Abstracts

Rationale: When the combination of clinical data and presurgical evaluation suggests a bilateral mesial temporal lobe epilepsy (BMTLE), the surgical approach is controversial and lateralizing the main epileptogenic focus may be challenging. Intracranial video-electroencephalography (IVEEG) has been performed in many BMTLE, whereas, some reports insisted that resection should be restricted to the side with more atrophied hippocampus or to the language non-dominant side without IVEEG study. We retrospectively evaluated the presurgical investigation including MRI hippocampal volumetry (HV), IVEEG and seizure outcome for determining the resection side in BMTLE. Methods: This study included 13 patients (mean±SD, 38.2±12.4 years, 21-63 years) who underwent IVEEG for presumed BMTLE on the basis of SVEEG with bilateral and independent seizure onsets. We analyzed hippocampal atrophy (HA) from MRI hippocampal volumetry (HV). We defined HA as hippocampal volume decline with 1SD or more difference from the baseline in14 age-matched controls. We compared HA and IVEEG findings with resection side for good seizure outcome. Results: All 13 patients had bilateral and independent seizure onsets as well as interictal epileptiform discharges on SVEEG before surgery. Twelve of 13 patients underwent MRI study for HV which revealed unilateral HA in 3 patients, bilateral in 7, and no HA in 2. IVEEG recorded a mean of 11.1 seizures per patients. Seven of 13 (53.8%) patients had unilateral seizure onset  and 6 (46.1%) had bilateral and independent seizure onsets on IVEEG. Four of 7 patients with bilateral HA had unilateral seizure onset on IVEEG. Two of 3 patients with unilateral HA had concordant results of IVEEG with unilateral seizure onset and another had discordant IVEEG results with seizure onset from opposite side of HA. We performed anterior temporal lobectomy in 10 patients and amygdalohippocampectomy in 3 on the side with unilateral seizure onset or predominant seizure frequency when bilateral seizures recorded on IVEEG. One patient with bilateral HA, who had the same number of seizures from both side on IVEEG underwent amygdalohippocampectomy on the language non-dominant side. Postoperatively, excellent seizure outcome (seizure-free) was achieved in all 7 patients with unilateral seizure onset on IVEEG and 4 of 6 patients (66.7%) with bilateral seizure onset. The patient who had the same number of seizures from both sides on IVEEG has also been seizure-free after surgery. Conclusions: Seizure lateralization was obtained by IVEEG in patients with bilateral MTLE presumed on the basis of SVEEG as well as MRI findings with bilateral HA, Unilateral HA on hippocampal volumetry could not guarantee the resection side for good seizure outcome. IVEEG is required for determining the resection side. Excellent seizure outcome can be obtained by the resection on the side with unilateral or predominant seizure onset on IVEEG. Funding: None