Language lateralization in epilepsy patients: fMRI validated with the Wada procedure

Area of Science:

• Neuroimaging
• Neurology
• Cognitive Neuroscience

Background:

• Language lateralization is critical for neurosurgical planning.
• The Wada test is the gold standard but is invasive.
• Functional magnetic resonance imaging (fMRI) offers a non-invasive alternative for assessing language dominance.

Purpose of the Study:

• To evaluate the efficacy of a three-task fMRI language-mapping protocol for language lateralization.
• To compare two localization methods and four metrics for quantifying hemispheric activation.
• To validate fMRI findings against Wada testing and discuss sources of discordance.

Main Methods:

• fMRI language mapping was conducted in 40 epilepsy patients using reading, auditory comprehension, and verbal fluency tasks.
• fMRI results were compared with Wada procedure outcomes.
• Whole-brain and midline exclusion analyses were performed, examining laterality indices across different statistical thresholds.

Main Results:

• fMRI showed high concordance with Wada testing: 83.87% for reading, 83.33% for auditory, 76.92% for verbal fluency, and 91.3% for conjunction analysis.
• Discrepancies were observed, particularly when midline regions were included in whole-brain analyses.
• Wada-categorized bilateral patients sometimes showed fMRI-detected hemispheric dominance.

Conclusions:

• fMRI is a valuable tool for language lateralization in clinical settings.
• The choice of analysis method (whole-brain vs. midline exclusion) significantly impacts lateralization scores.
• Careful consideration of analytical confounds, such as midline region inclusion, is essential for accurate fMRI interpretation.