Postictal Single Photon Emission Computed Tomography Research Articles

Developing an Asymmetry Method for Detecting Postictal Hyperperfusion in Poststroke Epilepsy.

Using dual single-photon emission computed tomography (SPECT) scanning, we recently found the postictal-interictal (P-I) subtraction method frequently detects prolonged postictal hyperperfusion in poststroke epilepsy (PSE) and thus may be valuable for auxiliary diagnosis. This study aimed to determine if the asymmetry method can localize hyperperfusion to reflect epileptic activity in PSE using a single postictal SPECT scan. Sixty-four patients with PSE who had undergone perfusion SPECT two times (postictal and interictal) were enrolled. We formulated a novel asymmetry method (subtraction analysis of reversed postictal SPECT from postictal SPECT, co-registered to magnetic resonance imaging) to identify paradoxical asymmetric increase, defined as a higher perfusion area adjacent to stroke lesions compared to the contralateral side. The postictal hyperperfusion area and detection rates were determined by the asymmetry and P-I subtraction methods independently. We subsequently calculated the sensitivity and specificity of the asymmetry method, compared to the gold standard P-I subtraction method. We also evaluated lateralization concordance between the asymmetry method and other clinical findings. Among 64 patients (median age, 75 years), prolonged postictal hyperperfusion was detected in 43 (67%) by the asymmetry, and 54 (84%) the P-I, method. The asymmetry method had high sensitivity (80%) and specificity (100%) in detecting postictal hyperperfusion, showing high lateralization concordance with seizure semiology (97%) and epileptiform electroencephalography findings (interictal/ictal epileptiform discharges or periodic discharges) (100%). The present study demonstrated the advantages of the objective asymmetry method for detecting prolonged hyperperfusion through using one postictal SPECT scan in PSE.

Injection of prophylactic lorazepam versus antiseizure drugs on the localization value of ictal SPECT studies and treatment-emergent adverse events: A single-center prospective study

ObjectiveWe aimed to examine the impact of resumption of home antiseizure drugs alone (ASD−) compared with adjunct administration of scheduled intravenous (IV) lorazepam 2 mg every 6 h (ASD+) following ictal single-photon emission computed tomography (SPECT) injection on the localization value of SPECT studies and treatment-emergent adverse events (TEAEs). MethodsWe conducted a prospective study at Mayo Clinic inpatient epilepsy monitoring unit (EMU) between January 2018 and May 2020 in Jacksonville, Florida. The ASD− and ASD+ groups were compared for concordance of SPECT studies with the epilepsy surgical conference (ESC) consensus or intracranial electroencephalography (icEEG) findings as reference. Treatment-emergent adverse events, obtained from surveys at 24 h and one week postictal SPECT injection, were also compared between both groups. ResultsTwenty-two consecutive patients with temporal (eight patients, 36%) and extratemporal (14 patients, 64%) epilepsy were included: 12 ASD+ and 10 ASD−. The two groups were well matched with regard to clinical and ictal SPECT injection characteristics including the occurrence of seizure between ictal and interictal SPECT injections. The localization value of SPECT studies was similar in the two groups. Patients in the ASD+ group reported higher rates of dizziness and excessive sedation at 24 h (p-value = 0.008). Fourteen patients (64%) underwent icEEG monitoring. For the entire cohort, the localization concordance of SPECT analysis by statistical parametric mapping (SPM) was superior to raw ictal SPECT (p-value = 0.003) and subtraction ictal SPECT coregistered to magnetic resonance imaging (MRI) (SISCOM; p-value = 0.021). Eventually, seven patients (31.8%) underwent resective brain surgery of whom four (57.1%) became seizure-free (median follow-up = 22 months). ConclusionsOur findings suggest that resuming home ASDs without the addition of scheduled IV lorazepam following inpatient ictal SPECT injection is equally efficacious for seizure onset zone (SOZ) localization on SPECT studies, especially SPM. This approach is also associated with fewer transient TEAEs and lower financial cost with no difference in preventing seizure between ictal and interictal SPECT injections.

Ictal SPECT

The localizing value of ictal single-photon emission computed tomography (SPECT) performed with cerebral blood flow agents in patients with epilepsy is based on cerebral metabolic and perfusion coupling. Ictal hyperperfusion is used to localize the epileptogenic zone noninvasively, and is particularly useful in magnetic resonance (MR)-negative partial epilepsy and focal cortical dysplasias. Subtraction ictal SPECT coregistered with MRI (SISCOM) improves the localization of the area of hyperperfusion. Ictal SPECT should always be interpreted in the context of a full presurgical evaluation. Early ictal SPECT injections minimize the problem of seizure propagation and of nonlocalization due to an early switch from ictal hyperperfusion to postictal hypoperfusion during brief extratemporal seizures. The degree of thresholding of SISCOM images affects the sensitivity and specificity of ictal SPECT. Ictal hypoperfusion may reflect ictal inhibition or deactivation. Postictal and interictal SPECT studies are less useful to localize the ictal-onset zone. Statistical parametric mapping analysis of groups of selected ictal-interictal difference images has the potential to demonstrate the evolution of cortical, subcortical, and cerebellar perfusion changes during a particular seizure type, to study seizure-gating mechanisms, and to provide new insights into the pathophysiology of seizures.

Single Photon Emission Computed Tomography (SPECT) in a Patient with Bilateral Temporal Seizures: Correlation Between Ictal EEG and Postictal/Ictal SPECT

We report a patient with bilateral independent temporal lobe seizures in whom two [99mTc]HMPAO single photon emission computed tomograph (SPECT) scans were performed during two different seizures. In the first periictal SPECT, [99mTc]HMPAO was injected in the interval between two closely spaced seizures (one localized in the left temporal lobe and the other in the right temporal lobe). SPECT images showed hypoperfusion in the left lateral temporal lobe, hyperperfusion of the left mesial temporal region, and pronounced hyperperfusion in the right anterior temporal lobe. These results suggest both a postictal left temporal SPECT pattern and an ictal right temporal pattern. In the second periictal SPECT, [99mTc]HMPAO was injected immediately after a right temporal lobe seizure and showed right lateral temporal lobe hypoperfusion and right mesial hyperperfusion, suggesting a postictal right temporal SPECT pattern. Interpretation of the periictal SPECT should take into account EEG changes at the time or in the minutes immediately after injection of [99mTc]HMPAO.

Postictal SPECT in Epileptic Versus Nonepileptic Seizures

Despite advances in video-electroencephalogram (EEG) technology, in many patients distinguishing epileptic seizures from nonepileptic seizures (NES) remains a challenge. Reliable methods to make this distinction are needed. In a pilot study, we performed postictal and interictal single photon emission computed tomography (SPECT) in 22 patients undergoing video-EEG monitoring who had altered responsiveness during an episode. Eleven had seizures, defined as episodes associated with EEG seizure patterns or postictal prolactin (PRL) elevations greater than 1.5 times the highest interictal baseline PRL; 11 had NES. Among the 11 seizures, postictal SPECT was abnormal in seven (regions of hypoperfusion in six and hyperperfusion in one) and normal in four. In six cases (55%), the interictal and postictal SPECT changed. Among the 11 NES cases, postictal SPECT was abnormal in three cases (all hypoperfusion abnormalities) and normal in eight cases. In no case did the interictal and postictal SPECT change. This small sample revealed a trend toward greater hypometabolism (postictal versus interictal) on SPECT for epileptic seizures compared to NES ( p < 0.12). There were postictal SPECT changes in two of five seizures unassociated with postictal PRL elevation. Prolactin was elevated in two cases unassociated with change on SPECT. Comparision of postictal to interictal SPECT may help distinguish epileptic seizures from NES. Results from SPECT may also help identify epileptic seizures unassociated with PRL elevation.

Evolution and Localization of Postictal Blood Flow Changes in Partial Seizures Demonstrated by SPECT: Use of Quantitative Difference Images

Ictal single photon emission computed tomography (SPECT) is a sensitive means of seizure localization in partial epilepsy. The purpose of this study is to enhance the diagnostic yield of postictal SPECT for epilepsy and to overcome the difficulties in its conventional interpretation. We developed a method for coregistration, normalization, and subtraction of interictal from ictal SPECT to reveal positive difference images (and ictal from interictal to reveal negative difference images) of cerebral blood flow (CBF) during seizures. This method also allows quantification of regions of greatest percent increase and decrease, normalized to seizure duration. We studied 12 patients who had confirmed epileptogenic regions by surgery and pathology (seven temporal, five extratemporal). In all 12 patients, with either early (during ictus) or late injection (after seizure termination), the difference images showed increases or decreases respectively in blood flow consistent with the epileptogenic region. We highlight the localizing value of the negative difference change in perfusion (state of hypoperfusion) that persists for up to 100 seconds after seizure termination and corresponds to the epileptogenic region. Application of this technique for the quantification of perfusion changes during seizure or immediately after seizure cessation enhances the diagnostic yield of SPECT in both temporal and extratemporal epilepsy.

Location of epileptic foci on interictal and immediate postictal single photon emission tomography in children with localization-related epilepsy.

Several neuroimaging techniques that supplement electrophysiologic methods of evaluating pediatric patients with localization-related epilepsies before surgery assess both structural and functional abnormalities. For example, single photon emission computed tomography (SPECT) with technetium-99m-hexamethylpropyleneamine oxime (99mTc-HMPAO) has been used to demonstrate abnormal cerebral perfusion. States of cerebral perfusion during the interictal and immediate postictal periods have been reported to correlate with epileptiform foci identified by electroencephalogram (EEG). Between January 1987 and March 1993, we studied 55 pediatric patients with intractable seizures with prolonged video EEG telemetry in the epilepsy monitoring unit, followed by computed tomography, magnetic resonance imaging, and SPECT, before surgery to determine whether SPECT studies with 99mTc-HMPAO improved the accuracy of locating the epileptic focus. Interictal SPECT was performed on all patients, and immediate postictal SPECT (within 10 minutes after seizure ended) on 17 patients monitored in the epilepsy monitoring unit. In 15 (88%) of the 17, the combination of interictal and postictal SPECT studies yielded results corresponding to the EEG abnormality, a result significantly better than that obtained from interictal studies alone: 21 (55%) of 38 (chi 2 = 5.647, P = .0175). SPECT scans showed localized abnormal perfusion in the ipsilateral temporal lobe in all six patients with mesial temporal sclerosis, but precise results were not obtained in cases of dual pathology and neuronal migration disorders. Depiction of cerebral perfusion by interictal and immediate postictal SPECT studies can lead to greater accuracy in the localization of epileptic foci.

Surface cortical cerebral blood flow monitoring and single photon emission computed tomography: prognostic factors for selecting temporal lobectomy candidates

A series of 23 patients with medically intractable temporal lobe epilepsy was studied with surface cortical cerebral blood flow monitoring, single photon emission computed tomography (SPECT) and subdural strip electrocorticographic (ECoG) monitoring for localization of the seizure focus. All patients underwent anterior temporal lobectomy and seizure outcome was determined after a mean of 9 months (range: 3-17 months). Invasive and non-invasive cerebral blood flow (CBF) parameters with prognostic value for seizure-free outcome were: (a) inter-ictal seizure focus with CBF < 65 ml/100 gm-min; (b) inter-ictal seizure focus CBF < or = normal temporal lobe CBF; and (c) concordance of inter-ictal and/or early post-ictal SPECT and ictal ECoG for seizure focus localization. These results should improve prognostic value of invasive and non-invasive cerebral blood flow data for selection of temporal lobectomy candidates.

Correlation of MRI hippocampal volume analysis, video/EEG monitoring and inter- and postictal single photon emission tomography in refractory focal epilepsy.

The effectiveness of surgery in patients with refractory complex partial seizures depends on accurate localisation of the epileptogenic zone. To assess the correlation between magnetic resonance imaging (MRI) hippocampal volume measurements. Tc 99m-hexamethyl-propyleneamineoxime inter- and postictal single photon emission computed tomography (SPECT) and clinico-electrophysiological (video/EEG) localisation of the epileptogenic zone we prospectively studied 16 consecutive patients with refractory complex partial seizures and no significant abnormality on standard MRI. Each test was interpreted blindly by independent observers. Eight patients (50%) had asymmetrical hippocampal volumes indicative of unilateral atrophy; correlation with the video/EEG and postical SPECT changes was very high (100% with definitive video/EEG localisation, 75% with interictal EEG and 83% with postictal SPECT). Moreover, the left/right hippocampal ratio was able to differentiate temporal from extratemporal video/EEG localisations. Postictal SPECT showed regional lateralised changes in 9 (64%) of 14 technically satisfactory studies. Disagreement between the video/EEG and postictal SPECT was seen with two extratemporal and one bitemporal foci.

Patterns of postictal cerebral blood flow in temporal lobe epilepsy

We used single-photon emission computed tomography (SPECT) to study postictal cerebral blood flow (CBF) in 51 patients with temporal lobe epilepsy. There were 78 seizures studied, 77 by early postictal injection of Tc-99m HMPAO (delay from seizure onset = 4.3 +/- 4.5 min) and one by ictal injection. Increased focal temporal lobe uptake, predominantly confined to the anteromesial region, was present in 83% and declined rapidly over 5 minutes. Reduced activity in the lateral temporal lobe accompanied the mesial increase in 80% of studies, extending over much of the ipsilateral hemisphere and closely associated with the degree and extent of postictal EEG slow waves. These patterns enabled correct seizure localization by blinded analysis in 69% (31/45) of the patients with a unilateral EEG focus. The remainder showed bilateral or no changes. One of six patients with bitemporal EEG foci had unilateral perfusion changes. The positive predictive value for the correct localization of a unilateral focus by postictal SPECT was 97% (31/32). Postictal CBF imaging with SPECT can be used to support noninvasive electrographic localization and may decrease the need for invasive electrode studies.