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 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.
In lieu of the frame, robots can be used to place the electrodes. This frameless approach is just as accurate as the frame, but takes a few less hours to set up and is easier to use, more comfortable and allows for more flexible modification of electrode locations. This approach is especially attractive for use in 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.
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.
More children achieve seizure freedom (Engel I) when SEEG is used compared to subdural grid studies.
Risks during the SEEG process are rare, but reported.
The most common risk of SEEG is cerebrospinal fluid leak. In a recent meta-analysis study, some children experienced cerebrospinal fluid leaks after SEEG. While most leaks stopped spontaneously, many children required intervention such as reinforcing sutures (also known as “stitches”), or application of collodion (a syrupy solution used as a surgical dressing). Intracranial bleeding is another risk.
Infections are also reported. Some children required surgical debridement, while others had infected bone flaps that required cranioplasty. Five patients across 3 studies needed treatment for aseptic meningitis.
Research shows that some children have temporary neurological deficits from SEEG implantation. The most common effect is temporary hemiparesis. Other complications can include temporary aphasia, dysphagia, facial weakness, and homonymous hemianopsia.
Although rare, some children have permanent neurological post-operative deficit. These include visual field defects ranging from minimal field alterations to hemianopsia (10 cases reported), hemiplegia (one case reported), and hemiparesis (2 cases reported).
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The Cleveland Clinic – A Guide to Stereotactic EEG: This downloadable PDF file provides a good overview of the stereotactic EEG procedure.