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

Tommaso Fedele,Peter Hilfiker,Thomas Grunwald,Johannes Sarnthein,Niklaus Krayenbühl,Sergey Burnos,Ece Boran

doi:10.1038/s41598-017-13064-1

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.

Highlights

The treatment of choice in patients with drug-resistant focal epilepsy is the surgical resection or disconnection of the epileptogenic zone (EZ)[1]
We evaluate the clinical relevance of High frequency oscillations (HFOs) in individual electrodes by comparing the HFO area with the resected area (RA) and by predicting seizure outcome in the individual patient
We determined whether the HFO area was fully or partly resected and whether seizure freedom was achieved (Table S1)

Summary

Introduction

The treatment of choice in patients with drug-resistant focal epilepsy is the surgical resection or disconnection of the epileptogenic zone (EZ)[1]. Recent studies have pointed to the high frequency oscillation (HFO) recorded in intracranial EEG (iEEG) as a new indicator for the EZ3–5. Interictal HFOs have proven more specific in localizing the seizure onset zone (SOZ) than spikes[8] and have presented a good association with the post-surgery outcome in epilepsy patients[9,10,11,12]. While we do not aim to outperform visual marking, we provide a prospective definition of a clinically relevant HFO. We evaluate the clinical relevance of HFO in individual electrodes by comparing the HFO area with the resected area (RA) and by predicting seizure outcome in the individual patient

Methods

Results

Conclusion