Focal seizure propagation in the intracranial EEG

Introduction: intracranial EEG offers a unique opportunity to study epileptic seizures in humans. Seizure propagation has not been extensively studied. We aimed to compare the propagation of focal seizures with onset in different brain regions.

Methods: seven zones were defined as medial frontal (MF), dorsolateral frontal (DLF), orbitofrontal (OF), medial temporal (MF), lateral temporal (LT), parietal (P) and occipital (O). Routes and times of ipsilateral (IPT) and contralateral (CPT) propagation as well as ictal frequency in onset zone and propagation zone were compared.

Results: forty patients had 112 seizures. (Mean and median number of seizures per zone was 16 and 15). Preferred routes of propagation, based on ictal onset, were: MF to contralateral MF; DLF to ispilateral temporal lobe; OF to contralateral OF and ispilateral temporal lobe; MT to contralateral MT; LT to ispilateral MT and OF and contralateral LT and MT; P to ispilateral temporal lobe, DLF and O; O to ipsilateral MT. IPT and CPT varied markedly between zones. Ictal onset frequency was faster than propagated frequency.

Conclusion: seizure propagation varies according to onset zone possibly following major pathways. This needs confirmation. The findings could aid in the interpretation of symptoms and EEG and may result useful for future treatment using brain stimulation or disconnective surgery. The limitations are clearly stated.