High-frequency oscillations recorded with surface EEG in neonates with seizures

Purpose: Neonatal seizures are often the first symptom of perinatal brain injury. High-frequency oscillations (HFOs; ripples: 80–250 Hz; fast ripples: 250–500 Hz) are promising new biomarkers for epileptogenic tissue and can be found in intracranial and surface EEG. To date, we cannot reliably predict which neonates with seizures will develop childhood epilepsy. We questioned whether epileptic HFOs can be generated by the neonatal brain and potentially predict epilepsy.

Method: We selected 24 surface EEGs sampled at 2048 Hz with 175 seizures from 16 neonates and visually reviewed them for HFOs. Interictal epochs were also reviewed.

Result: We found HFOs in thirteen seizures (7%) from four neonates (25%). 5025 ictal ripples (rate 10 to 1311/min; average frequency 135 Hz; average duration 66 ms) and 1427 fast ripples (rate 8 to 356/min; average frequency 298 Hz; average duration 25 ms) were marked. Two neonates (13%) showed interictal HFOs (285 ripples and 25 fast ripples). All HFOs co-occurred with sharp transients. We could not yet find a relationship between neonatal HFOs and clinical outcome.

Conclusions: The neonatal brain can generate epileptic ripples and fast ripples, particularly during seizures, and they co-occur with ictal and interictal sharp transients. The occurrence of neonatal HFOs is not common and their potential clinical value not evident yet.