Abstracts

Rationale: Drug resistant frontal lobe epilepsy (FLE) still remains challenging for a surgical approach. Especially in hidden lesions, adding magnetoencephalography (MEG) to presurgical evaluation and intraoperative navigation may provide a clue for localization of the epileptic focus and definition of the epileptic zone for resection. In this retrospective study, we investigated the impact of MEG-guided localisation and resection of epileptic tissue with the aid of neuronavigation and intraoperative MR imaging (iopMRI) on seizure outcome of FLE patients. Methods: Altogether, 43 patients with medically intractable FLE underwent presurgical evaluation at the Epilepsy Center, University Hospital Erlangen, and were subsequently operated on using iopMRI and neuronavigation in our Department of Neurosurgery between 2003 and 2013. Of those, we retrospectively investigated twelve patients (6 female, 6 male, mean age 28.7 yrs, from 12 to 43 yrs) who had MRI negative or ill-defined medically refractory FLE. Mean duration of epilepsy was 13.5 years (from 1 to 30 years). All patients received presurgical MEG (74-channel, two-sensor system Magnes II or whole head MEG system; 4-D Neuroimaging, San Diego, CA, USA) and invasive subdural strip-, grid- and depth electrode monitoring. Consecutive surgery was performed according to the definition of the epileptogenic zone by MEG and invasive monitoring with the aid of neuronavigation and iopMR imaging. Additionally, in seven patients functional MR imaging (for motor and speech areas) and DTI fiber tracking (for language and pyramidal tracts) were included in the surgical resection map. Results: Using MEG and invasive EEG, we achieved complete removal of the MEG focus and the defined epileptogenic zone by the aid of neuronavigation and iopMR imaging in nine out of twelve patients (75%). In three patients (25%), an intraoperative second look procedure according to intraoperative MRI findings of residual epileptogenic tissue was necessary to accomplish the extent of "tailored" resection. Surgery was performed without major complications besides a transient monoparesis in one patient (8.3%), which resolved within days. Excellent seizure outcome (Engel Class IA) was achieved in eight out of twelve patients (66.7%, mean FU 51.1 months, from 13-118 months). Conclusions: In our retrospective analysis, invasive monitoring and MEG-guided resection using neuronavigation and iopMR imaging led to promising seizure control rates in patients with MRI negative or ill-defined refractory frontal lobe epilepsy. Achieving a complete resection rate of the defined epileptogenic zone of 75% and acceptable risks of postsurgical neurological deficits, we present one possible approach to resect epileptic tissue using multimodal imaging techniques. This study was supported by DFG grand No. STE 380-14/1 and 15/1.