Comparison of Language Localizaton by Functional Magnetic Resonance (fMRI) and Direct Cortical Stimulation in Patients with Partial Epilepsy
Tohru Hoshida, Kazuo Goda, Tetsuya Morimoto, and Toshisuke Sakaki
Department of Neurosurgery, Nara Medical University, 840 Shijo-cho, Kashihara, 634, Japan
Blood oxygen level-dependent fMRI is a noninvasive method used to localize areas of eloquent cortex. We evaluated whether fMRI can localize regions of language cortex that may be helpful in surgical planning in epilepsy patients.
Three temporal and one occipital lobe epilepsy patients were studied. fMRI was taken in a 1.0 T imager and performed using a multislice echo planar imaging with a repetition time of 4000 msec, an echo time of 60 msec, and a 90° flip angle. Conventional T1 weighted axial images were acquired for subsequent overlays. Word generation task was performed. Patients generated aloud as many words as possible beginning with a head letter presented by an investigator. Twenty images were acquired, divided into two cycles of ten (five task off and five task on). Subtraction images were obtained to evaluate z-score mapping and analysis. Extra operative electrical cortical stimulation via chronically implanted subdural electrode arrays was tested over the lateral temporal cortex. Language tasks were in the following; spontaneous speech, picture naming, comprehension, responsive naming, reading and repetition. Position of electrodes demonstrated language areas by cortical stimulation were superimposed on MR films in which subdural electrodes arrays were implanted using a neuronavigation system during operation.
Increased activation was observed in left temporal area as well as left or bilateral frontal area during word generation task. The extent and distribution of activated areas detected by cortical stimulation and fMRI varied from subject to subject respectively. Increased signal intensity areas obtained by fMRI were usually more extensive than areas detected by cortical stimulation, but always included language areas detected by cortical stimulation.
Word generation task on fMRI is clinically useful method for detection of language areas in epilepsy surgery, and it may replace the role of the direct electrical cortical stimulation.