Abstracts

RATIONALE: fMRI has been used to map striate cortex in normal subjects, although, its role in mapping funcitonal striate cortex in patients with lesional occiptial epilespy has not been previously examined. METHODS: fMRI images, acquired using a 1.5T imager, were superimposed on anatomic images obtained with multi-slice spin echo sequences. Patients viewed a flickering 8Hz checkerboard pattern via a prism. t-scores were calculated to estimate the significance of the response task. Activation maps were created by highlighting all voxels exceeding a threshold t-value. Confrontational perimetry, electrocorticography, and surgical results were examined. RESULTS: 3 children (6, 11 & 14 yrs)had unilateral focal cortical dysplasia in the striate cortex. All had a normal neurological examinaiton, were of normal intellegence and had medically intractable epilepsy for 4 to 7 years. Each underwent fMRI to map straite cortex for a presurgical evaluation for intractable occipital epilepsy associated with a lesion in the striate cortex. Bedside testing of visual fields failed to show scotoma, although, two of three had scotoma demonstrated on perimetry. In each fMRI mapped striate cortex in an aberrent region that was away from dysplastic tissue. Regions showing increased activation included the contralateral striate cortex as well as increased activation in regions anterior to the lesion and at the occipital pole. Surgery performed in 2 of 3 children rendered them seizure free. Post-op perimetry showed a modest increase in the visual field deficit in both children. CONCLUSIONS: The relationship between cortical dysplasia and fMRI mapping of striate cortex may help determine the risk of a post-operative visual field deficit in patients undergoing epilepsy surgery for lesions in proximity to the striate cortex. Since the lesion in all three patients were long standing, probably sustained in-utero, displacement of regions activated may represent neuronal reorganization and placiticity.