Subdural and depth electrodes in the presurgical evaluation of epilepsy

Abstract

From 1987 to 1992, invasive EEG studies using subdural strips, grids or depth electrodes were performed in a total of 160 patients with medically intractable epilepsy, in whom scalp EEG was insufficient to localize the epileptogenic focus. Dependent on the individual requirements, these different electrode types were used alone or in combination. Multiple strip electrodes with 4 to 16 contacts were implanted in 157 cases through burrholes, grids with up to 64 contacts in 15 cases via boneflaps, and intrahippocampal depth electrodes in 36 cases using stereotactic procedures. In every case, localization of the electrodes with respect to brain structures was controlled by CT scan and MRI. Visual and computerized analysis of extra-operative recordings allowed the localization of a resectable epileptogenic focus in 143 patients (89%), who subsequently were referred for surgery, whereas surgery had to be denied to 17 patients (11%). We did not encounter any permanent morbidity or mortality in our series. In our experience, EEG-monitoring with chronically implanted electrodes is a feasible technique which contributes essentially to the exact localization of the epileptogenic focus, since it allows nearly artefact-free recording of the ictal and interictal activity. Moreover, grid electrodes can be used for extra-operative functional topographic mapping of eloquent brain areas.

Generators of the intracranial P50 response in auditory sensory gating

“…Intracranial electrodes in these patients were placed on frontal and temporal lobe locations (Behrens et al, 1994). The electrode array consisted of strips and/or grids with stainless steel contacts (diameter of 2.2 mm) embedded in silastic (interelectrode spacing of 1 cm).…”

Towards a functional topography of sensory gating areas: Invasive P50 recording and electrical stimulation mapping in epilepsy surgery candidates

“…Between November 2002 and February 2004, a total of thirty-seven patients with drug-resistant focal epilepsies were implanted for invasive seizure recordings as part of their presurgical evaluation at the University of Bonn Epilepsy Surgery Center (Behrens et al 1994,Kral et al 2002. In the course of diagnostic work-up, seventeen of these patients (9 males, mean age 34 [19 -57] ys., see table 1 for clinical details) underwent ESM for the delineation of eloquent areas.…”

“…MLAERs were recorded from subdural strip and grid electrodes (sampling rate 1000 Hz per channel, epoch length 1200 ms, prestimulus baseline 200 ms), with reference to both mastoids (bandpass filter setting .03 -85 Hz, 12 dB/octave). Subdural electrodes implanted at the Department of Neurosurgery at Bonn University Hospital consisted of strips or grids with stainless steel contacts with a diameter of 2.2 mm embedded in silastic with an interelectrode spacing of 1 cm (Behrens 1994). Electrode arrays were individually tailored according to the working hypothesis concerning the localization of the epileptogenic area (Kral et al 2002).…”

Modulation of Calcium Channels by Group I and Group II Metabotropic Glutamate Receptors in Dentate Gyrus Neurons from Patients with Temporal Lobe Epilepsy

“…The seizure frequency during the 3 months preceding presurgical evaluation was 2-30 complex partial seizures per month (mean 10.6 f 6.4/month, n = 9). In all patients, the hippocampus was shown to be intimately involved in the generation of temporal lobe seizures by noninvasive and invasive diagnostic procedures, as described elsewhere (26,27). Detailed histopathologic analysis of the surgical, specimens was performed by an independent and experienced neuropathologist.…”