Statistical mapping of ictal high-frequency oscillations in epileptic spasms

Abstract

Purpose: We assessed 636 epileptic spasms seen in 11 children (median 44 spasms per child) and determined the spatial and temporal characteristics of ictal high-frequency oscillations (HFOs) in relation to the onset of spasms.

Methods: Electrocorticography (ECoG) signals were sampled from 104-148 cortical sites per child, and the dynamic changes of ictal HFOs were animated on each individual's three-dimensional (3D) magnetic resonance (MR) image surface.

Key findings: Visual assessment of ictal ECoG recordings revealed that each spasm event was characterized by augmentation of HFOs. Time-frequency analysis demonstrated that ictal augmentation of HFOs at 80-200 Hz was most prominent and generally preceded those at 210-300 Hz and at 70 Hz and slower. Recruitment of HFOs in the rolandic cortex preceded the clinical onset objectively visualized as electromyographic deflection. The presence or absence of ictal motor symptoms was related more to the amplitude of HFOs in the Rolandic cortex than in the seizure-onset zone. In a substantial proportion of epileptic spasms, seizure termination began at the seizure-onset zone and propagated to the surrounding areas; we referred to this observation as the "ictal doughnut phenomenon." Univariate analysis suggested that complete resection of the sites showing the earliest augmentation of ictal HFOs was associated with a good surgical outcome.

Significance: Recruitment of HFOs at 80-200 Hz in the rolandic area may play a role in determining seizure semiology in epileptic spasms. Our study using macroelectrodes demonstrated that ictal HFOs at 80-200 Hz preceded those at 210-300 Hz.

Wiley Periodicals, Inc. © 2010 International League Against Epilepsy.

Figures

Figure 1

Ictal ECoG discharges associated with spasms (A) Ictal ECoG traces in patient #4 are shown (Type 1 spasms; Table 2). Low-frequency filter: 53 Hz. High-frequency filter: 300 Hz. Ictal augmentation of ripple-band HFOs occurred at channel #1 and gradually involved the surrounding channels. The offset of ripple-augmentation occurred at channel #1 and gradually involved the surrounding channels. The trigger point for time-frequency analysis was placed at the EMG onset (right deltoid muscle). (B) Time-frequency plots derived from 62 spasms are shown. Augmentation of ripple-band HFOs preceded the EMG onset (denoted as ±0 msec). (C) The amplitudes of ripple-band HFOs associated with spasms are shown (See also Video S1 on the website).

Figure 2

Ictal ECoG discharges associated with spasms (A) Ictal ECoG traces in patient #9 are shown (Type 1 spasms; Table 2). Low-frequency filter: 53 Hz. High-frequency filter: 300 Hz. Ictal augmentation of ripple-band HFOs occurred at channel #1 and gradually involved the surrounding channels. Augmentation of ripple-band HFOs lasted longer at channel #1 compared to the surrounding channels. The trigger point for time-frequency analysis was placed at the ictal ECoG onset. (B) Time-frequency plots derived from 110 spasms are shown. No significant augmentation of ripple-band HFOs was noted at channel #5 in the Rolandic area. No evidence of EMG deflections was noted at left deltoid EMG channel. (C) The amplitudes of ripple-band HFOs associated with spasms are shown (See also Video S2 on the website).

Figure 3

Ictal ECoG discharges associated with spasms (A) Ictal ECoG traces in patient #5 are shown (Type 1 spasms; Table 2). Low-frequency filter: 53 Hz. High-frequency filter: 300 Hz. Ictal augmentation of ripple-band HFOs occurred at channel #1 and gradually involved the surrounding channels. The offset of ripple-augmentation occurred at channel #1 and gradually involved the surrounding channels. The trigger point for time-frequency analysis was placed at the EMG onset (right deltoid muscle). (B) Time-frequency plots derived from 25 spasms are shown. Augmentation of ripple-band HFOs preceded the EMG onset (denoted as ±0 msec). (C) The amplitudes of ripple-band HFOs associated with spasms are shown (See also Video S3 on the website).