Anatomically Precise and Reproducible Localization of Grid Electrodes in Invasive Presurgical Epilepsy Diagnosis - A Method for Routine Application
Abstract number :
B.02
Submission category :
Year :
2000
Submission ID :
3324
Source :
www.aesnet.org
Presentation date :
12/2/2000 12:00:00 AM
Published date :
Dec 1, 2000, 06:00 AM
Authors :
Joerg Wellmer, Guido Widman, Joachim von Oertzen, Dirk Van Roost, Carlo Schaller, Horst Urbach, Johannes Schramm, Christian E Elger, Clin of Epileptology, Univ of Bonn, Bonn, Germany; Clin of Neurosurgery, Univ of Bonn, Bonn, Germany; Dept of Neuroradio
RATIONALE:_ In the presurgical evaluation of neocortical epilepsies chronically implanted grid electrodes are used for the spatial delineation of the epileptogenic zone and eloquent brain areas. So far, a precise localization of the implanted electrodes in relation to the cortical anatomy or underlying lesions was not possible, since CT and MRI are restricted in their resolution. We present a method that routinely allows a very precise and reproducible localization of grid electrodes. METHODS:_ During grid implantation, digital photographs are taken of either the visualized cortex and the grid in situ, fixed in its final position. Both photographs are fused to an implantation scheme that now localizes each single electrode contact on the cortex. According to the cortical anatomy as shown on the print, the electrode contacts are then projected onto a MRI surface rendering of the patient?s brain. The results of brain mapping and seizure detection are represented by color on the photographic scheme. Suggested margins for surgical intervention are drawn in relation to the cortical anatomy as it presents itself to the neurosurgeon. Photographs taken at explantation of the grid prove the accordance of electrode positions at implantation and explantation. RESULTS: _Digital photography allows a detailed portrayal of the cortex covered by the grid. The shift of electrode contacts from implantation to explantation is in the range of about 2 mm. The creation of the implantation scheme takes about 1.5-2 hours. CONCLUSIONS:_ Digital photography allows an anatomically precise and reproducible localization of chronically implanted grids on the cortical surface. Seizure onset and eloquent areas can be adjoined to single gyri with high resolution. Since the position of each single electrode contact is reproducible in relation to smallest details of the cortical anatomy (e.g. vessels), resections or MST can be performed even after the occasion of an emergency explantation of the grid. The method is time, cost and effort sparing. X-ray exposure of the patient as in the case of CT based electrode localization is avoided.