Abstracts

Rationale: Purpose: To develop lateralization models for distinguishing between unilateral and bilateral mesial temporal lobe epilepsy (mTLE) and determining laterality in cases of unilateral mTLE. Background: mTLE is the most common form of medically refractory focal epilepsy. Many mTLE patients fail to demonstrate an unambiguous unilateral ictal onset. Intracranial EEG (icEEG) monitoring can be performed to establish whether the ictal origin is unilateral or truly bilateral with independent bitemporal ictal origin. However, because of the expense and risk of intracranial electrode placement, much research has been done to determine if the need for icEEG can be obviated with noninvasive neuroimaging methods, such as diffusion tensor imaging (DTI).Methods: Methods: Fractional anisotropy (FA) was used to quantify microstructural changes reflected in the diffusivity properties of the corpus callosum, cingulum, and fornix, in a retrospective cohort of 31 patients confirmed to have unilateral (n=24) or bilateral (n=7) mTLE. All unilateral mTLE patients underwent resection with an Engel class I outcome. Ten had hippocampal sclerosis on pathological analysis; nine had undergone prior icEEG. The bilateral mTLE patients had undergone icEEG demonstrating independent epileptiform activity in both right and left hemispheres. Twenty-three nonepileptic volunteers were included as control subjects.Results: FA in all callosal subregions showed significant differences in right versus left mTLE, right versus bilateral mTLE, and right mTLE versus control cohort (Fig. 1). When compared with controls, FA in the callosal posterior midbody and isthmus showed significant differences in cases of left mTLE, while the genu and splenium showed significant differences in the cases of bilateral mTLE (P<0.05). FA in all cingulate subregions showed significant differences in right mTLE versus control cohort. FA in all cingulate subregions, except the left anteroinferior, showed significant differences between left and right mTLE cohorts (Fig. 1). FA in the left and right superior cingulate subregions showed significant differences in right versus bilateral mTLE cohorts (P<0.05). FA in all forniceal subregions showed significant differences in right mTLE versus control cohorts (Fig. 1). The left and right crura showed the same in left mTLE cases versus control cohort (P<0.05). Based on FA measurements in the cingulate, callosal and forniceal subregions, a response-driven lateralization model successfully differentiated all cases (54) into groups of unilateral right (12), unilateral left (12), and bilateral mTLE (seven), and nonepileptic control (23).Conclusions: Conclusion: The proposed response-driven DTI biomarker is intended to lessen diagnostic ambiguity of laterality in cases of mTLE and help optimize selection of surgical candidates. Application of this model shows promise in reducing the need for invasive icEEG.