Stereoelectroencephalography (SEEG)


Overview: Stereoelectroencephalography (SEEG) is an invasive diagnostic procedure used primarily in the presurgical evaluation of patients with drug-resistant (refractory) focal epilepsy. It involves the implantation of thin, depth electrodes into the brain to record electrical activity directly from within the brain tissue. This method helps in identifying the precise origin of epileptic seizures, known as the epileptogenic zone (EZ), which is crucial for planning surgical interventions.


Indications for SEEG:


  1. Localization of Seizure Onset Zone:

    • When non-invasive techniques like scalp EEG, MRI, or PET scans fail to clearly identify the seizure onset zone, especially in cases of non-lesional epilepsy or when there's discordance among these tests.

  2. Deep or Bilateral Exploration:

    • SEEG is particularly useful for exploring deep brain structures like the mesial temporal lobe, insula, or other areas not easily accessible by surface electrodes. It also facilitates bilateral exploration when needed, which is less invasive compared to bilateral subdural grid placement.

  3. Complex Epileptic Networks:

    • For patients where seizures involve or spread through complex networks, crossing multiple lobes or involving deep structures, SEEG can map these networks in three dimensions, providing detailed spatial and temporal information.

  4. Post-Surgical Assessment:

    • In cases where prior epilepsy surgery has failed or when there's suspicion of a new or secondary epileptic focus, SEEG can be used to reassess the brain's electrical activity.

  5. Avoidance of Craniotomy:

    • Unlike subdural electrode placement, which requires a craniotomy, SEEG can be performed through small burr holes, making it less invasive and potentially safer for certain patients, particularly children or those with risk factors for craniotomy complications.

  6. Functional Mapping:

    • SEEG can also be used for mapping eloquent cortex (areas responsible for language, motor, or sensory functions) to ensure these areas are spared during surgery, although this is more commonly done with subdural grids.

  7. Therapeutic Applications:

    • Beyond diagnosis, SEEG electrodes can be used for therapeutic interventions like radiofrequency thermocoagulation (RFTC) to ablate small epileptogenic areas directly.

  8. Pediatric Patients:

    • In children with drug-resistant epilepsy where traditional methods might not suffice or where the risk of complications from more invasive procedures is higher, SEEG can provide necessary data with a favorable safety profile.

  9. MRI-Negative Epilepsy:

    • In cases where no lesion is visible on MRI, SEEG can still localize the seizure onset, guiding surgical decisions in what are often more challenging cases.


SEEG's precision in delineating the epileptogenic zone leads to better surgical planning, potentially increasing the likelihood of seizure freedom post-surgery while minimizing unnecessary resection of healthy brain tissue. The decision to proceed with SEEG is typically made by a multidisciplinary team including neurologists, neurosurgeons, neuropsychologists, and radiologists, based on the patient's clinical presentation, seizure semiology, and the inadequacy of non-invasive methods.