Abstracts

Rationale: The purpose of this study was to utilize diffusion tensor imaging of the geniculo-calcarine radiations as part of the pre-surgical planning and post-surgical evaluation of patients undergoing antero-medial temporal resections for epilepsy or tumors. Visual field deficits (VFD's) are a common sequela following anterior temporal lobectomy, usually manifesting as a contralateral upper quandratanopsia. Resulting from damage to the most anterior portion of the optic radiation (Meyer's Loop). No data are available in the literature that evaluate damage to the geniculo-calcarine radiations (GCR) by correlating pre AND post resection diffusion tensor tractography and formal post-operative visual field evaluations indicating (VFD's). Methods: Whole-brain diffusion-weighted image volumes (32-direction Philips 3T sequence) were pre and post-operatively obtained in 12 patients undergoing anterior temporal lobectomy. Standardized masks were used to highlight the eloquent brain areas including one mask combining the visual areas V1, V2, V5 based upon cytoarchitectonic mapping and a second mask of the lateral geniculate body (LGB) transformed into regions in single subject space. A deterministic diffusion tensor tractography method (Euler tracking in DTI Query 2mm seed spacing, 1mm step, 0.45 deg termination threshold) was used to reconstruct any fiber pathways connecting the areas of both masks by placing volumes of interest around the eloquent mask areas and utilizing an "AND" operator. Utilization of "NOT" VOI's helped remove extraneous fibers, such as those of the inferior fronto-occiptal fasiculus. All patients underwent formal visual perimetry post-operatively. Results: Of the 12 patients evaluated so far, one had a complete, and two had a partial quadrantanopsia. Preliminary analysis indicates that the GCR fibers were successfully localized using pre and post-operative DTI. There was a strong correlation between a decrease in the numbers of fibers in the GCR and the occurrence of a visual deficit. No such change was noted in the cases where there was no VFD. Conclusions: Based upon this study, we conclude that DTI is a useful tool in pre-operative evaluation of patients to prevent damage to the geniculo-calcarine fibers during surgical resection. The availability of pre-resection DTI data show the effect of a “extended” temporal resection on the visual radiations.