Ictal SPECT statistical parametric mapping in temporal lobe epilepsy surgery

Abstract

Objective: Although subtraction ictal SPECT coregistered to MRI (SISCOM) is clinically useful in epilepsy surgery evaluation, it does not determine whether the ictal-interictal subtraction difference is statistically different from the expected random variation between 2 SPECT studies. We developed a statistical parametric mapping and MRI voxel-based method of analyzing ictalinterictal SPECT difference data (statistical ictal SPECT coregistered to MRI [STATISCOM]) and compared it with SISCOM. Methods:Two serial SPECT studies were performed in 11 healthy volunteers without epilepsy (control subjects) to measure random variation between serial studies from individuals. STATISCOM and SISCOM images from 87 consecutive patients who had ictal SPECT studies and subsequent temporal lobectomy were assessed by reviewers blinded to clinical data and outcome. Results:Interobserver agreement between blinded reviewers was higher for STATISCOM images than for SISCOM images ( ϭ 0.81 vs ϭ 0.36). STATISCOM identified a hyperperfusion focus in 84% of patients, SISCOM in 66% (p Ͻ 0.05). STATISCOM correctly localized the temporal lobe epilepsy (TLE) subtypes (mesial vs lateral neocortical) in 68% of patients compared with 24% by SISCOM (p ϭ 0.02); subgroup analysis of patients without lesions (as determined by MRI) showed superiority of STATISCOM (80% vs 47%; p ϭ 0.04). Moreover, the probability of seizure-free outcome was higher when STATISCOM correctly localized the TLE subtype than when it was indeterminate (81% vs 53%; p ϭ 0.03). Conclusion:Statistical ictal SPECT coregistered to MRI (STATISCOM) was superior to subtraction ictal SPECT coregistered to MRI for seizure localization before temporal lobe epilepsy (TLE) surgery. STATISCOM localization to the correct TLE subtype was prognostically important for postsurgical seizure freedom. Neurology ® 2010;74:70 -76 GLOSSARY CI ϭ confidence interval; ECD ϭ ethyl cysteinate dimer; HMPAO ϭ hexamethyl propylene-amine-oxime; SISCOM ϭ subtraction ictal SPECT coregistered to MRI; SPM ϭ statistical parametric mapping; STATISCOM ϭ statistical ictal SPECT coregistered to MRI; TLE ϭ temporal lobe epilepsy.Early methods of ictal SPECT interpretation relied on a visual comparison of ictal and interictal SPECT images to detect focal hyperperfusion changes (these represented potential sites of ictal hyperperfusion).1 SPECT imaging subsequently was improved by subtraction ictal SPECT with coregistration on MRI (SISCOM).2-5 With SISCOM, ictal SPECT data are subtracted from interictal SPECT data, 6,7 and the "difference image," which shows the focus of altered perfusion, is coregistered with the patient's MRI for anatomic correlation. A recent study that compared several functional imaging modalities showed that positive SISCOM has the greatest association with seizure-free outcome after focal epilepsy surgery. 8Despite the validation of its clinical usefulness, SISCOM detection of abnormal perfusion is based a priori on a defined threshold of perfusion changes, and it does not account for the...

Statistical Parametric Mapping Demonstrates Asymmetric Uptake with Tc-99m ECD and Tc-99m HMPAO SPECT in Normal Brain

“…O-15 PET images represent the immediate perfusion state of the brain at the time of image acquisition and are essentially limited to interictal (between seizures) studies because of the logistical challenge of injecting and immediately scanning the patient during a seizure. Cerebral blood flow is an important diagnostic metric in stroke (Liebeskind, 2009), neurodegenerative disease (Josephs et al, 2006), movement disorders (Takahashi et al, 2010), and epilepsy (Duncan, 2009;O'Brien et al, 2000;Kazemi et al, 2009), and is frequently used as a surrogate estimation of neural activity in clinical neurology and research studies of cerebral function.…”

Clinical Value of the First Dedicated, Commercially Available Automatic Injector for Ictal Brain SPECT in Presurgical Evaluation of Pediatric Epilepsy: Comparison with Manual Injection

“…More recently, subtraction ictal SPECT techniques and statistical comparison with normal control SPECT databases have been validated by several studies, showing a rate of epileptogenic focus localization that was equivalent or superior to that seen in interictal-ictal side-by-side visual analysis (17)(18)(19)(20)(21).…”

Neuroimaging for the prediction of response to medical and surgical treatment in epilepsy

“…They recently compared SISCOM and STATISCOM images from 87 consecutive patients submitted to temporal lobectomy and showed superiority of STATISCOM for seizure localization. Furthermore, the authors confirmed an increased probability of seizure-free outcome when STATISCOM correctly localized the TLE subtype [73].…”

“…All three methods showed value in predicting seizure-free outcome, however, in those cases with all three tests (27 patients), the ictal SPECT had the highest OR of 9.1 (p = 0.05). In order to take into account the normal variation between sequential SPECT scans of single individuals (i.e., ictal and interictal images) some investigators used neuroimaging postprocessing techniques with SPM (http://www.fil.ion.ucl.ac.uk/spm/) to create a statistical parametric mapping (SPM) and MRI voxel-based method to analyze ictal--interictal SPECT difference maps (statistical ictal SPECT coregistered to MRI (STATISCOM)) [73]. They recently compared SISCOM and STATISCOM images from 87 consecutive patients submitted to temporal lobectomy and showed superiority of STATISCOM for seizure localization.…”