Abstracts

Rationale: Seizure outcome after mesial temporal lobe epilepsy (TLE) surgery is complex and diverse, even across patients with consistent presurgical clinical profiles. In a recent study [1] we identified significant widespread functional connectivity (FC) changes across the brain after TLE surgery, many involving the contralateral hippocampus. Others have reported post-surgical contralateral hippocampal volume decreases [2]. In this work, we investigated the relationship between hippocampal volume and FC changes and outcome. We believe that characterizing these changes will lead to more accurate long-term seizure outcome prediction in these patients. Methods: We performed presurgical 3T MRI on 36 unilateral mesial temporal lobe epilepsy patients for FC and volumetric measures. Twenty of these patients returned for post-surgical repeat 3T MRI (mean 36.6 months after surgery). All patients had post-surgical seizure outcome evaluations. Hippocampal volume was computed using FreeSurfer (dev v. 3/21/19) including total head, total body and tail volumes for each side. These 6 values for each patient were normalized to standard deviations from age-matched control by fitting a linear model to 44 healthy control subjects for each volume. Then the volumes were converted to ipsi and contra relative the side of surgery. Values were compared pre and post-surgery and to contralateral hippocampal FC values found to decrease after surgery in previous work [1]. Ipsilateral volumes were excluded from post-surgical analyses. Results: Prior to surgery (n=36) the ispi head, body and tail volumes were less than age matched control (p<0.05, corrected) (Fig 1). After surgery (n=20), no contra volumes were significantly different from control. Further, there was no significant change in contra volumes pre to post surgery. There was only one weak non-significant association between post-surgical contralateral hippocampal FC and volume (Fig 2). Hippocampal volumes were not correlated with presurgical seizure frequency, duration of disease or post-surgical seizure outcome. Conclusions: We previously reported significant contralateral post-surgical FC decreases, specifically from the hippocampus [1]. Many changes were related to outcome, type of surgery and presurgical disease parameters. Here we showed the expected strong ipsilateral hippocampal volume decreases prior to surgery, but not after surgery on the contralateral side. We also did not detect a relationship between post-surgical FC and hippocampal volume in the same cohort. These results suggest that volume and FC are independent entities, and that FC reveals unique information to be considered in developing seizure outcome predictors.[1] Morgan et al. J Neurosurg 2019; in press.[2] Elliot et al. Ep Res 2016; 125:62-71. Funding: NIH R01 NS075270 (VLM), R01 NS110130 (VLM), R01 NS108445 (VLM) and R00 NS097618 (DJE)