J. De Reuck

Dipole Modeling in Epilepsy Surgery Candidates

Summary: Purpose: The validity and clinical significance of dipole modeling in epilepsy surgery candidates is not fully established.

VAGUS NERVE STIMULATION FOR MEDICALLY REFRACTORY EPILEPSY; EFFICACY AND COST-BENEFIT ANALYSIS

Summary Introduction. Vagus nerve stimulation is a novel treatment for patients with medically refractory epilepsy, who are not candidates for conventional epilepsy surgery, or who have had such surgery without optimal outcome. To date only studies with relatively short follow-up are available. In these studies efficacy increased with time and reached a maximum after a period of 6 to 12 months. Implantation of a vagus nerve stimulator requires an important financial investment but a cost-benefit analysis has not been published. Patients and Methods. Our own experience with VNS in Gent comprises 15 patients with mean age of 29 years (range: 17–44 years) and mean duration of epilepsy of 18 years (range: 4–32 years). All patients underwent a comprehensive presurgical evaluation and were found not to be suitable candidates for resective epilepsy surgery. Mean post-implantation follow-up is 24 months (range: 7–43 months). In patients with follow-up of at least one year, efficacy of treatment in terms of seizure control and seizure severity was assessed one year before and after the implantation of a vagus nerve stimulator. Epilepsy-related direct medical costs (ERDMC) before and after the implantation were also compared. Results. A mean reduction of seizure frequency from 14 seizures/month (range: 2–40/month) to 8 seizures/month (range: 0–30/month) was achieved (Wilcoxon signed rank test n=14; p=0.0016). Five patients showed a marked seizure reduction of ≥50%; 6 became free of complex partial seizures, 3 of whom became entirely seizure free for more than 12 months; 2 patients had a worthwhile reduction of seizure frequency between 30–50%; in 2 patients seizure frequency reduction has remained practically unchanged. Seizure freedom or ≥50% seizure reduction was achieved within the first 4 months after implantation in 6/11 patients. Before the implantation, the mean yearly epilepsy-related direct medical costs per patient were estimated to be 8830US

Dipole modelling and intracranial EEG recording: Correlation between dipole and ictal onset zone.

(n=13; range: 1879–31129US

Intra- and interobserver variability of MRI-based volume measurements of the hippocampus and amygdala using the manual ray-tracing method

; sd=7667); the average number of hospital admission days per year was 21 (range: 4–100; sd=25.7). In the 12 months after implantation, ERDMC had decreased to 4215US

Clinical and neurophysiological correlations in patients with refractory partial epilepsy and intracranial structural lesions

(range: 615–11794US

Accuracy of single-sequence MRI for investigation of the fluid-filled spaces in the inner ear and cerebellopontine angle.

; sd=3558) (Wilcoxon signed rank test n=13; p=0.018) and the average number of admission days to 8 (range: 0–35) (Wilcoxon signed rank test n=13; p=0.023). Conclusion. VNS is an effective treatment of refractory epilepsy and remains effective during long-term follow-up. Cost-benefit analysis suggests that the cost of VNS is saved within two years following implantation.

Neurotropin Treatment of Brain Edema Accompanying Acute Middle Cerebral Artery Infarction

SummaryThis study includes 11 patients (3 males, 8 females) with mean age of 29 years (range: 15–42 years) who underwent a presurgical evaluation for refractory complex partial seizures (CPS). In all patients, neuroimaging (1.5 T optimum-MR) demonstrated intracranial structural abnormalities (space-occupying: n = 2; atrophic: n = 8; dysplastic: n = 1) and video-EEG monitoring showed CPS. Because of discrepancies in the non-invasive examinations, all underwent additional intracranial EEG monitoring. After tailored resective procedures, all but one patient became seizure free. Mean follow-up was 30 months (range: 12–52 months). Results of intracranial EEG recording were compared with spatiotemporal dipole mapping of interictal and ictal epileptic discharges. Interictal dipole modelling revealed two distinct dipole patterns. Patients with lesions located in the medial temporal lobe uniformly presented a combined dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Patients with extrahippocampal lesions had a less stable dipole with a predominant radial component. Dipole modelling of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Elevation of ictal dipoles was always congruent with localisation based on intracranial EEG recordings. Interictal and ictal dipole mapping of medial temporal lobe sources may limit the number of surgical candidates for refractory CPS that need intracranial EEG recording. Whether ictal dipole modelling can be equally useful in extratemporal epilepsy remains to be proven.

Single-Voxel Proton MR Spectroscopy and Positron Emission Tomography for Lateralization of Refractory Temporal Lobe Epilepsy

Abstract We studied the intra- and interobserver variability of volume measurments of the hippocampus (HC) and the amygdala as applied to the detection of HC atrophy in patients with complex partial seizures (CPE), measuring the volumes of the HC and amygdala of 11 normal volunteers and 12 patients with presumed CPE, using the manual ray-tracing method. Two independent observers performed these measurements twice each using home-made software. The intra- and interobserver variability of the absolute volumes and of the normalised left-to-right volume differences (δV) between the HC (δVHC), the amygdala (δVA) and the sum of both (δVHCA) were assessed. In our mainly right-handed normals, the right HC and amygdala were on average 0.05 and 0.03 ml larger respectively than on the left. The interobserver variability for volume measurements in normal subjects was 1.80 ml for the HC and 0.82 ml for the amygdala, the intraobserver variability roughly one third of these values. The interobserver variability coefficient in normals was 3.6 % for δVHCA, 4.7 % for δVHC and 7.3 % for δVA. The intraobserver variability coefficient was 3.4 % for δVHCA, 4.2 % for δVHC amd 5.6 % for δVA. The variability in patients was the same for volume differences less than 5 % either side of the interval for normality, but was higher when large volume differences were encountered, is probably due to the lack of thresholding and/or normalisation. Cutoff values for lateralisation with the δV were defined. No intra- or interobserver lateralisation differences were encountered with δVHCA and δVHC. From these observations we conclude that the manual ray-tracing method is a robust method for lateralisation in patients with TLE. Due to its higher variability, this method is less suited to measure absolute volumes.

Value of single-voxel proton MR spectroscopy in temporal lobe epilepsy.

SummaryTwenty patients (13 males, 7 females), who presented with refractory partial epilepsy and a CT and/or MR detected intracranial intra-axial structural lesion were admitted to the University of Gent Epilepsy Monitoring Unit. Mean duration of the epilepsy was 17 years (2–47 years). All patients were enrolled in a comprehensive presurgical protocol including neurological examination, videoscalp-EEG monitoring with prolonged interictal and ictal recording, neuropsychological assessment and positron emission tomography (PET). Intracranial EEG monitoring was performed in 5 patients in whom discrepancies between different tests were found during the non-invasive evaluation. Clinical neurological examination was normal in 16 patients; 4 patients had a mild contralateral hemiparesis. Lesions were mainly located in the temporal lobe (55%). Most patients presented with complex partial seizures (90%). Clinical seizure characteristics correlated well with the lesion location in 55% of patients. Interictal EEG showed focal epileptic activity and focal slowing in respectively 85% and 30% of patients. Interictal EEG lateralization was congruent with the side of the lesion in 17 patients (85%). Interictal EEG localization was congruent with the lobe of the lesion in 13 patients (65%). Ictal EEG lateralized correctly in 14 patients (70%) and localized correctly in 10 patients (50%). Neuropsychological assessment lateralized and localized congruently in respectively 8/17 (47%) and 7/17 (41%) of patients. Interictal PET showed focal interictal hypometabolism, congruent with the lesion, in 13/16 (81%) of patients. Intracranial EEG was congruent with the lesion location in 3 patients but non-congruent in 2 patients.All patients underwent surgical procedures: average follow-up was 14 months (6–24 months). Complete surgical removal of the lesion with free margins resulted in a more than 90% reduction of seizures without postoperative neurological deficit in 12/13 patients.

An MR protocol for presurgical evaluation of patients with complex partial seizures of temporal lobe origin.

Abstract We prospectively studied 163 patients referred for MRI of the temporal bone. A presumed diagnosis was made using only one of three sequences: a single thick (12 mm) slice fast T2-sequence, 3D fourier transform constructive interference in steady state (3DFT-CISS) sequence and a gadolinium-enhanced T1-weighted sequence. The visibility of the cochlea, vestibule and superior, lateral and posterior semicircular canals of normal temporal bones was assessed on the T2-weighted images: they were almost always visible (98–100 %), with exception of the superior semicircular canal, seen in only 35 % of cases. The images were interpreted as abnormal in 34 patients (21 %). Using only the fast T2-weighted, 3DFT-CISS and gadolinium-enhanced T1-weighted sequences a presumed false positive diagnosis was made in 5, 1 and 0 cases and a false negative diagnosis in 2, 2 and 4 cases respectively. The overall reliability of the thick-section fast T2-weighted images is limited. This study suggests that a combination of gadolinium-enhanced T1-weighted and 3DFT-CISS images can be considered the gold standard for temporal bone MRI and neither sequence performed separately is as accurate as both together.