Abstracts

Rationale: To correlate the extent of corpus callosotomy when comparing anatomical and electrical findings utilizing MRI, DTI/Fiber Tractography and EEG. Methods: Five of the thirteen patients who underwent corpus callosotomy in the last 5 years in the management of intractable secondary generalized epilepsy in our center had the data required for the purpose of this study. Of these, 3 had failed VNS therapy. Patient selection for callosotomy followed standard presurgical evaluation for intractable epilepsy, with results not showing a selected area for ictal onset. The extent of callosotomy that was recommended for each patient depended on interictal and ictal features, imaging, and patient developmental profile. Post operative MRI volume studies (Siemens 1.5T and 3.0T) in axial and sagital planes were analyzed for delineation of the extent of the callostomy. MRI images were analyzed in detail by a blinded neuroradiologist with respect to findings of tractography or patient’s outcome. Volume studies and DTI (12-35 direction DTI) were coregistered utilizing Siemens Neuro3D software for seed points and fiber tractography. Images were coregistered on sagital plane on both sides of the corpus callosum for delineation of tracts across this structure. EEG reports and patient outcomes were analyzed and compared to imaging data in regards to the degree of EEG asynchrony and seizure frequency and severity. Results: The analysis of the plain MRI data disclosed full callostomy in only one of the patients. A second patient had an anterior 2/3 callosotomy which was subsequently completed. When fiber tractography was analyzed, there was a good correlation between MRI and fiber tractography, yet the visualization of connecting fibers was superior when tractography was utilized. Conversely, the degree of electrical asynchrony did not correlate with the extent of the disconnection. Seizure outcome showed significant improvement on 2 out of 3 patients following callosotomy, one of whom still had posterior connecting fibers on fiber tractography. Conclusions: We recommend the performance of fiber tractography, and will be evaluating the use of CISS/SPACE imaging (heavily T2 weighted 3D imaging) for patients status post corpus callosotomy for proper visualization of the degree of disconnection. According to seizure outcome, these high resolution images can be used to define the need for further surgical intervention in patients with suboptimal seizure outcome. The electrical correlation (EEG) appears to be poor. Remaining connecting fibers across the corpus callosum may be missed by plain MRI analysis.