Differentiation of specific ripple patterns helps to identify epileptogenic areas for surgical procedures
Karolin Kerber1, Matthias Dümpelmann1, Björn Schelter2
1Epilepsy Center, University Medical Center Freiburg, Mathildenstrasse 1, Breisacher Str. 64, 79106 Freiburg, Germany.
Objective:
High frequency oscillations (HFOs) at 80-500 Hz are promising markers of epileptic areas. Several retrospective studies reported that surgical removal of areas generating HFOs was associated with a good seizure outcome. Recent reports suggested that ripple (80-200 Hz) HFO patterns co-existed with different background EEG activities. We hypothesized that the coexisting background EEG pattern may distinguish physiological from epileptic ripples.
Methods:
Rates of HFOs were analyzed in intracranial EEG recordings of 22 patients. Additionally, ripple patterns were classified for each channel depending either as coexisting with a flat or oscillatory background activity. A multi-variate analysis was performed to determine whether removal of areas showing the above EEG markers correlated with seizure outcome.
Results:
Removal of areas generating high rates of 'fast ripples (>200 Hz)' and 'ripples on a flat background activity' showed a significant correlation with a seizure-free outcome. In contrast, removal of high rates of 'ripples' or 'ripple patterns in a continuously oscillating background' was not significantly associated with seizure outcome.
Conclusion:
Ripples occurring in an oscillatory background activity may be suggestive of physiological activity, while those on a flat background reflect epileptic activity.
Significance:
Consideration of coexisting background patterns may improve the delineation of the epileptogenic areas using ripple oscillations.
