Epilepsy
Advanced Neuroimaging for Modern Epilepsy Surgery Doris D Wang,1
Carlos Santos-Sanchez,2 Paul A Garcia3 and Edward F Chang4
1. Resident, Department of Neurological Surgery and Comprehensive Epilepsy Center; 2. Junior Specialist, Comprehensive Epilepsy Center and Department of Neurology; 3. Professor of Clinical Neurology, Comprehensive Epilepsy Center and Department of Neurology; 4. Assistant Professor of Neurological Surgery and Physiology, Department of Neurological Surgery and Comprehensive Epilepsy Center, University of California, San Francisco
Abstract
Localising the onset of seizures to guide epilepsy surgery can be notoriously difficult. Modern neuroimaging has revolutionised the field by improving the diagnosis and treatment of epilepsy. In order to ameliorate seizures without causing new neurological morbidity, many imaging tools have been developed to guide safe and effective resective surgery. In this article, we discuss recent advances in structural imaging using ultrahigh-field magnetic resonance imaging, metabolic functional imaging techniques of positron emission tomography and single photon emission computed tomography and electrophysiological imaging using magnetoencephalography. Our goal is to provide an overview of these state-of-the-art imaging modalities, their role in guiding surgery, and how they are incorporated into the pre-surgical evaluation of epilepsy.
Keywords
Epilepsy, imaging, neuroimaging, magnetic resonance imaging, single photon emission computed tomography, positron emission tomography, magnetoencephalography, magnetic source imaging, electroencephalography, epilepsy surgery, temporal lobe epilepsy, malformation of cortical development, outcome
Disclosure: The authors have no conflicts of interest to declare. Acknowledgements: The authors would like to acknowledge Christopher Hess and Pratik Mukherjee from the Department of Radiology as well as Spencer Behr from the Department of Nuclear Medicine for interpretation of imaging studies. The authors would also like to acknowledge the Journal of Neurosurgery and the American Association of Neurological Surgeons for permission to reproduce printed material for the purpose of this publication. Received: 1 November 2011 Accepted: 5 December 2011 Citation: European Neurological Review, 2011;6(4):257–61 Correspondence: Edward F Chang, Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Avenue, Box 0112, San Francisco, CA 94143-0112, US. E:
changed@neurosurg.ucsf.edu
When neurosurgeons first attempted to treat epilepsy by means of surgery in the late 1800s, they were operating on ‘invisible’ lesions. Without any imaging or electrophysiological technology, MacEwen and Horsley operated under the principles of functional cerebral localisation developed largely by John Hughlings Jackson.1
Epilepsy surgery has
come a long way, as now epileptologists and neurosurgeons are armed with a battery of tools for diagnosis and treatment of epilepsy. These tools have fundamentally changed the way we study and treat this enigmatic disease. Epilepsy is one of the most common diseases affecting the central nervous system, with a prevalence of 0.5 % and a lifetime cumulative incidence of about 3 %.2
Of those with epilepsy,
about 40–50 % become medically refractory, causing significant impairment to quality of life and increased morbidity, mortality, and healthcare costs. Among these medically refractory cases of epilepsy, many patients are candidates for surgical intervention, which can achieve freedom from seizures in up to 70–80 % of patients.3,4
The goal
of epilepsy surgery is to resect the epileptogenic foci in order to stop or reduce seizure burden without causing significant motor, speech, or cognitive impairments in the patient and, therefore, to improve the patient’s quality of life. In this article, we discuss advances in imaging techniques used in epilepsy surgery. These techniques include structural imaging techniques with magnetic resonance imaging (MRI), volumetric-based analysis, and high-resolution MRI to assess lesional causes of epilepsy. We also discuss functional imaging modalities that detect changes in brain metabolism during the
© TOUCH BRIEFINGS 2011
ictal and interictal period, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). Finally, we discuss the electrophysiological imaging technique magnetoencephalography (MEG) and its role in the identification of epileptogenic regions in the brain. Imaging is no longer limited to a mere static representation of the brain to acquire structural abnormalities. These new imaging modalities have been developed to capture dynamic brain functions and to yield crucial information about abnormal and normal brain activity. Together, these imaging techniques and future developments will continue to improve our understanding and treatment of epilepsy.
Structural Imaging Temporal Lobe Epilepsy
MRI has become standard practice for any pre-surgical evaluation for epilepsy surgery. MRI can detect relevant structural abnormalities in 85 % of patients with refractory partial seizures who are candidates for surgical treatment.5
The most common focal structural abnormality detected using MRI is mesial temporal sclerosis (MTS), or hippocampal sclerosis, which is commonly found in patients with temporal lobe epilepsy (TLE). Classic findings of mesial temporal sclerosis include atrophy of the hippocampus and amygdala with increased signal on T2-weighted or fluid-attenuated inversion recovery (FLAIR) images (see Figure 1A).6,7
We now recognise that subtle cases of MTS may manifest exclusively as indistinct architectural features within the affected
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