Abstracts

Rationale: Assessment of presence and lateralization of IED on pre and postoperative EEGs relatively to seizure control in TLE patients with MRI signs of HS.Methods: We followed patients with refractory MTLE and MRI signs of HS, without other associated MRI abnormalities, submitted to surgery. Treatment was based on comprehensive evaluation that included clinical, non invasive EEG, MRI and neuropsychological evaluation. Patients had at least five routine EEGs prior to surgery. We included 86 patients who also had postoperative EEGs performed at least 6 months after surgery. We used chi-square or Fisher s exact test to analyze the association between postoperative seizure control (Engel s classification I versus II-IV) and presence or absence of IES on pre and postoperative EEGs (ipsilateral, contralateral to surgical site, bilateral), and preoperative MRI signs of unilateral or bilateral HS.Results: Mean follow-up period was 53 months (range 6-144, median 46 months). Files from 298 digital preoperative EEGs were available for review. Based on lateralization of preoperative IES, 48 patients were grouped as unilateral (24 right, 24 left); and 38 as bilateral (33 of these underwent telemetry and early seizure activity was ipsilateral to the side of HS on MRI). Sixty-nine patients underwent amygdalohippocampectomy and 17 had cortical-amygdalohippocampectomy. One patient underwent reoperation. Total of 322 post-operative EEGs were analyzed (average 4 per patient; median=3, range=1-11). However, we did not find association between the presence of unilateral or bilateral IED on pre or postoperative EEGs and postoperative seizure outcome. On the other hand, preoperative MRI signs of unilateral HS were significantly (p=0.0002) associated with good surgical outcome (Engel class I).Conclusions: Occurrence of unilateral or bilateral IED on pre or postoperative EEGs was not significantly associated with postoperative seizure control. Patients with unilateral HS frequently exhibit bilateral IED, and that may explain this finding. Moreover, these findings contribute to the assumption that surgical treatment does not cure epilepsy, but sensitizes patients to better control with medical treatment.