Resection of high frequency oscillations predicts seizure outcome in the individual patient

Abstract

High frequency oscillations (HFOs) are recognized as biomarkers for epileptogenic brain tissue. A remaining challenge for epilepsy surgery is the prospective classification of tissue sampled by individual electrode contacts. We analysed long-term invasive recordings of 20 consecutive patients who subsequently underwent epilepsy surgery. HFOs were defined prospectively by a previously validated, automated algorithm in the ripple (80–250 Hz) and the fast ripple (FR, 250–500 Hz) frequency band. Contacts with the highest rate of ripples co-occurring with FR over several five-minute time intervals designated the HFO area. The HFO area was fully included in the resected area in all 13 patients who achieved seizure freedom (specificity 100%) and in 3 patients where seizures reoccurred (negative predictive value 81%). The HFO area was only partially resected in 4 patients suffering from recurrent seizures (positive predictive value 100%, sensitivity 57%). Thus, the resection of the prospectively defined HFO area proved to be highly specific and reproducible in 13/13 patients with seizure freedom, while it may have improved the outcome in 4/7 patients with recurrent seizures. We thus validated the clinical relevance of the HFO area in the individual patient with an automated procedure. This is a prerequisite before HFOs can guide surgical treatment in multicentre studies.

Phase‐amplitude coupling between interictal high‐frequency activity and slow waves in epilepsy surgery

“…As the sampling rate of digital recording systems have recently improved, investigators have described the value of interictal high‐frequency activity at >80 Hz (HFA >80 Hz ) for localizing the EZ. Specifically, resection of recording sites showing frequent episodes of HFA during invasive monitoring has been associated with excellent seizure outcome . However, whether preresection interictal HFA can inform postresection clinical outcome, independently of the effects of resection size, SOZ on ictal recording, and neuroimaging data, remains an open question …”

“…Specifically, resection of recording sites showing frequent episodes of HFA during invasive monitoring has been associated with excellent seizure outcome. [9][10][11][12][13][14][15][16] However, whether preresection interictal HFA can inform postresection clinical outcome, independently of the effects of resection size, SOZ on ictal recording, and neuroimaging data, remains an open question. 16 To evaluate whether interictal coupling between HFA and slow waves could be used as a preoperative electrographic biomarker, we examined whether a modulation index (MI) was associated with postoperative success rates in 123 patients with drug-resistant focal epilepsy.…”

Spatiotemporal patterns of high-frequency activity (80-170 Hz) in long-term intracranial EEG

“…The variability resulting from post-implantation effects may account for the contradictory HFO results observed across many studies. 8,9,11,12,26…”

“…8 Fedele et al found that HFOs could reliably predict surgical outcomes when HFO locations were consistent over time. 11 Therefore, this study cautions against only relying on HFO or spike analysis for identifying the EZ.…”

“…5 HFOs occur more frequently in the SOZ, [6][7][8] and removing brain areas exhibiting HFOs is correlated with a good surgical outcome. [9][10][11] However, the literature shows contradictory results regarding HFOs. 8,12 This may be partly due to post-implantation effects, which cause changes in intracranial EEG (iEEG) signals lasting months.…”