Neurosurgical Interventions for Encephalitis-Related Seizures and Epilepsy

Encephalitis, an inflammatory process involving the brain, has a variety of etiologies, including viral and autoimmune. Clinically, seizures frequently occur at the acute stage of encephalitis but may recur as a sequela in the late stage following resolution (postencephalitic epilepsy). In the acute stage of disease, the direct infectious or noninfectious damaged lesion is the major cause of seizures, showing serious evolution to status epilepticus. Epileptogenesis in the late stage may involve chronic inflammatory processes triggered by the immune response as well as postinsult neurodegenerative changes. Encephalitis-related seizures in both stages are highly resistant to conventional antiepileptic drugs, and additional medical management with antiviral or immunomodulatory therapy is currently used depending on the etiology and disease stage. Despite such medical management, seizures may remain refractory and markedly impact the daily activities of patients. Surgical interventions should be considered under such circumstances. To date, surgical treatments have been performed mainly for postencephalic epilepsy and a specific form of autoimmune encephalitis known as Rasmussen encephalitis. Conventional resective surgery is beneficial for patients with focal epileptogenic lesion, but the postoperative seizure-free rate is lower than for those with other etiologies (approximately 40% vs. 70%, respectively). In patients with Rasmussen encephalitis, hemispheric surgery including hemispherectomy and hemispherotomy results in the best outcome, with a seizure-free rate of 65%–80%, while its feasibility is determined by neurologic condition (i.e., degree of hemiparesis and language disability). Palliative surgeries including callosotomy and vagus nerve stimulation may be available for patients not meeting the indications for resective surgery. Neurosurgical interventions in the early stage of encephalitis are still less established but can be considered under the limited situation of refractory status epilepticus. Timing for those neurosurgical interventions should be considered based on the etiology, pathophysiology, stages, clinical condition, and effect of medical management.