New research focusing on high-frequency oscillations, termed ripples and fast
ripples, recorded by intracranial electroencephalography (EEG), may provide an
important marker for the localization of the brain region responsible for
seizure activity. According to the study now available in Epilepsia, a
journal of the International League Against Epilepsy (ILAE), the resection of
brain regions containing fast ripples, along with the visually-identified
seizure-onset zone, may achieve a good seizure outcome in pediatric epilepsy.
High-frequency oscillations at
80-200 Hz are known as ripples and those above 200 Hz are considered fast
ripples. Medical evidence suggests that fast ripples are a specific surrogate
marker of the seizure generation zone. Studies in adults have suggested that
resection of the brain region containing fast ripples was associated with good
seizure outcome. However, these studies used a small number of electrode (EEG)
contacts, with limited brain coverage, which may not be optimal for pediatric
patients who often exhibit a more generalized epileptic network than adults.
Hiroshi Otsubo, MD, with The Hospital for Sick Children in Toronto,
Canada and lead researcher of the current study explains, “In pediatric
patients, extensive surgical resection are often used, but may overestimate the
link between high-frequency oscillations and seizure outcome. Good surgical
success may also be achieved by more limited surgeries that include both the
brain region with high-frequency oscillations and the brain region that appears
to initiate seizures, even when they are independent.” To further explore this
hypothesis, the research team evaluated the relationship of resection of brain
regions containing high-frequency oscillations and the area of seizure onset in
pediatric epilepsy patients.
Researchers retrospectively analyzed 28
pediatric patients with epilepsy who underwent intracranial EEG monitoring prior
to focal resection surgery. Brain regions containing a high occurrence of
high-frequency oscillations were determined, and spatial relationships between
regions with fast ripples and seizure-onset zones were investigated. The team
compared seizure outcome with the size of these regions, the surgical resection,
and amount of the regions with fast ripples and areas of seizure onset within
the resection area.
Results show that 2 years after surgery, 10 patients
were completely seizure free and 18 continued to have some seizure activity.
Complete resection of the brain regions exhibiting fast ripples was
significantly associated with better seizure outcome. Improved seizure outcome
was also observed with complete resection of brain regions with ripples;
surprisingly, however, resection of the area of seizure onset did not correlate
with seizure outcome. The size of surgical resection was not linked to seizure
outcome.
Furthermore, the authors, Drs. Akiyama and Otsubo et al., noted
that the visually- determined seizure onset zone partially overlapped with
regions containing high-rate fast ripples. “The entire epileptic network,
containing fast ripples, ripples and seizure onset zones, must be thoroughly
analyzed to ensure complete resection of the area causing seizures with the
smallest resection possible,” advised Drs. Akiyama and Otsubo et al. “While our
results are preliminary and further validation is necessary, the analysis of
high frequency oscillations offers clinicians a new surgical approach that could
potentially improve seizure outcome in children with epilepsy.”
Source: Medical News Today
