Abstracts

Rationale: Discordance between the IAP and noninvasive procedures in a minority of patients has precluded routine replacement of the IAP with fMRI or MSI. The basis of the discordance and its implications for epilepsy surgery has not been extensively investigated. The aim of this study was to clarify the nature of the discordance among procedures for determining hemisperic language lateralization and postoperative language outcome. Methods: Eleven patients ages 4 to 16 years underwent IAP, fMRI and MSI to determine hemispheric language lateralization as part of their evaluation for epilepsy surgery. The concordance of these procedures was evaluated, and when patients proceeded to surgery, discordant cases were reviewed in relation to results of cortical language mapping with electrical stimulation studies and postoperative language outcome.Results: There was complete concordance among IAP, fMRI and MSI in only two cases, and in two additional cases, all procedures identified language representation in the to-be-operated hemisphere that was later verified with electrical stimulation studies. In three patients, fMRI or MSI suggested bilateral language representation when the IAP classified the right hemisphere as nondominant; all underwent right temporal lobectomy, two patients undergoing 2/3 lateral temporal resection and one patient undergoing 5 cm lateral resection, with no postoperative language decline observed in any. In two patients, either fMRI or MSI suggested the absence of language in a hemisphere identified by IAP as having a minor role in language; neither patient experienced persistent postoperative language decline following temporal lobectomy of the presumed nondominant language hemisphere. In only two patients did a noninvasive procedure identify a to-be-operated hemisphere as nondominant when the IAP indicated that it was the primary language hemisphere; one patient proceeded to surgery, with electrical stimulation studies verifying frontal and temporal language areas as predicted by IAP. Conclusions: Noninvasive procedures overestimated or underestimated a hemisphere's role in language in approximately one third of patients in relation to the IAP. Although overestimating a hemisphere's role in language may lead to more conservative resection and potentially lesser seizure control, a greater risk is posed to the patient in the form of postoperative aphasia when a noninvasive procedure indicates the absence of language in the major language hemisphere.