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  • Updated 11.04.2008
  • Released 02.18.2005
  • Expires For CME 11.04.2011

Epilepsy surgery in adults

Introduction

Overview

Epilepsy surgery continues to expand in clinical use as an effective treatment for correctly selected patients with medically intractable and disabling focal epilepsy. In a broad overview, the authors discuss the history of epilepsy surgery, its scientific basis, indications, presurgical evaluation, and surgical approaches for both mesial temporal lobe epilepsy and neocortical focal epilepsies. Though resective epilepsy surgery has become an important conventional treatment option, it continues to be underutilized. This review details expected postoperative seizure control and quality-of-life outcomes, showing quantitatively how epilepsy surgery benefits patients. Updates include new data on postoperative outcomes for resective epilepsy surgery, emphasizing results from the ongoing prospective Multicenter Study of Epilepsy Surgery. New information about seizure control after operative treatment of epileptogenic cavernous malformations is also discussed. Other updates concern the novel presurgical diagnostic modality of simultaneous electroencephalography and functional magnetic resonance imaging, currently developing in its clinical utility.

Historical note and terminology

Early epilepsy surgery. Epilepsy surgery for focal seizures began more than a century ago and progressed with the technical innovations of EEG and neuroimaging. In the 1860s and 1870s, the pioneering clinical work of the epileptologist John Hughlings Jackson laid the groundwork for understanding the cortical localization of focal epilepsies, while the animal experiments of the neurophysiologists Gustav Theodor Fritsch, Eduard Hitzig, and David Ferrier gave parallel confirmation of Hughlings Jackson’s conclusions (112). The “beginning of modern epileptology” has been dated to the 1870 publication of Hughlings Jackson’s article "A study of convulsions," in which he stated that focal motor seizures originate in the contralateral cerebral cortex or underlying striatum and not in the medulla, the previously accepted site of origin (38). The experimental work of the surgeon and physiologist Victor Horsley in turn was predicated on and also contributed to Hughlings Jackson’s explication of certain seizure propagation mechanisms (37).

In the 1870s and 1880s, the first documented resections for epilepsy were performed, making use of newly formulated cortical localization principles (112). In 1879 the surgeon William Macewen correctly localized and resected a frontal mass in an epileptic patient in Glasgow; the patient survived removal of the meningioma and his seizure disorder was cured (86; 112). In 1884 the neurologists Jackson and Alexander Hughes Bennett localized a putative mass in another epileptic patient; the surgeon Rickman Godlee successfully resected the underlying tumor found at their hypothesized site (13; 112).

In 1886 Victor Horsley publicly presented his guidelines for antiseptic and hemostatic brain surgery in humans at the British Medical Association annual meeting, focusing on 3 cases of young men subject to “fits” (140). His lecture consisted of a detailed description of 3 epilepsy surgery cases. Jackson, on whose patient Horsley had operated, was in the audience and advised the conference attendees that surgery should be performed for seizures even in the absence of a mass lesion. Hughlings Jackson’s comments were paraphrased in the 1886 publication of Horsley’s lecture: “Believing that the starting point of the fit was a sign to us of the seat of the ‘discharging lesion,’ he [Hughlings Jackson] would advise cutting out that lesion, whether it was produced by tumour or not” (Horsley 1886). Hughlings Jackson was in fact recommending the resection of what was later to be called “the epileptogenic zone,” regardless of the presence of structural abnormality.

Electrical stimulation brain mapping. Electrical stimulation to reproduce seizure semiology and to map functional cortex has been crucial to the development of epilepsy surgery. In 1870 Fritsch and Hitzig were the first physiologists to stimulate the cerebral cortex of animals. In 1874 Bartholow extrapolated this technique to the human brain when he treated a 30-year old woman whose brain abscess had eroded through her skull (09; 16). Horsley used electrical stimulation mapping of the motor cortex first in nonhuman primates and then in human patients to guide his neurosurgical operations. In the 1920s Wilder Penfield learned this technique from Otfrid Foerster in operations on patients with posttraumatic epilepsy due to World War I gunshot wounds to the head (56; 32). After Penfield founded the Montreal Neurological Institute in 1934 for the study of the science and surgery of epilepsy, he and his colleagues extended the use of electrical stimulation in the human to map cognitive functions such as language and memory (103; 105).

Advances in localization. In the era before modern imaging, the innovation of preoperative and intraoperative EEG allowed the epilepsy surgeon both to localize an underlying intracranial lesion and to target a nonlesional epileptogenic zone with greater accuracy than clinical semiology had permitted. Human EEG was first reported in 1929 by Hans Berger, following Richard Caton’s extensive electrophysiologic recordings from animals (112). The neurologist Herbert Jasper introduced the use of EEG at the Montreal Neurological Institute in 1937 and established an EEG laboratory there in 1939, where techniques of intraoperative electrocorticography were developed (54). During the 1930s through the 1950s, Penfield and Jasper studied different techniques to optimize operations for epilepsy and systematically demonstrated that resection of epileptogenic tissue benefited patients (105; 156).

In the 1950s and 1960s, Bancaud and Talaraich improved localization of the epileptogenic zone by recording from stereotactically implanted depth electrodes, and Crandall and Walker further advanced this work (08; 16). In the 1980s, Spencer, Spencer, and colleagues described the stereotactic placement of multicontact depth electrodes, which are currently used both for the presurgical identification of ictal onset regions and for basic neuroscience investigation with microelectrodes and microdialysis probes (131; 36; 59; 74; 159; 40). With the advent of modern neuroimaging, in particular with routine clinical use of MRI beginning in the 1980s, radiographic visualization of previously occult structural lesions has improved patient selection and presurgical planning for epilepsy surgery. The development of clinically useful nuclear imaging studies such as interictal 18F-FDG-PET and ictal SPECT contributed further to localization (45; 46). At present, techniques such as MEG and fMRI are being optimized for clinical application to operative planning for epilepsy surgery to continue to improve localization (112; 39; 01; 113).

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