Chapter 51 - Neuroimaging of epilepsy

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Abstract

Imaging is pivotal in the evaluation and management of patients with seizure disorders. Elegant structural neuroimaging with magnetic resonance imaging (MRI) may assist in determining the etiology of focal epilepsy and demonstrating the anatomical changes associated with seizure activity. The high diagnostic yield of MRI to identify the common pathological findings in individuals with focal seizures including mesial temporal sclerosis, vascular anomalies, low-grade glial neoplasms and malformations of cortical development has been demonstrated. Positron emission tomography (PET) is the most commonly performed interictal functional neuroimaging technique that may reveal a focal hypometabolic region concordant with seizure onset. Single photon emission computed tomography (SPECT) studies may assist performance of ictal neuroimaging in patients with pharmacoresistant focal epilepsy being considered for neurosurgical treatment. This chapter highlights neuroimaging developments and innovations, and provides a comprehensive overview of the imaging strategies used to improve the care and management of people with epilepsy.

Section snippets

Computed tomography (CT)

CT has the advantage of being available in most hospitals worldwide and has a relatively low operating cost. In addition, the logistics of CT make it easier for unstable patients as compared to MRI. CT can detect most tumors (except for some low-grade tumors), large arteriovenous malformations and extensive brain malformations, stroke, and infectious lesions. CT is sensitive for detection of calcified lesions and bone lesions, while MRI often misses these. CT has low sensitivity for detecting

When to perform an MRI in a patient with seizures

All patients with epilepsy should undergo an MRI, except those with very typical forms of primary generalized epilepsy (e.g., juvenile myoclonic epilepsy, childhood absence) or benign focal epilepsies of childhood with characteristic clinical and EEG features (e.g., benign epilepsy with centrotemporal spikes, early-onset childhood epilepsy with occipital spikes (Panayiotopoulos type)) and adequate response to antiepileptic drugs (AEDs) (Commission on Neuroimaging of the International League

How to perform an MRI in patients with epilepsy

The epileptogenic lesion may be detected using routine MRI protocols. However, routine MRIs often miss smaller or subtle lesions and are considered normal. Therefore, in these cases, an optimized epilepsy protocol with adequate spatial resolution and multiplanar reformatting is essential (Gaillard et al., 2011, Cendes, 2013).

A proper MRI investigation of patients with focal epilepsy requires the use of specific protocols, selected based on identification of the region of onset by clinical and

MRI in mesial temporal-lobe epilepsy

In MTLE, EEG findings, clinical history, and neuroimaging findings are important to define the diagnosis. Although there are other etiologies that cause TLE, HS is the most common pathologic substrate. MTLE with HS is often associated with a precipitating injury such as complex febrile seizures, birth trauma, meningitis, or head injury that happens in early life. A latent period of several years may precede dyscognitive seizures (previously known as complex partial seizures) (Cendes et al., 2014

Epilepsy due to neocortical lesions

MRI investigation will detect most common lesions causing neocortical epilepsy, which are: low-grade tumors, malformations of cortical development, posttraumatic and postischemic lesions, inflammatory infectious scars, cavernous malformations, and arteriovenous malformations. However, routine MRI may be unremarkable, particularly in some forms of malformations of cortical development. In these cases, multimodal imaging techniques can be useful for localizing suspected lesions. Among the

Focal cortical dysplasia

Refractory epilepsy, particularly in childhood, is often associated with malformations of cortical development, especially FCD. Many patients have seizures refractory to medication and are candidates for surgical treatment. However, not all patients with malformations of cortical development present with refractory epilepsy (Barkovich et al., 2012).

FCD is characterized by disorganization of the cortical lamination associated with bizarre (dysplastic) neurons or cells with eosinophilic cytoplasm

Diffusion tensor imaging and tractography

DTI data provide information regarding the direction of the diffusion of water in each voxel, which can be used to estimate the orientation of white-matter tracts. Based on this information, it is possible to trace major myelinated tracts (tractography), offering additional information for surgical approach; for example, it can be used for visualization of the optic radiation and for predicting visual field deficits after surgery (Winston et al., 2011). In addition, DTI allows other

Magnetic resonance spectroscopy (MRS)

Proton-MRS assesses neuronal integrity by quantifying the peak of N-acetyl-aspartate (NAA), a marker of neuronal integrity, usually by comparing its concentrations with choline or creatine peaks. Unlike MRI, SPECT, and PET techniques, the entire brain is not included in typical MRS measurements and often only a few relatively large voxels are sampled with proton MRS (Cendes et al., 2002). The relatively poor signal-to-noise ratio of proton MRS and the relatively long time required to obtain

Positron emission tomography

The role of PET, particularly using 18F-FDG, is well established. In addition to seizure focus localization, PET has been used for cognitive studies (now superseded by functional MRI), investigation of comorbidity, particularly psychiatric disorders, and investigations of neurotransmitter receptor binding. These studies may be important both for focus localization and understanding the pathophysiology of epilepsy. Coregistration with MRI has become standard for PET studies in epilepsy.

Single-photon emission computed tomography

SPECT has been proven as a useful tool in epileptogenic zone localization. The development of multimodal coregistration and also comparison of ictal SPECT images with a control group have ensured its clinical relevance. Ictal SPECT provides a unique window of opportunity to look at cerebral perfusion during seizure. Seizure activity dramatically increases brain metabolism and cerebral blood flow (CBF) in the epileptic focus during seizure initiation and propagation. Intravenous injection of

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