Language functional MRI and direct cortical stimulation in epilepsy preoperative planning

Abstract

Objective: Presurgical language assessment can help minimize damage to eloquent cortex during resective epilepsy surgery. Two methods for presurgical language mapping are functional MRI (fMRI) and direct cortical stimulation (DCS) of implanted subdural electrodes. We compared fMRI results to DCS to help optimize noninvasive language localization and assess its validity.

Methods: We studied 19 patients referred for presurgical evaluation of drug-resistant epilepsy. Patients completed four language tasks during preoperative fMRI. After subdural electrode implantation, we used DCS to localize language areas. For each stimulation site, we determined whether language positive electrode pairs intersected with significant fMRI activity clusters for language tasks.

Results: Sensitivity and specificity depended on electrode region of interest radii and statistical thresholding. For patients with at least one language positive stimulation site, an auditory description decision task provided the best trade-off between sensitivity and specificity. For patients with no language positive stimulation sites, fMRI was a dependable method of excluding eloquent language processing.

Interpretation: Language fMRI is an effective tool for determining language lateralization before electrode implantation and is especially useful for excluding unexpected critical language areas. It can help guide subdural electrode implantation and narrow the search for eloquent cortical areas by DCS. Ann Neurol 2017;81:526-537.

Figure 1. Electrodes projected to the cortical surface

Patients 16 and 25; green = cleared electrodes, red = language positive electrodes, grey = electrodes were not tested

Figure 2. Functional MRI masks and electrode ROIs

Patient 19, a right handed 28 year old female, with left lateralizing fMRI activation; Left = Right; 2A: Task A (ADDT), at thresholds P1, P2, and P3, from left to right; 2B: Task B (AUDCAT), at thresholds P1, P2, and P3, from left to right (color overlay represents value of T statistic); 2C: ADDT × AUDCAT combined activation map at P1; 2D: a DCS language positive electrode (red), and a DCS cleared electrode pair (green).

Figure 3. Sensitivities and specificities of each task for DCS+ Patients

A: ADDT, B: AUDCAT, C: Listening, D: Reading

Figure 4. Sensitivities and specificities of combined activation maps for all patients

A: ADDT × AUDCAT × Listening × Reading, B: ADDT × AUDCAT, C: ADDT × Reading