Abstracts

Rationale: Focal cortical dysplasia (FCD) is the most frequent neocortical pathology underlying partial refractory epilepsies. Surgical outcome is related to completeness of resection of the visible and adjacent microscopic lesion and of the epileptogenic tissue. Extent of resection is often based upon costly preoperative invasive EEG studies. Alternatives to provide reliable delineation of the epileptogenic zone (EZ) following low-cost noninvasive presurgical evaluation are needed. We report surgical outcome of a large series of patients with extratemporal FCD operated following noninvasive presurgical evaluation, with refinement of localization of the EZ through intraoperative, stepwise electrocorticography (ECoG). Methods: 66 consecutive patients with MRI evidence of extratemporal FCD were operated following noninvasive presurgical evaluation. Ictal or continuous epileptogenic discharges (I/CEDs) on acute intraoperative ECoG were present in 58 (89%). Sequential recordings were then performed and complete resection of the cortical tissue displaying I/CEDs, yet preserving eloquent cortex, was attempted. Resections of the lesion and the cortex displaying I/CEDs were deemed complete or incomplete, according to surgical strategy, post-op MRI and sequential ECoG. Lesions were classified as involving or not truly eloquent (ie, indispensable: rolandic, language) cortex. Histopathology confirmed FCD in all patients (13 FCD type I; 53 FCD type II). Mean and median post-operative follow up were 6.6 and 4.0 years, respectively (range, 1- 21). Outcome was verified prospectively through routine visits to the clinic and classified according to Engel. Results: Complete resection of the lesion was achieved in 40 patients (61%) and of the tissue harboring I/CEDs in 30 of the 58 (52%) with these discharges. Twenty-one patients (32%) were reoperated. Before reoperation, 36 patients (54%) were seizure-free (Engel class I) and, after a second procedure, 40 patients (61%) were in class I. There was a strong correlation between surgical outcome and completeness of resection of the lesion and of the I/CEDs: 33 of the 40 (82%) with complete resection of the visible lesion and 28 of the 30 (93%) with complete resection of I/CEDs were seizure free, compared to 7/26 (27%) and 7 /28 (25%) of those in whom parts of the lesion or I/CEDs remained in place (both p Conclusions: The combination of noninvasive presurgical evaluation and intraoperative sequential ECoG may lead to complete seizure control in a large percentage of patients with complex extratemporal focal dysplastic lesions. Outcome is more likely related to lesion location and resulting feasibility of complete resection of the lesion and relevant epileptogenic tissue – rather than issues of localization of the epileptogenic zone.  Funding: None