Intracranial EEG Seizure‐Onset Patterns in Neocortical Epilepsy

Abstract

Summary: Purpose:We investigated neocortical seizureonset patterns recorded by intracranial EEG with regard to anatomic location, pathologic substrate, and prognostic >slue for surgical outcome.Methods: 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 nonspecific 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.Results: 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).Conclusions: 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.

Quantitative visualization of ictal subdural EEG changes in children with neocortical focal seizures

“…Quantitative ictal subdural EEG analysis was performed, using spectral analysis similar to that in previous reports (Alarcon et al, 1995;Gotman et al, 1993Gotman et al, , 1995Wu and Gotman, 1998), based on the assumption that epileptic seizures are represented as sustained and synchronized rhythmic ictal discharges with certain frequencies on the EEG (Lee et al, 2000) and that the ictal discharges within the first epoch are stationary. In short, the ictal EEG magnitude within a preset frequency band (including the ictal discharge frequency at the first epoch) was the main parameter on ictal EEG analysis in the present study.…”

“…Ictal EEG recordings were visually reviewed in the referential and bipolar montages by two electroencephalographers (EA and AS), who obtained a consensus for each electrode to determine whether it should be classified as being part of the seizure-onset zone. Seizure onset was defined as a sustained rhythmic change in the EEG accompanied by subsequent clinically typical seizure activity, not explained by level of arousal, and clearly distinguished from background EEG and interictal activity (Lee et al, 2000;Spencer et al, 1992). Some types of initial EEG changes before seizure onset including brief bursts of spikes and periodic spikes at a frequency of <2 Hz were not considered part of seizure onset for this analysis, according to the concept described by Lee et al (2000), who reported that brief bursts of spikes and slow periodic spikes are often seen interictally without clinical symptoms and do not necessarily indicate epileptic seizures.…”

“…Seizure onset was defined as a sustained rhythmic change in the EEG accompanied by subsequent clinically typical seizure activity, not explained by level of arousal, and clearly distinguished from background EEG and interictal activity (Lee et al, 2000;Spencer et al, 1992). Some types of initial EEG changes before seizure onset including brief bursts of spikes and periodic spikes at a frequency of <2 Hz were not considered part of seizure onset for this analysis, according to the concept described by Lee et al (2000), who reported that brief bursts of spikes and slow periodic spikes are often seen interictally without clinical symptoms and do not necessarily indicate epileptic seizures. Therefore, when such phenomena were the initial EEG changes, we defined the ictal onset electrodes based on the subsequently evolving rhythmic discharge (Lee et al, 2000).…”

Ictal and interictal high frequency oscillations in patients with focal epilepsy

“…The electrographic onset, defined as sustained rhythmic discharges which cannot be explained by physiological changes or state changes and which resulted in the habitual clinical seizures (Gotman et al, 1993), was derived from the clinical EEG report and evaluated by the authors (MZ, JJ, filter 0.3-70 Hz). When the rhythmic discharge was preceded by a change in spikes, as can be seen in mesiotemporal epilepsy, the onset rhythmic discharge was taken as the seizure onset (Lee et al, 2000). This moment was marked within the EEG, as well as 10 s before the first EEG change and 5 s after the first EEG change.…”

Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

“…But these features are commonly used to identify the seizure onset zone (SOZ), so long as the changes are relatively focal in one or a small number of electrodes and are recorded before the first clinical sign. Low-voltage fast activity [2][3][4][5] is the most commonly reported IOP in neocortical epilepsy, and low-frequency high-amplitude repetitive spiking is the most commonly reported IOP in mesial temporal lobe epilepsy (mTLE). Delta activity is usually held to be a spread pattern rather than a true IOP from the SOZ.…”