Abstracts

Rationale: Video-EEG monitoring (vEEG) of unilateral mesial temporal sclerosis (uMTS) patients may show ictal EEG onset contralaterally to the MTS. This finding may indicate false lateralization (seizure onset in the lesion, with contralateral EEG manifestation) or true seizure onset on the contralateral side. Surgical prognosis should be favorable in the first scenario and unfavorable in the latter. Ictal SPECT performed in seizures with contralateral EEG onset may show increased flow ipsilaterally to the lesion (“correcting” false lateralization) or contralaterally to the lesion (indicating true contralateral onset, or also falsely lateralizing seizure onset side). We evaluated ictal SPECT results in seizures originating contralaterally to the MTS and compared surgical prognosis in cases with concordant and cases with discordant SPECT findings. Methods: In a series of 77 consecutive patients with uMTS undergoing vEEG, 47 underwent ictal SPECT studies. We identified eight cases in which an ictal SPECT study was obtained during a seizure with contralateral EEG onset in relation to the MTS. We determined predominant side of increased SPECT flow in all cases and classified cases as concordant if MRI and ictal SPECT were congruent and as discordant if MRI and ictal SPECT were not congruent. All patients underwent anteromesial temporal lobectomy on the lesion side, regardless of MRI-vEEG concordance or discordance. We compared surgical prognosis in both groups, and in a control group of uMTS patients with fully concordant ictal EEG, ictal SPECT and MRI. Good surgical prognosis (GP) was defined as Engel’s class I. Results: Of the eight cases with contralateral ictal EEG seizure onset, 6/8 (75%) had a good surgical prognosis. Of these, five had a concordant SPECT and three a discordant SPECT. Three out of the five (75%) concordant cases had a GP; all three cases (100%) in the discordant group had a GP. Mean postoperative follow-up period was 57.2+/-14.1, median 60, range 35-70 months in the concordant group, and 55.7+/-25.1 months, median 66, range (27-74) months in the discordant group. In the control group, 25/33 (75.6%) had a GP (mean postoperative follow-up 55.7+/-21.1 months, range 24-96, median 62). Conclusions: In this series, contralateral ictal EEG onset did not determine a worse surgical prognosis, suggesting contralateral scalp ictal EEG onset represents a false lateralization. Although ictal SPECT “corrected” false lateralization in more than half of the cases, lack of ictal SPECT “correction” of lateralization did not preclude a good surgical outcome, indicating that, in these cases, ictal SPECT also provided “false lateralization” data. Although ictal SPECT falsely lateralizes less frequently than ictal scalp EEG, it cannot be reliably interpreted as showing the correct seizure onset side in these cases.