Stereoelectroencephalography (SEEG)

What is stereoelectroencephalography (SEEG)?

Stereoelectroencephalography (also referred to as stereo-EEG or SEEG) is a minimally invasive procedure that can help identify the region in the brain that is capable of generating epileptic seizures (called the epileptogenic zone) in certain patients with epilepsy that hasn’t responded to medication (called medically refractory epilepsy). The cutting edge, diagnostic procedure is usually used to determine if people with drug-resistant epilepsy (epilepsy that is not controlled by 2 or more medications) are good candidates for a resective surgery.

During the surgical procedure, a neurosurgeon will place thin electrodes inside the brain through small incisions in the scalp. After the electrodes are placed, the patient remains in the hospital and is monitored in the Epilepsy Monitoring Unit (EMU) where typical seizures are captured. The epileptologists will then analyze the tracings to try to pinpoint the origin of the seizure (the ictal onset zone) and define the area in the brain capable of generating seizures, called the epileptogenic zone.

When is an SEEG procedure performed?

Patients with medically refractory epilepsy undergo a series of noninvasive tests initially, which include a stay in the EMU to capture their seizures through scalp electrodes, epilepsy-dedicated MRI, PET scan as well as other tests determined by the neurologist taking care of them. This is referred to as a phase I evaluation.

In some patients, it remains uncertain where the seizures are beginning, or there may be a lack of agreement in the information obtained from each test. In addition, an MRI may not show a clear lesion known to cause epilepsy. In such patients, the information from the phase 1 evaluation is thoroughly discussed by a multidisciplinary team to determine where the seizures may be beginning.

Neurosurgeons will perform an SEEG implantation plan covering the suspected areas, to determine the precise epileptogenic zone, and understand the spread of the seizure in each patient. The data from SEEG recordings is analyzed by the epileptologist (neurologist) and discussed again by a multidisciplinary team determine the surgical approach that will provide the highest success in rendering that patient seizure-free.

The SEEG also allows for precise mapping of the seizure spread into other anatomical brain structures, and helps the neurosurgeon understand the functionality of these anatomical structures.

As epilepsy surgery is an elective type of surgery, the aim is to help the patient become seizure free without causing any functional deficits. SEEG also allows the epileptologist to study different areas of interest in the brain during the stay in the EMU to ensure that these areas are not important or critical for the patient’s daily function (language, motor movement, facial movements, sensation, etc.). The procedure which uses electrical stimulation is referred to as brain mapping and ensures that the patient does not suffer from any disability from the resection of the epileptogenic zone.

SEEG is not only used diagnostically, but also sometimes as part of the treatment, through SEEG-guided Radiofrequency Thermocoagulation (or thermal ablation), a procedure which applies heat energy and radio waves to the brain cells generating the seizures to destroy them, without the need for a resective surgery.

Who is suitable for SEEG?

An SEEG isn’t suitable for everyone with epilepsy. It may be offered to those with complex focal epilepsy (where the seizures originate from one part of the brain) if other tests haven’t produced clear results. The patient must also be deemed as a good candidate and be able to understand and withstand this type of surgery.

People with generalized epilepsy, where seizures start in bilateral hemisphere simultaneously, are not eligible for SEEG. Eligibility is determined by a multidisciplinary team who review all patient information in detail.

What are the advantages of SEEG?

• A minimally invasive procedure that does not require a craniotomy (a large opening of the skull bone).
• A safer procedure when compared to other invasive monitoring of seizures that require a craniotomy and placement of subdural grid electrodes.
• It reaches deeper areas of the brain compared to previously used methods of subdural grid electrodes.
• It allows for a 3-D visualization of the seizures and how they spread in the brain.
• It is more accurate in pinpointing the precise source of epileptic seizures in the brain when scalp EEG and other noninvasive procedures are insufficient.
• It allows for mapping of the anatomical brain structures (studying the function of different areas of interest in the brain) and reduces post-surgical functional deficits.
• It helps doctors to decide the best surgical strategy to render the patient seizure-free and improve surgical outcomes.

What happens during an SEEG procedure?

Before the procedure, your doctor will provide instructions about preparing for an SEEG. This will involve discussing any medications you may be taking and answering any questions or concerns.

On admission to the hospital, you will meet a neurologist and neurosurgeon who will be involved in the surgery along with the anesthesia team and neurophysiology technicians. Some tests and repeat images such as neuronavigation MRI will be performed on admission, as well as blood work and an EKG.

On the day of the procedure, you will be given a general anesthetic to put you to sleep. A frame will be placed over your head to keep it still and a series of tiny holes will be drilled into the scalp. Tiny electrodes are inserted through the holes which are guided by pre-planning images of the vessels and brain structures, to the areas of the brain where the seizures are thought to begin.

CT scans and X-rays of the brain are then taken to confirm the precise location of the electrodes. The procedure can take up to six hours to perform.

SEEG is a safe procedure, but as with any brain surgery, there are small risks such as infection, bleeding on the brain or stroke.

What happens after an SEEG procedure?

You will be taken to an EMU and the electrodes are attached to equipment that monitors brain activity for seizures. You will stay in the unit until seizure activity is recorded. The epileptologist will also use electric stimulation to induce seizures typical of the seizures the patient experiences at home to confirm the exact location of ictal onset zone. The findings will be thoroughly analyzed, and the electrodes are then removed via a short, simple procedure.

Recovery from SEEG usually takes a couple of days.

Comprehensive epilepsy care at Cleveland Clinic Abu Dhabi

SEEG is one of the many state-of-the-art diagnostic and treatment options offered at our Epilepsy Program, ensuring patients receive the most accurate and effective care. Cleveland Clinic Abu Dhabi is the first hospital in the UAE to offer SEEG implantation.