Prognostic Value of Electrocorticography and Surface EEG in Epilepsy Patients with Unilateral Hippocampal Sclerosis Undergoing Selective Amygdalohippocampectomy
Purpose: To evaluate the predictive value of intraoperative electrocorticography (ECoG) and surface electroencephalography (EEG) in patients with unilateral hippocampal sclerosis (HS) undergoing transsylvian selective amygdalohippocampectomy (sAHE). Methods: ECoG was recorded before and after res...
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|Summary:||Purpose: To evaluate the predictive value of intraoperative electrocorticography (ECoG) and surface electroencephalography (EEG) in patients with unilateral hippocampal sclerosis (HS) undergoing transsylvian selective amygdalohippocampectomy (sAHE).
Methods: ECoG was recorded before and after resection in 22 patients with medication resistant mesial temporal lobe epilepsy. The sAHE was performed, regardless of ECoG findings. ECoG findings recorded from the mesial temporal lobe (MTL) and lateral temporal lobe (LTL) before and after the sAHE were correlated with seizure outcome 12 months later. The preoperative surface EEG findings as well as their correlation with seizure outcome were also discussed. According to pre-resection ECoG findings, patients were divided into the following subgroups: 1) Pre-resection spikes restricted to the MTL; 2) Pre-resection spikes both in MTL and LTL); 3) Pre-resection spikes restricted to the LTL; 4) No pre-resection spikes recorded. According to the distribution of interictal epileptiform discharges (IEDs), the surface EEG findings were divided into four groups: 1) ipsilateral anterior temporal IEDs; 2) ipsilateral lateral temporal IEDs; 3) ipsilateral extratemporal IEDs; 4) contralateral IEDs. Based on seizure occurrence after sAHE, patients were divided into two groups: Group 1 included only patients completely free of any seizures (Engel Classification Ia); Group 2 included patients with post-operative occurrence of any types of seizure and aura only.
Results: Ten patients (45%) had a right sided and 12 (55%) left sided hippocampal sclerosis. Average age was 37.1 years (between 10 and 57 years). Fifteen patients (68%) remained completely seizure free and 19 (86%) were in Engel class I post-operatively.
In 21 of 22 patients (95%), interictal epileptiform discharges were recorded on preoperative surface EEG., thirteen patients (13/21, 62%) had unilateral temporal IEDs ipsilateral to the hippocampal sclerosis, one patients (1/21, 5%) had ipsilateral extratemporal IEDs and seven patients (7/21, 33%) had bilateral IEDs. In 10 of 14 patients (71%) with unilateral IEDs ipsilateral to the HS, IEDs were restricted to the anterior temporal lobe (ATL). In the remaining one patient (1/22, 5%), no IEDs but temporal intermittent rhythmic delta activity (TIRDA) was recorded.
The patients with unilateral temporal IEDs ipsilateral to the HS remained seizure free more frequently (92%) as compared to those patients with bilateral and / or ipsilateral extratemporal IEDs (25%) (P = 0.003).The patients with restricted IEDs in the ATL ipsilateral to the HS became more often seizure free (90%) than those with IEDs in the ipsilateral LTL, extratemporal lobe, and with bilateral IEDs (45%). This difference was not statistically different (P = 0.06).
Pre-resection spikes were restricted to the MTL in 11 patients (50%) and to the LTL in one (4%). In three patients (14%) spikes were recorded from MTL and LTL and in seven (32%) no spikes were recorded before the resection. Patients with pre-resection spikes restricted to the MTL (n = 11) remained seizure free more frequently (9/11, 82%) as compared to other patients (6/11, 55%) (P = 0.36). Two of four patients with LTL-spikes and four of seven patients without pre-resection spikes remained seizure free. A trend was found that patients with pre-resection spikes of lower frequency (<5 spikes/10s) tended to have a better outcome (6/6, 100%) than those with higher frequency (> 5 spikes/10s) pre-resection spikes (5/9, 56%) (P = 0.1). The persistence of pre-resection spikes on post-resection ECoG was not significantly related to seizure outcome.
In 9 patients with both preoperative IEDs restricted to the temporal lobe (TL) and pre-resection ECoG spikes restricted to the MTL, eight patients (89%) remained seizure free, while 7 of the remainder of the patients (54%) became seizure free (P = 0.16). In 7 patients with preoperative IEDs restricted to the ATL and pre-resection ECoG spikes restricted to the MTL, six patients (86%) became seizure free after operation, while 9 of the remainder of the patients (60%) became seizure free (P = 0.35).
Conclusions: Pre-resection ECoG may be helpful in the prediction of seizure outcome in patients undergoing sAHE for mesial temporal lobe epilepsy. Patients with ECoG spikes restricted to the mesial temporal lobe remained seizure free more often than others. Pre-resection spikes of lower frequency tended to be associated with a better postoperative seizure outcome than those of higher frequency. Post-resection ECoG had no predictive value regarding seizure outcome although these differences were not statistically significant. Patients with unilateral temporal IEDs on preoperative surface EEG became seizure free more frequently than those with bilateral and / or extratemporal IEDs. Patients with both preoperative IEDs restricted to the LTL or ATL and pre-resection ECoG spikes restricted to the MTL remained more frequently seizure free than other patients however, the difference was not statistically significant. A combination of the results of preoperative surface EEG and the findings of intraoperative ECoG especially pre-resection ECoG may be more reliable to predict postoperative seizure outcome in patients with hippocampal sclerosis. A larger study including more than 102 patients is needed to determine the predictive value of ECoG in patients with mesial temporal lobe epilepsy.|
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