Long-term video-electroencephalographic (EEG) monitoring may be used to confirm the diagnosis of a seizure disorder, classify seizure-type(s), assess response to therapy, and evaluate patients for surgical treatment of epilepsy.^1–7 In adult patients, video-EEG monitoring (VEM) is mainly used for diagnostic classification (i.e., epilepsy vs nonepileptic spells) and to evaluate surgical candidacy in patients with medically refractory partial seizure disorders. The latter indication is usually restricted to patients with intractable partial epilepsy being considered for a focal cortical resection.¹ VEM is essential in determining the localization of the epileptogenic zone (i.e., the site of seizure onset and initial seizure propagation) in adult patients being considered for surgical ablative procedures.⁶ The high diagnostic yield of VEM in adult patients with recurrent and unprovoked spells has been confirmed.³ Recognition of the ictal EEG pattern may be pivotal in making the diagnosis of epilepsy in such patients. The scalp-recorded interictal EEG study, neurologic history and examination, and current neuroimaging procedures may not always permit appropriate spell classification. The potential disadvantages of video-EEG recordings include the inherent cost of the electrophysiological study and hospitalization and the need for special resources and personnel.³ The ictal EEG patterns may also be difficult to interpret because of myogenic and movement artifacts (e.g., eye blinking). The presence of a subtle epileptiform discharge may be difficult to distinguish from the background. In certain seizure types, for example, auras and simple partial seizures, there may not be a definite scalp-recorded EEG alteration.^1–6,8–11 Finally, patients may not have a typical clinical spell during VEM. The prolonged interictal EEG study may not prove to be a reliable indicator of spell classification.¹²

Partial or localization-related epilepsy is the most common seizure disorder.^1–3 The most frequently occurring seizure type in the adult patient is a complex partial seizure of mesial temporal lobe origin.^1–3 Approximately 45% of patients with partial epilepsy will experience medically refractory seizures that are physically and socially disabling.^12–14 A minority of patients who fail to respond to first-line antiepileptic drug (AED) therapy will be rendered seizure-free with newer medical treatments introduced in the past decade.^15–18 Epilepsy surgery is an effective alternative form of therapy for certain patients with intractable partial epilepsy.^{13,14,19–22} Patients with mesial temporal lobe epilepsy (MTLE) and lesional epilepsy may be favorable candidates for epilepsy surgery and have a surgically remediable epileptic syndrome.^23–26 The majority of these patients experience a significant reduction in seizure tendency following surgical ablation of the epileptic brain tissue.¹⁹ The hallmark pathology of MTLE is mesial temporal sclerosis.^14,26 The surgically excised hippocampus in these patients almost invariably shows focal cell loss and gliosis.^{13,14,16–18} Patients with lesional epilepsy may have a primary brain tumor, vascular anomaly, or malformation of cortical development (MCD).^{19,24,27–29} The common surgical pathologies encountered in patients with lesional epilepsy are a low-grade glial neoplasm, cavernous hemangioma, and focal cortical dysplasia.²⁸

Individuals with mesial temporal sclerosis and lesional pathology almost invariably have an abnormal structural magnetic resonance imaging (MRI) study, and the seizure types are classified as substrate-directed partial epilepsy.²³ The MRI in these individuals may detect a specific intra-axial structural abnormality that may suggest the likely site of seizure onset and the surgical pathology.²³ MRI has a pivotal role in the selection and evaluation of patients for alternative forms of therapy.^14,25,30 The rationale for the presurgical evaluation is to identify the site of ictal onset and initial seizure propagation (i.e., epileptogenic zone) and to determine the likely pathologic findings underlying the epileptic brain tissue.²³ In patients with an MRI-identified foreign tissue lesion or unilateral mesial temporal sclerosis, the purpose of the electroclinical correlation is essentially to confirm the epileptogenicity of the structural abnormality.²⁵ The demonstration of concordance between the pathologic substrate and the ictal onset zone indicates a highly favorable operative outcome in select individuals.

Approximately 80% of patients with unilateral mesial temporal sclerosis, a low-grade glial neoplasm, or a cavernous hemangioma are rendered seizure-free following surgical treatment.¹⁹ Over 90% of patients with these pathologic findings will experience an excellent surgical outcome (i.e., auras only or rare nondisabling seizures).¹⁹ The operative outcome is distinctly less favorable in individuals with focal cortical dysplasia and other MCDs.²⁹

The most common operative strategy in patients with intractable partial epilepsy involves a focal cortical resection of the epileptogenic zone with an excision of the surgical pathology.^19,20 The goals of surgical treatment are to render the individual seizure-free and allow the patient to become a participating and productive member of society.^19,20

The seizure types in patients with localization-related seizure disorders and normal MRI studies are classified as non-substrate-directed partial epilepsy²² (Figure 33-1). The anatomical localization of the epileptogenic zone in these individuals commonly involves the neocortex (i.e., extrahippocampal)^22,31 (Figure 33-2). The most frequent site of seizure onset in patients with neocortical nonlesional partial epilepsy is the frontal lobe.²² The surgical pathology in these patients includes gliosis, focal cell loss, MCD, and no histopathological alteration.²² The MRI rarely may be indeterminate in some lesional pathology (e.g., focal cortical dysplasia).²⁹ Only a minority of patients with neocortical, extratemporal seizures are rendered seizure-free following surgical treatment.^22,31 An estimated 20 to 30% of these patients with extratemporal, mainly frontal lobe, seizures will enter seizure remission following a focal cortical resection.²² An important reason for the unfavorable operative outcome in patients with non-substrate-directed partial epilepsy is the inherent difficulty in identifying the epileptogenic zone. The potential limitations of interictal and ictal extracranial and intracranial EEG monitoring in patients with partial seizures of extratemporal origin have been well defined.^31,32 The anatomical region of seizure onset may represent a continuum in these patients that lends itself to an incomplete focal resection of the epileptogenic zone. A large resection increases the likelihood of rendering the patient seizure-free, but it also increases the potential for operative morbidity.³¹Advances in peri-ictal imaging (see below) have assisted the selection of operative candidates with non-substrate-directed partial epilepsy, altered the preoperative evaluation, and tailored the surgical excision.^32–36

The outpatient scalp-recorded EEG (routine EEG) is the most commonly performed diagnostic study obtained in the evaluation of patients with presumed seizure disorders.⁸ The potential limitations of the routine EEG study have been identified. The sleep and wake routine EEG recording is brief in duration, predominantly observes interictal EEG changes, and may be altered by the presence of AEDs.^10–12 The outpatient routine EEG study almost invariably records interictal EEG alterations (as opposed to an ictal EEG pattern) because of the intermittent nature of seizure activity.¹² The interictal EEG pattern also may be an unreliable indicator of the classification of seizure type and result in ineffective treatment strategies.¹² The routine EEG may be insensitive (i.e., fail to identify epileptiform discharges) and yield nonspecific findings. Paroxysmal alterations (either nonspecific or potentially epileptiform discharges) may be identified in a patient with nonepileptic behavioral events.^10,12 Patients with seizure disorders, even medically refractory epilepsy, may have repetitive “normal” interictal EEG studies.¹⁰ The adult “oligospikers” or “hypospikers” with epilepsy may be more likely to have a partial seizure disorder of extratemporal origin.¹² Interictal epileptiform activity may prove satisfactory in many instances for classifying the seizure type.⁸ The sensitivity and specificity of ictal EEG, however, is superior as a diagnostic tool to interictal EEG.^8,10–12 Performing standard provocative maneuvers (e.g., hyperventilation and photic stimulation) and obtaining a sleep recording may increase the diagnostic yield of the routine EEG.^2,8 Supplementary electrodes (e.g., sphenoidal or additional scalp electrodes) may provide additional information regarding the localization of the epileptic brain tissue.¹¹

Surgical Localization

VEM is performed in individuals with pharmacoresistant partial epilepsy for surgical localization.¹¹ Identification of a potential surgical candidate is a major indication for VEM in highly select patients with physically, socially, and medically disabling seizures.^{11,12,37–39} Surgical treatment has been shown to be safe and effective for select patients with intractable partial epilepsy.^36,40 The putative beneficial effect of surgery is an improvement in the quality of life that allows the individual to become a participating and productive member of society.³⁶ Surgical treatment for intractable temporal lobe epilepsy has been demonstrated to be more effective than medical therapy.²⁰

Identification of patients for epilepsy surgery requires a comprehensive, multidisciplinary evaluation.^28,31,37,39 A convergence of diagnostic studies is required to determine the localization of the epileptogenic zone, the underlying pathology, and the likely operative outcome. Invariably, patients undergo extracranial ictal EEG monitoring, neuropsychological studies, visual perimetry, and a sodium amobarbital study^28,31,37,39 (Figure 33-3). The above evaluation may be used to counsel and guide the patient concerning the selection of an alternative form of treatment for partial epilepsy.

Subsequent to admission to the epilepsy monitoring unit, the patient’s characteristic seizure activity is observed.³⁷ Multiple clinical events may need to be recorded prior to making a determination of the site

of seizure onset.¹¹

Examination of the patient during the ictus by trained personnel may be important to determine the presence of a peri-ictal neurologic abnormality. This may indicate the lateralization and localization of the epileptic brain tissue. Single-photon emission computed tomography (SPECT) has been used in patients with intractable partial epilepsy to identify a cerebral perfusion alteration that may indicate the localization of the epileptic brain tissue.^32–36 Peri-ictal functional neuroimaging procedures can be performed during ictal EEG monitoring to identify a potential functional zone that corresponds to the site of seizure onset. Innovative techniques that allow co-registration of a functional imaging alteration with structural MRI have now been introduced and validated.^32–36 There is a consensus that ictal SPECT studies are more sensitive and specific than interictal examinations for lateralizing the site of seizure onset.³⁸ Computer-aided subtraction of the interictal from the ictal SPECT images followed by co-registration to the MRI (SISCOM) is a recent development that has been shown to be diagnostically superior to routine visual inspection of the interictal and ictal scans.^32–36 Patients with SISCOM images that revealed a localized abnormality were more likely to experience an excellent outcome following epilepsy surgery than individuals with nonconcordant or nonlocalizing findings (p < .001)³² (Figure 33-4).