Seizure Analysis: Stereo EEG vs. Subdural Electrodes

Brain surgery is increasingly being used to control seizures when they occur repeatedly, despite antiepileptic medications. The challenge, however, is often pinpointing seizure-producing areas of the brain, according to several neurosurgeons at the American Epilepsy Society (AES) 2015 Annual Meeting in Philadelphia.

Presenters from prestigious medical institutions across the United States and Canada outlined some of their most challenging cases for which they were charged with analyzing patients’ seizures using stereo electroencephalogram (sEEG) depth electrodes, subdural strip and grid electrodes, or a combination of both.

Subdural electrodes are typically used if the seizure focus is believed to be on the surface of the brain. If the seizure focus is believed to be deep-such as within a lesion-invasive monitoring is done using sEEG depth electrodes. In both procedures, patients are observed in the electroencephalogram (EEG) video monitoring unit to locate the exact origin of the seizures.

David A. Steven, MD, a neurosurgeon at the University of Western Ontario, shared a complex case of his patient, a 27-year-old woman, who experienced hypermotor seizures several times per day since the age of 2. Her auras included heart palpitations, tingling sensations, and numbness in her left arm, face, and leg-mostly in the arm and face.

Although anti-seizure medications can successfully treat seizures in two-thirds of all people with epilepsy, surgical evaluation is recommended in the remaining one-third of people, like this patient, who continue to have seizures regardless of medications.¹

Dr. Steven said he was originally unable to determine where her seizures originated within the brain using a scalp EEG, but thought that they appeared to be frontal lobe seizures. After a magnetic resonance image revealed a lesion on the patient’s brain, Dr. Steven placed 1 sEEG electrode within the lesion and 10 strip and grid electrodes surrounding the area. By doing so, he was able to determine that the lesion was primarily responsible for her seizures and ultimately performed a lesionectomy on the patient.

In this particular case, Dr. Steven said the use of both types of electrodes was necessary because the precise location of the seizure focus was uncertain. Both methods also helped ensure that the patient’s seizure focus was surgically removed without causing damage to important nearby brain regions.

The overall consensus among the speakers was that the decision to use sEEG over subdural electrodes and vice versa must be made on a case-by-case basis. Data generated by each type of electrodes produce different results and the methods are not a catch-all approach to epilepsy care.

The AES 2015 Annual Meeting was held December 4-8 in Philadelphia.

Session: Surgery: Battle Royale: Stereo EEG vs. Subdural Electrodes. Dec. 7, 2015.

References:

1. Koubeissi M. Pre-surgery Intracranial Monitoring: Stereo-EEG Versus Subdural Electrodes. Epilepsy Foundation website http://www.epilepsy.com/information/professionals/diagnosis-treatment/surgery/presurgical-evaluation/pre-surgery. Accessed December 7, 2015.