Localisation of eloquent cortex using magnetoencephalography and its clinical implications

Area of Science:

• Neuroscience
• Medical Imaging
• Epilepsy Research

Background:

• Eloquent cortex localization is crucial for neurosurgical planning.
• Magnetoencephalography (MEG) offers a non-invasive method to assess brain function.
• Epilepsy and brain tumors near eloquent areas pose significant diagnostic challenges.

Purpose of the Study:

• To localize the eloquent cortex using magnetoencephalography (MEG).
• To measure evoked field (EF) parameters in patients with epilepsy and tumors.
• To compare EF parameters between patients and healthy controls and analyze lesion effects.

Main Methods:

• Recruited 41 patients (26 epilepsy, 15 tumors) and compared with controls.
• Measured visual evoked fields (VEF), auditory evoked fields (AEF), sensory evoked fields (SSEF), and motor-evoked fields (MEF).
• Analyzed latency, amplitude, and localization, assessing lesion proximity and hemisphere effects.

Main Results:

• Reduced AEF and VEF amplitudes and latencies observed bilaterally.
• Significant reductions in SSEF amplitude in temporal lobe lesion patients.
• MEF amplitude reduction and latency prolongation in frontal lobe lesion patients.
• Evoked field displacement ranged from 16% to 57% across different EFs.

Conclusions:

• Evoked field (EF) amplitude reduction and latency prolongation occurred in the affected hemisphere.
• Distant EF abnormalities were noted, particularly in epilepsy patients.
• EF changes suggest eloquent cortical displacement, potentially undetectable by MRI.