Imaging Criteria to Identify the Epileptic Focus: Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, Positron Emission Tomography Scanning, and Single Photon Emission Computed Tomography

Mesial temporal lobe epilepsy with hippocampal sclerosis: study of 42 children

PURPOSE

We present the electroclinical features, treatment, and evolution of patients with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS).

MATERIAL AND METHODS

We analyzed the charts of forty-two patients who met the diagnostic criteria of MTLE-HS. The mean follow-up after seizure onset was 10.5 years.

RESULTS

According to age, we defined three groups. The first group included nine patients that started with seizures before 2 years of age. Motor seizures were the hallmark clinical manifestation. All patients of this group also presented with motor arrest and oro-alimentary automatisms. In three of them, the interictal EEG recordings showed bilateral paroxysms predominantly in anterior regions, in addition to focal abnormalities, and two had an apparently generalized ictal pattern. The second group included 17 patients that started with seizures between 2 and 10 years of age. In this group the automatisms were also oroalimentary, but more complex and the patients had less motor manifestations. The interictal EEG recordings showed temporal abnormalities. The ictal EEG recordings showed lateralized abnormalities with a maximum in the temporal electrodes. The third group included 16 patients that started with seizures between 10 and 16 years of age. The most common clinical manifestation was abdominal aura followed by oroalimentary, gestural, and verbal automatisms. The interictal and ictal EEG recordings showed well-localized abnormalities in temporal lobes. Thirty-eight patients underwent surgical treatment. Thirty-five patients are seizure free.

CONCLUSION

MTLE-HS represents a well-defined and distinct symptomatic epileptic syndrome. Surgical treatment was successful in most patients.

Lateralizing significance of quantitative analysis of head movements before secondary generalization of seizures of patients with temporal lobe epilepsy

PURPOSE

To quantitatively evaluate the lateralizing significance of ictal head movements of patients with temporal lobe epilepsy (TLE).

METHODS

We investigated EEG-video recorded seizures of patients with TLE, in which the camera position was perpendicular to the head facing the camera in an upright position and bilateral head movement was recorded. Thirty-eight seizures (31 patients) with head movement in both directions were investigated. Ipsilateral and contralateral head movements were defined according to ictal EEG. Head movements were quantified by selecting the movement of the nose in relation to a defined point on the thorax (25/s) in a defined plane facing the camera. The duration of the head version was determined independently of the camera angle. The angle, duration, and angular speed of the head movements were computed and inter and intrasubject analyses were performed (Wilcoxon rank sum).

RESULTS

Ipsilateral movement always preceded contralateral movement. The positive predictive value was 100% for movement in both directions. The duration of contralateral head version was significantly longer than ipsilateral head movement (6.4 +/- 4.1 s vs. 3.9 +/- 3.1 s, p<0.001). The angular speed of both movements was similar (15.5 +/- 12.1 deg/s vs. 17.3 +/- 13.0 deg/s).

CONCLUSION

The quantitative analysis shows the importance of sequence in the seizure's evolution and duration, but not angular speed for correct lateralization of versive head movement. This quantitative method shows the high lateralizing value of ictal lateral head movements in TLE.

Magnetoencephalography: clinical application in epilepsy

Magnetoencephalography (MEG) has developed to the point that it has now entered routine clinical application. Epilepsy MEG studies show that it can accurately localize spike sources--both ictal and interictal--as compared with both directly. Limitations involve difficulties in detecting complex or deep sources when recording spontaneous cerebral activity. MEG not only provides a novel tool to localize and characterize epileptiform disturbances, it also has an important role in determining the significance of abnormalities seen on both structural and functional imaging. Ultimately, MEG should play a major role in totally noninvasive epilepsy surgery evaluation.

1H MR spectroscopy in patients with mesial temporal epilepsy

The study provides a review of the basic examination procedures and results of proton magnetic resonance spectroscopy (1H MRS) in patients suffering from mesial temporal lobe epilepsy (MTLE). The source of seizures in MTLE is most often an epileptogenic focus secondary to hippocampal sclerosis. 1H MRS currently plays an important role in the non-invasive diagnosis of this type of epileptogenic lesion. The decisive 1H MRS parameter characterizing an epileptogenic lesion is a statistically significantly decreased value of N-acetylaspartate levels compared with control values, most often associated with a decrease in the ratios of the intensities of NAA/Cr, NAA/Cho and NAA/(Cr + Cho) signals. Moreover, MRS makes it possible to distinguish bilateral involvement of mesial temporal structures typically associated with a bilateral decrease in the levels of metabolites and/or their ratios. As regards other metabolic compounds which play an important role in the pathobiochemistry of epilepsy, MRS is employed to study the action of gamma-aminobutyric acid (GABA), inositol, lactate, glutamine, and glutamate, the clinical function of which has not been fully clarified as yet. It is in this context that one should consider the application of 1H MRS in evaluating the action of some new anti-epileptic agents affecting excitatory and inhibitory amino acids. There is no doubt that in vivo 1H MRS, along with other imaging methods, has made a significant contribution to the clinical and biochemical description of epileptic seizures and has assumed a prominent position among the techniques of pre-operative examination in epileptic surgery.

Regional distribution of interictal 31P metabolic changes in patients with temporal lobe epilepsy

PURPOSE

We compared the 31P metabolites in different brain regions of patients with temporal lobe epilepsy (TLE) with those from controls.

METHODS

Ten control subjects and 11 patients with TLE were investigated with magnetic resonance imaging (MRI) and [31P]MR spectroscopic imaging (MRSI). [31P]MR spectra were selected from a variety of brain regions inside and outside the temporal lobe.

RESULTS

There were no asymmetries of inorganic phosphate (Pi), pH, or phosphomonoesters (PME) between regions in the left and right hemispheres of controls. In patients with TLE, Pi and pH were higher and PME was lower throughout the entire ipsilateral temporal lobe as compared with the contralateral side and there were no significant asymmetries outside the temporal lobe. The degree of ipsilateral/contralateral asymmetry for all three metabolites was substantially greater for the temporal lobe than for the frontal, occipital, and parietal lobes, and these asymmetries provided additional data for seizure localization. As compared with levels in controls, Pi and pH were increased and PME were decreased on the ipsilateral side in patients with TLE. There were changes in Pi, pH, and PME on the contralateral side in persons with epilepsy as compared with controls, contrary to changes on the ipsilateral side.

CONCLUSIONS

Our findings provide some insight into the metabolic changes that occur in TLE and may prove useful adjuncts for seizure focus lateralization or localization.

Magnetoencephalography in partial epilepsy: clinical yield and localization accuracy

The goals of this study were to determine (1) the yield of magnetoencephalography (MEG) according to epilepsy type, (2) if MEG spike sources colocalize with focal epileptogenic pathology, and (3) if MEG can identify the epileptogenic zone when scalp ictal electroencephalogram (EEG) or magnetic resonance imaging (MRI) fail to localize it. Twenty-two patients with mesial temporal (10 patients), neocortical temporal (3 patients), and extratemporal lobe epilepsy (9 patients) were studied. A 37-channel biomagnetometer was used for simultaneously recording MEG with EEG. During the typical 2-3-hour MEG recording session, interictal epileptiform activity was observed in 16 of 22 patients. MEG localization yield was greater in patients with neocortical epilepsy (92%) than in those with mesial temporal lobe epilepsy (50%). In 5 of 6 patients with focal epileptogenic pathology, MEG spike sources were colocalized with the lesions. In 11 of 12 patients with nonlocalizing (ambiguous abnormalities or normal) MRI, MEG spike sources were localized in the region of the epileptogenic zone as ultimately defined by all clinical and EEG information (including intracranial EEG). In conclusion, MEG can reliably localize sources of spike discharges in patients with temporal and extratemporal lobe epilepsy. MEG sometimes provides noninvasive localization data that are not otherwise available with MRI or conventional scalp ictal EEG.