Clinical Scorecard: Utilizing Indirect Cognitive Mapping Techniques in Glioma Surgery for Patients Ineligible for Awake Craniotomy – My Approach

At a Glance

Key Highlights

• Subcortical white matter tracts (ventral and dorsal streams, corticospinal tract) are critical for cognitive and motor functions and must be preserved during glioma surgery.
• Monopolar cathodal subcortical electrical stimulation allows localization of motor pathways intraoperatively, with a current-to-distance relationship (1 mA ≈ 1 mm).
• Indirect cognitive mapping uses motor tract localization as anatomical landmarks to protect adjacent eloquent cognitive pathways when awake craniotomy is not feasible.

Guideline-Based Recommendations

Diagnosis

• Preoperative MRI with diffusion tensor imaging (DTI) to delineate tumor and subcortical tracts.
• Functional MRI (fMRI) to identify eloquent cortical areas related to speech and cognition.

Management

• Use asleep-awake-asleep model when possible; if awake craniotomy is contraindicated, employ indirect mapping techniques.
• Perform monopolar cathodal subcortical stimulation intraoperatively to identify corticospinal tract and estimate distance to motor pathways.
• Limit tumor resection based on stimulation thresholds corresponding to safe distances from critical tracts.

Monitoring & Follow-up

• Continuous electromyography (EMG) monitoring of target muscles during subcortical stimulation.
• Intraoperative neurophysiological monitoring to detect motor evoked potentials (MEPs).

Risks

• Potential neurological deficits if subcortical tracts are damaged during resection.
• Brain shift during surgery reduces reliability of neuronavigation at millimeter precision.

Patient & Prescribing Data

Glioma patients with cognitive impairment or anesthesiological contraindications to awake craniotomy

Indirect cognitive mapping with monopolar stimulation enables maximal safe tumor resection while preserving motor and cognitive functions, even without awake patient participation.

Clinical Best Practices

• Preoperatively map subcortical tracts with DTI and functional areas with fMRI to guide surgical planning.
• Use monopolar cathodal stimulation with a train of five pulses (500 µs pulse length, 4 ms interstimulus interval) for intraoperative motor tract localization.
• Interpret stimulation intensity to estimate distance to corticospinal tract (1 mA ≈ 1 mm) and limit resection accordingly.
• Consider motor pathways as anatomical landmarks to indirectly protect adjacent cognitive tracts when awake mapping is not possible.
• Be prepared to convert planned awake craniotomy to asleep procedure if patient cannot tolerate awake surgery.
• Recognize limitations of neuronavigation due to brain shift during large tumor resections.

References

• White matter pathways and cognitive connectivity
• Asleep-awake-asleep neurosurgical-anaesthesiological model
• Electrical stimulation parameters and motor tract localization