Determination of hemispheric language dominance using functional magnetic resonance imaging and the Shiritori (Japanese word chain) task in patients with epilepsy: Comparison with the Wada test

• fMRI using a Japanese word chain activated ROI of Brodmann areas (BA) 44 and 45.
• Laterality index (LI) was calculated using the formula: [VL − VR]/[VL + VR] × 100.
• VL and VR meant the number of activated voxels in the Lt and Rt ROIs, respectively.
• LI of BA 44 and 45 predicted hemispheric language dominance at a cut-off of LI + 50.

PurposeThe Wada test has been the gold standard for determining hemispheric language dominance (HLD) in the presurgical evaluation of patients scheduled for neurosurgical procedures. As it poses inherent risks associated with intra-arterial catheter techniques and as it occasionally fails to indicate language dominance, an alternative reliable test is needed. We quantitatively assessed the results of functional magnetic resonance imaging (fMRI) using the Shiritori task, a Japanese word chain, to identify the threshold for correctly predicting HLD.MethodsThe subjects were 28 patients with intractable epilepsy scheduled to undergo the Wada test and focus resection. We set the region of interest (ROI) on the bilateral Brodmann areas 44 and 45 (BA 44 and 45). To compare the functional activity at both ROIs we calculated the language laterality index (LI) using the formula: [VL − VR]/[VL + VR] × 100, where VL and VR indicated the number of activated voxels in the left and right ROIs, respectively.ResultsAs 2 patients were excluded due to the lack of activation in either ROI, the final study population consisted of 26 patients. By the Wada test, HLD was left in 20, right in 3, and equivocal in 3. At a cut-off of LI + 50, the predictive sensitivity and specificity for left HLD were 85% (17/20) and 100%; right HLD was predicted in a single patient (sensitivity 33.3%, specificity 100%).ConclusionThe fMRI using the Shiritori task showed good activation in ROI of BA 44 and 45. At a cut-off of LI + 50, LI of BA 44 and 45 predicted HLD identified by the Wada test with high specificity.