F178. Epilepsy and temporal encephaloceles: Presurgical evaluation and surgical outcomes

Abstract

Introduction Temporal encephalocele (TE) is an under-recognized surgically-remediable cause of medically refractory temporal lobe epilepsy. This study assessed preoperative evaluations [MRI, FDG-PET, routine and prolonged video scalp EEG, intraoperative and extraoperative electrocorticography (ECog)] and short-term surgical outcomes in patients with medically refractory temporal lobe epilepsy due to TE. Methods Patients with medically refractory temporal lobe epilepsy who underwent surgical intervention for known TE at the Mayo Clinic Rochester between January 2008 and July 2017 were identified. Additional patients who underwent surgery for temporal lobe epilepsy were found retrospectively on review of PET-CT or PET-MRI by an experienced neuroradiologist. Minimum required follow-up was 3 months. Results Fifteen patients were identified (female 80%, median age 42.1 years, interquartile range (IQR) 19.3–54.9 years). TE was identified in 7 patients prior to surgery (left 3, right 2, bilateral 2), from radiology re-review in 7 (left 1, right 1, bilateral 5), and intraoperatively in 1 (right). Temporal hypometabolism was present on FDG-PET in 7 of 10 patients, including 5 initial MRI reviews not suggestive of TE. Routine EEG was normal in 7 patients (47%). Prolonged video EEG showed interictal discharges and ictal onset ipsilateral to the TE in all unilateral cases. In bilateral TE, temporal interictal discharges were lateralized in 4 patients and focal ictal onset present in 5 patients. Intraoperative or extraoperative ECog showed widespread mesial and neocortical temporal discharges in 12 of 14 patients. Three patients (20%) underwent focal TE resection, 11 patients (73.3%) anterior temporal lobectomy (ATL), and 1 patient amygdalohippocampal laser ablation. Eight patients (53.3%) were seizure-free at last follow-up (median follow-up duration 7.1 months, IQR 4.2–41.9, 1 focal TE resection, 7 ATL). Focal TE resection was performed only in recent years (median duration of follow-up in focal TE resection 7.2 months, IQR 7–13.8, versus ATL 18.7 months, IQR 4.1–48.8), and comparison of surgical outcome between surgical groups was limited to short-term follow-up. At 6 months, seizure-freedom was achieved in 2 of 3 patient with focal TE resection and 4 of 6 patients with ATL (p > 0.05). Conclusion TE is an easily overlooked etiology of medically refractory temporal lobe epilepsy. Normal routine EEG and unrevealing initial MRI review were seen in nearly half of the patients. Although prolonged video scalp EEG provided concordant localizing information consistent with TE, ECog often showed epileptogenic discharges extending beyond regions around the TE and should be interpreted with caution as short-term follow up remained favorable despite focal TE resection. Long-term follow-up is needed to clarify which surgical approach optimizes seizure outcome while minimizing resection.