Surgical Treatment for Extratemporal Epilepsy.
Partial seizures of extratemporal origin may present unique challenges in the patient with medically refractory seizures. The efficacy of an extratemporal focal cortical resection may be less effective than an anterior temporal lobectomy for intractable epilepsy. The potential operative complications may be increased in individuals with extratemporal epilepsy because of functional cerebral cortex involvement and the need for a large cortical resection to significantly reduce seizure tendency. Partial seizures of extratemporal origin are predominantly associated with frontal lobe epilepsy. The most effective treatment for intractable partial epilepsy is a focal cortical resection with excision of the epileptogenic zone, that is, an area of ictal onset and initial seizure propagation. The preoperative evaluation and operative strategy in patients with partial epilepsy of extratemporal origin associated with pharmacoresistant seizures is determined by the anatomic localization of the epileptogenic zone and the presence of a substrate-directed disorder. The goals of surgical treatment in extratemporal epilepsy include rendering the patient seizure-free, avoiding operative morbidity, and allowing the individual to become a participating and productive member of society. Before surgical treatment, the individual with extratemporal epilepsy will require a comprehensive preoperative evaluation, including routine electroencephalogram (EEG), long-term EEG monitoring, neuropsychologic studies, and magnetic resonance imaging (MRI). Patients with a normal MRI study, conflicting preoperative evaluation, or involvement of suspected functional cerebral cortex would require chronic intracranial EEG monitoring. The rationale for intracranial EEG includes localization of the ictal onset zone or intraoperative functional mapping, or both. Two-fluorodeoxyglucose positron emission tomography studies are usually unremarkable in patients with extratemporal epilepsy and normal MRI scans. Subtraction ictal single photon emission computed tomography coregistered to MRI (SISCOM) study may be useful to demonstrate a localized cerebral perfusion alteration in patients with intractable partial epilepsy. The diagnostic yield of SISCOM has been confirmed in patients with extratemporal epilepsy undergoing surgical treatment. The results of the SISCOM study may tailor the placement of intracranial EEG electrodes and affect the operative strategy. Patients with extratemporal epilepsy overall are less favorable operative candidates than individuals with medial temporal lobe epilepsy. However, individuals with MRI-identified lesional pathology of SISCOM-identified perfusion alterations concordant with the epileptogenic zone may be considered for surgical treatment. Chronic intracranial EEG monitoring may be necessary to confirm the localization of the ictal onset zone before epilepsy surgery. Patients with normal neuroimaging studies and extratemporal epilepsy are unlikely to be rendered seizure-free with focal cortical resection and should be considered candidates for other alternative forms of treatment for intractable partial epilepsy. Patients with non-substrate-directed extratemporal epilepsy should undergo a preoperative evaluation and surgical treatment at a comprehensive epilepsy center with extensive experience in chronic intracranial EEG monitoring and contemporary neuroimaging procedures because of the inherently high acuity associated with the operative management clinical disorder.
Cascino
Gregory D.
GD
Division of Epilepsy, Department of Neurology, Mayo Clinic Rochester, 200 First Street, SW, Rochester, MN 55905, USA. gcascino@mayo.edu