There are different types of epilepsy surgery to help control seizures. An important step before surgery occurs is to identify the precise area in the brain where seizures start.
In resective epilepsy surgery, doctors remove the area of the brain where seizures are thought to begin. Sometimes, when seizures start in different areas, more brain tissue needs to be removed. In a type of surgery known as a subtotal hemispherectomy, half of the outer layer of the brain is removed, without affecting the areas involved in sensation and movement.
Before surgery, researchers identify precisely where in the brain seizures are starting using a common technique called electroencephalography, or EEG. This technique monitors seizure activity by placing recording electrodes on the scalp or directly on the brain. Studying particular patterns of brain activity can be helpful, since the areas where seizures start often show different activity patterns than the rest of the brain. One particular type of activity, known as high frequency oscillations (HFOs), may help researchers identify the brain regions that generate seizures. Dr. Hiro Otsubo and his colleagues studied HFOs in children with epilepsy to see if this information would be linked to improved seizure control after surgery.
Dr. Otsubo and his team studied 23 children between the ages of 1 and 17 with drug-resistant epilepsy who underwent resective surgery, including some who had a subtotal hemispherectomy. The areas of the brain associated with seizures were identified using conventional EEG and brain mapping techniques. The researchers wanted to know if HFOs would be more prominent in the areas where seizures were thought to start, and compare this to areas in the brain where seizures do not tend to start, such as the motor area.
The researchers found that HFOs occurred much more often in the areas to be removed than in the motor area. They also found that people who had fewer seizures after surgery had more HFOs in the removed areas relative to people who continued to have seizures after surgery. This suggests that HFOs might be a useful marker for identifying the areas where seizures start, and that removing these areas may lead to a better chance of seizure freedom after surgery.
Lastly, in people with better surgical outcomes, HFOs were linked to another, slower type of brain activity in the regions to be removed. These results suggest that by looking at where HFOs occur, and at the relationship between HFOs and these slow brain waves, researchers can better identify which regions should be removed. In the future, using HFOs may help to improve the accuracy of resective surgery, leading to better surgical outcomes.