Discordant Wada and fMRI language lateralization: a case report

Abstract

Functional MRI (fMRI) is gaining importance in the preoperative assessment of language for presurgical planning. However, inconsistencies with the Wada test might arise. This current case report describes a very rare case of an epileptic patient who exhibited bilateral distribution (right > left) in the inferior frontal gyrus (laterality index [LI] = -0.433) and completely right dominance in the superior temporal gyrus (LI = -1). However, the Wada test revealed a dissociation: his motor speech was located in the left hemisphere, while he could understand vocal instructions with his right hemisphere. A clinical implication is that the LIs obtained by fMRI should be cautiously used to determine Broca's area in atypical patients; for example, even when complete right dominance is found in the temporal cortex in right-handed patients. Theoretically, as the spatially separated functions of motor speech and language comprehension (by the combined results of fMRI and Wada) can be further temporally separated (by the intracarotid amobarbital procedure) in this case report, these findings might provide direct support to Broca's initial conclusions that Broca's area is associated with acquired motor speech impairment, but not language comprehension per se. Moreover, this current finding supports the idea that once produced, motor speech can be independent from language comprehension.

Keywords: Broca’s area; Wada; case report; fMRI; laterality index.

Figure 1.

Top: magnetic resonance imaging scans showing early-life lesions in the left anterior temporal cortex of a right-handed male college student in his early 20s with a history of febrile convulsions since 6 months old. Bottom: brain activation during the verb generation task overlapped on a rendered standard brain; P < 0.05, Family-Wise Error corrected. Right asymmetries were found in both the IFG (1158 versus 458; LI = –0.433) and STG (1277 versus 0; LI = –1). IFG, inferior frontal gyrus; STG, superior temporal gyrus; PreCG, precentral/central gyri; L, left; R, right. The colour version of this figure is available at: http://imr.sagepub.com.