The morphology of high frequency oscillations (HFO) does not improve delineating the epileptogenic zone.

TL;DR: It is hypothesized that high frequency oscillations (HFOs) with irregular amplitude and frequency more specifically reflect epileptogenicity than HFOs with stable amplitude and Frequency, and surgical outcome is better when locations with higher HFO rates are included in the resection.

About: This article is published in Clinical Neurophysiology.The article was published on 2016-04-01 and is currently open access. It has received 72 citations till now.

Summary

1. INTRODUCTION

• In many patients with therapy-refractory focal epilepsy, surgical resection of the epileptogenic zone represents the therapeutic option of choice.
• Over the last years, high frequency oscillations (HFOs) have been proposed as a novel indicatorfor the epileptogenic zone (Jacobs et al., 2012; Urrestarazu et al., 2007; Zijlmans et al., 2012).
• Hz revealed four different types of HFO .
• After visual review of filtered (>80 Hz) data, the authors observed ripples with varying frequency .
• Receiver operating characteristic (ROC) curves measure the performance of the detector when varying these three thresholds and were used for the evaluation of the detector.

3. RESULTS

• The accuracy of the detector in emulating visual marking was determined in Dataset 2.
• In the separate analysis of HFO types , the rates of HFO of each type were significantly higher inside the SOZ than outside the SOZ.
• 4 HFOs and the surgical outcome Figure 5 shows results of the comparison of the ratio of HFO rates of each type against the surgical outcome in Dataset 3.

4. DISCUSSION

• The authors classification of HFOs according to their morphology showed that all four HFO types reflect epileptogenicity equally well since all types of HFO are highly associated with the SOZ.
• The authors could also show that the most frequently occurring HFO types (1 and 2) are associated with the resected area and the surgical outcome.
• This was significant also after applying the BonferroniHolm correction, which places a stricter requirement on statistical significance than most other publications on this topic.
• The automatic detector the authors presented here has several important features, which distinguish it from existing detectors.
• It may therefore be that the epileptogenic zone is strongly associated with true HFOs as well as with sharp spikes, which appear as “false” HFOs after filtering.

5. CONCUSIONS

• All four HFO types are highly associated with the SOZ.
• The strong correlation between type 1 and type 2 HFOs together with their association with the SOZ, resected area and surgical outcome show that both HFO types similarly reflect epileptogenic activity.
• The exclusion of HFO type 3 and 4 has probably no influence on the results, because of their low rates and similar association with the SOZ.
• The surgical outcome is better when locations with higher HFO rates are included in the resection.
• This standardized analysis relied on a newly developed and fully automated HFO detection method.

8. LEGENDS

• Figure 1. Representative examples of the four HFO type.
• (5 A-C) Example of a type 4 HFO, with irregular amplitude and irregular frequency.
• Boxplots illustrating rates of all HFOs in channels inside the seizure onset zone (SOZ, N=248) and outside (nonSOZ, N=1107).
• The red numbers present the number of outliers exceeding the maximum rate of the y-axis.
• Boxplots illustrating rates of all HFOs and types 1-2 HFO in channels inside the resected area (Res, N=347) and outside (nonRes, N=1008).

Figures

Table 1. Information on the three datasets investigated in this study. SOZ seizure onset zone; ETLE extratemporal lobe epilepsy; mTLE mesial temporal lobe epilepsy; TLE temporal lobe epilepsy.

Table 2. Correlation (Spearman’s rho) between rates of the four HFO types across channels inside the SOZ. All p<0.001.

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The authors investigated the association of different HFO types with the seizure onset zone ( SOZ ), resected area and surgical outcome. The following work is licensed under a Creative Commons: Attribution-NonCommercial-NoDerivatives 4. 0 International ( CC BY-NC-ND 4. 0 ) License. 2016. 01. 002 1 The morphology of high frequency oscillations ( HFO ) does not improve delineating the epileptogenic zone Sergey Burnos, Birgit Frauscher, Rina Zelmann, Claire Haegelen, Johannes Sarnthein, Jean Gotman Neurosurgery Department, University Hospital Zurich, Zurich, Switzerland Neuroscience Center, ETH and University of Zurich, Zurich, Switzerland Montreal Neurological Institute and Hospital, Montreal, Quebec, Canada MediCIS, INSERM, Faculté de Médecine, University of Rennes, Rennes, France Corresponding author: Sergey Burnos Klinik für Neurochirurgie, UniversitätsSpital Zürich, 8091 Zürich, Switzerland sergey.