Abstracts

Rationale: Functional imaging studies are increasingly being used to determine hemispheric language lateralization prior to epilepsy surgery. However, concern remains regarding validity of noninvasive procedures given a minority of patients who have demonstrated discordance between hemispheric dominance based on the Wada procedure and functional imaging. The goal of this study was to examine the basis of the discordance in language lateralization between the Wada procedure and magnetic source imaging. Methods: The sample included 19 patients ages 13-60 years who demonstrated left hemispheric dominance on the amobarbital procedure, and demonstrated a temporal lobe seizure origin on EEG. Those who were classified as MSI right hemisphere language dominant (n=6; MSI-R) were compared to those who were classified as MSI left hemisphere language dominant (n=13; MSI-L) on the following variables: presence of language impairment (Wechsler VC ? 85 and Boston Naming Test ? 45 raw or standard score < 70), presence of verbal memory impairment (word list delayed recall ? 8), early age of seizure onset (? 5 years), presence of satisfactory right hemispheric memory capacity on IAP(> 50% recognition), right versus left temporal seizure onset, and presence of a left mesial temporal structural lesion. Results were analyzed using the Fisher s Exact Test. Results: Patients who displayed MSI-R were more likely to evidence language impairment (p=.003), satisfactory verbal memory (p=.057) and early age of seizure onset (p=.057) than those who displayed MSI-L. Groups did not differ in presence of a left mesial temporal structural lesion, side of seizure onset, or IAP right hemispheric memory capacity. Conclusions: For those who demonstrate clear left hemisphere dominance on the Wada test, discordant classification of MSI appears to be associated with impaired language function and early age of seizure onset. These factors have previously been associated with diminished integrity of the language dominant hemisphere. This might account for underestimation of the role of the left hemisphere in language processing by MSI.