Subtraction Ictal Single-photon Emission Research Articles

Subtraction ictal single-photon emission computed tomography (SPECT) co-registered to MRI (SISCOM) in presurgical diagnostics of epilepsy

Subtraction ictal single-photon emission computed tomography (SPECT) co-registered to MRI (SISCOM) in presurgical diagnostics of epilepsy

MNI SISCOM: an Open-Source Tool for Computing Subtraction Ictal Single-Photon Emission CT Coregistered to MRI.

Subtraction ictal single-photon emission computed tomography (SPECT) coregistered to MRI (SISCOM) is a well-established technique for quantitative analysis of ictal vs interictal SPECT images that can contribute to the identification of the seizure onset zone in patients with drug-resistant epilepsy. However, there is presently a lack of user-friendly free and open-source software to compute SISCOM results from raw SPECT and MRI images. We aimed to develop a simple graphical desktop application for computing SISCOM. MNI SISCOM is a new free and open-source software application for computing SISCOM and producing practical MRI/SPECT/SISCOM image panels for review and reporting. The graphical interface allows any user to quickly and easily obtain SISCOM images with minimal user interaction. Additionally, MNI SISCOM provides command line and Python interfaces for users who would like to integrate these features into their own scripts and pipelines. MNI SISCOM is freely available for download from: https://github.com/jeremymoreau/mnisiscom .

On the optimal z-score threshold for SISCOM analysis to localize the ictal onset zone

BackgroundIn epilepsy patients, SISCOM or subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging has become a routinely used, non-invasive technique to localize the ictal onset zone (IOZ). Thresholding of clusters with a predefined number of standard deviations from normality (z-score) is generally accepted to localize the IOZ. In this study, we aimed to assess the robustness of this parameter in a group of patients with well-characterized drug-resistant epilepsy in whom the exact location of the IOZ was known after successful epilepsy surgery. Eighty patients underwent preoperative SISCOM and were seizure free in a postoperative period of minimum 1 year. SISCOMs with z-threshold 2 and 1.5 were analyzed by two experienced readers separately, blinded from the clinical ground truth data. Their reported location of the IOZ was compared with the operative resection zone. Furthermore, confidence scores of the SISCOM IOZ were compared for the two thresholds.ResultsVisual reporting with a z-score threshold of 1.5 and 2 showed no statistically significant difference in localizing correspondence with the ground truth (70 vs. 72% respectively, p = 0.17). Interrater agreement was moderate (κ = 0.65) at the threshold of 1.5, but high (κ = 0.84) at a threshold of 2, where also reviewers were significantly more confident (p < 0.01).ConclusionsSISCOM is a clinically useful, routinely used modality in the preoperative work-up in many epilepsy surgery centers. We found no significant differences in localizing value of the IOZ using a threshold of 1.5 or 2, but interrater agreement and reader confidence were higher using a z-score threshold of 2.

Accuracy of arterial spin labeling magnetic resonance imaging (MRI) perfusion in detecting the epileptogenic zone in patients with drug‐resistant neocortical epilepsy: comparison with electrophysiological data, structural MRI, SISCOM and FDG‐PET

Locating the epileptogenic zone (EZ) in patients with neocortical epilepsy presents major challenges. Our aim was to assess the accuracy of arterial spin labeling (ASL), an emerging non-invasive magnetic resonance imaging (MRI) perfusion technique, to locate the EZ in patients with drug-resistant neocortical epilepsy. Twenty-five consecutive patients with neocortical epilepsy referred to our epilepsy unit for pre-surgical evaluation underwent a standardized assessment including video-electroencephalography (EEG) monitoring, structural MRI, subtraction ictal single-photon emission computed tomography co-registered to MRI (SISCOM) and fluorodeoxyglucose positron emission tomography (FDG-PET) studies. An ASL sequence was included in the MRI studies. Areas of hypoperfusion or hyperperfusion on ASL were classified into 15 anatomic-functional cortical regions; these regional cerebral blood flow maps were compared with the EZ determined by the other tests and the strength of concordance was assessed with the kappa coefficient. Of the 25 patients [16 (64%) women; mean age 32.4 (±13.8) years], 18 (72%) had lesions on structural MRI. ASL abnormalities were seen in 15 (60%) patients (nine hypoperfusion, six hyperperfusion). ASL had a very good concordance with FDG-PET (k = 0.84), a good concordance with structural MRI (k = 0.76), a moderate concordance with video-EEG monitoring (k = 0.53) and a fair concordance with SISCOM (k = 0.28). Arterial spin labeling might help to confirm the location and extent of the EZ in the pre-surgical workup of patients with drug-resistant neocortical epilepsy.

Predictors of Length of Stay in Children Admitted for Presurgical Evaluation for Epilepsy Surgery

RationaleOne challenge for families whose children are undergoing presurgical evaluation for epilepsy surgery is the unpredictable length of hospitalization for video-electroencephalograph monitoring. The goal of this study was to retrospectively evaluate length of stay in children admitted for presurgical evaluation at a tertiary referral center. MethodsDuration of stay for children with medically intractable epilepsy admitted for presurgical evaluation to the Pediatric Epilepsy Monitoring Unit at Mayo Clinic Rochester between 2010 and 2013 was evaluated retrospectively. ResultsOf 140 children, surgical candidacy was determined in 122 (87.1%) (72 candidates, 50 noncandidates). The mean length of stay was 4.0 ± 3.7 days and was not predicted by candidacy for surgery, age at monitoring, duration of epilepsy, number of antiepileptic drugs at admission, or focal/hemispheric magnetic resonance imaging abnormality. Shorter length of stay was predicted by younger age at epilepsy onset (P < 0.05) and shorter interval since most recent seizure (P = 0.001). Subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging was performed in 43 (35.2%) children, and correlated with longer length of stay (mean 5.1 ± 4.1 days for subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging users versus 3.5 ± 3.3 days for nonusers, P = 0.022). Antiepileptic drugs were reduced either upon or after admission in 67 (54.9%) children, and the length of stay was significantly longer in these patients (mean 5.5 ± 4.1 days if antiepileptic drugs were reduced versus 2.2 ± 2.1 days if not reduced, P < 0.001). ConclusionsSignificant predictors of shorter length of stay include younger age at epilepsy onset, shorter interval from most recent seizure, lack of subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging, and lack of need for AED reduction on or after admission.

I cannot stand this anymore!

A 28-year-old right-handed man presented with medically intractable focal reflex epilepsy. He previously underwent resection of a right parietal lobe cortical dysplasia. Postoperatively, he developed focal reflex epilepsy triggered by...

Correspondence between large-scale ictal and interictal epileptic networks revealed by single photon emission computed tomography (SPECT) and electroencephalography (EEG)-functional magnetic resonance imaging (fMRI).

Epilepsy is increasingly recognized as a network disorder, but the spatial relationship between ictal and interictal networks is still largely unexplored. In this work, we compared hemodynamic changes related to seizures and interictal spikes on a whole brain scale. Twenty-eight patients with refractory focal epilepsy (14 temporal and 14 extratemporal lobe) underwent both subtraction ictal single photon emission computed tomography (SPECT) coregistered to magnetic resonance imaging (MRI) (SISCOM) and spike-related electroencephalography (EEG-functional MRI (fMRI). SISCOM visualized relative perfusion changes during seizures, whereas EEG-fMRI mapped blood oxygen level-dependent (BOLD) changes related to spikes. Similarity between statistical maps of both modalities was analyzed per patient using the following two measures: (1) correlation between unthresholded statistical maps (Pearson's correlation coefficient) and (2) overlap between thresholded images (Dice coefficient). Overlap was evaluated at a regional level, for hyperperfusions and activations and for hypoperfusions and deactivations separately, using different thresholds. Nonparametric permutation tests were applied to assess statistical significance (p ≤ 0.05). We found significant and positive correlations between hemodynamic changes related to seizures and spikes in 27 (96%) of 28 cases (median correlation coefficient 0.29 [range -0.12 to 0.62]). In 20 (71%) of 28 cases, spatial overlap between hyperperfusion on SISCOM and activation on EEG-fMRI was significantly larger than expected by chance. Congruent changes were not restricted to the territory of the presumed epileptogenic zone, but could be seen at distant sites (e.g., cerebellum and basal ganglia). Overlap between ictal hypoperfusion and interictal deactivation was statistically significant in 22 (79%) of 28 patients. Despite the high rate of congruence, discrepancies were observed for both modalities. We conclude that hemodynamic changes related to seizures and spikes varied spatially with the same sign and within a common network. Overlap was present in regions nearby and distant from discharge origin.

PET/MRI and PET/MRI/SISCOM coregistration in the presurgical evaluation of refractory focal epilepsy

We aimed to investigate the usefulness of coregistration of positron emission tomography (PET) and magnetic resonance imaging (MRI) findings (PET/MRI) and of coregistration of PET/MRI with subtraction ictal single-photon emission computed tomography (SPECT) coregistered to MRI (SISCOM) (PET/MRI/SISCOM) in localizing the potential epileptogenic zone in patients with drug-resistant epilepsy. We prospectively included 35 consecutive patients with refractory focal epilepsy whose presurgical evaluation included a PET study. Separately acquired PET and structural MRI images were coregistered for each patient. When possible, ictal SPECT and SISCOM were obtained and coregistered with PET/MRI. The potential location of the epileptogenic zone determined by neuroimaging was compared with the seizure onset zone determined by long-term video-EEG monitoring and with invasive EEG studies in patients who were implanted. Structural MRI showed no lesions in 15 patients. In these patients, PET/MRI coregistration showed a hypometabolic area in 12 (80%) patients that was concordant with seizure onset zone on EEG in 9. In 7 patients without MRI lesions, PET/MRI detected a hypometabolism that was undetected on PET alone. SISCOM, obtained in 25 patients, showed an area of hyperperfusion concordant with the seizure onset zone on EEG in 7 (58%) of the 12 of these patients who had normal MRI findings. SISCOM hyperperfusion was less extensive than PET hypometabolism. A total of 19 patients underwent surgery; 11 of these underwent invasive-EEG monitoring and the seizure onset zone was concordant with PET/MRI in all cases. PET/MRI/SISCOM coregistration, performed in 4 of these patients, was concordant in 3 (75%). After epilepsy surgery, 13 (68%) patients are seizure-free after a mean follow-up of 4.5 years. PET/MRI and PET/MRI/SISCOM coregistration are useful for determining the potential epileptogenic zone and thus for planning invasive EEG studies and surgery more precisely, especially in patients without lesions on MRI.

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

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. 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. 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. 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.

SISCOM and FDG‐PET in patients with non‐lesional extratemporal epilepsy: correlation with intracranial EEG, histology, and seizure outcome

To assess the practical localising value of subtraction ictal single-photon emission computed tomography (SISCOM) coregistered with MRI and (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with extratemporal epilepsy and normal MRI. We retrospectively studied a group of 14 patients who received surgery due to intractable epilepsy and who were shown to have focal cortical dysplasia, undetected by MRI, based on histological investigation. We coregistered preoperative SISCOM and PET images with postoperative MRI and visually determined whether the SISCOM focus, PET hypometabolic area, and cerebral cortex, exhibiting prominent abnormalities on intracranial EEG, were removed completely, incompletely, or not at all. These results and histopathological findings were compared with postoperative seizure outcome. Two patients underwent one-stage multimodal image-guided surgery and the remaining 12 underwent long-term invasive EEG. SISCOM findings were localised for all but 1 patient. FDG-PET was normal in 3 subjects, 2 of whom had favourable postsurgical outcome (Engel class I and II). Complete resection of the SISCOM focus (n=3), the area of PET hypometabolism (n=2), or the cortical regions with intracranial EEG abnormalities (n=7) were predictive of favourable postsurgical outcome. Favourable outcome was also encountered in: 4 of 8 patients with incomplete resection and 1 of 2 with no resection of the SISCOM focus; 4 of 7 patients with incomplete resection and 1 of 2 with no resection of the PET hypometabolic area; and 2 of 7 patients with incomplete resection of the area corresponding to intracranial EEG abnormality. No correlation between histopathological FCD subtype and seizure outcome was observed. Complete resection of the dysplastic cortex localised by SISCOM, FDG-PET or intracranial EEG is a reliable predictor of favourable postoperative seizure outcome in patients with non-lesional extratemporal epilepsy.

Prospective use of subtraction ictal SPECT coregistered to MRI (SISCOM) in presurgical evaluation of epilepsy

In patients with drug-refractory focal epilepsy, nonlesional magnetic resonance imaging (MRI) or discordant data of presurgical standard investigations leads to failure generating a sufficient hypothesis for electrode implantation or epilepsy surgery. The seizure-onset zone can be further investigated by subtraction ictal single-photon emission computed tomography (SPECT) coregistered to MRI (SISCOM). This is an observational study of a large consecutive cohort of patients undergoing prospective SISCOM to generate hypothesis for electrode implantation or site of epilepsy surgery. One hundred seventy-five consecutive patients undergoing presurgical evaluation with either nonlesional MRI or discordant data of standard investigations preventing the generation of hypothesis for seizure onset were evaluated with SISCOM. Results were compared to gold standard for seizure onset detection, either electrocorticography (ECoG) and/or postoperative outcome. One hundred thirty patients had successful SPECT injection. Hypothesis for electrode implantation/site of surgery was generated in 74 patients. Forty patients had gold standard comparison. Twenty-eight patients underwent resective surgery. SISCOM was concordant to site of surgery in 82%. An additional 12 patients underwent invasive EEG monitoring but were not suitable for surgery. SISCOM was concordant multifocal in 75%. Two years postsurgical follow-up of 26 patients showed favorable outcome in 22 (Engel class I and class II). SISCOM is a highly valuable diagnostic tool to localize the seizure-onset zone in nonlesional and extratemporal epilepsies. Outcome in this patient group was unexpectedly good, even in patients with nonlesional MRI. The high correlation with ECoG and site of successful surgery is a strong indicator that outcome prediction in this patient group should be adapted accordingly, which may encourage more patients to undergo electrode implantation and subsequent successful surgery. Statistical analysis showed that SISCOM with shorter duration of seizures, focal seizures, and lesional MRI was more likely to generate implantation hypothesis.

SISCOM in Children with Tuberous Sclerosis Complex-Related Epilepsy

Identification of a single epileptogenic focus in patients with tuberous sclerosis complex is a challenge. Noninvasive imaging modalities, including subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging (SISCOM), have been used to determine the dominant epileptogenic focus for surgical resection. We assessed whether complete resection of SISCOM hyperperfusion abnormality correlates with seizure-free outcome in 6 children with tuberous sclerosis complex-related epilepsy. The median seizure onset age was 4 months (range 1 day to 16 months). The age at surgery ranged from 8 months to 13 years. A dominant SISCOM hyperperfusion focus was identified in 5 patients with multiple tubers. SISCOM provided additional localizing information for epilepsy surgery in 3 patients with nonlocalizing or discordant electrophysiologic and neuroimaging findings. At a minimum of 2 years' follow-up, 3 patients were free of seizures overall. Freedom from seizures was associated with complete resection of SISCOM abnormality in 2 patients. These findings demonstrate that SISCOM can be useful in identifying the epileptogenic zone and in guiding the location and extent of epilepsy surgery in children with tuberous sclerosis complex and multifocal abnormalities. In children with tuberous sclerosis complex and intractable epilepsy, complete resection of the SISCOM hyperperfusion abnormality is associated with freedom from seizures.

Imaging epilepsy with SISCOM

We read with interest the Review by Duncan (Imaging in the surgical treatment of epilepsy. Nat. Rev. Neurol. 6, 537–550; 2010) on the role of imaging in epilepsy surgery.1 The combination of functional MRI with EEG or magnetoencephalography is a useful method for studying the irritative zone during the interictal period. These technologies are, however, of limited use for studying ictal activity, a fundamental step in the presurgical evaluation of refractory epilepsy. Although mentioned by Duncan in his article, we feel a slightly expanded discussion is warranted concerning the use of computer-aided subtraction ictal single-photon emission CT coregistered to MRI (SISCOM) and its variants to identify an epileptogenic zone.2,3 In our view, this methodology has been poorly explored in the context of refractory epilepsy, and provides valuable information for the identification of ictal activity and seizure propagation that has not been matched by other methods to date. SISCOM can be used to visualize ictal activity in the brain, and allows abnormal neural perfusion to be mapped onto surrounding neural structures. This technique may prove useful during several scenarios in the presurgical evaluation of refractory epilepsy. In patients with normal or nearnormal MRI, SISCOM can be employed to improve localization of the epileptogenic zone for electrode placement, surgical resections and determination of surgical prognosis (Figure 1).4,5 In addition, SISCOM is useful in the planning of invasive investigations and the tailoring of surgery in patients with large lesional zones. In such patients, resection of part of the epileptogenic zone can sometimes be sufficient to control seizures.6,7 SISCOM might also have a role in evaluating and surgical planning in patients who have undergone unsuccessful resections.8 Presurgical SISCOM can provide valuable prognostic information. In some studies, resection of the entire epileptogenic zone, as identified by SISCOM, has been associated with good surgical outcome.4–7 SISCOM might also be used to contraindicate surgical resections.3 Finally, SISCOM might permit the study of the epileptogenic zone, seizure propagation and the relationship between seizures and the underlying morphological neural substrates, allowing insights into the mechanisms of seizure propagation.9,10 The use of SISCOM might improve the presurgical evaluation of patients with temporal lobe epilepsy11–13 and might be particularly useful for preoperative assessment of patients with extratemporal disease.3,6,14,15 When SISCOM localization findings are concordant with other presurgical findings (for example, EEG or PET findings) patients are more likely to have a good surgical outcome than those with nonconcordant or nonlocalizing findings.2,3,9,15 Thus, SISCOM improves the sensitivity and specificity of presurgical evaluation by improving localization for epilepsy surgery, and may allow surgery in previously ineligible patients. In spite of these advances, further studies are necessary to determine the accuracy of SISCOM in MRInegative patients, the impact of SISCOM in surgical decision-making, and the predictive power of SISCOM for surgical outcomes.

In vivo activation of endocannabinoid system in temporal lobe epilepsy with hippocampal sclerosis

The endocannabinoid system modulates neuronal excitability, protects neurons against hyperexcitability and is involved in epileptogenesis in animal models of mesial temporal lobe epilepsy with hippocampal sclerosis. We performed in vivo positron emission tomography imaging of the type 1 cannabinoid receptor in patients with mesial temporal lobe epilepsy with hippocampal sclerosis. Twelve patients with refractory mesial temporal lobe epilepsy due to hippocampal sclerosis received a [(18)F]MK-9470 scan to assess type 1 cannabinoid receptor availability in vivo. Parametric modified standard uptake values were used as quantitative measure of type 1 cannabinoid receptor availability and images were spatially normalized to standard space. Voxel-based analysis was performed comparing patients with hippocampal sclerosis to controls and correlations between type 1 cannabinoid receptor status and seizure characteristics were done using volumes of interest. Type 1 cannabinoid receptor positron emission tomography was co-registered with subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging of a complex partial seizure (n = 9). An increased type 1 cannabinoid receptor availability in the ipsilateral temporal lobe was observed, which correlated negatively with the latency since last seizure before scanning and positively to the number of seizures in the month before scanning. A decreased type 1 cannabinoid receptor availability was present in the superior insular cortex, ipsilateral more than contralateral. The ipsilateral insular region displayed a mild ictal hyperperfusion in the transition zone of subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging temporal lobe hyperperfusion-frontal lobe hypoperfusion during complex partial seizures. Type 1 cannabinoid receptor availability showed opposite changes in different brain regions that are involved during complex partial seizures in refractory mesial temporal lobe epilepsy with hippocampal sclerosis. The increase in type 1 cannabinoid receptor availability at the seizure onset zone might be a protective mechanism of neurons against hyperexcitability and seizure activity, or contribute to the process of epileptogenesis, or both. The decreased type 1 cannabinoid receptor availability in the insula may play a role in surround inhibition and prevention of seizure propagation.

Neuroimaging in identifying focal cortical dysplasia and prognostic factors in pediatric and adolescent epilepsy surgery

The purpose of this study is to determine the sensibility of each imaging tool in identifying focal cortical dysplasia (FCD) in children and adolescents with epilepsy and to define the prognostic factors of pediatric and adolescent epilepsy surgery. We identified 48 children with FCD who underwent resective surgery and analyzed their preoperative data. The results of various anatomic and functional neuroimaging studies were compared for accuracy in locating the lesion. We also investigated clinical factors that affected the outcome of surgical treatment. Brain magnetic resonance imaging (MRI) was able to localize FCD in 30 patients and fluorodeoxyglucose positron emission tomography (FDG-PET) and/or subtraction ictal single photon emission computed tomography (SPECT) coregistered with MRI provided additional information that helped to define the lesion in 13 patients. When comparing the pathologic results between a mild malformation of cortical development (MCD) and FCD type I and II, we noted a strong tendency for patients with FCD to have MRI abnormalities (p = 0.005). In addition, severe pathologic features (Palmini's classification, FCD type II) (p = 0.025) showed significant correlation with a better surgical outcome. To define the primary epileptogenic area, various interictal epileptiform discharges and the results of multimodal neuroimaging studies were helpful, and younger age at the time of operation could aid in more favorable surgical outcomes (p = 0.048). Our study showed a significant relationship between pathologic grade and the detectability of FCD by brain MRI. In addition, early surgery can be justified by showing that advanced neuroimaging studies in children with FCD and even with extensive epileptiform discharges have a higher rate of success.

Localization of temporal epilepsy foci by subtraction ictal perfusion single photon emission computed tomography is enhanced when using 3D-OSEM iterative reconstruction

Subtraction ictal single photon emission computed tomography (SPECT) images, provided by filtered back-projection (FBP), may exhibit a confusing high level of noise. This study was aimed at assessing an optimized three-dimensional ordered subset expectation maximization (3D-OSEM) iterative reconstruction in this setting. On phantom images, parameters of 3D-OSEM reconstruction were selected as those providing the higher signal/noise ratio but a high enough spatial resolution, equivalent to that of conventional FBP reconstruction (full width at half-maximum = 11 mm). Thereafter, subtraction ictal ethylene cysteine dimer-SPECT coregistered to MRI and reconstructed with either FBP or 3D-OSEM were compared in 21 patients with well-characterized temporal epilepsy foci (subsequent successful surgical treatment). On subtraction images, the use of the selected 3D-OSEM reconstruction (five iterations, 16 subsets and a 9 mm Gauss filter) instead of FBP was associated with: (i) marked reductions in background activity (0.05 ± 0.09 vs. 0.25 ± 0.18 cps, P < 0.001) and in the size of temporal foci (10 ± 7 vs. 14 ± 11 cm, P = 0.01) and (ii) a trend toward higher accuracy in identifying the involved temporal lobes (86 vs. 76%). Localization of temporal epilepsy foci by subtraction ictal SPECT is likely to be enhanced by using 3D-OSEM rather than FBP reconstruction because of marked reductions in background activity and in the size of detected foci.

Does SISCOM Contribute to Favorable Seizure Outcome after Epilepsy Surgery?

To assess the additional value of subtraction ictal single-photon emission computed tomography (SPECT) coregistered to MRI (SISCOM) for localization of the epileptogenic zone in patients with drug-resistant epilepsy scheduled for invasive video-EEG (VEEG) before epilepsy surgery by a descriptive study from clinical practice. Forty-nine consecutive epilepsy patients between January 2000 and March 2006 were included. Thirty-six of the 49 patients were offered surgery, and 34 underwent resective surgery during the study period. Localizing and outcome data are presented from 31 patients with a follow-up period of >or=12 months. Successful ictal SPECT was performed in 26 patients, and SISCOM showed significant hyperperfusions with 3.5 SD above reference. Twenty patients had SISCOM-guided electrode placement, invasive monitoring, and 1-year postsurgical follow-up data. Two independent epileptologists evaluated whether SISCOM results (a) altered the hypothesis and extended the strategy for electrode placement at invasive recording, or (b) were confirmatory of other localizing data and did not alter the strategy. We defined that SISCOM had an impact on seizure outcome if the seizure-onset zone was seen in electrodes overlying a brain region with a significant hyperperfusion. When SISCOM was concordant with ictal onset in the extended electrodes, SISCOM was considered a prerequisite for the outcome at postoperative follow-up. SISCOM findings altered and extended the strategy for electrode placement at invasive recording in 15 patients (group A). SISCOM was a prerequisite for seizure outcome in all six patients with favorable outcomes. Nine patients had poor results from surgery in this group; SISCOM was concordant with invasive VEEG in six patients, and discordant with invasive VEEG in three patients. SISCOM findings were confirmatory with other localizing data and did not alter the strategy at invasive recording in five patients (group B). Two patients had favorable surgical outcomes. In this group, three patients had poor results; SISCOM and other localizing findings were concordant with invasive VEEG in one patient and discordant with invasive VEEG in two patients. SISCOM is valuable for the identification of the epileptogenic zone in patients with drug-resistant epilepsy scheduled for invasive VEEG. SISCOM analysis was either a prerequisite for favorable result or concordant with other localizing methods in all patients with favorable seizure outcome at 1 year of follow-up [40%; confidence interval (CI), 19-64).

Micturition induced seizures: Ictal EEG and subtraction ictal SPECT findings

We report an 8-year-old girl with seizures induced by micturition. Her seizures were characterized by extension of upper extremities with preserved consciousness. Magnetic resonance imaging and interictal electroencephalograms were normal. Ictal electroencephalogram showed low voltage fast waves without clear focal features followed by frontal dominant rhythmic multiple spikes. Subtraction ictal single photon emission computed tomography revealed a significant increase in blood flow in the mesial frontal area.

Composite SISCOM Perfusion Patterns in Right and Left Temporal Seizures

To compare composite subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging (also known as SISCOM) patterns between right and left medial temporal-onset seizures to document neuroanatomical involvement in perfusion patterns. A retrospective comparative survey. Epilepsy monitoring unit in a tertiary care referral center. Subjects with temporal lobe epilepsy (TLE) who underwent ictal single-photon emission computed tomography studies. Comparison of ictal perfusion pattern changes in subjects with right and left temporal seizures. Composite subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance images showed similar regions of hyperperfusion change in the ipsilateral anteromedial temporal-corpus striatum-insula region in both groups. In the midbrain reticular formation, there was a significant difference in hyperperfusion between the left and right TLE groups. In addition, the right, but not the left, TLE group shows contralateral hypoperfusion of the temporoparietal junction. While anteromedial temporal-corpus striatum-insula perfusion patterns are similar, there are brainstem and hemispheric perfusion pattern differences in right and left TLE seizures, confirming pathophysiological differences between the groups. These findings help define neuronal network involvement in TLE seizures, and may explain the differences in clinical symptoms of right and left TLE seizures.

Subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging in evaluating the need for repeated epilepsy surgery

The aim of this study was to determine whether ictal single-photon emission computed tomography (SPECT) is useful in localizing the site of seizure onset in patients in whom surgery for intractable epilepsy failed and who are being considered for repeated surgery. Subtraction ictal SPECT coregistered to magnetic resonance imaging (SISCOM) studies were retrospectively analyzed in 58 patients who were being evaluated for possible repeated resection for intractable partial epilepsy between January 1, 1996, and October 31, 1999. All patients had persistent seizures subsequent to an initial resection and underwent another excision. The SISCOM-demonstrated abnormalities were classified as concordant, discordant, or indeterminate, compared with the localization of the epileptogenic zone revealed on video electroencephalography monitoring. The ability of SISCOM to predict operative outcome was also determined in patients who had undergone repeated surgical procedures. The SISCOM studies revealed a localized hyperperfused alteration in 46 (79%) of 58 patients. Forty-one (89%) of these 46 patients had a SISCOM-demonstrated alteration in the hemisphere of the previous epilepsy surgery. Imaging changes in 33 (72%) of the 46 patients were at the site of the previous focal cortical resection. Eight (17%) of the 46 had SISCOM-demonstrated abnormalities remote from the lobe in which surgery had been performed but in the ipsilateral hemisphere. The hyperperfusion focus was in the contralateral hemisphere in the remaining five patients (11%). The site of the epileptogenic zone was concordant with the SISCOM focus in 32 (70%) of 46 patients. Twenty-six patients underwent repeated resection and were followed up for a mean of 44 months thereafter; 11 of these patients (42%) had a significant reduction in seizure tendency. Only five patients (19%) were seizure free. Ten (50%) of 20 patients with a concordant SISCOM focus compared with none (0%) of three patients with a discordant focus had a favorable surgical outcome (p = 0.23). The SISCOM method might be useful in the evaluation of, and the surgical planning for, patients with intractable partial epilepsy in whom previous resective treatment has failed and who are being considered for reoperation.