Imaging for Epilepsy Surgery

Abstract

Approximately 20 to 30% of patients with epilepsy are considered drug refractory, 1 defined by the International League Against Epilepsy (ILAE) as the persistence of seizures despite adequate trials of two well-tolerated and appropriately chosen anti-epileptic drugs (AEDs) under the supervision of an experienced neurologist over the course of at least 1 year. 2 This population represents the potential pool of candidates for surgical treatment, but not all of these patients are amenable to resective surgery. Successful surgical intervention for epilepsy requires a thorough investigation to identify those patients with clearly localizable epileptic foci, with the goal being freedom from seizure with no permanent neurologic deficits.The goal of any presurgical evaluation in a patient with drug-resistant epilepsy is to identify a localized region of epileptic cortex and subsequently resect or disconnect that abnormal cortex. The initial investigation relies on a detailed clinical history and neurologic exam with consultation of both the patient and family members who have witnessed the seizures of the patient. The presence of auras, semiology, and timing of seizures are vital pieces of knowledge that inform seizure onset localization. Signs and symptoms, suggestive of a focal seizure onset, are further investigated through long-term video electroencephalogram (EEG) monitoring. Additional testing may include behavioral evaluation and neuropsychological testing. Various neuroimaging techniques are also employed to identify structural and/or metabolic abnormalities that may be the source of the seizures. 3 In the perfect scenario, all data streams are concordant with ictal EEG, confirming that the clinical seizures do indeed arise from a clearly identified cortical region. However, in many cases, there remains some level of discordance in the functional and anatomic seizure localizations, and in these situations, invasive intracranial investigation with implanted electrodes may also be necessary to determine the precise zone of seizure onset.Most focal epilepsy arises in the temporal lobe, notably the mesial temporal lobe, followed by the frontal, parietal, and occipital lobes. 4 In some cases, the epileptic zone is multilobar or even panhemispheric. In cases of clear cut mesial temporal sclerosis (MTS), between 65 and 85% of patients are cured of epilepsy following resection. 5,6 Surgical success is much less predictable when bilateral MTS is present or when no identifiable temporal lobe lesion exists. This is even true in the extratemporal epilepsies. The most important predictor of a favorable surgical outcome is the identification of a clear cut structural lesion that is consistent with the clinical semiology of the seizures and the ictal EEG onset. 7 Therefore, advanced neuroimaging techniques have become increasingly important in identifying and defining epileptogenic lesions that might previously have gone undetected. Keywords AbstractSuccessful epilepsy surgery requires accurate localization of the zone of seiz...

Comparison between simultaneously acquired arterial spin labeling and 18F-FDG PET in mesial temporal lobe epilepsy assisted by a PET/MR system and SEEG

“…During presurgical evaluation of mesial temporal lobe epilepsy (MTLE), a significant relationship between treatment outcome and accuracy in identifying the epileptogenic zone has been recognized ( Hardy et al, 2003 ). Conventional non-invasive presurgical evaluation includes semiology, electroencephalography (EEG), structural imaging, and functional imaging ( Chavakula and Cosgrove, 2017 ; Duncan, 2010 ; Fisher et al, 1997 ; Rosenow and Luders, 2001 ). In recent years, 18 F-fluorodeoxyglucose positron emission tomography ( 18 F-FDG PET) has been considered as the leading functional imaging option for presurgical evaluation during the interictal phase, particularly in patients with structural imaging-negative refractory epilepsy.…”

A Standardized Electrode Nomenclature for Stereoelectroencephalography Applications

“…Noninvasive investigations prove sufficient to adequately localize the seizure focus and guide definitive treatment in many cases. 14 However, in approximately 20% of cases either a clear structural abnormality cannot be detected on imaging, or scalp recordings do not clearly establish a corroborating focal seizure origin. 15,16 In such cases, invasive monitoring with intracranial recordings may be considered.…”