Abstract
Background High-frequency oscillations (HFOs) are spontaneous electroencephalographic (EEG)
events that occur within the frequency range of 80 to 500 Hz and consist of at least
four distinct oscillations that stand out from the background activity. They can be
further classified into “ripples” (80–250 Hz) and “fast ripples” (FR; 250–500 Hz)
based on different frequency bands. Studies have indicated that HFOs may serve as
important markers for identifying epileptogenic regions and networks in patients with
refractory epilepsy. Furthermore, a higher extent of removal of brain regions generating
HFOs could potentially lead to improved prognosis. However, the clinical application
criteria for HFOs remain controversial, and the results from different research groups
exhibit inconsistencies. Given this controversy, the aim of this study was to conduct
a meta-analysis to explore the utility of HFOs in predicting postoperative seizure
outcomes by examining the prognosis of refractory epilepsy patients with varying ratios
of HFO removal.
Methods Prospective and retrospective studies that analyzed HFOs and postoperative seizure
outcomes in epilepsy patients who underwent resective surgery were included in the
meta-analysis. The patients in these studies were grouped based on the ratio of HFOs
removed, resulting in four groups: completely removed FR (C-FR), completely removed
ripples (C-Ripples), mostly removed FR (P-FR), and partial ripples removal (P-Ripples).
The prognosis of patients within each group was compared to investigate the correlation
between the ratio of HFO removal and patient prognosis.
Results A total of nine studies were included in the meta-analysis. The prognosis of patients
in the C-FR group was significantly better than that of patients with incomplete FR
removal (odds ratio [OR] = 6.62; 95% confidence interval [CI]: 3.10–14.15; p < 0.00001). Similarly, patients in the C-Ripples group had a more favorable prognosis
compared with those with incomplete ripples removal (OR = 4.45; 95% CI: 1.33–14.89;
p = 0.02). Patients in the P-FR group had better prognosis than those with a majority
of FR remaining untouched (OR = 6.23; 95% CI: 2.04–19.06; p = 0.001). In the P-Ripples group, the prognosis of patients with a majority of ripples
removed was superior to that of patients with a majority of ripples remaining untouched
(OR = 8.14; 95% CI: 2.62–25.33; p = 0.0003).
Conclusions There is a positive correlation between the greater removal of brain regions generating
HFOs and more favorable postoperative seizure outcomes. However, further investigations,
particularly through clinical trials, are necessary to justify the clinical application
of HFOs in guiding epilepsy surgery.
Keywords
high-frequency oscillations - intractable epilepsy - intracranial electrography -
epilepsy prognosis - electrocorticogram
