The neurovasculature as a target in temporal lobe epilepsy

The blood-brain barrier (BBB) is a physiological barrier maintaining a specialized brain micromilieu that is necessary for proper neuronal function. Endothelial tight junctions and specific transcellular/efflux transport systems provide a protective barrier against toxins, pathogens, and immune cells. The barrier function is critically supported by other cell types of the neurovascular unit, including pericytes, astrocytes, microglia, and interneurons. The dysfunctionality of the BBB is a hallmark of neurological diseases, such as ischemia, brain tumors, neurodegenerative diseases, infections, and autoimmune neuroinflammatory disorders. Moreover, BBB dysfunction is critically involved in epilepsy, a brain disorder characterized by spontaneously occurring seizures because of abnormally synchronized neuronal activity. While resistance to antiseizure drugs that aim to reduce neuronal hyperexcitability remains a clinical challenge, drugs targeting the neurovasculature in epilepsy patients have not been explored. The use of novel imaging techniques permits early detection of BBB leakage in epilepsy; however, the detailed mechanistic understanding of causes and consequences of BBB compromise remains unknown. Here, we discuss the current knowledge of BBB involvement in temporal lobe epilepsy with the emphasis on the neurovasculature as a therapeutic target.

Evaluation of cerebral blood flow in older patients with status epilepticus using arterial spin labeling

Introduction

Although older patients with status epilepticus (SE) have a high mortality rate and poor outcome, it is difficult to perform emergent electroencephalography (EEG) to diagnose SE in community hospitals. Arterial spin labeling (ASL) is a non-invasive magnetic resonance imaging (MRI) technique that can rapidly assess cerebral blood flow (CBF). Further, ASL can detect increased CBF in the ictal period. Therefore, ASL may be a useful tool for diagnosing SE in older patients. However, its effectiveness in this population is unknown.

Methods

We retrospectively investigated differences in CBF abnormalities between older patients (≥70 years) and non-older patients (<70 years) with SE using ASL. Participants were diagnosed with convulsive status epilepticus (CSE) or non-convulsive status epilepticus (NCSE) based on symptoms, brain MRI, and EEG.

Results

ASL detected CBF abnormalities in 40% of older patients with CSE or NCSE. Rates of CBF abnormalities in older patients were not significantly different compared with that in non-older patients.

Conclusions

ASL did not detect a higher rate of CBF abnormalities in older patients, but may help physicians diagnose SE in older patients in a community hospital setting if emergent EEG cannot be immediately performed.

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ASL is a non-invasive MRI technique.

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ASL can assess CBF in a short time.

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ASL showed abnormality in CBF in 40% of older patients with SE.

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ASL detected CBF abnormality more often in older patients with NCSE than with CSE.

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ASL may be an aid to diagnosing SE in older patients.

Specificities of arterial spin labeling (ASL) abnormalities in acute seizure

PURPOSE

Arterial spin labeling (ASL) is a non-invasive tool measuring cerebral blood flow (CBF) and is useful to assess acute neurological deficit. While acute stroke presents as hypoperfused vascular territory, epileptic activity causes cortical hyperperfusion. Other neurological conditions exhibit hyperperfusion, like migraine or secondary "luxury perfusion" in strokes. Our objectives were to evaluate the usefulness and potential specificities of ASL in acute seizure and correlate it with electroencephalogram.

MATERIALS AND METHODS

Amongst a cohort of patients with neurological deficit, addressed for suspicion of stroke, we retrospectively reviewed 25 consecutive patients with seizures who underwent magnetic resonance imaging (MRI) with ASL and electroencephalography (EEG). We compared them with a control group of patients with migraine and stroke secondary re-perfusion, exhibiting ASL hyperperfusion.

RESULTS

Lateralized cortical hyperperfusion (high relative CBF) was observed in all patients. Good topographic correlation with EEG was found in 18 patients (72%). Eight (32%) had hyperperfusion of ipsilateral pulvinar, 5 (20%) had hyperperfused contralateral cerebellar hemisphere, 16 (64%) presented diffusion abnormalities and 20 (80%) had underlying epileptogenic lesions. Pulvinar hyperperfusion was not observed in the control group, nor were diffusion abnormalities in migrainous patients. Contralateral cerebellar hyperperfusion was observed in two migrainous patient, without associated pulvinar activation, whereas all patients with cerebellar hyperperfusion in the study group had associated pulvinar activation.

CONCLUSIONS

Elevated CBF can be observed in the epileptogenic zone, ipsilateral pulvinar and contralateral cerebellum (diaschisis) in seizure. These abnormalities seem specific when compared with other causes of hyperperfusion. Arterial spin labeling can be highly effective in the differential diagnosis of strokes.

Identification of cerebral perfusion using arterial spin labeling in patients with seizures in acute settings

This study aimed to explore the utility of arterial spin labeling perfusion-weighted imaging (ASL-PWI) in patients with suspected seizures in acute settings. A total of 164 patients who underwent ASL-PWI for suspected seizures in acute settings (with final diagnoses of seizure [n = 129], poststroke seizure [n = 18], and seizure mimickers [n = 17]), were included in this retrospective study. Perfusion abnormality was analyzed for: (1) pattern, (2) multifocality, and (3) atypical distribution against vascular territories. Perfusion abnormality was detected in 39% (50/129) of the seizure patients, most (94%, 47/50) being the hyperperfusion pattern. Of the patients with perfusion abnormality, multifocality or hemispheric involvement and atypical distribution against vascular territory were revealed in 46% (23/50) and 98% (49/50), respectively. In addition, seizures showed characteristic features including hyperperfusion (with or without non-territorial distribution) on ASL-PWI, thus differentiating them from poststroke seizures or seizure mimickers. In patients in whom seizure focus could be localized on both EEG and ASL-PWI, the concordance rate was 77%. The present study demonstrates that ASL-PWI can provide information regarding cerebral perfusion status in patients with seizures in acute settings and has the potential to be used as a non-invasive imaging tool to identify the cerebral perfusion in patients with seizures.

Capability of arterial spin labeling MR imaging in localizing seizure focus in clinical seizure activity

PURPOSE

The purpose of this study was to evaluate cerebral blood flow using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging in patients with clinical seizure activity and determine its diagnostic performance in identifying seizure focus.

MATERIALS AND METHODS

Institutional Review Board of our hospital approved this retrospective study. Informed consent was waived. Clinical seizure focus was determined by a neurologist based on seizure semiology, electroencephalography, and conventional imaging modalities. The diagnostic performance of ASL perfusion MR imaging to identifying seizure focus compared to clinical seizure focus was analyzed.

RESULTS

Clinical seizure focus was localized in 95% (42/44) of patients. The sensitivity and specificity of ASL perfusion MR imaging for identifying seizure focus were 74% (95% CI: 58%, 86%) (clinical seizure focus was localizable in 31 of 42 patients, including complete concordance in 10 patients and partial concordance in 21 patients) and 0% (95% CI: 0%, 84%) (for the two patients whose clinical seizure foci were not localizable, they were identified by ASL perfusion MR imaging), respectively. Thus, the overall accuracy of ASL perfusion MR imaging for localizing seizure focus was 70% (33/44). For 4 patients who had abnormal perfusion on ASL, their seizure foci based on ASL perfusion MR imaging were discordant with clinical seizure foci.

CONCLUSION

ASL perfusion MR imaging can provide information about perfusion status and important diagnostic clue in localizing seizure focus in patients with clinical seizure activity. It has the potential as a non-invasive complementary diagnostic tool for patients with clinical seizure activity.

Patient-specific detection of cerebral blood flow alterations as assessed by arterial spin labeling in drug-resistant epileptic patients

Electrophysiological and hemodynamic data can be integrated to accurately and precisely identify the generators of abnormal electrical activity in drug-resistant focal epilepsy. Arterial Spin Labeling (ASL), a magnetic resonance imaging (MRI) technique for quantitative noninvasive measurement of cerebral blood flow (CBF), can provide a direct measure of variations in cerebral perfusion associated with the epileptic focus. In this study, we aimed to confirm the ASL diagnostic value in the identification of the epileptogenic zone, as compared to electrical source imaging (ESI) results, and to apply a template-based approach to depict statistically significant CBF alterations. Standard video-electroencephalography (EEG), high-density EEG, and ASL were performed to identify clinical seizure semiology and noninvasively localize the epileptic focus in 12 drug-resistant focal epilepsy patients. The same ASL protocol was applied to a control group of 17 healthy volunteers from which a normal perfusion template was constructed using a mixed-effect approach. CBF maps of each patient were then statistically compared to the reference template to identify perfusion alterations. Significant hypo- and hyperperfused areas were identified in all cases, showing good agreement between ASL and ESI results. Interictal hypoperfusion was observed at the site of the seizure in 10/12 patients and early postictal hyperperfusion in 2/12. The epileptic focus was correctly identified within the surgical resection margins in the 5 patients who underwent lobectomy, all of which had good postsurgical outcomes. The combined use of ESI and ASL can aid in the noninvasive evaluation of drug-resistant epileptic patients.

pASL versus DSC perfusion MRI in lateralizing temporal lobe epilepsy

BACKGROUND

Accurate lateralization of the epileptogenic focus in temporal lobe epilepsy (TLE) is crucial. Pulsed arterial spin labeling (pASL) has the capability of quantifying local relative cerebral blood flow (rCBF) by measuring the inflow of electromagnetically labeled arterial blood into the target area, and can be used in the presurgical workup of refractory TLE.

PURPOSE

To evaluate pASL in detecting mesial temporal lobe (mTL) perfusion asymmetry for the lateralization of the epileptogenic focus in patients with refractory TLE and to compare it with dynamic susceptibility contrast enhanced (DSC) magnetic resonance imaging (MRI) technique.

MATERIAL AND METHODS

This study was approved by the local ethical committee, and written informed consent was obtained in each patient. Thirty-six patients with medically refractory TLE and 11 healthy volunteer was enrolled in this study. Following brain MRI, pASL and DSC perfusion were performed in all subjects at 3T. rCBF measurements with two different perfusion MRI technique were compared between the patient and healthy volunteers. Lateralization based on perfusion asymmetry index (AI) were also evaluated and compared with clinical lateralization.

RESULTS

rCBF ratios measured in healthy volunteers by two different perfusion technique did not show any statistically significant difference. In TLE patients rCBF ratio of the ipsilateral (affected) side was found to be significantly lower than the contralateral (unaffected) side with both technique. The AI in the patient group was 8.86 ± 3.88 with pASL and 8.39 ± 4.06 with DSC. Correlation coefficient between clinical laterality and perfusion AI were 0.86 for pASL and 0.83 for DSC.

CONCLUSION

pASL can successfully detect interictal asymmetry in patients with TLE and can readily be combined with routine structural assessment for lateralization, providing an alternative to DSC perfusion.

Usefulness of pulsed arterial spin labeling MR imaging in mesial temporal lobe epilepsy

PURPOSE

Arterial spin labeling (ASL) is a developing magnetic resonance imaging (MRI) method for noninvasive measurement of cerebral blood flow (CBF). The purpose of this study was to evaluate the usefulness of ASL for detecting interictal temporal hypoperfusion in temporal lobe epilepsy (TLE). ASL-derived CBF measurements were compared with those derived from H(2)(15)O positron emission tomography (PET).

METHODS

11 normal controls and 10 patients with medically intractable TLE were studied. Pulsed ASL (PASL) with quantitative imaging of perfusion using a single subtraction, second version (QUIPSS II) was performed in all subjects and H(2)(15)O PET was performed in patients. Regional CBF values in the mesial and lateral temporal lobes were measured utilizing quantitative analysis of perfusion images. A perfusion asymmetry index (AI) was calculated for each region.

RESULTS

In patients, mean CBF in the mesial temporal lobe was not significantly different between PASL and H(2)(15)O PET, and ipsilateral mesial temporal CBF was lower than contralateral CBF with both techniques. PASL detected significant mesial temporal perfusion asymmetry agreeing with EEG laterality in four patients. H(2)(15)O PET found ipsilateral interictal hypoperfusion in three. Both scans found unilateral hypoperfusion in one patient with bilateral EEG discharges.

CONCLUSIONS

Pulsed ASL may be a promising approach to detecting interictal hypoperfusion in TLE. This method has potential as a clinical alternative to H(2)(15)O PET due to noninvasiveness and easy accessibility.

Functional imaging in temporal lobe epilepsy

This article highlights the importance of functional imaging methods in the diagnosis and preoperative planning in temporal lobe epilepsy TLE). It starts with a discussion of the role of ictal and interictal single-photon emission computed tomography (SPECT) and interictal positron emission tomography (PET) in lateralizing TLE. The next section discusses the role of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) and perfusion MRI, particularly for lateralization of language and memory in TLE patients. The final section explores the relatively new role that the emerging technique of diffusion tensor imaging (DTI) is playing in the evaluation of TLE.

Characteristics of abnormal diffusivity in normal-appearing white matter investigated with diffusion tensor MR imaging in tuberous sclerosis complex

BACKGROUND AND PURPOSE

Although patients with tuberous sclerosis complex (TSC) manifest various structural abnormalities, we hypothesized that white matter (WM) structures that appear normal on conventional MR imaging may be accompanied by microstructural changes, such as gliosis and myelinization defects. Our objective was to determine in vivo whether there was evidence for WM microstructural changes by using diffusion tensor imaging (DTI).

MATERIALS AND METHODS

We used DTI to evaluate diffusivity and anisotropy in normal-appearing WM (NAWM) of 6 children with TSC and 12 age-matched control subjects. The anterior and posterior limbs of the internal capsule, the external capsule, and the genu and splenium of the corpus callosum were assessed. We hypothesized that previously reported DTI abnormalities of NAWM in patients with TSC may not be equal in all diffusion directions as measured by the major, middle, and minor eigenvalues.

RESULTS

When combining NAWM regions in patients with TSC, we observed a significant increase in mean diffusivity (P = .003) and a decrease in anisotropy (P = .03) compared with those of controls. However, the increase in diffusivity was more pronounced in directions orthogonal to the axons measured by the minor and middle eigenvalues (P = .005) than by the major eigenvalue (P = .02).

CONCLUSION

Our findings revealed a decrease in anisotropy and an increase in longitudinal and radial diffusivities in NAWM beyond the location of TSC lesions seen on conventional MR imaging. The axonal microstructural changes suggested by our study may be related to changes in myelin packing due to giant cells accompanied by gliosis and myelination defects known to occur in TSC WM.

Imaging surgical epilepsy in children

INTRODUCTION

Epilepsy surgery rests heavily upon magnetic resonance imaging (MRI). Technical developments have brought significantly improved efficacy of MR imaging in detecting and assessing surgical epileptogenic lesions, while more clinical experience has brought better definition of the pathological groups.

DISCUSSION

MRI is fairly efficient in identifying developmental, epilepsy-associated tumors such as ganglioglioma (with its variants gangliocytoma and desmoplastic infantile ganglioglioma), the complex, simple and nonspecific forms of dysembryoplastic neuroepithelial tumor, and the rare pleomorphic xanthoastrocytoma. The efficacy of MR imaging is not as good for the diagnosis of focal cortical dysplasia (FCD), as it does not necessarily correlate with histopathological FCD subtypes and does not show the real extent of the dysplasia which may even be missed in a high percentage of cases. Further developments with better, multichannel coils, higher magnetic fields, specific sequences, and different approaches (such as diffusion tensor imaging) for depicting the structural abnormalities may hopefully improve this efficacy. A general review of the MR features of the diverse pathologies concerned with epilepsy surgery in the pediatric context is provided with illustrative images.

Acute infantile encephalopathy predominantly affecting the frontal lobes

To establish a novel subtype of acute infantile encephalopathy, the clinical and radiologic features of nine infants with acute encephalopathy involving the bilateral frontal lobes were examined. These patients had convulsive status epilepticus with hyperpyrexia followed by a prolonged impairment of consciousness for 2-20 days. After the recovery of consciousness, all the patients manifested regression of verbal function and lack of spontaneity. Some of them also exhibited stereotypic movements, instability of mood, or catalepsy. Transient postictal edema in both frontal lobes was suggested by diffusion-weighted magnetic resonance imaging. Attenuated cerebral perfusion in the frontal lobes was demonstrated by single-photon emission computed tomography at the tenth day after onset or subsequently. Serial studies disclosed atrophic changes in the frontal lobes. All patients manifested regression or retardation of motor and verbal functions. The recovery of intellectual deficit was slower and less prominent than that of motor dysfunction. These unique features suggest that the frontal lobes are the focus of this novel subtype of acute encephalopathy, which we propose to call acute infantile encephalopathy predominantly affecting the frontal lobes.

Diffusion tensor imaging in late posttraumatic epilepsy

PURPOSE

The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy.

METHODS

DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n=14; without epilepsy, n=9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T2/FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients.

RESULTS

The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57+/-0.059) than in those without epilepsy (0.68+/-0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15+/-0.140) relative to those without epilepsy (1.09+/-0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without.

CONCLUSIONS

Severity of injury as predicted by the DTI-derived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI.

Postictal diffusion tensor imaging

The objective of the study was to investigate postictal diffusion tensor imaging (DTI) in focal epilepsy. DTI and statistical parametric mapping (SPM) were used to examine objectively the diffusion properties of the brains of 18 patients with intractable focal epilepsy both postictally and interictally and to compare them with 27 normal controls scanned twice. Three sets of statistical tests were performed on each patient's fractional anisotropy and mean diffusivity data: interictal versus controls, postictal versus controls and a third "difference analysis" to test for significant changes in comparison with the differences noted between the two sets of control scans. Thirteen of the 18 patients (72%) had significant increases in mean diffusivity in the interictal scan. No decreases in mean diffusivity were detected. The difference analysis detected significant relative decreases in mean diffusivity postictally in nine patients (50%). These changes were focal in seven patients. In six of these, the site of the epileptic focus was known and co-localized with the diffusivity change in three. No significant changes in anisotropy were noted between the post- and interictal states. The postictal decrease in diffusivity probably reflects cellular swelling in the area of seizure onset and possibly areas of seizure spread. Postictal diffusivity changes appear complex and dynamic and timing after the seizure may be critical. Anisotropy measures appear less sensitive to these changes. Further systematic studies are needed and correlation with outcome after epilepsy surgery will determine the role of postictal diffusion measures in the presurgical evaluation of epilepsy patients.