Stereoelectroencephalography (SEEG) to Help

Treat Refractory Epilepsy Doug Coppa

Refractory Epilepsy

Epilepsy that cannot be controlled or treated by medication, also known as intractable or drug resistant epilepsy.

Affects about a third of epilepsy patients (20-40%)

Some disagreement on the precise definition of refractory epilepsy, difficult to diagnose

Treatment of Refractory Epilepsy

Inactivation or complete disconnection of Epileptogenic Zone (EZ) ◦ Epileptogenic Zone is defined as the “area of cortex x that is necessary and sufficient for initiating seizures and whose removal (or disconnection) is necessary for complete abolition of seizures” (Lüders et al. 1993)

◦ Can be inactivated by precise lesions in the brain or removed surgically

Detecting the Epileptogenic Zone

Brain Imaging ◦ Functional Magnetic resonance imaging (fMRI) ◦ Different forms of electroencephalography, both noninvasive and invasive (EEG) Focus on stereoelectroencephalography

EEG ◦ Measures electrical activity of the brain Ionic currents in neurons produce voltage fluctuations

Stereoelectroencephalography (SEEG)

EEG through electrodes implanted in/on brain tissue (invasive) ◦ Subdural Grid Electrodes

Square or rectangular grid used to cover large surface area of brain

SEEG continued Stereotactic Depth Electrodes

◦ Thin wires with electrodes, implanted deep into cerebral tissue

Implantation of Depth Electrodes

Multiple Brain Images produced to create mapping of brain

Stereotactic Planning software used to evaluate placement of depth electrodes

Implantation of Depth Electrodes Continued

Surgeons use robots to assist with lining up guiding screws for electrodes

SEEG Monitoring

Patients monitored for 3-15 days to allow for seizures to occur, doctors pinpoint epileptogenic zone

Advantages of SEEG depth electrodes

Minimally invasive compared to subdural electrodes

Low complication rates (1-5%)

Allows for monitoring of deep brain structures to determine EZ

Seizure-free rate after SEEG-guided resections was 62% after 12 months

Disadvantages

High cost for procedure

Complications are serious ◦ Can result in loss of motor function or death

Somewhat new method

Discussion

Can become more accurate and have less complications in future

Depth electrodes can pave way for brain-machine interfaces ◦ Electric signals in brain can be interpreted and used to operate computers

◦ Only 2 dimensional movement as of now, could become more advanced in the future

Sources Lüders HO, Engel J, Munari C. General Principles. In : Engel Jr. J, ed. Surgical

Treatment of the Epilepsies, Second Edition Ed. New York : Raven Press, 1993 : 137-53.

Vadera S, et al. Stereoelectroencephalography for continuous two-dimensional cursor control in a brain-machine interface http://thejns.org/doi/full/10.3171/2013.3.FOCUS1373

Cardinale F, et al. Stereoelectroencephalography: Surgical Methodology, Safety, and Stereotactic Application Accuracy in 500 Procedures https://academic.oup.com/neurosurgery/article/72/3/353/2236040/StereoelectroencephalographySurgical-Methodology

Gonzales-Martinez J, et al. Stereotactic placement of depth electrodes in medically intractable epilepsy http://thejns.org/doi/full/10.3171/2013.11.JNS13635

Turning to SEEG for Pediatric Patients with Refractory Epilepsy https://consultqd.clevelandclinic.org/2015/03/turning-to-seeg-for-pediatric-patients-with-refractory-epilepsy/

https://www.researchgate.net/figure/259111389_fig6_Intracranial-EEG-recording-recording-A-Localization-of-SEEG-electrodes-shown-on

Pre -surgery Intracranial Monitoring: Stereo-EEG Versus Subdural Electrodes https://www.epilepsy.com/learn/professionals/diagnosis-treatment/surgery/presurgical-evaluation/pre-surgery-intracranial