CHAPTER 48 Epilepsy Surgery Overview
Neurological surgery has played an important role in the management of patients with epilepsy throughout the history of our specialty.1 The types of operative procedures performed and the indications for surgical intervention have evolved and changed in parallel with technical and scientific advances in multiple related disciplines. The chapters in this section are organized to provide a comprehensive review of these topics and are authored by leading investigators and neurosurgeons in their respective fields. In this introduction to the section on epilepsy surgery we provide a brief overview of the topics that will be covered and the rationale for their inclusion.
The history of epilepsy surgery has been strongly influenced by the dynamic balance between the perceived values of surgical procedures and medical treatments. The risk-benefit calculation for epilepsy surgery is affected by multiple factors, many of which are difficult to rigorously quantify and extrapolate across large patient populations and may not be directly related to the surgical treatment itself. The probability of a seizure-free outcome after surgery, for example, is dependent on the ability to accurately characterize a patient’s seizure disorder.2–6 Thus, technologic advances in nonsurgical disciplines that have an impact on the presurgical evaluation process (e.g., magnetoencephalography [MEG]) have the potential to indirectly alter the surgical risk-benefit assessment. On the medical management side, enormous resources have been committed over a period of many decades to research and develop new antiepileptic drugs (AEDs). In the past, the actual effectiveness of AEDs or the anticipated usefulness of new AEDs in the development pipeline provided a rationale for treating physicians to not explore surgical treatment options.
In the modern era, the epilepsy surgical decision-making calculus has changed significantly. Contemporary clinical reports, including a landmark prospective study of epilepsy surgery versus best medical management for intractable temporal lobe seizures, provide incontrovertible evidence of the safety and efficacy of epilepsy surgery.7–11 It is also now widely accepted that neuronal cell loss occurs with persistent seizures and that uncontrolled epilepsy can be associated with progressive, irreversible loss of brain functions.7,8,12 Hopes that new AEDs would prove to be markedly more effective than older generation drugs have largely been unrealized to date.13,14 The side effects of newer AEDs are better tolerated by some patients, but the complex underlying pathophysiology of refractory seizure disorders continues to resist a medical “magic bullet.” For these and other reasons, it is now widely accepted that patients with intractable seizures should be evaluated for possible epilepsy surgery after a circumscribed period of expert medical management. Persistent seizures should not be tolerated if a viable surgical option exists. The probability of a new drug succeeding in eliminating a patient’s seizure disorder when other drugs have failed is exceedingly low.7,14
Contemporary reviews of bench epilepsy research and experimental animal models are included in this section because of their direct relevance to epilepsy surgery. Much of this research is designed to gain new insights into the neurophysiologic and molecular mechanisms of epilepsy that can be used to develop more effective AEDs. However, information gained from this research also guides the design and implementation of new, nonablative functional neurosurgical applications. As an example, drugs that are demonstrated to disrupt pathologic epileptic circuitry in animal models but have unacceptable side effects when given systemically to humans at the desired concentration could be delivered in a brain site–specific manner by using stereotactically implanted catheters and drug pumps.15,16 Knowledge of the fine details of abnormal epileptic discharges and the effects of precisely timed electrical stimulation of the abnormal medial temporal lobe circuitry set the stage for ongoing clinical trials of patterned electrical stimulation through implanted electrodes as a new neurosurgical treatment.17–19 In these and other examples, the concept of bench-to-bedside translational research has had a direct impact on the treatment of epilepsy patients.
The vast majority of epilepsy surgery procedures are performed at major centers that have the resources to support a comprehensive multidisciplinary program.20 One of the main tasks of this group is to correctly identify patients who will probably benefit from epilepsy surgery. In most instances, neurologists, neuropsychologists, and neuroradiologists gather and perform the primary analysis of the data that are used to make this determination. The epilepsy surgeon, however, must have a thorough understanding of the strengths and limitations of these preoperative examinations. Preoperative evaluation topics are addressed in sections throughout many of the chapters in this section. Technical advances in areas such as functional brain imaging have had an impact on the preoperative evaluation process, with some caveats. One of the most difficult diagnostic challenges is to identify brain activation patterns that typify a patient’s seizure-onset patterns. This necessitates measuring brain activity during a seizure, and in most instances, because of technical constraints, it is not feasible to obtain functional magnetic resonance imaging (fMRI), MEG, or positron emission tomography (PET) data during these ictal events. Functional brain imaging data provide valuable information that influences clinical decision making; however, well-established electroencephalography (EEG)-based diagnostic methods that can be used in both the interictal and ictal states continue to play a preeminent role in the preoperative evaluation process.2,3,21,22
