The role of neuroimaging in epilepsy

Abstract

Neuroimaging examines the relationship between abnormalities of brain function in epilepsy patients (seizures, impaired cognitive function, psychiatric co-morbidity etc.) and focal or more widespread brain pathology. Since the mid-1980s, the introduction of magnetic resonance imaging (MRI) into clinical neurology has had an impact on the diagnosis, treatment, and research of epilepsy only comparable with the advent of the electroencephalography (EEG) fifty years ago. MRI plays the important role of identifying single or multiple structural lesions responsible for the epileptic seizures. Thus, visual assessment of MRI plays an important role in the differentiation between symptomatic, cryptogenic, and idiopathic epilepsies. This diagnostic step leads to therapeutic decisions (medical treatment vs. surgery) and prognostic evaluations. If a structural lesion identified with MRI correlates with seizure-type, EEG and other clinical data, the likelihood of rendering the patient seizure free with epilepsy surgery is increased. Clinical research into epilepsy uses quantitative MRI (volumetry, T2-relaxometry, magnetic resonance spectroscopy [MRS], voxel-based morphometry) to reduce those cases initially labeled as cryptogenic. Quantitative MRI questions the belief that there is epilepsy without structural brain abnormality at all. Functional MRI (fMRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT) demonstrate changes associated with epileptic seizures and pathology, and changes associated with EEG abnormalities and their cessation. Functional neuroimaging is also used for the identification of functional brain tissue before surgery. Physiologically or pathologically active neuronal tissue is believed to be identified by glucose or oxygen consumption (PET), cerebral blood flow (PET, SPECT, perfusion MRI), and cerebral blood oxygenation (blood oxygenation level dependent [BOLD] fMRI). PET also offers the opportunity to visualize the in-vivo distribution of neuronal receptors which are implicated in the generation, the spread, and the cessation of seizures.

Multi-voxel magnetic resonance spectroscopy at 3T in patients with idiopathic generalised epilepsy

“…( 1 H-MRS) give non-invasive insights to diverse functional and structural alterations in patients with neurological disorders as epilepsy. [1][2][3][4][5][6][7][8][9] The multi-voxel technique refers to chemical shift imaging (CSI) which combines features of MR imaging and spectroscopy yielding data from multiple adjacent voxels eventually covering the whole brain. 10-12 1 H-MRS performed at a higher magnetic field strength as 3 T has the advantages of higher signalto-noise ratio (SNR) and improved spectral resolution in clinically acceptable scan times.…”

Hippocampal atrophy in temporal lobe epilepsy is correlated with limbic systems atrophy

“…Magnetic resonance imaging (MRI) based region of interest (ROI) analyses such as volumetry can provide a reliable quantification of hippocampal atrophy [26,39,45]. More recently, automated, MRI based estimation of gray matter amount throughout the entire brain using voxel-based morphometry (VBM) has proven to be a sensitive tool with which to detect hippocampal atrophy in patients with TLE and also to detect gray matter atrophy in other brain regions in patients with extratemporal epilepsy [23,24,28,31,46,47].…”