Very High-Frequency Oscillations in Mesial Temporal Lobe Epilepsy: Identifying the Epileptogenic Zone

To investigate the reliability of very high-frequency oscillations (VHFOs, 500-2000 Hz) as biomarkers in identifying the epileptogenic zone (EZ) in mesial temporal lobe epilepsy (MTLE) patients.

We reviewed 19 MTLE patients who underwent stereo-electroencephalography-guided radiofrequency thermocoagulation. Interictal and ictal VHFOs were captured in four regions of interest (ROIs): amygdalohippocampal complex (AHC), parahippocampal gyrus (PG), white matter, and lateral temporal lobe. We analyzed the occurrence of VHFOs per minute, per contact: (a) in each ROI; (b) during awake resting state, sleep, and seizure within the seizure onset zone (SOZ) and non-SOZ contacts; (c) in the EZ, propagation zone (PZ), and non-involved zone (NIZ). The percentage and ratio of thermocoagulated VHFOs contacts in seizure-free (SF) and non-seizure-free (NSF) patients were also analyzed.

At the last follow-up (19.31 ± 6.36 months), 13 patients were SF and 6 were NSF. The VHFOs rate was significantly higher in the SOZ contacts during the ictal than interictal period compared to non-SOZ contacts. Very-fast ripples rate was more prevalent in the EZ than in the NIZ. VHFOs rate was higher in the AHC and PG compared to other regions. At a group level, SF patients had a higher percentage and ratio of thermocoagulated VHFOs contacts compared to NSF patients. At a patient level, some NSF patients had most of their VHFO-generating tissues ablated, while some SF did not.

The presence and ablation of VHFO-generating areas was associated with good surgical outcome at a group level. However, at a patient level, VHFOs may not be as reliable in identifying the EZ.