Abstracts

Rationale: Approximately 30% of patients with epilepsy do not respond to anti-epileptic drugs (AED) [1]. Where epileptogenic foci can be identified in these patients, surgical resection often provides the best clinical outcome [2]. Traditional identification of epileptogenic lesions requires electroencephalogram (EEG) and electrocorticography (ECoG) studies to localize seizure onset boundaries prior to resection. However recent advances in MRI imaging allow for enhanced visualization of small lesions, specifically occult encephaloceles. Interestingly, recent data also suggests that temporal lobe encephaloceles are highly epileptogenic in nature [3]. As a result, our work sought to identify any associated radiological findings in patients with epilepsy related encephaloceles (EREs). We next explored whether conservative resection of temporal lobe encephaloceles – specifically avoiding resection of hippocampal structures – was sufficient to decrease seizure frequencies while limiting collateral tissue loss. Finally, we preformed histological analysis of resected encephaloceles to better characterize their highly epileptogenic nature. Methods: We evaluated six patients that underwent temporal lobe encephalocele resection at our center from 2011-2019. The analysis for this study was case-based and retrospective with data collected from electronic medical records (EMR). Candidates for neurosurgical resection of EREs must have failed prior optimized AED therapy. Once identified, all patients underwent standard CT, MRI, EEG and ECoG studies to confirm the presence of an ERE. Outcomes were tracked through review of post-operative EMRs ranging from 6 months to 7 years post-operatively. Results: A total of six patients with EREs underwent neurosurgical resection from 2011-2019. Three patients underwent lesionectomy, two underwent anteromedial temporal resections (AMTR), and one underwent a standard 5 cm temporal lobectomy. 2/6 patients (33%) had Engel Outcome 1A, 1/6 (17%) had Engel Outcome 1B, and 3/6 (50%) had Engel Outcome 2B. The average reduction in self-reported, focal impaired seizure frequency was -94.6% [95% CI: 84.32-104.9]. In patients with generalized tonic-clonic (GTC) seizure activity (n=4), the average reduction in self-reported, GTC seizure frequency was -95.6% [95% CI: 82.54-108.8]. Prior to surgery, our patients were treated with an average of 5 AED medications (95% CI: 5.28-5.38). Associated radiological findings in our cohort included dilated optic sheaths, an empty or partially empty sella tursica, elevated CSF opening pressures. Histological examination of resected EREs demonstrated diffuse gliosis. Conclusions: All patients in our cohort saw substantial reduction in monthly seizures, with 33% becoming seizure-free since surgery and 50% having one or less seizures post-operatively. Associated radiological findings included dilated optic sheaths, empty or partially empty sellas, and elevated CSF opening pressures potentially allowing for early identification of occult encephaloceles. Histology of EREs showed diffuse gliosis, helping explain their role as highly epileptogenic foci. Finally given the significant reduction in post-operative seizure frequencies, we propose that early recognition of ERE-associated radiological findings and conservative neurosurgical resection of these lesions can substantially reduce disease burden in select patients with refractory epilepsy.References1: Mohanraj et al. Diagnosing refractory epilepsy: response to sequential treatment schedules. Eur J Neurol. 2006 Mar;13(3):277-82.2: Téllez-Zenteno et al. Surgical outcomes in lesional and non-lesional epilepsy: a systematic review and meta-analysis. Epilepsy Res. 2010 May;89(2-3):310-8. 3: Panov et al. Epilepsy with temporal encephalocele: Characteristics of electrocorticography and surgical outcome. Epilepsia. 2016 Feb;57(2):e33-8. Funding: JK was supported with funds from the Yale MD/PhD Program (MSTP T32)