Ictal high-gamma oscillation (60–99 Hz) in intracranial electroencephalography and postoperative seizure outcome in neocortical epilepsy

Park, Seong-Cheol; Lee, Sang Kun; Che, Huije; Chung, Chun Kee

doi:10.1016/j.clinph.2012.01.008

Cited by 35 publications

(25 citation statements)

References 57 publications

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“…In adults with neocortical epilepsy, resection of contacts containing HFOs was found to be associated with favorable seizure outcome. [252642] As an extension of these findings, a more limited resection confined mainly to ictal HFOs with sustained evolution (HFO+) as opposed to those without evolution (HFO−) based on a prospectively-defined protocol was shown to be associated with good outcome in 5/6 (83%) patients. [27] Favorable outcome was also seen in a case of frontal lobe epilepsy after multiple subpial transections of the gyri containing HFOs.…”

Section: Hfos: Clinical Implicationsmentioning

confidence: 99%

High frequency oscillations and infraslow activity in epilepsy

Modur

2014

Ann Indian Acad Neurol

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In pre-surgical evaluation of epilepsy, there has been an increased interest in the study of electroencephalogram (EEG) activity outside the 1-70 Hz band of conventional frequency activity (CFA). Research over the last couple of decades has shown that EEG activity in the 70-600 Hz range, termed high frequency oscillations (HFOs), can be recorded intracranially from all brain regions both interictally and at seizure onset. In patients with epilepsy, HFOs are now considered as pathologic regardless of their frequency band although it may be difficult to distinguish them from the physiologic HFOs, which occur in a similar frequency range. Interictal HFOs are likely to be confined mostly to the seizure onset zone, thus providing a new measure for localizing it. More importantly, several studies have linked HFOs to underlying epileptogenicity, suggesting that HFOs can serve as potential biomarkers for the illness. Along with HFOs, analysis of ictal baseline shifts (IBS; or direct current shifts) and infraslow activity (ISA) (ISA: <0.1 Hz) has also attracted attention. Studies have shown that: IBSs can be recorded using the routine AC amplifiers with long time constants; IBSs occur at the time of conventional EEG onset, but in a restricted spatial distribution compared with conventional frequencies; and inclusion of IBS contacts in the resection can be associated with favorable seizure outcome. Only a handful of studies have evaluated all the EEG frequencies together in the same patient group. The latter studies suggest that the seizure onset is best localized by the ictal HFOs, the IBSs tend to provide a broader localization and the conventional frequencies could be non-localizing. However, small number of patients included in these studies precludes definitive conclusions regarding post-operative seizure outcome based on selective or combined resection of HFO, IBS and CFA contacts. Large, preferably prospective, studies are needed to further evaluate the implications of different EEG frequencies in epilepsy.

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Section: Hfos: Clinical Implicationsmentioning

confidence: 99%

High frequency oscillations and infraslow activity in epilepsy

Modur

2014

Ann Indian Acad Neurol

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“…A number of ECoG studies have reported the presence of ictal HFOs at >60 Hz during focal seizures [61–64]; there was an impressive convergence between the locations showing ictal and interictal HFOs >80 Hz [65], and more complete resection of the sites showing ictal HFOs >60 Hz was associated with a better seizure outcome [66]. We have also studied ictal HFOs seen in 636 events of epileptic spasms [9] and found ictal HFOs at 80–200 Hz to be causally associated with the generation of epileptic spasms (Figure 5 and Table 6).…”

Section: Significance Of Ictal Discharges Consisting Of Hfos On Ecog mentioning

confidence: 99%

How to establish causality in epilepsy surgery

Asano

Brown

Juhász

2013

Brain and Development

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Focality in electro-clinical or neuroimaging data often motivates epileptologists to consider epilepsy surgery in patients with medically-uncontrolled seizures, while not all focal findings are causally associated with the generation of epileptic seizures. With the help of Hill's criteria, we have discussed how to establish causality in the context of the presurgical evaluation of epilepsy. The strengths of EEG include the ability to determine the temporal relationship between cerebral activities and clinical events; thus, scalp video-EEG is necessary in the evaluation of the majority of surgical candidates. The presence of associated ictal discharges can confirm the epileptic nature of a particular spell and whether an observed neuroimaging abnormality is causally associated with the epileptic seizure. Conversely, one should be aware that scalp EEG has a limited spatial resolution and sometimes exhibits propagated epileptiform discharges more predominantly than in situ discharges generated at the seizure-onset zone. Intraoperative or extraoperative electrocorticography (ECoG) is utilized when noninvasive presurgical evaluation, including anatomical and functional neuroimaging, fails to determine the margin between the presumed epileptogenic zone and eloquent cortex. Retrospective as well as prospective studies have reported that complete resection of the seizure-onset zone on ECoG was associated with a better seizure outcome, but not all patients became seizure-free following such resective surgery. Some retrospective studies suggested that resection of sites showing high-frequency oscillations (HFOs) at >80 Hz on interictal or ictal ECoG was associated with a better seizure outcome. Others reported that functionally-important areas may generate HFOs of a physiological nature during rest as well as sensorimotor and cognitive tasks. Resection of sites showing task-related augmentation of HFOs has been reported to indeed result in functional loss following surgery. Thus, some but not all sites showing interictal HFOs are causally associated with seizure generation. Furthermore, evidence suggests that some task-related HFOs can be transiently suppressed by the prior occurrence of interictal spikes. The significance of interictal HFOs should be assessed by taking into account the eloquent cortex, seizure-onset zone, and cortical lesions. Video-EEG and ECoG generally provide useful but still limited information to establish causality in presurgical evaluation. A comprehensive assessment of data derived from multiple modalities is ultimately required for successful management.

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“…High-frequency oscillatory activity, especially in the gamma band, has been frequently observed in EEG data both before and during epileptic events (Allen et al, 1992;Fisher et al, 1992;Rampp and Stefan, 2006). Recent invasive intracranial and depth electrode studies suggest that an increase in gamma band power before ictal onset is highly localized to the ictal onset zone (Harris et al, 2014;Medvedev et al, 2011;Park et al, 2012;Park et al, 2014).…”

Section: Wide Time Window and Multiple Frequency Band Source Localizamentioning

confidence: 96%

“…The changes included conspicuous fast activities, diffuse desynchronisations, Jeong Page 8 slowings, or polyspikes with evolutions (Kim et al, 2010;Park et al, 2012;Park et al, 2014).…”

Section: Source Localization Of Ictal Eventmentioning

confidence: 98%