Epilepsy is a neurological disorder characterized by excessive synchronized neuronal discharge in the brain, leading to transient dysfunction. Approximately one-third of epilepsy cases are classified as drug-resistant epilepsy, which may require surgical intervention. The epileptogenic zone (EZ) is typically defined as the region generating epileptiform electrophysiological signals prior to clinical seizure onset, as well as its initial propagation area. Recurrent seizures often result in cerebral ischemia and hypoxia, which can impair brain function. Therefore, the goal of epilepsy surgery extends beyond seizure control and aims to improve overall brain function.
Indications for Surgery
Around 20% of epilepsy patients continue to experience seizures despite the use of antiepileptic medications. Surgical treatment is indicated for patients with drug-resistant epilepsy or those experiencing severe side effects from medications.
Preoperative Evaluation
High-Resolution MRI and CT
High-resolution MRI is highly effective in identifying medial temporal sclerosis (MTS) through hippocampal asymmetry and neuronal developmental abnormalities, such as cortical dysplasia, which can trigger seizures. Additional findings may include tumors, arteriovenous malformations, or cavernous angiomas.
Video Electroencephalography (V-EEG)
V-EEG combines conventional EEG recording with video monitoring to capture the clinical manifestations during seizures.
Positron Emission Tomography (PET)
For cases where MRI and EEG fail to precisely localize the epileptogenic zone, 18F-fluorodeoxyglucose (18F-FDG) PET scanning can be used. PET may reveal regions of decreased metabolism on the same side as the temporal lobe lesion.
Magnetoencephalography (MEG)
MEG facilitates the diagnosis of epilepsy and can help localize the epileptogenic zone as well as cortical functional areas. It can also assist in preoperative surgical planning.
Surgical Treatment
Lesion Resection
Lesional resections are common in temporal lobe epilepsy (TLE), which includes lateral temporal epilepsy and mesial temporal epilepsy caused by hippocampal sclerosis. Procedures include anterior temporal lobectomy or anterior temporal lobectomy combined with hippocampal and amygdala resection. Beyond the temporal lobe, resections of epileptogenic zones in the frontal, parietal, occipital, and insular cortices are also performed, though outcomes for non-temporal lobe epilepsy are generally less predictable.
Surgical Treatment for Generalized Seizures
Procedures such as corpus callosotomy aim to disrupt the transmission of epileptic electrical activity, thereby reducing seizure frequency and severity. This approach may be appropriate for patients with severe and complex epilepsy.
Hemispherectomy or hemispheric disconnection is reserved for patients with extensive unilateral epileptic activity. Conventional hemispherectomy carries a risk of complications, including hydrocephalus, aseptic meningitis, and hemosiderin deposition on the brain surface. Modified hemispherectomy or hemispheric disconnection techniques now aim to sever connection fibers to adjacent brain regions or the contralateral hemisphere, blocking the propagation of seizure discharges while preserving cortical and vascular structures of the affected hemisphere.
Neuromodulation Surgery
For patients with diffuse epileptogenic zones that cannot be surgically resected, or when the epileptogenic zone is located in critical functional areas where resective surgery carries a high risk of disability, neuromodulation techniques can be employed as palliative treatments. These include deep brain stimulation (DBS) and vagus nerve stimulation (VNS), which may alleviate seizures to some extent.