L. Barnaföldi 1, L. Halász 2, E. Tóth 3, V. Bokodi 2,4, B. Hajnal 2, D. Fabó 2, L Erőss 2, L. Entz 2
1 Semmelweis University, Budapest, 2 National Institute of Clinical Neurosciences, Budapest,3 Department of Neurology, University of Alabama at Birmingham, AL, USA,4 Pázmány Péter Catholic University, Budapest
Introduction : For some of the drug-resistant epileptic patients, surgery may be the best treatment option. However, often very complex diagnostic algorithms with invasive electrode implantation may be necessary to precisely localize the epileptic network before resective surgery.
Aims: We attempt to predict the results of CCEP mapping with subdural strip, grid or SSEG electrodes using probabilistic tractography (a noninvasive imaging technique) in order to better describe the fibers (structural connections) participating in the seizure genesis.
Method: In our study four epilepsy patients were included and implanted with subdural electrodes prior surgical resection. CCEP mapping was performed using bipolar stimulation (0.5Hz, 0.2ms, 10mA). We selected midpoints between stimulation electrode pairs as seed regions, and each recording electrode was chosen as a target region for probabilistic tractography. Probabilistic fiber tracking was initiated from each possible reconstructed bipolar stimulation zone to the remaining contacts. The z-score of the CCEP amplitudes and mean connectivity values of probabilistic tractography were correlated between the stimulated and the recording electrodes using bivariate Pearson correlation.
Results: Out of the total 122 cortico-cortical stimulations, 44 were placed over ictal areas whose 55.2% correlated significantly with the results of tractography. Two patients showed high overall correlation ratio (mean:75%) and two patients showed low overall correlation ratio (mean: 35.42%).
Conclusion: The CCEPs uncover the functional connections of the brain, and the probabilistic tractography shows the morphology of the fiber tracts’ structural projections, their combination may reveal the expansivity of the ictal system and improve the outcome of the surgery. Using non-invasive mapping methods, we attempt to substitute invasive surgical investigations to reveal the epileptic network.
Doctoral School: Szentágothai Doctoral School, Clinical Medicine
Program: Clinical Neurosciences
Supervisor: Dr. László Entz, PhD, Dr. Erőss Loránd, PhD