Abstracts

Rationale: Negative MRI is one of the presurgical factors associated with poor outcome after standard anterior temporal lobectomy or selective amygdalohippocampectomy. Non-lesional TLE (NLTLE) is characterized by highly variable clinical features, complex and diverse pattern of ictal onset and seizure spread, combined involvement of medial and lateral temporal structures, and presence of eloquent regions in cases of the dominat-sided surgery, making it difficult to treat by standardized approach. So far proposed is standard anterior temporal lobectomy plus tailored and often extensive lateral resection. We present our approach and its results. Methods: Presurgical evaluation includes long-term video and scalp EEG monitoring with sphenoidal electrodes, MRI, fMRI, MEG, FDG-PET, IMZ-SPECT, ECD-SPECT, Wada test and neuropsychometry. Chronic ECoG is monitored with implanted subdural electrodes for NLTLE in principle. Instead of resection we preferentially employ multiple subpial transection (MST) and multiple hippocampal transection (MHT) for NLTLE. These procedures are delivered until major epileptiform discharges are abolished in intraoperative ECoG under spike-activating anesthesia with sevoflurane. Seventeen patients were treated between September 2003 and June 2007. Results: Chronic ECoG identified the seizure initiation in the unilateral medial temporal area in 6 patients, unilateral lateral temporal area in 3 patients, unilateral medial and lateral temporal areas simultaneously, independently bilaterally medial temporal areas, independently bilateral medial and lateral temporal areas, respectively in 1 patient. Two patients had seizure onset from extremely extensive bilateral regions simultaneously. Chronic ECoG was skipped in 3 patients because of patients' refusal and their seizure origins were unilateral sphenoidal electrode in 2 patients and unilateral frontotemporal in one. Ten patients underwent dominant-sided surgery, 4 non dominant-sided surgery, and 2 stepwise bilateral surgeries. Twelve patients necessitated both MHT and MST. Seizure outcomes are Engel class I in 11, class II in 4, and class III in 2 patients. Two patients with bilateral extensive foci underwent bilateral extensive MST in a stepwise fashion but resulted in class III. Postoperative neuropsychometry revealed transient mild cognitive impairment immediately after dominant-sided surgery but later recovery to the presurgical level within several months. Conclusions: Seizure onset pattern was complex and diverse in NLTLE. Our result on surgical outcome seems comparable to the reported ones after resective surgery, while those patients who underwent dominat-sided surgery would have been subjected to permanent cognitive deficit after resective surgery. Surgery based on the intraoperative ECoG under spike-activating anesthesia may result in more extensive area of treatment, but employment of function-preserving MST and MHT can compensate the issue. The treatment strategy for bilateral extensive foci remains as a major challenge.