Abstracts

Rationale: The Wada test is commonly used for presurgical language lateralization. fMRI is being increasingly used as a potential replacement for the Wada test. Although minor discordance has been noted between the two tests, especially in patients with bilateral language representation, extreme discordance is believed to be very rare. We investigated this pattern of extreme discordance. Methods: We retrospectively identified intractable epilepsy patients who underwent fMRI and Wada tests. fMRI language protocol included word and category fluency. Wada language protocol consisted of naming, comprehension, reading and repetition, assessed serially over multiple trials. Memory was assessed using dually-encodable objects with a forced choice recall format. Results: Among 24 patients who had fMRI, 4 patients also had Wada tests (Table). All four patients were male with a mean duration of epilepsy of 22 years (range 8-36 years). Two patients (1, 2) had discordant language lateralization based on fMRI and Wada test, and subsequently underwent cortical stimulation mapping and resection. Patient 3 underwent intracranial monitoring but no resection due to inadequate localization. Patient 4 is awaiting surgery. Discordant patients had handedness contralateral to Wada defined language lateralization, early onset epilepsy, proven or suspected congenital etiology, left hemispheric seizure onset (frontal or parietal), and well defined left hemispheric language function on cortical stimulation mapping. In contrast, concordant patients had either late onset epilepsy due to acquired etiology with left temporal seizure onset or early onset epilepsy due to congenital etiology with right frontal seizure onset. Conclusions: fMRI-defined language lateralization is more likely to be bilateral and discordant from the Wada-defined language lateralization in patients with known or presumed left hemispheric congenital lesions. This possibility needs to be carefully considered during presurgical evaluation to avoid potential adverse outcome.