'Stereo-EEG’ Shows Advantages for Epilepsy Surgery

Published December 2020 | Frontiers in Human Neuroscience

When children with epilepsy need surgical intervention, neurosurgeons need reliable sensors to detect abnormal electrical activity in the brain. But which techniques for collecting that data work best?

“Some patients with epilepsy, despite all the advances and treatment of epilepsy, will not respond to medicines. Some do require surgery,” says Ravindra Arya, MD, DM, a pediatric epileptologist at Cincinnati Children’s and an associate professor of computer science at the University of Cincinnati.

To prepare for surgery, patients often undergo intracranial EEG, which involves inserting electrodes on the surface of the brain to track electrical activity and localize the seizure onset zone. Over the past decade, this method has been largely replaced by stereotactic depth electrode EEG (stereo-EEG), which involves inserting probes deeper into the brain. This transition between EEG types has been a major paradigm shift in epilepsy surgery.

Another aspect of stereo-EEG evaluation is functional mapping with electrical stimulation. Prior to epilepsy surgery, neurosurgeons must determine the functions of the brain tissue they plan to remove. In subdural EEG versus stereo-EEG, “the geometry of these electrodes differs. They probably interact with different elements of the brain,” Arya says.

The former rests on the surface of the brain, the latter enter at different angles and have different interactions with various cells of the brain. Arya and colleagues report that electrical stimulation mapping (ESM) with stereo-EEG may be safer. Stereo-EEG also is more feasible for mapping sensorimotor and speech/language areas, and allows for functional sampling from areas of the brain where subdural electrodes simply do not reach.

Arya plans to continue studies to develop and validate the effectiveness and safety of novel brain mapping techniques.

Comparing Sensor Methods

Subdural electrodes require a craniotomy for implantation, while stereo-EEG electrodes are implanted through burr holes. Subdural electrodes cover the crowns of gyri, nearly perpendicular to the dendrites of pyramidal cells, while stereo-EEG electrodes pass at various angles concerning pyramidal cells and passing through both gray and white matter. (Lower section: a subdural electrode grid and an stereo-EEG electrode.)