Description of the condition
Epilepsy is defined by the International League Against Epilepsy as "a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain" (Fisher 2005). It is a common condition with a prevalence of around 1 in 200 people. Despite optimal pharmacotherapy, about 20% to 30% of individuals do not become seizure-free (Annegers 1979; Collaborative 1992; Cockerell 1995; Kwan 2000). For some of these people, surgery is a therapeutic option.
Description of the intervention
The intervention involves the localisation of the epileptogenic focus and then, if the potential benefit is assessed to outweigh the risk, its surgical resection. The first surgical intervention for focal epilepsy is attributed to Victor Horsley in 1886. Techniques for localising epileptogenic foci initially relied on detailed analysis of seizure semiology and comparison with animal data. Techniques for temporal lobe surgery were developed by Penfield and Jasper later refining these techniques to more limited resections of the antero-mesial temporal lobe. In the second half of the twentieth century, more refined techniques were developed using cortical mapping and imaging, initially with computerised tomography, latterly with magnetic resonance imaging (MRI) and most recently with single photon emission computed tomography (SPECT) and positron emission tomography (PET) (Feindel 2009).
Success of resective epilepsy surgery is estimated to have increased from 43% to 85% during the period 1986 to 1999 (National 1990a; Engel 1993; Engel Jr 2003). Data from multiple sources suggest that 55% to 70% of individuals undergoing temporal resection and 30% to 50% of individuals undergoing extratemporal resection become completely seizure-free. A prospective randomised controlled trial of surgery for temporal lobe epilepsy showed that 58% of individuals randomised to surgery were seizure-free compared to 8% of the medical group (Wiebe 2001).
Surgery is considered a valuable option for medically-intractable epilepsy, even in the absence of proven drug resistance (Engel Jr 1993).
How the intervention might work
The rationale of the intervention is the initial localisation of the epileptogenic focus and then its surgical resection.
Why it is important to do this review
Surgical outcomes may be greatly influenced by the presence of selected prognostic indicators (Tonini 1997; Berg 1998). However, there are still uncertainties about which patients are most likely to achieve good surgical outcomes. Good surgical outcomes appear to be associated with a number of factors (hippocampal sclerosis, anterior temporal localisation of interictal epileptiform activity, absence of preoperative generalised seizures, and absence of seizures in the first post-operative week) (McIntosh 2001). However, the published trial results are frequently confusing and contradictory, thus preventing inferences for clinical practice. This will be the first Cochrane review to look at these factors. It will complement the only systematic review to date which was performed by Tonini et al in 2004, and is therefore now out of date (Tonini 2004). It will inform the surgical selection process and allow the refinement of the risk/benefit analysis for surgical intervention.