Surgery for epilepsy

Cochrane: Focal epilepsies are caused by abnormal electrical discharges in specific (localised) parts of the brain. In most people the resulting epileptic seizures can be controlled with medication. In up to 30% of people these seizures are not controlled by medication. If the site of origin of these signals (the epileptogenic zone) can be located from the description of the seizures, or from magnetic resonance imaging (MRI) (a medical imaging scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body) and electroencephalography (EEG) findings (recording of electrical activity along the scalp) the person should be offered the chance of having the epileptogenic zone removed. We studied the factors (characteristics of the people undergoing surgery and details of surgery type) that might be linked to the best chance of surgical cure of epileptic seizures.


We examined evidence from 177 included studies reporting the experience of 16,253 people of all ages. In total, 10,518 people (65% of the total who had surgery in all studies) experienced a good outcome from surgery, defined as freedom from epileptic seizures.

One randomised controlled trial (RCT) established the superiority of surgery over continuing to try different medication in drug-resistant (intractable) epilepsy for the individuals in this trial. Three RCTs compared different types of surgery. No difference in seizure outcome was found in two trials; one removing 2.5 cm or 3.5 cm of the anterior temporal lobe (ATL, a part of the brain in which the epileptogenic zone is often located) or surgically removing the ATL with or without an additional procedure to sever the nerves that connect the two halves (hemispheres) of the brain. In the third trial, completely removing the hippocampus (a part of the brain in which the epileptogenic zone is often located) was found to be superior to only removing part of the hippocampus.

Most of the studies in this review were poor quality and had a retrospective design (a design where individuals are recruited after the result of surgery has been recorded, which looks back for the existence of factors related to the result of surgery). They used variable surgical approaches for different sites of the brain, different processes to select candidates for surgery, different definitions of freedom from seizures after surgery and measured these outcomes at varying points. Fewer than half the studies gave details of complications and deaths associated with surgery.

We identified some factors that predicted a better outcome from surgery. These were: a well-defined lesion (abnormality) on the MRI scan that corresponded with what was expected from the description of the seizures and the EEG findings, complete surgical removal of the lesion and a history of febrile seizures (a seizure associated with fever in a young child) often associated with mesial temporal sclerosis (scarring in the inner portions of the temporal lobe of the brain). More diffuse (spread out) brain abnormalities that might be associated with brain injury (from trauma or otherwise) or an abnormality of brain development were not associated with a good outcome. The presence of such abnormalities is often associated with a need to embark on more detailed pre-operative investigations including intracranial (inside the skull) EEG monitoring. We would have liked to examine the collective effect of these factors (i.e. what would be the effect on outcome if a person has a history of febrile seizures, trauma and an MRI lesion altogether), however the studies did not report enough information to allow this.

We recommend that future studies should have a prospective design (a design where individuals are recruited before surgery has taken place, which identifies factors of interest before surgery and follows up individuals after surgery to record the outcome). Studies should examine the collective effect of factors that may predict the outcome of surgery using appropriate statistical methods. Future studies should use pre-operative investigations to guide the selection of the best candidates for surgery and the best surgical approach, use clearly defined methods to measure the result of surgery at specific time points and include pre- and postoperative cognitive and mental state assessment. Deaths during or after surgery, and complications and side effects from surgery, should be clearly recorded.

Authors' conclusions:
The study design issues and limited information presented in the included studies mean that our results provide limited evidence to aid patient selection for surgery and prediction of likely surgical outcome. Future research should be of high quality, have a prospective design, be appropriately powered and focus on specific issues related to diagnostic tools, the site-specific surgical approach and other issues such as the extent of resection. Prognostic factors related to the outcome of surgery should be investigated via multivariable statistical regression modelling, where variables are selected for modelling according to clinical relevance and all numerical results of the prognostic models are fully reported. Protocols should include pre- and postoperative measures of speech and language function, cognition and social functioning along with a mental state assessment. Journal editors should not accept papers where adverse events from a medical intervention are not recorded. Improvements in the development of cancer care over the past three to four decades have been achieved by answering well-defined questions through the conduct of focused RCTs in a step-wise fashion. The same approach to surgery for epilepsy is required.