, or visual field changes.
    • In asleep subjects, flashes of light can evoke responses from visual pathways recorded with microelectrodes from optic tract below globus pallidum during deep brain stimulation surgery.

Functions that can be assessed

  • Language
    • Number counting, visual object naming, auditory comprehension, sentence completion, picture naming, naturalistic and narrative comprehension, verbal fluency, shiritori
  • Motor
    • Simple and complex movements of extremities both spontaneous and on command, dual and sequential motor tasks
  • Other lobar and cortical functions
    • Writing, drawing, vision, memory, parietal lobe functions - calculation, stereognosis, spatial recognition, construction
  • Cognitive functions
    • Executive functions, abstract thinking, working memory, theory of mind, social cognition, inhibitory control, emotional recognition

Sequence of surgery

  • Scalp block, induction of sedation
  • Positioning and head fixation - supine / lateral
  • Wake up and check for comfort, estimate of wakefulness
  • Resection
  • Draping and craniotomy
  • Durotomy. Placement of fence posts / depth electrodes if planned
  • Stop sedation and wake up
  • Assessment and tumour removal
  • Final assessment, restart sedation and closure

Tract based assessment

TRACTS
ASSESSMENT
Superior longitudinal fasciculus
Reading, Digit Forward Test, Trail B (oral version), abstraction, verbal fluency
Arcuate fasciculus
Word, phrases and sentence repetition which increases in complexity and explanation of the content to the assessor, reading, calculation
Dorsal IFOF
Reading and writing
Ventral IFOF
Reading and writing, naming, working memory assessed using digit backward
Uncinate fasciculus
Audio recordings and deciphering the emotions, naming, Famous faces, Digit backward test – numbers substituted with words
Inferior longitudinal fasciculus
Reading, writing, verbal fluency, facial recognition, famous faces naming, RMET, emotion naming
Anterior cingulum
Immediate and delayed memory testing, Digit forward (attention), Trail B (oral version)
Posterior cingulum
Verbal fluency, naming, immediate and delayed memory, retrograde memory, interlocked pentagons, wire cube
Frontal aslant tract
Verbal fluency, naming, Sheritori, sequential motor movements (LEFT): TMT B – oral version, sequential motor movements (RIGHT); Sequential motor movements (Luria’s 3 steps), Alternate finger tapping (BOTH)