gms | German Medical Science

Objective: 2000, we have stereotactically implanted 669 deep brain electrodes in 212 patients suffering from pharmacologically intractable seizures to determine the epileptogenic focus.

Methods: In a subgroup, 23 patients received 189 macroelectrodes. 77 of these electrodes were equipped with additional Behnke-Fried bundles consisting of eight individually isolated 40 µm microwires at the tip of the macroelectrode. 20 patients were implanted in the mesiotemporal lobes by a temporo-lateral approach, 8 on the left and 12 on the right side. Twelve patients were admitted for a "Stereo-EEG" with an average of 10.4 implanted electrodes. Patients were selected by an independent multidisciplinary board for an invasive diagnostic procedure when recordings from scalp electrodes could not localize the primary epileptogenic focus. While the localization of the primary seizure focus was based on the analysis of the signals provided by the macroelectrodes according to international standards, the additional microwires were used for the recording of single units and local field potentials during complex cognitive tasks. The purpose of this technique is both clinical as well as cognitive state-of-the-art research. All patients gave their informed consent. The tracts of the macroelectrodes were only determined by clinical needs. Surgical tools and materials were designed in cooperation with industrial partners in order to optimize the procedure based on CT, MRI (T1, T2, flair, 1 mm) and PET.

Results: No patients suffered any kind of complication such as intracerebral bleeding, infection, meningitis or neurological deficits. The precision of the macroelectrode positioning confirmed by a postoperative MRI (MP-Rage, 1 mm, sagittal) was not influenced by the use of microwires. In more than 80% of the patients the epileptogenic focus could be identified and was mostly followed by a highly selective surgical resection. Optimized imaging and precise preoperative planning combined with the intraoperative use of specially designed guided tools ensure the precise, safe and time efficient (10 minutes per electrode) stereotactic implantation of electrodes.

Conclusions: Stereotactic implantation of deep electrodes equipped with microwires for invasive epilepsy diagnostics is a safe neurosurgical procedure providing benefits for both patients and clinical research if it is based on optimized technical equipment, high resolution imaging, intensive preoperative analysis and careful three-dimensional planning.