Single photon emission computed tomography in seizure disorders

Patterns of cerebral glucose metabolism in early and late stages of Rasmussen's syndrome

Rasmussen's syndrome is a chronic encephalitis characterized by intractable focal epilepsy and progressive neurologic deterioration with lateralized brain destruction. In the early stages of the disease, the diagnosis can be difficult to make, and brain biopsy is often performed. We evaluated the patterns of cerebral glucose metabolism using 2-deoxy-2-[18F]-fluoro-D-glucose positron emission tomography (PET) in 15 children (age range 2.9-15.4 years, mean age 8.7 +/- 4.3 years) with Rasmussen's syndrome. In 6 patients evaluated early (< or = 1 year of onset of seizures), the PET scan showed areas of abnormal metabolism restricted mostly to the frontal and temporal regions, whereas the posterior cortex was preserved. Pathologic changes seen in the resected cortex were more pronounced in cortical areas of abnormal metabolism than in regions showing normal metabolism. In 9 patients evaluated later (>1 year after onset of seizures), the PET scan showed more diffuse hemispheric metabolic abnormalities including the occipital cortex, but the abnormalities remained highly lateralized. These patterns of glucose metabolic abnormalities in the early and late stages of the disease may facilitate the diagnosis of Rasmussen's syndrome and assist guidance of biopsy in early cases, when structural neuroimaging is still normal.

Temporal lobe seizure interhemispheric propagation time depends on nonepileptic cortical cerebral blood flow

In some patients with epilepsy, activation of eloquent cortex using various forms of environmental stimulation and mental activity may induce seizures. The increased neuronal activity resulting from cortical stimulation may be associated with increased regional cerebral blood flow. The vascular steal theory of temporal lobe epilepsy suggests that as nonepileptogenic cortical cerebral blood flow (CBFn) increases, temporal lobe epileptogenicity increases as a result, in part, of decreasing interhemispheric propagation time (IHPT). Recently, IHPT has been shown to be a quantitative electrocorticographic measure of temporal lobe epileptogenicity. In the current study, long-term combined subdural-EEG and surface cortical cerebral blood flow (CBF) monitoring was performed to test the hypothesis that IHPT depends upon CBFn. The results show that IHPT is a nonlinear (negative exponential) function of nonepileptic cortical CBF (r=0.507, df=32, t=-2.204, P<0.05). In temporal lobe epilepsy, nonepileptic cortical hypoperfusion may represent a protective mechanism for delaying interhemispheric seizure propagation. The fact that IHPT decreases exponentially with increasing CBFn suggests that small increases in CBFn should substantially decrease IHPT and increase epileptogenicity. This study confirms that inter-hemispheric propagation time depends upon perfusion of nonepileptogenic cortex.

CPD - education and self-assessment: functional imaging in epilepsy

Functional imaging plays a growing role in the clinical assessment and research investigation of patients with epilepsy. This article reviews the literature on functional MRI (fMRI) investigation of EEG activity, fMRI evaluation of cognitive and motor functions, magnetic resonance spectroscopy (MRS), single photon emission computed tomography (SPECT) and positron emission tomography (PET) in epilepsy. The place of these techniques in clinical evaluation and their contribution to a better neurobiological understanding of epilepsy are discussed.

Redistribution on I-123 IMP SPECT in children and adolescents with partial seizures

To evaluate the redistribution phenomenon on delayed I-123 IMP SPECT images of children and adolescents with partial seizures, 25 patients were selected and investigated in the interictal state. Early and delayed SPECT were performed 15-20 minutes and 5 hours, respectively, after I-123 IMP injection. Redistribution patterns were classified into three groups: 1) redistribution (RD) (-) group (n = 5), in which a low-uptake area on the early image persisted or was enlarged on the delayed image, 2) RD (+) group (n = 14), in which a low-uptake area on the early image changed to normal distribution on the delayed image, and 3) marked redistribution (MRD) (+) group (n = 6), In which a low-uptake area on the early image changed to a high uptake area on the delayed image. Among the patients who were followed for at least 12 months after the SPECT scans, the short-term clinical outcome tended to be good in the RD (+) group, intermediate in the MRD (+) group, and poor in the RD (-) group. These results of our preliminary comparative study indicate that the redistribution pattern of I-123 IMP may be related to the clinical aspects in patients with partial seizures and that it may play an important role in predicting their short-term clinical outcome.

Recent advances in pediatric nuclear medicine

This review is devoted to some controversial topics in the field of pediatric nuclear medicine. In most cases, drug sedation can be avoided and the nuclear medicine procedure can be successfully achieved simply by taking the emotional life of the child into account. Factors such as past negative experiences (painful procedures, hospitalizations), unfamiliar environment (frightening examination room), physical aggressions related to the nuclear medicine procedure (intravenous injections, cystography), and the feeling of loss of parents' protection all contribute to the child's anxiety. People in charge of pediatric procedures should be adequately trained to be aware of these factors and to create the best environmental conditions to avoid unnecessarily frightening the child. Methods for measuring renal clearance in children are numerous. It is my aim to review the different methods proposed in the literature, including the nonradioisotopic methods, the reference radioisotopic methods, the various simplified algorithms using blood samples, and the gamma-camera methods. Gastroesophageal reflux scintigraphy is a well-established procedure for the detection of gastro-esophageal reflux in children. However, despite the numerous advantages of this technique, it has not gained wide acceptance in the field of pediatric gastroenterology. This review focuses mainly on the comparison between scintigraphy and pH metry. Finally, the applications of 99m technetium-hexamethylpropylenamine brain single photon emission computer tomography in the field of pediatric neurology are still under development; this part of the review is an attempt to summarize the real contribution of this technique.

SPECT and epilepsy with continuous spike waves during slow-wave sleep

Ten cases of epilepsy with continuous spike waves in slow-wave sleep (CSWS) were evaluated using single photon emission computed tomography (SPECT); in eight patients the EEG paroxysmal abnormalities showed a predominant localization. SPECT carried out using 99mTc-HMPAO allows study of cerebral blood flow (CBF); the examination was performed during phases of drowsiness and the results compared to the EEG data. In four cases SPECT revealed areas of low CBF in sites corresponding to those of the prevalent EEG discharges; in two cases the areas of hypoperfusion did not correspond to those indicated by the EEG; lastly, in four cases SPECT results were negative. The areas of hypoperfusion were predominantly located in the frontal, temporal, and parietal regions. Furthermore, the percentage of positive SPECT results was significantly higher (five cases out of six) in the group in which the CSWS phase was prolonged for at least 1 year, compared to the group in which this phase lasted less than 1 year. Thus, in this type of epilepsy, SPECT reveals focal cortical areas of decreased CBF which correlated generally to the predominant sites of EEG abnormalities. A longer duration of the CSWS phase seems to be associated with a more significant cortical disorder, documented by the presence of areas of hypoperfusion.

FDG-PET in children and adolescents with partial seizures: role in epilepsy surgery evaluation

We used FDG-PET to measure interictal glucose metabolism in 16 children and adolescents (mean age 14.7 years) and complex partial seizures (CPS) (mean seizure onset age 5.0 years). Video-EEG localized the epileptic foci. Glucose metabolism was determined in 14 paired anatomic areas using a standard template. PET hypometabolism was defined as greater than 15% asymmetry. Nine of the 13 (69%) patients with a unilateral EEG focus had regional hypometabolism ipsilateral to the epileptogenic zone. Three subjects had bilateral EEG foci; all had nonfocal PET. MRI (15 patients) concurred with EEG and PET in two, and was normal in seven of nine with focal hypometabolism. One of seven patients with normal PET had a focal MRI abnormality. FDG-PET results are similar to those found in adults, but are present earlier in the natural history of CPS (9.7 vs 22.2 years duration epilepsy) than previously reported. The presence of FDG-PET hypometabolism may be associated with a poor response to drug treatment. PET can identify metabolic abnormalities associated with epileptic foci in children and adolescents and is useful in directing surgical intervention for the control of refractory complex partial epilepsy.

The relative contributions of MRI, SPECT, and PET imaging in epilepsy

Functional and structural neuroimaging techniques are increasingly indispensable in the evaluation of epileptic patients for localization of the epileptic area as well as for understanding pathophysiology, propagation, and neurochemical correlates of chronic epilepsy. Although interictal single photon emission computed tomography (SPECT) imaging of cerebral blood flow is only moderately sensitive, ictal SPECT markedly improves yield. Positron emission tomography (PET) imaging of interictal cerebral metabolism is more sensitive than measurement of blood flow in temporal lobe epilepsy. Furthermore, PET has greater spatial resolution and versatility in that multiple tracers can image various aspects of cerebral function. Interpretation of all types of functional imaging studies is difficult and requires knowledge of time of most recent seizure activity and structural correlates. Only magnetic resonance imaging (MRI) can image the structural changes associated with the underlying epileptic process, and quantitative evidence of hippocampal volume loss has been highly correlated with seizure onset in medial temporal structures. Improved resolution and interpretation have made quantitative MRI more sensitive in temporal lobe epilepsy, as judged by pathology. When judged by electroencephalography (EEG), ictal SPECT and interictal PET have the highest sensitivity and specificity for temporal lobe epilepsy; these neuroimaging techniques have lower sensitivity and higher specificity for extratemporal EEG abnormalities. Regardless of the presence of structural abnormalities, functional imaging by PET or SPECT provides complementary information. Ideally these techniques should be used and interpreted together to improve the localization and understanding of epileptic brain.

Serial IMP-SPECT and EEG studies in an infant with hemimegalencephaly

An 8-month-old girl of hypomelanosis of Ito associated with hemimegalencephaly had frequent seizures beginning 44 h after birth. The seizures were secondarily generalized or unilateral initially, followed by infantile spasms at about 1.5 months of age. Frequent partial seizures appeared at 4 months of age. [123I]N-Isopropyl-p-iodoamphetamine (IMP) single photon emission computed tomography (SPECT) was performed serially during an interictal period at 1, 3 and 7 months of age. At 1 and 3 months, IMP-SPECT showed a marked increase of IMP uptake in the pathological left hemisphere and electroencephalography (EEG) revealed left-sided dominant hypsarrhythmia. At 7 months of age, a reversal was seen, there being decreased uptake on SPECT in the pathological hemisphere and abundant high amplitude background activity mingled with epileptic discharges on EEG in the non-pathological hemisphere. These serial changes of IMP uptake on SPECT seemed to reflect either changes in epileptic activity or maturational changes in cerebral perfusion in hemimegalencephaly.

Functional neuroimaging with SPECT in children with partial epilepsy

Single-photon emission computed tomography (SPECT) is being used increasingly in the investigation of children with intractable partial seizures. SPECT imaging of regional cerebral blood flow with 99mTc-hexamethylpropylene amine oxime, iodinated radiopharmaceuticals, and 133Xe typically reveals decreased cortical perfusion interictally and increased cortical perfusion ictally in the region of the epileptic focus. Studies in both adults and children indicate significantly greater sensitivity and specificity with ictal injection of radiopharmaceutical, with interictal SPECT not infrequently revealing nonlocalizing or falsely localizing information. Recent SPECT studies employing iodinated neuroreceptor ligands report altered receptor binding in the region of the epileptic focus, providing insight into the underlying neuropharmacology of partial epilepsy. SPECT has an established role in the presurgical localization of seizure foci in children with intractable partial seizures and may be a useful modality to study the functional anatomy and clinical semiology of partial seizures in childhood.

Epilepsy and SPECT

SPECT studies for rCBF imaging in clinical epilepsy are reviewed divided into interictal, ictal and postictal SPECT studies in partial and generalized epilepsies, as compared with the corresponding PET studies, and at times referring to SPECT studies in experimental models of epilepsy. All of the interictal, ictal and postictal SPECT scans in partial epilepsy are useful for the regional determination of epileptic foci, in view of the high appearance rates of focal abnormalities on these SPECT scans and good correlation with epileptic EEG foci. Mechanisms underlying the focal abnormality on interictal SPECT scans (i.e., focal hypoperfusion) image are complicative, and therefore, studies concerning the underlying mechanisms are reviewed with regard to correlations of the SPECT abnormality with the following various clinical factors: focal organic lesions on X-ray CT or MRI scans, frequencies of clinical seizures or interictal seizure discharges on EEGs, background EEG activity, propagation of epileptic activity, antiepileptic drugs, and cognitive functions. Further, new neurochemical SPECT studies using 123I-Iomazenil for benzodiazepine receptor imaging in clinical epilepsy are reviewed and compared with earlier SPECT studies for rCBF imaging with regard to their utility in regional determination of epileptic foci. In addition, the few SPECT or PET studies available on epileptic psychosis are reviewed.

Ictal 99mTc-HMPAO single photon emission computed tomography in children with temporal lobe epilepsy

Seventeen ictal 99mTc-HMPAO single photon emission computed tomography (SPECT) studies were performed in 15 children with temporal lobe epilepsy (TLE) aged 7-14 years (mean 10.3 years). Ictal SPECT was informative in 16 of 17 (94%) studies in 14 of 15 (93%) children, showing unilateral temporal lobe hyperperfusion. In all 16 informative ictal SPECT studies, lateralization was concordant with ictal EEG, magnetic resonance imaging (MRI), and pathology. In 4 children, ictal SPECT provided additional localizing information that was not apparent from concurrent ictal EEG recording. Blinded interpretation of ictal SPECT studies by two independent investigators showed correct lateralization of the epileptic focus in every child. Results of visual analysis of ictal SPECT images were corroborated by quantitative analysis. Although interictal SPECT studies showed a degree of temporal lobe hypoperfusion in all children, in 9 of 15 hypoperfusion was either minimal, bilateral, contralateral, or associated with extratemporal hypoperfusion. In children with TLE, ictal SPECT provides reliable lateralizing information to corroborate or supplement that obtained from surface EEG and MRI.

Technetium 99mTc-HMPAO SPECT in children and adolescents with neurologic disorders

We evaluated regional cerebral blood flow with technetium 99mTc hexamethylpropyleneamineoxime single photon emission computed tomography (SPECT) in 20 children and adolescents with neurologic dysfunction of varied etiology and abnormal electroencephalograms (EEGs). All patients were also examined with computed tomography (CT) and magnetic resonance imaging (MRI). Abnormal perfusion was found in 17 (85%) of 20 SPECT scans. Abnormal CT or MRI scans were noted in nine (45%) and in 10 (50%) of 20 cases, respectively. In eight (73%) of 11 cases with normal CT scans and in seven (70%) of 10 with normal MRI scans, the SPECT scan was abnormal. Abnormal regional cerebral blood flow on SPECT scans correlated better with EEG abnormalities than with neurologic examination or CT or MRI scan findings. We conclude that in children and adolescents with a spectrum of neurologic diseases and abnormal EEGs, abnormalities of brain structure or function are more likely to be documented by SPECT than by CT or MRI scans. SPECT findings correlate well with the location and type of EEG abnormality.

Brain perfusion SPECT in children with frequent fits

We studied 14 children with frequent fits using 99mTc-HM-PAO single photon emission computed tomography (SPECT). There were 11 patients with partial secondary generalized epilepsy (PSGE) and 3 with Lennox-Gastaut syndrome (LGS). The typical regional cerebral blood flow (rCBF) finding in PSGE was a single area of abnormally low perfused cortex, and that in LGS, multiple hypoperfused areas. Clinically, the LGS patients were more severely affected. SPECT was more sensitive in detecting abnormalities than EEG, CT or MRI. Extensive impairment of rCBF may thus indicate unfavourable development of intellectual performance and poor seizure control.

Regional cerebral blood flow in diagnosis of childhood onset partial epilepsy

We compared regional cerebral blood flow assessed by [123I]N-isopropyl-p-iodoamphetamine (IMP) single-photon emission tomography (SPECT) with magnetic resonance imaging (MRI), computed tomography (CT) and interictal surface electroencephalography (EEG) to evaluate its diagnostic potential in 24 patients with partial seizures with onset in childhood. Focal low uptake areas were observed on SPECT scans of 18 patients and were presumed to represent epileptogenic areas in 17. MRI revealed an abnormality in 12 and CT in 6 patients, and all organic lesions showed SPECT abnormalities, too. Six patients without focal structural abnormalities showed regional perfusion deficit on SPECT. Routine scalp EEG revealed an epileptic focus in 17 patients and three of them showed discordant results between SPECT and EEG, which suggested more serious brain disorders. In two patients without EEG localization only SPECT showed focal abnormalities in the probable epileptic area. [123I]IMP-SPECT was useful in locating the epileptic focus, particularly during the early period after the onset of partial seizures when the EEG gave inconclusive results.

Interictal and postictal focal hypermetabolism on positron emission tomography

Decreased glucose utilization in the epileptogenic zone is typically observed interictally on positron emission tomography (PET), whereas ictal PET studies reveal complex patterns of increased and decreased metabolism. PET findings of 7 children, ages 2 months to 16 years, are described and demonstrate small focal regions of hypermetabolism in the absence of clinical or electrographic seizure during the 2-deoxy-2[18F]fluoro-D-glucose (FDG) uptake period. Magnetic resonance imaging scans were nonlocalizing in 5 of 7 children. In 4 children, seizures had not occurred for at least several hours prior to PET. Electroencephalography during PET disclosed active spike-and-wave activity on the side of interictal hypermetabolism in these 4 children. The remaining 3 children had seizures within 15 min prior to FDG injection and were considered postictal; their PET images revealed focal hypermetabolism. Results indicated the need for electroencephalographic monitoring during functional neuroimaging studies of all epileptic patients. The biochemical basis of interictal hypermetabolism is probably related to increased energy consumption by an active epileptogenic focus, whereas postictal hypermetabolism is likely due to energy expenditure for the restoration of resting membrane potentials and chemical homeostasis following an epileptic event.

SPECT (Single Photon Emission Computed Tomography) in 31 children and adolescents with autism and autistic-like conditions

SPECT with Tc-99m-HM-PAO was used in examining 31 patients with autism and autistic-like conditions. Sixteen of these had autistic disorder/autistic-like conditions with associated epilepsy. The autistic disorder group without epilepsy was relatively high functioning. All 31 patients showed reduction of regional cerebral blood flow in the temporal lobes. There was no clear difference between the groups with and without epilepsy, suggesting that seizure disorder per se could not account for the findings.

Single photon emission computed tomography using perfusion tracers in seizure disorders

Single photon emission computed tomography (SPECT) using perfusion tracers makes it possible to estimate regional cerebral blood flow (rCBF) and, indirectly, local brain metabolism. It may be possible to detect and follow physiopathological alterations, such as may be seen in seizure disorders. The authors review the principles of and some data on perfusion SPECT in seizure disorders, stress advantages as well as major drawbacks and add their initial experience with Tc-99m hexamethylpropyleneamine oxime (HMPAO) SPECT in febrile convulsions.

Technetium-99m hexamethylpropylene amine oxime single photon emission tomography in febrile convulsions

We report our initial experience with technetium-99m hexamethyl propylene amine oxime (99mTC-HMPAO) brain single photon emission tomography (SPET) in the investigation of 19 children presenting with febrile convulsions. Two patients with complex febrile convulsions showed focal SPET lesions contralateral to the neurological deficit. However, in 9 out of 17 patients with simple febrile convulsions, focally disturbed perfusion was shown. In 4 out of 6 patients with electroencephalogram (EEG) abnormalities on admittance, SPET revealed at least 2 focal lesions. The temporofrontal region was the one most commonly involved. The SPET findings presented here also suggest a temporal relationship with the febrile convulsions, with markedly fewer lesions if examined after 12 days. In our initial experience, perfusion SPET did not show any particular pattern helpful in the differential diagnosis of the child presenting with febrile convulsions. Physiopathologically, our findings may support the hypothesis that brain tissue is regionally more vulnerable to fever, in patients presenting with febrile convulsions.

Localization of extratemporal epileptic foci during ictal single photon emission computed tomography

We obtained single photon emission computed tomography (SPECT) scans with technetium-99M-hexamethyl-propylene-amine-oxime in 11 patients during 12 extratemporal partial seizures (9 simple partial, 3 complex partial). Ten ictal SPECT studies in 9 patients showed a focal region of hyperperfusion, which agreed with electrical seizure onset in 5 and with clinical seizure localization in 4 in whom ictal electroencephalography was not localized. Contralateral cerebellar and ipsilateral basal ganglia hyperperfusion was seen in 3 patients with a frontal lobe seizure focus. Ictal hyperperfusion was well circumscribed, unlike the diffuse hyperperfusion changes reported during temporal lobe seizures. This observation may indicate a different degree of seizure spread in temporal as opposed to extratemporal epilepsy. Because electroencephalographic localization is often elusive in extratemporal seizures, ictal SPECT may be very helpful for the localization of extratemporal foci.

Ictal 99mTc-HMPAO SPECT in alternating hemiplegia

99mTc-hexamethylpropylenamine oxime (99mTc-HMPAO) single-photon emission computed tomography (SPECT) was performed in a patient with alternating hemiplegia during 2 episodes of the disease. The regional cerebral blood flow patterns correlated with the clinical manifestations during both episodes. Hyperperfusion of the contralateral hemisphere was suggested by asymmetric 99mTc-HMPAO uptake, whereas symmetric 123I-N-isopropyl-p-iodoamphetamine uptake was detected during the interictal period. The results suggested that alternating hemiplegia in infants represents an atypical manifestation of epilepsy, despite the lack of paroxysmal electroencephalographic abnormalities during the episodes. 99mTc-HMPAO SPECT appears to be a useful method for detecting transient regional cerebral blood flow alterations during paroxysmal events because the tracer is rapidly available for emergencies and retains a fixed distribution for 5-8 hours, sufficient time to allow for SPECT acquisition.

Paediatric nuclear medicine

Until the 1980s no serious attempts were made to develop paediatric nuclear medicine, as for various reasons many centres were reluctant to perform radionuclide examinations on children. Then two books were published on paediatric nuclear medicine in 1984 and 1985, respectively. In 1987, a group of physicians formed an informal club of paediatricians and nuclear medicine specialists in an effort to improve the relationship and cooperation between these specialties. Carrying out nuclear medicine examinations on children requires a completely different approach than on adults. Suggestions are made and tips given, and the specific problems involved are discussed in detail.

Single photon emission computed tomography in epilepsy

Functional brain imaging by either single photon emission computed tomography (SPECT) or positron emission tomography (PET) is now a well-established technique in the diagnosis and evaluation of the epilepsies. Perhaps only in stroke have these emerging technologies proven of greater significance. Scalp, cortical, or depth electroencephalographic (EEG) data previously have been the gold standards for the localization and subcharacterization of epileptic activity in the human brain. Yet, they are fraught with difficult interpretations, technical difficulties, and limitations in sampling accuracy. Both SPECT and PET have localizing power approaching that of combined scalp and depth EEG. In the following discussion, a brief overview of the results of PET investigations in epilepsy is presented as background and comparative material for the concurrent and, more recently, dominant role of SPECT in evaluating patients with seizure activity. SPECT results in the interictal state in partial and generalized seizure activity are reviewed followed by an analysis of the role of ictal SPECT imaging in epilepsy. Next, relationships among interictal hypoperfusion (or hypometabolism) and computed tomography, magnetic resonance imaging, neuropathology, clinical severity, and cognitive function are discussed. The role of perfusion or metabolism imaging in the management of antiepileptic pharmacotherapy is also discussed, and the potential for receptor imaging in the evaluation of the epilepsies is examined. Finally, application in pediatric epilepsy are presented.

Single photon emission computed tomography (SPECT) in seizure disorders in childhood

In 38 children with partial seizures, the EEG, CT and NMR findings were compared to the results obtained with Tc99m HMPAO single photon emission computed tomography (SPECT) in order to determine whether SPECT is a useful adjunct to EEG, CT and NMR in this age group. In 3 out of 7 patients with a normal EEG, SPECT showed focal abnormalities. Nine patients whose EEGs did not show adequate lateralization had an abnormal SPECT which revealed a focus. In 14 out of 21 patients with a normal CT, SPECT showed focal changes in 13 patients and diffuse changes in the other one. In 7 out of 12 patients with a normal NMR, SPECT showed focal abnormalities. Although clinical history and a careful description of the seizures are the most valuable information in partial seizure disorders, SPECT imagining gives valuable additional information, which might target treatment. SPECT was superior to CT and NMR with respect to the depiction of some kind of abnormality.