MRI-Based Lateralization of Anterior Speech Area

Choi, Chul; Choi, Ha Young; Bae, Si Hyun

Abstract

Speech lateralization by Wada is a necessary step in the presurgical evaluation of patients with intractable epilepsy. It, however, is invasive. We studied the usefulness of a noninvasive technique: MRI-based volumetric and anatomical analysis of the anterior speech area as compared to Wada test. Thirty nine patients with intractable epilepsy under presurgical evaluation includding Wada test for hemispheric lateralization for language, were studied: patients with left language dominance(n=20) and right language dominance (n=19). Sagittal and coronal T1-weighted turbo FLASH scans were acquired. Every image in each patient was reconstructed and inferior frontal gyrus was identified on the 3D-surface rendered brain. Then cortical gray matter of inferior frontal gyrus in each image was segmented and reconstructed using a 3D software(Allegro, ISG, Toronto, Canada). Sulcal and gyral patterns of the inferior frontal gyrus were evaluated and classified comparing with the normotive data of Steinmetz. Total volume of inferior frontal gyrus(ifg), regional volumes of pars triangularis(tr) and pars opercularis(op) were obtained. Asymmetry Quotient(AQ) of inferior frontal gyrus, (right-left)/0.5(right+left), between left and right were calculated in each patient. AQ from both groups of patients were compared and data was analysed. Complicated gyral pattern and presentation of a diagonal sulcus in the pars opercularis were prominent in the left side in patients with the left hemispheric dominance for language(p<0.006, p<0.02), and in the right side in patients with the right hemispheric dominance(p<0.002, p<0.03). In patients with language dominance in the left hemisphere, AQ of each portion of anterior speech area showed significant leftward asymmetry(M: Mean, SEM: Standard Error of Mean, Mifg=-.24; SEMifg=0.04, Mtr=-.19; SEMtr=0.09, Mop=-.26; SEMop=0.06). In patients with language dominance in the right hemisphere, AQ showed mild rightward asymmetry or no asymmetry(Masa=0.21; SEMifg=0.06, Mtr=0.15; SEMtr=0.08, Mop=0.24; SEMop=0.09). Fisher's Exact test demonstrated significant value of AQ in each portion of inferior frontal gyrus correlated with hemispheric dominance for language with confidence index(CI)in 95%. Interestingly, AQ of pars triangularis plus pars opercularis showed the highest value(p=0.00001) in predicting the language dominant hemisphere. MRI-based sulcal, gyral patterns and volumetric asymmetry of inferior frontal gyrus correlate with speech lateralization on Wada test. This is a promising noninvasive technique in hemispheric lateralization for language.