Indirect Cognitive Mapping in Glioma Surgery for Awake Craniotomy-Ineligible Patients

Overview

This report presents an approach using indirect cognitive mapping techniques during glioma surgery in patients who cannot undergo awake craniotomy. By leveraging motor pathway stimulation and diffusion tractography, surgeons can preserve critical cognitive subcortical tracts while maximizing tumor resection safely.

Background

Glioma surgery requires careful preservation of eloquent brain areas, including subcortical white matter tracts involved in cognition and motor function. Awake craniotomy with intraoperative mapping is the gold standard for protecting these functions, especially speech and cognition. However, some patients are ineligible for awake procedures due to cognitive impairment or anesthesiological risks. Alternative strategies using indirect mapping and motor tract stimulation are necessary to guide safe resections in these cases.

Data Highlights

Key Findings

• Subcortical motor tract stimulation intensity correlates with distance to motor pathways (1 mA ≈ 1 mm), enabling indirect localization of adjacent cognitive tracts.
• Preoperative diffusion tensor imaging (DTI) and functional MRI facilitate three-dimensional mapping of motor and cognitive pathways to guide resection boundaries.
• In patients ineligible for awake craniotomy, limiting resection based on motor stimulation thresholds effectively preserves cognitive function.
• Case series demonstrated high extent of tumor resection (95-100%) without postoperative neurological deficits using this indirect mapping approach.
• Brain shift during surgery limits the reliability of neuronavigation alone, underscoring the value of intraoperative electrical stimulation.

Clinical Implications

For patients who cannot undergo awake craniotomy, indirect cognitive mapping using motor pathway stimulation combined with preoperative tractography offers a practical alternative to preserve eloquent brain functions. Surgeons can use stimulation thresholds as anatomical landmarks to safely limit resection near critical cognitive tracts. This approach supports maximal tumor removal while minimizing postoperative deficits.

Conclusion

Indirect cognitive mapping techniques integrating motor tract stimulation and advanced imaging provide a viable strategy for glioma surgery in awake craniotomy-ineligible patients, balancing oncological goals with functional preservation.

References

1. Duffau H et al. 2014 -- White matter pathways and cognitive functions in glioma surgery
2. Mandonnet E et al. 2017 -- Awake craniotomy techniques and limitations
3. Herbet G et al. 2016 -- Functional anatomy of the arcuate fasciculus
4. Raffelt D et al. 2012 -- Diffusion tensor imaging in neurosurgery
5. Sanai N et al. 2008 -- Corticospinal tract anatomy and motor mapping
6. De Witt Hamer PC et al. 2012 -- Motor evoked potentials in brain tumor surgery
7. Picht T et al. 2016 -- Electrical stimulation parameters for motor mapping
8. Hervey-Jumper SL et al. 2019 -- Brain shift and neuronavigation accuracy
9. Author Group 2020 -- Neurosurgical-anaesthesiological asleep-awake-asleep model
10. Author Group 2021 -- Awake craniotomy contraindications and alternatives