Abstracts

Rationale: Surgical resection of the mesial temporal lobe is a common treatment of drug-resistant temporal lobe epilepsy (TLE). The ability to predict seizure outcome in these patients could prevent unsuccessful surgery, or identify alternative surgical targets or treatments. However, the mechanism for seizure recurrence may vary across a population with seemingly similar presurgical clinical assessments. Our goal was to use presurgical MRI to identify patterns of functional (FC) and structural (SC) connectivity associated with post-surgical seizure recurrence. Methods: We enrolled 25 TLE patients and 35 age and gender matched controls. The TLE group included 13 who were seizure free (Engel 1A) after resection of the anterior temporal lobe (sz free group, 8F, 8 right TLE), 9 with seizure recurrence (sz recur group, 5F, 8 right TLE) and 3 less than 1year post-surgery. Presurgical 3T MRI images were acquired using resting state functional MRI for FC (TR=2 s, 3x3x4 mm3, 600 vols) and diffusion weighted MRI for SC (b=1600 s/mm2, 92 directions, 2.5 x 2.5 x 2.5 mm3, 3 averages). The seizure network was defined ipsilateral and contralateral to seizure onset (hippocampus: HipI, HipC; insula: InsI, InsC; thalamus: ThalI, ThalC), with two midline bilateral structures (precuneus: Prec; midcingulate: Cing). FC was calculated as correlations of pairwise regional time series transformed to Z scores. For SC, FSL probabilistic fiber tracking was used to compute the fraction of total fibers from the seed to each of seven targets normalized to size of regions. Patient FC and SC values were transformed to standard deviations from age matched control. Next, a pattern of FC and SC consistent across the sz free group was determined. Then, the FC and SC of each patient in the sz recur group was qualitatively compared to this pattern. Results: Figure 1A shows the paths with consistent connectivity patterns across the sz free group. Diagrams of these paths are shown in Figure 1B including FC greater than control (FC+) between the Prec and ThalI and ThalC, FC less than control (FC-) from the HipI and InsI, and SC less than control (SC-) from the HipI and InsI. Figure 2 shows four patterns of connectivity in sz recur patients. One patient had auras only (Engel 1B) and does not differ from the sz free patients (4A). One patient had a mesial temporal tumor with several differences from the sz free group (4B, orange arrows). Figure 4C shows two distinct patterns of differentiation from the sz free group (purple arrows) showing increased SC HipI-HipC (red) or increased SC InsI-Cing (green). These groups differed from each other, but not from the sz free group in FC HipI-Prec (brown arrow). Conclusions: This study identifies a common pattern of FC and SC across a population of sz free TLE patients. From this, at least four distinct patterns of connectivity were qualitatively identified in the sz recur patients. Interestingly, the patient with auras was not distinguishable from the sz free pattern. Overall, we introduce a possible method of predicting post-surgical outcome in TLE, which further may imply mechanisms of this recurrence. Funding: NIH R01 NS75270 ?" VLM