The mechanism of epilepsy pathogenesis is complex and not fully defined, and about 20-30% of patients with seizures that cannot be completely controlled by drugs become drug-resistant epilepsy. For focal drug-resistant epilepsy, surgical removal of the epileptogenic zone can control seizures, but the overall seizure-free rate in the long term after surgery is 60-70%, and the results are still not satisfactory. Accurate assessment of the location and extent of the epileptogenic zone and its adequate excision are prerequisites for the success or failure of surgery. Intracranial EEG (iEEG) has been shown to be the most accurate method for determining the location and boundaries of the epileptogenic zone. It can selectively record the local cortical electrical activity through intracranial electrodes and achieve high temporal resolution for long-range recording, reliably reflecting the continuous dynamic changes of EEG during interictal and ictal periods. The in-depth analysis of iEEG can improve the efficacy of epilepsy surgery and provide important information to reveal the pathogenesis of epilepsy.

Inclusion Criteria:

1. Complete clinical history;
2. IEEG monitoring at least one habitual seizure；
3. Follow up for at least 1 year；
4. Signed informed consent.

Exclusion Criteria:

1. Habitual seizures were not found in iEEG monitoring;
2. No operation was performed;
3. Lost to follow-up for various reasons within 1 year after surgery.

We reviewed consecutive patients with drug-resistant focal epilepsy who underwent intracranial electroencephalography (IEEG) evaluation as well as resective surgery in our epilepsy centre. They were all followed-up for > 1 years after surgery. The patients had a comprehensive evaluation including detailed history, neuropsychological testing, neuroimaging study and video-EEG examination.