Intracranial EEG seizure-onset patterns in neocortical epilepsy

We investigated neocortical seizure-onset patterns recorded by intracranial EEG with regard to anatomic location, pathologic substrate, and prognostic value for surgical outcome.

Seizure onset was analyzed in 53 neocortical resective epilepsy surgery patients. Anatomic location was divided into temporal and extratemporal. Pathologic substrate was classified as developmental, mature, and negative or non-specific gliosis. Onset frequency was categorized by visual analysis into tradition EEG frequency bands. Spatial extent was divided into focal (fewer than four contacts) and regional (more than five contacts). Waveform at seizure onset was divided into several types based on their morphology. Onset features were examined with respect to anatomic location, pathologic substrate, and surgical outcome.

Seizure-onset frequency was significantly related to spatial distribution and to anatomic location. Extratemporal and regional onset were more commonly in the gamma range, and temporal and focal onset in the beta frequency range or slower. Waveform could be categorized into five different patterns, of which low voltage fast activity (LVFA) was the most common form (57%). LVFA and rhythmic alpha-theta spike activity were more common in developmental than in mature pathology, whereas rhythmic sinusoidal waves at onset were found in only mature substrates. Waveform pattern showed a possible correlation with surgical outcome (p = 0.097): LVFA and rhythmic sinusoidal waves onset patterns were associated with favorable outcome more often (40.4%) than the other three patterns (6.3%). Slow onset suggested poor outcome in the subgroup of developmental pathology (p = 0.062).

Certain electrographic seizure-onset features are associated with specific substrates and outcomes, whereas others reflect the anatomic location and its connections independent of the pathology.