Overview
This lecture covers the rationale, indications, techniques, and outcomes of stereo EEG (SEEG) for localizing epileptic foci in patients with drug-resistant epilepsy.
Epilepsy Treatment Overview
- About one-third of epilepsy patients are not controlled with medications after trying three drugs.
- Surgical options are considered for patients who fail medical therapy.
- The goal of epilepsy surgery is to cure seizures by targeting the epileptogenic zone.
Epilepsy Evaluation & Workup
- Phase 1 workup includes thorough history, seizure semiology, video EEG, and imaging (MRI).
- Surface (scalp) EEG has limited anatomical localization, especially without visible lesions.
- Some patients may continue medications, proceed directly to surgery, or require further (Phase 2) monitoring.
Indications for Intracranial Monitoring
- Intracranial monitoring is considered if MRI is negative, if EEG and imaging are discordant, if multiple lesions are present, or if lesions are in eloquent areas.
- Intracranial electrodes include subdural strips/grids and depth electrodes.
- SEEG allows individualized, 3D mapping of seizure onset and spread using multiple depth electrodes.
SEEG Technique & Workflow
- Preoperative planning involves MRI with contrast, CT angiogram, and careful hypothesis of seizure focus.
- Trajectories must be individualized to avoid unnecessary or excessive coverage.
- Procedure is performed under general anesthesia; often assisted by robotics for precise electrode placement.
- Electrodes are placed via small drill holes; SEEG is minimally invasive and suitable even for patients with prior craniotomies.
Postoperative Monitoring & Outcomes
- After implantation, medications are weaned and seizures are recorded over about a week.
- Typical (not rare) seizures should be captured for accurate localization.
- Mapping eloquent cortex is more difficult with SEEG compared to grids.
- Leads are removed with a brief procedure and patients typically go home the next day.
Safety and Efficacy
- SEEG carries a 0.6% risk of permanent neurological deficit and 1.3% surgical morbidity.
- Subdural grids have higher risks of hemorrhage, infection, and CSF leak, especially in children.
- One-year seizure freedom after SEEG-guided resection is reported at 44–68%, comparable to subdural grid outcomes.
SEEG Advantages and Limitations
- SEEG is minimally invasive, well-tolerated, and suited for deep or hard-to-access lesions.
- It is less effective for mapping functional (eloquent) cortex than subdural grids.
- The adoption of robotics has facilitated SEEG’s growth in North America.
Key Terms & Definitions
- Epileptogenic Zone — The area of brain tissue responsible for generating seizures.
- Semiology — The clinical features and symptoms observed during a seizure.
- SEEG (Stereo EEG) — Stereotactic technique placing multiple depth electrodes for 3D seizure mapping.
- Subdural Grids/Strips — Electrodes placed on the brain surface for seizure localization.
- Eloquent Cortex — Brain regions responsible for language, motor, or sensory function.
- Robotics in SEEG — Use of robotic systems for precise electrode placement.
Action Items / Next Steps
- Review Kwan et al. paper on medication response in epilepsy.
- Study the phases of epilepsy surgical evaluation.
- Understand the technical steps of SEEG placement and planning.
- Be familiar with SEEG safety data and compare it to subdural grids.