In some cases of drug-resistant focal epilepsy, a routine EEG may not be enough to determine where a seizure begins or to identify parts of the brain that control motor function and speech. In these cases, stereotactic electroencephalography (SEEG) may be useful.
In SEEG, electrodes are inserted into the brain to help define the epileptogenic zone (where seizures begin) and can often identify a target for surgery. The position of the electrodes is reconstructed using computed tomography (CT) superimposed on magnetic resonance imaging (MRI), or via direct MRI if the electrodes are compatible. This process can capture a three-dimensional understanding of seizure activity in the brain.
Typically, the procedure begins when a metal frame is placed over the patient’s head to help label, align and implant the electrodes. During the first stage, brain imaging is done with MRI and locations are marked. Then, long, thin electrodes are inserted through the skin and the skull into the brain. The frame allows doctors to probe within 3 millimeters of the target site in the brain; however, the frame takes time to position and can cause discomfort. It can also be challenging to work around the frame and adjust the angle and location of the electrodes when SEEG is performed during surgery. The is why children are sedated during this procedure.
Sometimes robots such as the ROSA™ are used to place the electrodes. This is called a “frameless approach” and is just as accurate as the frame. Using a robot usually takes less time to set up. It’s also easier to use a robot than the frame, more comfortable, and allows for more flexible modification of electrode locations. This approach is often preferred for children.
There are several advantages to SEEG. The procedure allows extensive examination of both sides of the brain without requiring removal of large sections of the skull, and reduces some risks during surgery. Consequently, SEEG is most useful in cases where deeper areas of the brain are involved in seizure activity.
In a recent study of 38 children who had SEEG prior to resection surgery, it was found that:
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SEEG in pediatric patients reduces operative time compared with subdural electrodes;
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SEEG decreases use of narcotic drugs for pain among pediatric population.
The pros and cons of SEEG can vary by type of epilepsy:
Temporal lobe: In temporal lobe epilepsy (TLE), SEEG is useful if seizures originate from both sides of the brain. This procedure can be used to distinguish mesial TLE from lateral TLE, but basal temporal regions are more difficult to sample. When epilepsy surgery was tailed according to SEEG results in people with TLE, nearly 90 percent of patients became free of disabling seizures.
Frontal lobe: Identifying the source of seizures in patients with frontal lobe epilepsy (FLE) may be challenging, and SEEG can prove useful. This procedure is particularly helpful in patients without visible damage on MRI, but may also be useful in patients with abnormal MRI findings.
Insular lobe epilepsy: Insular seizures may mimic or coexist with temporal, frontal, or perisylvian epilepsy. The insula is one of the most ideal targets for SEEG because it is buried deep in the brain and inaccessible to EEG electrodes.
MRI-negative partial epilepsy: Surgical treatment for seizures where there are no structural abnormalities found in the brain (known as MRI-negative or MRIa=-occult epilepsy) is a challenge. When combined with MEG, SEEG can help determine the area where seizures begin in people with focal spikes, but not when spikes occur across one or both sides of the brain. People are most likely to become seizure free when SEEG completely spans the area identified by MEG.
Seizure-Free Outcome
More children achieve seizure freedom (Engel I) when SEEG is used compared to subdural grid studies.
Operative Risks
Risks during the SEEG process are rare. About 3% of children developed significant bleeding after SEEG compared to 10.7% after subdural grids.
Side Effects
Headache is the most common side effect.
Sources:
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Campana C, Zubler F, Gibbs S, de Carli F, Proserpio P, Rubino A, Cossu M, Tassi L. Schindler K and Nobili L. 2017. Suppression of interictal spikes during phasic rapid eye movement sleep: a quantitative stereo-electroencephalography study. J Sleep Res. 26(5):606-613.
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Learn More:
The Cleveland Clinic – A Guide to Stereotactic EEG: This downloadable PDF file provides a good overview of the stereotactic EEG procedure.
