ABSTRACT
Objective Introduce a technique for creating 3-dimensional (3D) brain models of subdural electrodes , ideal for demonstrating the space-relationship of seizure localization and eloquent cortices , and discuss its usefulness for presurgical evaluation of epileptic patients. Methods Patients with medically intractable epilepsy were underwent a thorough preoperative MR brain scan including a T1-weighted high-resolution 3D sequence. Intraoperative photographs were taken with the digital camera. After the surgical implantation of subdural electrodes for epileptic zone localization , the thin-slice CT scan of the electrodes were taken and coregistered to preoperative brain 3D MR images in the Medtronic StealthMerge software environment. After the iEEG monitoring , multiple habitual seizures were recorded , eloquent areas were also identified by electrical stimulation of the cortex. The epileptic zone and the eloquent areas were marked on the subdural electrodes respectively. Then, 3D tessellations of the epileptic zone and the eloquent areas were rendered. Results Six patients (4 male, 2 female) were enrolled in this study. The mean time of iEEG monitoring was 13.7 days. After the coregistration of postoperative CT with preoperative 3D MRI , the 3D stereoscopic reconstruction provided an accurate representation of the implanted electrodes with highly detailed visualization of the underlying anatomy. The visual comparison between 3D reconstructions and intraoperative photographs indicated a good correspondence. The patients were followed for 3 to 6 months after the secondary operation , and had continuing improvement in seizure control. Conclusions The results indicate that the 3D reconstruction of subdural electrodes can reveal the precise localization of subdural electrodes , and can be useful for the presurgical evaluation of epileptic patients.
ABSTRACT
BACKGROUND: Analysis of intracranial ictal patterns may help to predict surgical outcomes. We investigated intracranial EEG patterns to correlate with surgical outcomes and compared the yield of 'subdural electrodes alone (SE)' versus 'combined depth and subdural electrodes (CDSE)' for ictal lateralization in temporal lobe epilepsy (TLE). METHODS: We reviewed a total of 95 seizures recorded by bilateral temporal depth and subdural electrodes in 25 TLE patients who underwent surgery. We classified surgical outcomes as 'seizure-free' or 'not-seizure-free'. Each seizure was analyzed based on the presence or absence of peri-ictal discharges, ictal distribution, waveform patterns, onset frequency and involved number of electrodes, and interhemispheric propagation time (IHPT). The accuracy of lateralizing seizure foci by CDSE was compared to that by SE. RESULTS: 20 patients (80.0%) were 'seizure-free' and 5 (20.0%) were 'not-seizure-free'. The presence of peri-ictal discharges (p<0.001), distribution of depth only or depth and medial electrodes (p<0.001) and higher onset frequency (p=0.021) were associated with 'seizure-free' outcomes. Ictal onset pattern with fast spike trains was common in 'seizure-free', whereas pattern with rhythmic activity was common in 'not-seizure-free' (p=0.005). SE correctly lateralized in 18 of 20 patients, and incorrectly lateralized in the remaining 2 patients, but CDSE correctly lateralized in all 20 patients. CONCLUSIONS: Some intracranial ictal patterns were significantly correlated with good surgical outcomes. These findings suggest that the analysis of ictal EEG patterns help to predict surgical outcomes. CDSE is more accurate for the lateralization of seizure foci compared to SE.