Ictal SPECT

Single-photon emission tomography

Single-photon emission computed tomography (SPECT) is a functional nuclear imaging technique that allows visualization and quantification of different in vivo physiologic and pathologic features of brain neurobiology. It has been used for many years in diagnosis of several neurologic and psychiatric disorders. In this chapter, we discuss the current state-of-the-art of SPECT imaging of brain perfusion and dopamine transporter (DAT) imaging. Brain perfusion SPECT imaging plays an important role in the localization of the seizure onset zone in patients with refractory epilepsy. In cerebrovascular disease, it can be useful in determining the cerebrovascular reserve. After traumatic brain injury, SPECT has shown perfusion abnormalities despite normal morphology. In the context of organ donation, the diagnosis of brain death can be made with high accuracy. In neurodegeneration, while amyloid or (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) are the nuclear diagnostic tools of preference for early and differential diagnosis of dementia, perfusion SPECT imaging can be useful, albeit with slightly lower accuracy. SPECT imaging of the dopamine transporter system is widely available in Europe and Asia, but since recently also in the USA, and has been accepted as an important diagnostic tool in the early and differential diagnosis of parkinsonism in patients with unclear clinical features. The combination of perfusion SPECT (or FDG-PET) and DAT imaging provides differential diagnosis between idiopathic Parkinson's disease, Parkinson-plus syndromes, dementia with Lewy bodies, and essential tremor.

NeuroGam Software Analysis in Epilepsy Diagnosis Using 99mTc-ECD Brain Perfusion SPECT Imaging

BACKGROUND The aim of this study was to explore the value of NeuroGam software in diagnosis of epilepsy by 99Tcm-ethyl cysteinate dimer (ECD) brain imaging. MATERIAL AND METHODS NeuroGam was used to analyze 52 cases of clinically proven epilepsy by 99Tcm-ECD brain imaging. The results were compared with EEG and MRI, and the positive rates and localization to epileptic foci were analyzed. RESULTS NeuroGam analysis showed that 42 of 52 epilepsy cases were abnormal. 99Tcm-ECD brain imaging revealed a positive rate of 80.8% (42/52), with 36 out of 42 patients (85.7%) clearly showing an abnormal area. Both were higher than that of brain perfusion SPECT, with a consistency of 64.5% (34/52) using these 2 methods. Decreased regional cerebral blood flow (rCBF) was observed in frontal (18), temporal (20), and parietal lobes (2). Decreased rCBF was seen in frontal and temporal lobes in 4 out of 36 patients, and in temporal and parietal lobes of 2 out of 36 patients. NeuroGam further showed that the abnormal area was located in a different functional area of the brain. EEG abnormalities were detected in 29 out of 52 patients (55.8%) with 16 cases (55.2%) clearly showing an abnormal area. MRI abnormalities were detected in 17 out of 43 cases (39.5%), including 9 cases (52.9%) clearly showing an abnormal area. The consistency of NeuroGam software analysis, and EEG and MRI were 48.1% (25/52) and 34.9% (15/43), respectively. CONCLUSIONS NeuroGam software analysis offers a higher sensitivity in detecting epilepsy than EEG or MRI. It is a powerful tool in 99Tcm-ECD brain imaging.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.

SPECT findings in autism spectrum disorders and medically refractory seizures

A high rate of seizures and electroencephalogram abnormalities has been noted in individuals with autism spectrum disorders (ASDs). Common underlying neurodevelopmental abnormalities may exist in the brains of individuals with both ASDs and epilepsy. Single-photon emission computed tomography (SPECT) studies of the brain have provided sensitive brain function findings. Such studies often reveal not only localized areas of hyperperfusion, which could be related to the seizure-onset zone, but also localized areas of hypoperfusion that may correlate with the focal reductions in function observed in the prefrontal lobes, cingulate gyrus, superior temporal gyrus, and mesial temporal lobes of many individuals with both ASDs and epilepsy. The focal neuronal dysfunction revealed by SPECT could be caused by aberrant neuronal connectivity. This article is part of a Special Issue entitled "Autism and Epilepsy".

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.

Determination of epileptic focus side in mesial temporal lobe epilepsy using long-term noninvasive fNIRS/EEG monitoring for presurgical evaluation

Noninvasive localization of an epileptogenic zone is a fundamental step for presurgical evaluation of epileptic patients. Here, we applied long-term simultaneous functional near-infrared spectroscopy (fNIRS)/electroencephalogram (EEG) monitoring for focus diagnosis in patients with mesial temporal lobe epilepsy (MTLE). Six MTLE patients underwent long-term (8-16 h per day for 4 days) fNIRS/EEG monitoring for the occurrence of spontaneous seizures. Four spontaneous seizures were successfully recorded out of the six patients. To determine oxy-Hb amplitude, the period-average values of oxy-Hb across 20 s from the EEG- or clinically defined epileptic onset were calculated for both hemispheres from the simultaneously recorded fNIRS data. The average oxy-Hb values for the temporal lobe at the earlier EEG- or clinically defined epileptic onsets were greater for the epileptic side than for the contralateral side after EEG activity suppression, spike train, and clinical seizure in all four cases. The true laterality was determined based on the relief of seizures by selective amygdalo-hippocampectomy. Thus, oxy-Hb amplitude could be a reliable measure for determining the epileptic focus side. Long-term simultaneous fNIRS/EEG measurement serves as an effective tool for recording spontaneous seizures. Cerebral hemodynamic measurement by fNIRS would serve as a valuable supplementary noninvasive measurement method for presurgical evaluation of MTLE.

Sensitivity and Specificity of Interictal EEG-fMRI for Detecting the Ictal Onset Zone at Different Statistical Thresholds

There is currently a lack of knowledge about electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) specificity. Our aim was to define sensitivity and specificity of blood oxygen level dependent (BOLD) responses to interictal epileptic spikes during EEG-fMRI for detecting the ictal onset zone (IOZ). We studied 21 refractory focal epilepsy patients who had a well-defined IOZ after a full presurgical evaluation and interictal spikes during EEG-fMRI. Areas of spike-related BOLD changes overlapping the IOZ in patients were considered as true positives; if no overlap was found, they were treated as false-negatives. Matched healthy case-controls had undergone similar EEG-fMRI in order to determine true-negative and false-positive fractions. The spike-related regressor of the patient was used in the design matrix of the healthy case-control. Suprathreshold BOLD changes in the brain of controls were considered as false positives, absence of these changes as true negatives. Sensitivity and specificity were calculated for different statistical thresholds at the voxel level combined with different cluster size thresholds and represented in receiver operating characteristic (ROC)-curves. Additionally, we calculated the ROC-curves based on the cluster containing the maximal significant activation. We achieved a combination of 100% specificity and 62% sensitivity, using a Z-threshold in the interval 3.4–3.5 and cluster size threshold of 350 voxels. We could obtain higher sensitivity at the expense of specificity. Similar performance was found when using the cluster containing the maximal significant activation. Our data provide a guideline for different EEG-fMRI settings with their respective sensitivity and specificity for detecting the IOZ. The unique cluster containing the maximal significant BOLD activation was a sensitive and specific marker of the IOZ.

Hemodynamic changes during posterior epilepsies: an EEG-fNIRS study

Posterior epilepsies are mainly characterized clinically by visual symptoms. Functional near-infrared spectroscopy (fNIRS) is an emerging non-invasive imaging technique that has the potential to monitor hemodynamic changes during epileptic activity. Combined with electroencephalography (EEG), 9 patients with posterior epilepsies were recorded using EEG-fNIRS with large sampling (19 EEG electrodes and over 100 fNIRS channels). Spikes and seizures were carefully marked on EEG traces, and convolved with a standard hemodynamic response function for general linear model (GLM) analysis. GLM results for seizures (in 3 patients) and spikes (7 patients) were broadly sensitive to the epileptic focus in 7/9 patients, and specific in 5/9 patients with fNIRS deoxyhemoglobin responses lateralized to the correct lobe, and to plausible locations within the occipital or parietal lobes. This work provides evidence that EEG-fNIRS is a sensitive technique for monitoring posterior epileptic activity.

[PET and SPECT in epilepsy]

Epilepsy is one of the most frequent chronic neurological disorders, affecting 1-2% of the population. Patients with complex partial drug resistant episodes may benefit from a surgical treatment consisting in the excision of the epileptogenic area. Localization of the epileptogenic area was classically performed with video-EEG and magnetic resonance (MR). Recently, functional neuroimaging studies of Nuclear Medicine, positron emission tomography (PET) and single photon emission tomography (SPECT) have demonstrated their utility in the localization of the epileptogenic area prior to surgery. Ictal SPECT with brain perfusion tracers show an increase in blood flow in the initial ictal focus, while PET with (18)FDG demonstrates a decrease of glucose metabolism in the interictal functional deficit zone. In this review, the basic principles and methodological characteristics of the SPECT and PET in epilepsy are described. The ictal SPECT injection mechanism, different patterns of perfusion based on the time of ictal, postictal or interictal injection are detailed and the different diagnostic sensitivities of each one of these SPECT are reviewed. Different methods of analysis of the images with substraction and fusion systems with the MR are described. Similarly, the injection methodology, quantification and evaluation of the images of the PET in epilepsy are described. Finally, the main clinical indications of SPECT and PET in temporal and extratemporal epilepsy are detailed.

Localisation of epileptic foci using novel imaging modalities

Purpose of review

This review examines recent reports on the use of advanced techniques to map the regions and networks involved during focal epileptic seizure generation in humans.

Recent findings

A number of imaging techniques are capable of providing new localizing information on the ictal processes and epileptogenic zone. Evaluating the clinical utility of these findings has been mainly performed through post-hoc comparison with the findings of invasive EEG and ictal single-photon emission computed tomography, using postsurgical seizure reduction as the main outcome measure. Added value has been demonstrated in MRI-negative cases. Improved understanding of the human ictiogenic processes and the focus vs. network hypothesis is likely to result from the application of multimodal techniques that combine electrophysiological, semiological, and whole-brain coverage of brain activity changes.

Summary

On the basis of recent research in the field of neuroimaging, several novel imaging modalities have been improved and developed to provide information about the localization of epileptic foci.

Imaging the seizure during surgery with a hyperspectral camera

An epilepsy patient with recurring sensorimotor seizures involving the left hand every 10 min, was imaged with a hyperspectral camera during surgery. By calculating the changes in oxygenated, deoxygenated blood, and total blood volume in the cortex, a focal increase in oxygenated and total blood volume could be observed in the sensory cortex, corresponding to the seizure-onset zone defined by intracranial electroencephalography (EEG) findings. This probably reflects very local seizure activity. After multiple subpial transections in this motor area, clinical seizures abated.

Eating epilepsy: phenotype, MRI, SPECT and video-EEG observations

BACKGROUND

Eating epilepsy is one of the rare forms of reflex epilepsy precipitated by eating. Previous studies have demonstrated lesions due to variable aetiology involving the temporolimbic and suprasylvian regions.

OBJECTIVE

To study anatomical correlates of reflex eating epilepsy using multimodality investigations (MR imaging, video-EEG and SPECT).

METHODOLOGY

Six patients (M:F=3:3; mean age: 20.7±4.9 years) with eating epilepsy were subjected to MRI of brain, video-EEG studies and SPECT scan. These were correlated with phenotypic presentations.

RESULTS

Among the five patients with ictal recording of eating epilepsy during video-EEG, semiology was characterized by behavioural arrest followed by either flexion or extension of trunk and neck and two patients had speech arrest and four had salivation from angle of mouth. Another patient had EEG changes during "thought about eating". Four patients had perisylvian frontal lobe lesions and one had high frontal lesion on MRI. Ictal EEG (n=6) showed ictal rhythmic slowing/fast activity in parieto-temporal (n=2) or fronto-temporal (n=4) regions with subsequent secondary generalization in three. Ictal and interictal SPECT imaging showed changes in frontal lobe (n=1), anterior temporal lobe (n=1), and parieto-insular region (n=1) suggesting it to be seizure onset zone. Three of four patients with structural lesions in MRI had concordant ictal EEG and ictal SPECT changes.

CONCLUSION

Lesions near the perisylvian region might play a major role in eating epilepsy.

Optimizing SPECT SISCOM analysis to localize seizure-onset zone by using varying z scores

PURPOSE

Subtraction ictal single photon emission computed tomography (SPECT) co-registered to magnetic resonance imaging (MRI) (SISCOM) is a useful modality to identify epileptogenic focus. Using this technique, several studies have generally considered the area of highest ictal hyperperfusion, as outlined by thresholding the difference images with a standard z score of 2, to be highly concordant to the epileptogenic focus. In clinical practice, several factors influence ictal hyperperfusion and using different SISCOM thresholds can be helpful. We aimed to systematically evaluate the localizing value of various z scores (1, 1.5, 2, and 2.5) in a seizure-free cohort following resective epilepsy surgery, and to examine the localizing information of perfusion patterns observed at each z score.

METHODS

Twenty-six patients were identified as having ictal-interictal SPECT images, preoperative and postoperative MRI studies, and having remained seizure free for at least 6 months after temporal or extratemporal surgical resection. SISCOM analysis was performed using preoperative MRI studies, and then blindly reviewed for localization of hyperperfused regions. With the added information from postoperative, coregistered MRI, perfusion patterns were determined.

KEY FINDINGS

Using pair-wise comparisons, we found that the optimal z score for SPECT-SISCOM localization of the epileptogenic zone was 1.5, not the commonly used z score of 2. The z score of 1.5 was 84.8% sensitive and 93.8% specific. The z score of 1.5 had a moderate interrater agreement (0.70). When an hourglass configuration hyperperfusion pattern was present, a trend toward correctly localizing the seizure onset region was suggested (100% of the 11 observed occurrences). Nonetheless this trend was not statistically significant, possibly reflecting the small number of occurrences in our study.

SIGNIFICANCE

SISCOM is a useful modality in evaluating patients for epilepsy surgery. This study shows that the z score of 1.5 represents a highly sensitive and specific SISCOM threshold that should be examined in conjunction with the traditionally used z score of 2 to enhance the chances of correct localization. Further prospective investigations are needed to confirm this finding in large patient series.

Clinical value of the first dedicated, commercially available automatic injector for ictal brain SPECT in presurgical evaluation of pediatric epilepsy: comparison with manual injection

The most challenging technical problem in ictal brain SPECT for localization of an epileptogenic focus is obtaining a timely injection of a radiopharmaceutical. In our institution, the first dedicated commercially available, remotely controlled automatic injector has been used in the pediatric epilepsy unit in conjunction with 24-h video and electroencephalogram monitoring. The goal of this study was to demonstrate the improved success rate of ictal injection by use of the automatic injector in the pediatric population.

METHODS

Eighty-four pediatric patients and eighty-four (99m)Tc-ethylcysteinate dimer ((99m)Tc-ECD) ictal brain SPECT studies were retrospectively analyzed in a masked manner. The group with manual injection consisted of 45 studies performed from 2004 to 2010 before the introduction of the automatic injector. The group with automatic injection consisted of 39 studies performed from 2010 to 2011 after the introduction of the automatic injector. The 2 groups were comparable in the total duration of seizure, injected dose, and time from the injection to the image acquisition. The latency time from the seizure onset to the initiation time of injection, the ratio of latency time to total duration of seizure (L/T), the number of patients with repeated studies, the number of days of additional hospitalization for each study, and the localization rate for identifying a single focus in each study were compared between the groups.

RESULTS

The median latency time in the group with automatic injection (8 s) was significantly lower than that of the group with manual injection (18 s) (P < 0.05). Also there was a statistically significant decrease in the number of patients with repeated studies in the group with automatic injection (2/39 [5%]), compared with the group with manual injection (14/45 [31%]) (P < 0.05). The median number of days of additional hospitalization in the group with manual injection (range, 0-7) was statistically significantly different, compared with the group with automatic injection (range, 0-1) (P < 0.05). In the group with automatic injection, 31 of 39 scans demonstrated a single localizing focus, compared to 22 of 45 scans from the manual-injection group, a significant difference (P < 0.05). The radiation exposure rate to nursing staff during the periods with automatic injection was lower than during the periods with manual injection.

CONCLUSION

The automatic injector combined with 24-h video and electroencephalogram monitoring demonstrated significant clinical value by decreasing latency time, the number of patients with repeated studies, and the number of days of additional hospitalization while increasing the number of studies with a single localizing focus.

Localizing value of ictal SPECT is comparable to MRI and EEG in children with focal cortical dysplasia

PURPOSE

To assess the predictive value of ictal single-photon emission computed tomography (SPECT) for outcome after excisional epilepsy surgery in a large population of children with focal cortical dysplasia (FCD).

METHODS

One hundred seventy-three ictal SPECT studies in 106 children with histologically proven FCD were retrospectively analyzed. The extent and location of ictal hyperperfusion and completeness of surgical removal were assessed. Completeness of resection of epileptogenic regions defined by ictal SPECT, electroencephalography (EEG), and magnetic resonance imaging (MRI) were compared and correlated with postoperative seizure outcome. In addition, subcortical activation of the cerebellum, basal ganglia, and thalamus were analyzed.

KEY FINDINGS

The extent of hyperperfusion was focal or lobar in 58%, whereas multilobar activations occurred in only 32%; hemispheric or bilateral findings were rare. Favorable postsurgical seizure outcome was achieved in 67% patients with nonlocalized SPECT findings, 45% with nonresected ictal hyperperfusion, 36% with partially resected ictal hyperperfusion, and 86% when the zone of ictal hyperperfusion was completely resected (p = 0.000198). The favorable postsurgical outcome after complete removal of the SPECT hyperperfusion zone surpassed the 75% rate of seizure freedom in patients with removal of MRI/EEG-defined epileptogenic region. A similar predictive value of ictal SPECT for seizure outcome was found in nonoperated patients and subjects who were undergoing reoperation. Subcortical activation conferred no predictive value.

SIGNIFICANCE

Ictal SPECT helps to define the epileptogenic zone in a high proportion of children with FCD undergoing surgical evaluation. Complete removal of both SPECT and MRI/EEG-defined regions is a strong predictor of surgical success and has important implications for surgical planning.

Localization of epileptic foci using multimodality neuroimaging

Approximately 30% of epilepsy patients are medically intractable. Epilepsy surgery may offer cure or palliation, and neuromodulation and direct drug delivery are being developed as alternatives. Successful treatment requires correct localization of seizure onset zones and understanding surrounding functional cortex to avoid iatrogenic disability. Several neurophysiologic and imaging localization techniques have inherent individual weaknesses which can be overcome by multimodal analysis. We review common noninvasive techniques, then illustrate the value of multimodal analysis to localize seizure onset for targeted treatment.

Neuroimaging during trance state: a contribution to the study of dissociation

Despite increasing interest in pathological and non-pathological dissociation, few researchers have focused on the spiritual experiences involving dissociative states such as mediumship, in which an individual (the medium) claims to be in communication with, or under the control of, the mind of a deceased person. Our preliminary study investigated psychography – in which allegedly “the spirit writes through the medium's hand” – for potential associations with specific alterations in cerebral activity. We examined ten healthy psychographers – five less expert mediums and five with substantial experience, ranging from 15 to 47 years of automatic writing and 2 to 18 psychographies per month – using single photon emission computed tomography to scan activity as subjects were writing, in both dissociative trance and non-trance states. The complexity of the original written content they produced was analyzed for each individual and for the sample as a whole. The experienced psychographers showed lower levels of activity in the left culmen, left hippocampus, left inferior occipital gyrus, left anterior cingulate, right superior temporal gyrus and right precentral gyrus during psychography compared to their normal (non-trance) writing. The average complexity scores for psychographed content were higher than those for control writing, for both the whole sample and for experienced mediums. The fact that subjects produced complex content in a trance dissociative state suggests they were not merely relaxed, and relaxation seems an unlikely explanation for the underactivation of brain areas specifically related to the cognitive processing being carried out. This finding deserves further investigation both in terms of replication and explanatory hypotheses.

Proposition: limbic encephalitis may represent limbic status epilepticus. A review of clinical and EEG characteristics

Limbic encephalitis (LE) with waxing and waning neuropsychiatric manifestations including behavioral, personality, psychiatric, and memory changes can evolve over days to months. Many features of LE show remarkable overlap with the characteristics of mesial-temporal (limbic) status epilepticus (MTLSE or LSE). With LE, these prolonged impaired states are assumed not to be due to ongoing epileptic activity or MTLSE, because scalp EEGs usually show no epileptiform spike-wave activity; cycling behavioral and motor changes are attributed to LE; there may be little immediate improvement with antiepileptic drugs (AEDs); and of course, implanted electrodes are rarely used. Conversely, it is known that in pre-surgical patients with refractory limbic epilepsy, implanted electrodes have revealed limbic seizures that cannot be seen at the scalp. This paper assembles a chain of inferences to advance the proposition that refractory LE might represent LSE more often than is thought, and that implanted electrodes should be considered in some cases. We present two cases that suggest that LE was also LSE, one of which warranted implanted electrodes (case 1).

SISCOM technique with a variable Z score improves detectability of focal cortical dysplasia: a comparative study with MRI

OBJECTIVE

Focal cortical dysplasia (FCD) is one of the causes of epilepsy, but its diagnosis by MRI remains difficult. The purpose of this study was to evaluate the use of subtraction ictal SPECT coregistered to MRI (SISCOM) and MRI to detect the epileptogenic focus in patients with FCD.

METHODS

MRI and SISCOM findings of 20 patients with pathologically proven FCD were retrospectively reviewed. MRI was visually assessed for detecting FCD. SISCOM was evaluated by a new method selecting a higher standard deviation (Z score) area as the epileptogenic focus. We scored the detectability in both SISCOM and MRI while referring to the pathology.

RESULTS

Sixteen patients agreed with pathology on SISCOM and 14 patients on MRI. Although MRI could not point out foci in two cases of FCD type I, SISCOM could do so in both of them. A combined diagnosis of SISCOM and MRI agreed with the pathology in 18 patients.

CONCLUSIONS

Narrowing the target by elevating the Z score on SISCOM seems to be an appropriate method to detect the foci without the need for expertise of radiologists. We recommend this combined method of SISCOM and MRI for presurgical evaluation in patients with FCD.

Preictal changes in cerebral haemodynamics: review of findings and insights from intracerebral EEG

The possibility of recording changes in brain signals occurring before epileptic seizures is of considerable interest, both as markers for seizure anticipation and as a window into the mechanisms of seizure generation. Several studies have reported preictal changes on electrophysiological traces. More recently, observations have been made of changes occurring on haemodynamic signals before interictal events or before seizures, often without concurrent changes observed on electrophysiology. We present here a critical review of these findings, in optical imaging, SPECT and fMRI, followed by a discussion based on data from intracerebral EEG.

Special surgical considerations for functional brain mapping

The development of functional mapping techniques gives neurosurgeons many options for preoperative planning. Integrating functional and anatomic data can inform patient selection and surgical planning and makes functional mapping more accessible than when only invasive studies were available. However, the applications of functional mapping to neurosurgical patients are still evolving. Functional imaging remains complex and requires an understanding of the underlying physiologic and imaging characteristics. Neurosurgeons must be accustomed to interpreting highly processed data. Successful implementation of functional image-guided procedures requires efficient interactions between neurosurgeon, neurologist, radiologist, neuropsychologist, and others, but promises to enhance the care of patients.

Role of single photon emission computed tomography in epilepsy

Molecular imaging with ictal single photon emission computed tomography (SPECT) is an established functional imaging modality for the presurgical evaluation of patients with refractory partial onset seizures. SPECT coregistered on to the MRI has greater sensitivity to identify the ictal onset zone. Ictal SPECT should always be interpreted in the context of other presurgical investigations. Ictal SPECT is sensitive method for the lateralization of TLE, but ictal SPECT is more sensitive when MRI is normal. Ictal SPECT and interictal PET are complementary to each other in lateralizing the side in patients with TLE and normal MRI. In extratemporal epilepsy, ictal SPECT will guide the placement of surface grid and depth electrodes.

Brain perfusion SPECT and EEG findings in children with autism spectrum disorders and medically intractable epilepsy

OBJECTIVE

We performed brain perfusion single-photon emission computed tomography (SPECT) to detect the abnormal brain region in children with both autism spectrum disorders (ASD) and medically intractable epilepsy.

METHODS

Fifteen children aged 4-16 years underwent multimodal examinations (MRI, interictal and/or ictal ECD-SPECT, EEG and MEG) to investigate their indications for surgical treatment. All children were diagnosed with ASD according to DSM-IV criteria and intractable epilepsy. Despite medical treatment for more than a year, all experienced at least one seizure per month. All had no underlying basic disorders. Each SPECT result was statistically analyzed by comparing with standard SPECT images obtained from our institute (easy Z-score imaging system; eZIS). The relationship between the eZIS pattern and EEG abnormalities or clinical symptoms was investigated.

RESULTS

All children showed focal abnormal patterns on eZIS and focal spikes on EEG. In all children, eZIS revealed a mixed hypoperfusion pattern, especially in the prefrontal cortex, medial frontal cortex, anterior cingulate cortex, medial parietal cortex, and/or anterior temporal cortex. In seven of 12 children who underwent interictal SPECT studies, areas of hypoperfusion were related to the focus observed on EEG; in six children, the focal EEG spikes represented areas of hyperperfusion. The children were divided into two groups according to the main type of hypoperfusion patterns seen on eZIS; medial-cingulate type and temporal type. No significant relationship was observed between the areas of hypoperfusion and clinical symptoms. eZIS showed the epileptic focus clearly on ictal SPECT.

CONCLUSIONS

SPECT was useful to detect the abnormal brain region not only in searching for the epileptic focus but also in assessing the low or high functioning region of the brain.

Multimodal neuroimaging in presurgical evaluation of childhood epilepsy

In pre-surgical evaluation of pediatric epilepsy, the combined use of multiple imaging modalities for precise localization of the epileptogenic focus is a worthwhile endeavor. Advanced neuroimaging by high field Magnetic resonance imaging (MRI), diffusion tensor images, and MR spectroscopy have the potential to identify subtle lesions. ¹⁸F-FDG positron emission tomography and single photon emission tomography provide visualization of metabolic alterations of the brain in the ictal and interictal states. These techniques may have localizing value for patients which exhibit normal MRI scans. Functional MRI is helpful for non-invasively identifying areas of eloquent cortex. These advances are improving our ability to noninvasively detect epileptogenic foci which have gone undetected in the past and whose accurate localization is crucial for a favorable outcome following surgical resection.

What Do Changes in Brain Perfusion Induced by Etomidate Suggest about Epilepsy in Human Patients?

Epilepsy is one of the major neurological disorders, affecting roughly 1-2% of the world's population, of which approximately 20–25% of patients are drug resistant. A variety of drugs have been used to activate and identify the epileptic area in patients during presurgical evaluation. We studied the cerebral blood flow (CBF) by single photon-emission computed tomography (SPECT) and bioelectrical brain activity responses to etomidate in 11 patients. Etomidate (0.1 mg/kg) was administered while patients were monitored by video-electroencephalography with foramen ovale electrodes (FOEs). After etomidate administration, a brief period of high-frequency activity was observed, followed by a generalized, high-voltage delta pattern. Increased regional CBF was observed bilaterally in thalamus, putamen, and posterior hippocampus. Besides, the only interhemispheric difference was observed in the posterior hippocampus, where CBF decreased in the epileptic temporal lobe. Activation by etomidate induces a specific and repetitive response in the bioelectrical activity. In addition, CBF changes induced by etomidate may serve as a diagnostic tool in the near future.

New directions in clinical imaging of cortical dysplasias

Neuroimaging is essential in the work-up of patients with intractable epilepsy. In pediatric patients with medically refractory epilepsy, cortical dysplasias account for a large percentage of the epileptogenic substrate. Unfortunately, these are also the most subtle lesions to identify. For this reason, there has been ongoing interest in utilizing new advanced magnetic resonance imaging (MRI) techniques to improve the ability to identify, diagnose, characterize, and delineate cortical dysplasias. Technologic gains such as multichannel coils (32 phased array and beyond) and higher field strengths (3T, 7T, and greater) coupled with newer imaging sequences such as arterial spin labeling (ASL), susceptibility weighted imaging (SWI) and diffusion tensor/spectrum imaging (DTI/DSI) are likely to increase yield. Improved MRI techniques coupled with a multimodality approach including magnetoencephalography (MEG), positron emission tomography (PET), and other techniques will increase sensitivity and specificity for identifying cortical dysplasias.

PET and SPECT in epilepsy: a critical review

Molecular imaging with ictal and interictal single-photon emission computed tomography (SPECT) as well as positron emission tomography (PET) rank among the established functional imaging tests for the presurgical evaluation of epileptic onset zone in patients with intractable partial epilepsy. In temporal lobe epilepsy the sensitivity of these methods was shown to be excellent, in particular if a multimodal platform is used, which combines the functional imaging with the additional morphological information of magnetic resonance imaging (MRI), but was lower in extra temporal lobe epilepsy. Functional imaging with SPECT and PET reflects seizure related changes of cerebral perfusion, glucose-metabolism and neuroreceptor status. In this review the usefulness of SPECT and PET imaging in clinical routine in epilepsy as well as the role of different neuroreceptor PET-tracer, which were used in epilepsy are discussed. The use of perfusion SPECT tracer allows the investigation of ictal activations, but the low temporal resolution of ictal perfusion SPECT often results in the detection of both the ictal onset zone as well as the propagation pathways, an area that has not always need to be resected in order to render a patient seizure free. The additional use of interictal PET with fluorine-18 fluorodeoxyglucose which measures regional cerebral metabolism or interictal perfusion SPECT enhance the informational value of ictal SPECT and were shown to be important tools to better define the ictal onset and surround inhibition zones. In recent years PET imaging of different cerebral neuroreceptor-systems inter alia GABA(A) receptors, serotonin receptors (5-HT(1A)), opioid receptors as well as dopamine receptors was used to investigate the neurochemical basis of epilepsy, the role of these neurotransmitters for the epileptogenesis as well as the spread of epileptic activity during seizures and partially entered in clinical routine. Currently some of these radioligands are also used to investigate new treatment approaches.

Hemodynamic surrogates for excitatory membrane potential change during interictal epileptiform events in rat neocortex

Hemodynamic changes in the brain are often used as surrogates for epileptic neuronal activity in both the laboratory and the clinic (e.g., intrinsic signal, functional magnetic resonance imaging and single-photon emission computed tomography) in spite of the fact that perfusion-based signals have been shown to overestimate the population of spiking neurons. In addition, mechanisms of neurovascular coupling that apply during normal cortical processing may not be relevant in pathological circumstances such as epilepsy. For these reasons, we investigated the spatiotemporal dynamics of epileptic neurovascular coupling using voltage-sensitive dyes (VSDs) to generate spatial maps of excitatory membrane activity and intrinsic optical spectroscopy (IOS) to measure deoxy-hemoglobin and total hemoglobin, i.e., cerebral blood volume (CBV), in vivo during interictal spikes in rat neocortex to examine their spatiotemporal correlations. We hypothesized that the IOS signal would correlate spatially with subthreshold excitatory activity, which involves a larger area of cortex than suprathreshold neuronal spiking. However, we found that both perfusion and oximetric signals spatially overshot the extent of the excitatory VSD signal by approximately 2x. Nevertheless, a high correlation could be found at specific time points in the evolution and dissolution of the hemodynamic signals. The increase in deoxy-hemoglobin reached the highest correlation with the excitatory VSD signal earlier than CBV signals although CBV signals correlated equally well at certain time points. The amplitude of the hemodynamic signals had a linear correlation with the amplitude of the VSD signals except for small nonlinearities in the very center of the focus and in the periphery of the surround, indicating a tight spatial coupling. Our data suggest that hemodynamic signals can accurately define the spatial extent of excitatory interictal epileptiform subthreshold membrane activity at specific time points in their evolution.

Utility of neuronavigation and neuromonitoring in epilepsy surgery

The management of medically refractory epilepsy poses both a valuable therapeutic opportunity and a formidable technical challenge to epilepsy surgeons. Recent decades have produced significant advancements in the capabilities and availability of adjunctive tools in epilepsy surgery. In particular, image-based neuronavigation and electrophysiological neuromonitoring represent versatile and informative modalities that can assist a surgeon in performing safe and effective resections. In the present article the authors discuss these 2 subjects with reference to how they can be applied and what evidence supports their use. As technologies evolve with demonstrated and potential utility, it is important for all clinicians who deal with epilepsy to understand where neuronavigation and neuromonitoring stand in the present and what avenues for improvement exist for the future.

Pharmacologically intractable epilepsy in children: diagnosis and preoperative evaluation

It is important to correctly diagnose medically intractable epilepsy in children and to identify those children whose medically refractory, localization-related seizures may be surgically remediable as soon as possible to optimize the surgical outcome. In this paper the authors review the definition of medically intractable seizures and discuss the various causes and risk factors for this disorder in children. They also outline the presurgical diagnostic evaluation process for pharmacologically intractable epilepsy in children who may be candidates for surgical treatment of localization-related seizures. The treatment of children with medically intractable epilepsy is both challenging and rewarding. Surgery has the potential of altering the natural history of epilepsy by improving or eliminating seizures in carefully selected patients.

Different structures involved during ictal and interictal epileptic activity in malformations of cortical development: an EEG-fMRI study

Malformations of cortical development (MCDs) are commonly complicated by intractable focal epilepsy. Epileptogenesis in these disorders is not well understood and may depend on the type of MCD. The cellular mechanisms involved in interictal and ictal events are notably different, and could be influenced independently by the type of pathology. We evaluated the relationship between interictal and ictal zones in eight patients with different types of MCD in order to better understand the generation of these activities: four had nodular heterotopia, two focal cortical dysplasia and two subcortical band heterotopia (double-cortex). We used the non-invasive EEG-fMRI technique to record simultaneously all cerebral structures with a high spatio-temporal resolution. We recorded interictal and ictal events during the same session. Ictal events were either electrical only or clinical with minimal motion. BOLD changes were found in the focal cortical dysplasia during interictal and ictal epileptiform events in the two patients with this disorder. Heterotopic and normal cortices were involved in BOLD changes during interictal and ictal events in the two patients with double cortex, but the maximum BOLD response was in the heterotopic band in both patients. Only two of the four patients with nodular heterotopia showed involvement of a nodule during interictal activity. During seizures, although BOLD changes affected the lesion in two patients, the maximum was always in the overlying cortex and never in the heterotopia. For two patients intracranial recordings were available and confirm our findings. The dysplastic cortex and the heterotopic cortex of band heterotopia were involved in interictal and seizure processes. Even if the nodular gray matter heterotopia may have the cellular substrate to produce interictal events, the often abnormal overlying cortex is more likely to be involved during the seizures. The non-invasive BOLD study of interictal and ictal events in MCD patients may help to understand the role of the lesion in epileptogenesis and also determine the potential surgical target.

Differences in ictal hyperperfusion of limbic-related structures between mesial temporal and neocortical epilepsy

BACKGROUND

Ictal propagation to the cortical and subcortical structures is well known in mesial temporal epilepsy (MTE) and neocortical epilepsy (NE). We analyzed the ictal changes of regional blood flow in limbic-related cortical and subcortical structures to evaluate the differences in ictal propagation patterns between MTE and NE.

METHODS

In 65 patients (mean age, 29.1+/-10.83 years) with intractable MTE (n=46) or NE (n=19), ictal 99m-Tc ethyl cystinate dimer SPECT was performed. A subtracted ictal SPECT coregistered to MRI images was obtained in each patient. The patterns of subtracted ictal hyperperfusion in the limbic, paralimbic and subcortical structures in patients with MTE and NE were compared.

RESULTS

The ictal hyperperfusion of the amygdala, hippocampus, temporal pole and insula were significantly higher in MTE (P<0.01), but cingulate and orbitofrontal hyperperfusion were not. A significant difference in striatal ictal hyperperfusion between the MTE and NE group was found (P=0.035). Ictal hyperperfusion of NE was greater in the superior part (P=0.011), whereas that of MTE was greater in the inferior and middle parts.

CONCLUSIONS

These findings suggest that the ictal propagation of MTE may differ from that of NE via different pathways not only in the cortical regions but also in the subcortical structures.

Preictal versus ictal injection of radiotracer for SPECT study in partial epilepsy: SISCOM

A 27-year-old man had complex partial seizures and a dysembryoplastic neuroepithelial tumor (DNT) in the left inferior-basal temporal region. The patient's seizures consisted of incomprehensible speech, staring, unresponsiveness, fumbling and then looking around. For the brain SPECT study, radiotracer was injected during the preictal (11s prior to seizure onset), ictal (at 25 s out of 47 s seizure duration) and interictal periods. Interictal SPECT was subtracted from preictal or ictal-injection SPECTs and then the subtracted SPECTs were overlaid on the patient's MRI (SISCOM). SISCOM with preictal-injection SPECT showed hyperperfusion at the brain lesion, whereas SISCOM with ictal-injection SPECT showed hyperperfusion at the ipsilateral amygdala-hippocampus and hypoperfusion around the tumor lesion. After the DNT and nearby temporal lobe tissues were resected with preservation of amygdala-hippocampus, the patient became seizure free without complaint of subjective postsurgical memory decline. In this patient, SISCOM with preictal injection of radiotracer localized an epileptogenic zone, whereas SISCOM with the ictal injection showed hyperperfusion at the symptomatogenic zone.