Functional brain imaging in pediatrics

PET/MRI in paediatric disease

Nuclear medicine and molecular imaging have a small but growing role in the management of paediatric and neonatal diseases. During the past decade, combined PET/MRI has emerged as a clinically important hybrid imaging modality in paediatric medicine due to diagnostic advantages and reduced radiation exposure compared to alternative techniques. The applications for nuclear medicine, radiopharmaceuticals and combined PET/MRI in paediatric diagnosis is broadly similar to adults, however there are some key differences. There are a variety of clinical applications for PET/MRI imaging in children including, but not limited to, oncology, neurology, cardiovascular, infection and chronic inflammatory diseases, and in renal-urological disorders. In this article, we review the applications of PET/MRI in paediatric and neonatal imaging, its current role, advantages and disadvantages over other hybrid imaging techniques such as PET/CT, and its future applications. Overall, PET/MRI is a powerful imaging technology in diagnostic medicine and paediatric diseases. Higher soft tissue contrasts and lower radiation dose of the MRI makes it the superior technology compared to other conventional techniques such as PET/CT or scintigraphy. However, this relatively new hybrid imaging has also some limitations. MRI based attenuation correction remains a challenge and although methodologies have improved significantly in the last decades, most remain under development.

Role of ¹⁸F-FDG PET imaging in paediatric primary dystonia and dystonia arising from neurodegeneration with brain iron accumulation

PURPOSE

No current neuroimaging modality offers mechanistic or prognostic information to guide management in paediatric dystonia. We assessed F-fluorodeoxyglucose (¹⁸F-FDG) PET/computed tomography (CT) brain imaging in childhood primary dystonia (PDS) and neurodegeneration with brain iron accumulation (NBIA) to determine whether it would identify altered metabolism and hence constitute a potentially useful 'biomarker' indicating functional disturbances associated with dystonia and severity of the disease.

MATERIALS AND METHODS

A total of 27 children (15 PDS and 12 NBIA) underwent brain ¹⁸F-FDG PET/CT imaging under anaesthesia during acquisition. The images were assessed visually and the two groups were compared quantitatively with statistical parametric mapping. PET/CT images were spatially transformed to Montreal Neurological Institute standard space. Voxelwise ¹⁸F-FDG uptake was normalized to whole-brain uptake. Data of both groups were correlated separately with duration and severity of dystonia as assessed using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS).

RESULTS

Visual inspection did not identify any abnormalities in ¹⁸F-FDG uptake within the cerebral cortex, basal ganglia, or thalami in either group. Quantitative analysis identified higher uptake in the posterior cingulate and bilateral posterior putamina but decreased uptake in the occipital cortex and cerebellum in NBIA compared with PDS. The NBIA group had more severe dystonia scores compared with the PDS group. BFMDRS was negatively correlated with age but not with duration of dystonia.

CONCLUSION

Compared with PDS, NBIA is dominated by relative overactivity in the putamen and by cerebellar underactivity, patterns that may reflect the increased severity of dystonia in NBIA cases. Hence, there is a potential role for ¹⁸F-FDG PET/CT imaging in paediatric dystonia, particularly in the NBIA group.

Quantitative analysis of developmental process of cranial suture in korean infants

OBJECTIVE

The purpose of this study was to elucidate the anatomical development of physiologic suture closure processes in infants using three dimensional reconstructed computed tomography (CT).

METHODS

A consecutive series of 243 infants under 12 months of age who underwent three dimensional CT were included in this study. Four major cranial sutures (sagittal, coronal, lambdoidal and metopic suture) were classified into four suture closure grades (grade 0=no closure along the whole length, grade 1=partial or intermittent closure, grade 2=complete closure with visible suture line, grade 3=complete fusion (ossification) without visible suture line), and measured for its closure degree (suture closure rates; defined as percentage of the length of closed suture line divided by the total length of suture line).

RESULTS

Suture closure grade under 12 months of age comprised of grade 0 (n=195, 80.2%), grade 1 (n=24, 9.9%) and grade 2 (n=24, 9.9%) in sagittal sutures, whereas in metopic sutures they were grade 0 (n=61, 25.1%), grade 1 (n=167, 68.7%), grade 2 (n=6, 24%) and grade 3 (n=9, 3.7%). Mean suture closure rates under 12 months of age was 58.8% in metopic sutures, followed by coronal (right : 43.8%, left : 41.1%), lambdoidal (right : 27.2%, left : 25.6%) and sagittal sutures (15.6%), respectively.

CONCLUSION

These quantitative descriptions of cranial suture closure may help understand the process involved in the cranial development of Korean infants.

PET imaging in pediatric neuroradiology: current and future applications

Molecular imaging with positron emitting tomography (PET) is widely accepted as an essential part of the diagnosis and evaluation of neoplastic and non-neoplastic disease processes. PET has expanded its role from the research domain into clinical application for oncology, cardiology and neuropsychiatry. More recently, PET is being used as a clinical molecular imaging tool in pediatric neuroimaging. PET is considered an accurate and noninvasive method to study brain activity and to understand pediatric neurological disease processes. In this review, specific examples of the clinical use of PET are given with respect to pediatric neuroimaging. The current use of co-registration of PET with MR imaging is exemplified in regard to pediatric epilepsy. The current use of PET/CT in the evaluation of head and neck lymphoma and pediatric brain tumors is also reviewed. Emerging technologies including PET/MRI and neuroreceptor imaging are discussed.

Glutaric aciduria type II [corrected] and brain tumors: a case report and review of the literature

Heritable diseases associated with childhood tumors are sometimes defined as a probable etiologic factor or a coincidence. First of all, we must know the actual number of patients. Herein a case with medulloblastoma associated with glutaric aciduria type II [corrected] is reported for this purpose. A 5-year-old boy was admitted with nausea, vomiting, and lethargy. In medical history, consanguinity and siblings with mental-motor retardation and epilepsy are remarkable. Growth retardation, macrocephaly, lethargy, tremor, bilateral nistagmus, and papilledema were prominent features in physical examination. Noncontrast computed tomography of the brain showed a hyper dense mass in the cerebellar vermis. Gross total resection was made and the histopathology of the tumor was medulloblastoma. Besides medical history and physical findings, radiologic white matter changes in the subcortical, periventricular regions, bilateral basal ganglia, and caudate nuclei in magnetic resonance images other than tumor led us to investigate the child for glutaric aciduria type II [corrected]. The level of the 2-OH glutaric acid was determined as being 12-fold high in the urine. Chemo-radiotherapy was performed after surgery. Our case was the third patient with medulloblastoma in the literature and is still alive with no evidence of the disease 19 months after the initial diagnosis.

Structural and Functional Imaging Correlates for Age-Related Changes in the Brain

In recent years, investigators have made significant progress in documenting brain structure and function as it relates to aging by using positron emission tomography, conventional magnetic resonance (MR) imaging, advanced MR techniques, and functional MR imaging. This review summarizes the latest advances in understanding physiologic maturation and aging as detected by these neuroimaging modalities. We also present our experience with MR volumetric and positron emission tomography analysis in separate cohorts of healthy subjects in the pediatric and adult age groups respectively. Our results are consistent with previous studies and include the following: total brain volume was found to increase with age (up to 20 years of age). Whole brain metabolism and frontal lobe metabolism both decrease significantly with age (38% and 42%, respectively), whereas cerebellar metabolism does not show a significant decline with age. Defining normal alterations in brain function and structure allows early detection of disorders such as Alzheimer's and Parkinson's diseases, which are commonly associated with normal aging.

Normal patterns and variants in single-photon emission computed tomography and positron emission tomography brain imaging

One of the most important issues in evaluating functional brain scans for research or clinical purposes is to be able to identify normal variants. Determining the baseline "normal" state of the brain is not easy to characterize since many normal brain functions and mental processes affect brain activity. This article reviews issues pertaining to the technical and neurophysiological aspects of functional brain imaging that might alter "normal" activity and will also consider how normal brain activity changes throughout the lifespan.

Newer techniques to study neonatal hypoglycemia

Severe neurological sequelae may occur after symptomatic neonatal hypoglycemia. New neuroimaging techniques allow both structural and functional detection of these disturbances. The new diagnostic modalities have shown also transient structural findings associated with neonatal hypoglycemia. The prognostic value of these techniques remains still obscure.

Clinical, fluorine-18 labeled 2-fluoro-2-deoxyglucose positron emission tomography (FDG PET), MRI of the brain and biochemical observations in a patient with 4-hydroxybutyric aciduria; a progressive neurometabolic disease

We report a five-year-old boy with 4-hydroxybutyric aciduria. The child presented with global developmental delay, severe hypotonia and myoclonic seizures. The urine 4-hydroxybutyric acid was 1038 times that of normal, and other organic acids related to its further metabolism were also increased. Electroencephalography showed findings indicative of cerebral dysfunction. However, other neurophysiological studies were normal. Clinical improvement was observed after the administration of vigabatrin and dextromethorphan. Magnetic resonance imaging of the brain revealed cerebellar vermin atrophy and subtle white matter changes in the cerebral hemispheres. Fluorine-18 labeled 2-fluoro-2-deoxyglucose positron emission tomographic (FDG PET) scan of the brain showed a marked decrease in the cerebellar metabolism, probably related to atrophy of cerebellar vermis and secondary cerebellar deafferentation. FDG PET scan is found to be of value in the understanding and assessment of brain functional alterations. It may be useful in monitoring and optimizing treatment strategies of this rare disease.

Clinical and cerebral FDG PET scan in a patient with Krabbe's disease

A 2-year, 6-month-old Saudi male with infantile Krabbe's disease was studied with fluorine-18-labeled-2-fluoro-2-deoxyglucose positron emission tomography (FDG PET) scan. The patient presented with a gradual loss of developmental milestones, irritability, and crying. At the advanced stage of the disease, he developed tonic-clonic seizures and became a microcephalic, extremely irritable, blind, spastic quadriplegic child, with no deep tendon reflexes. Laboratory studies revealed normal blood chemistry, muscle enzymes, very long chain fatty acids, and acylcarnitines. No abnormal urinary organic acids were detected. The cerebrospinal fluid protein concentration was increased. Magnetic resonance imaging of the brain revealed mild brain atrophy and white matter disease mainly in the centrum semiovale. Electroretinography was normal; however, electroencephalography and visual-evoked potentials were abnormal. Peripheral nerve conduction studies documented a demyelinating neuropathic process. The FDG PET study of the brain demonstrated a marked decrease in the metabolism of the left cerebral cortex and no uptake in the caudate heads. Normal glucose uptake was observed in the thalami, lentiform nuclei, and cerebellum. The patient did not present for subsequent clinic visits and is presumed dead.

The perfusion defect seen with SPECT in West syndrome is not correlated with seizure prognosis or developmental outcome

We used interictal single photon emission computed tomography (SPECT) on 40 patients with West syndrome to determine whether cortical perfusion abnormalities are closely related to the development of West syndrome and whether they are correlated with the long-term seizure prognosis or the developmental outcome. Localized cortical perfusion abnormalities were seen in 24 patients (60%), while 15 patients (38%) were classified as normal. The remaining patient showed hyperperfusion of the basal ganglia bilaterally. Of 24 patients with localized perfusion abnormalities, unifocal cortical hypoperfusion was present in 11, multifocal hypoperfusion in 10, multiple cortical hypo- and hyperperfusion in one, hyperperfusion of the bilateral frontal cortices and brain stem in one, and focal hyperperfusion in the residual frontal cortex in one. For statistical analysis, we focused on 26 patients (cryptogenic; 10, symptomatic; 16), who were followed for more than 2 years after the onset of tonic spasms (mean 5.0 years). The results showed that focal cortical perfusion abnormalities were not correlated with the long-term seizure prognosis, the developmental outcome, or the response to ACTH therapy. In agreement with previous reports, the results of interictal SPECT suggested that focal cortical lesions play an important role in the development of West syndrome. However, statistical analysis showed that the existence of cortical dysfunction as defined by SPECT did not predict the seizure prognosis or the developmental outcome.

Cerebral fluorine-18 labeled 2-fluoro-2-deoxyglucose positron emission tomography (FDG PET), MRI, and clinical observations in a patient with infantile G(M1) gangliosidosis

The clinical, biochemical, pathological and neuroradiological findings of a 2-year-old Saudi boy with infantile G(M1) gangliosidosis are reported. The patient had a progressive neurologic deterioration, manifesting with developmental regression, sensorimotor and psychointellectual dysfunction and generalized spasticity that started at 4 months of age. Cherry-red macula, facial dysmorphia, hepatomegaly, exaggerated startle response to sounds, skeletal dysplasia, and vacuolated foamy lymphocytes that contain finely fibrillar material in addition to lamellar membranes and electron-dense rounded bodies were seen. MRI of the brain demonstrated mild diffuse brain atrophy and features of delayed dysmyelination and demyelination. Brain FDG PET scan revealed a mild decrease in the basal ganglia uptake, and moderate to severe decrease in thalamic and visual cortex uptake, and an area of increased glucose uptake in the left frontal lobe, probably representing an active seizure focus. The functional changes indicated by FDG PET scan and the structural abnormalities shown on MRI were found to be complementary in the imaging evaluation of infantile G(M1) gangliosidosis.

Approximate doubling of numbers of neurons in postnatal human cerebral cortex and in 35 specific cytoarchitectural areas from birth to 72 months

From 1939 to 1967, J.L. Conel quantitatively studied the microscopic features of the developing human cerebral cortex and published the findings in eight volumes. We have constructed a database using his neuroanatomical measurements (neuronal packing density, myelinated large fiber density, large proximal dendrite density, somal breadth and height, and total cortical and cortical layer thickness) at the eight age periods (0 [term birth], 1, 3, 6, 15, 24, 48, and 72 postnatal months) he studied. In this report, we examine changes in neuron numbers over the eight age-points for 35 von Economo areas for which Conel gave appropriate data. From birth to 3 months postnatal age, total cortical neuron number increases 23-30%, then falls to within 3.5% of the birth value at 24 months, supporting our previous work showing that the observed decrease in the number of neurons per column of cortex under a 1-mm2 cortical surface from birth to 15 months is almost entirely due to cortical surface expansion. The present study also shows a 60-78% increase in total cortical neuron number above the birth value from postnatal ages 24 to 72 months. The generalization, to humans at least, of the finding of no postnatal neurogenesis in rhesus macaques, a species belonging to a superfamily that diverged from that of Homo sapiens more than 25 million years ago, is not warranted until explicitly proven for humans. The data of the present study support the existence of substantial postnatal neurogenesis in humans for the 35 cortical areas studied.

Functional brain imaging in neuropsychiatric disorders of childhood

This review article presents a summary of the current state-of-the-art of functional brain imaging, with a primary focus on childhood neuropsychiatric disorders. Coverage is emphasized for developments that appear to be of current or potential future importance for the child neurologist and related pediatric specialist, and also from the perspective of the developmental neuroscientist. Emphasis is placed on the modalities of single photon emission computed tomography (SPECT), positron emission tomography (PET), and both "conventional" and "functional" magnetic resonance imaging, (MRI) including reference to the major new radiopharmaceutical and magnetic resonance-based imaging agents and techniques. The fundamental physicochemical processes underlying such studies are outlined, with citation of sources of more detailed information for the interested reader. A variety of imaging studies are reviewed for selected groups of childhood neuropsychiatric disorders, designed to illustrate the achievements and future promise of these imaging modalities. Areas of concentration are suggested for future imaging research in the field of childhood behavioral disorders, where these methods seem critical to improved understanding of pathogenetic mechanisms, as well as development of more effective treatment strategies.

Clinical and brain 18fluoro-2-deoxyglucose positron emission tomographic findings in ethylmalonic aciduria, a progressive neurometabolic disease

We report a 2-year-old boy with ethylmalonic aciduria and vasculopathy syndrome evaluated by 18fluoro-2-deoxyglucose positron emission tomographic (18FDG PET) brain scan, with intense uptake of 18FDG in the caudate nucleus and putamen bilaterally but with no morphological changes on magnetic resonance imaging (MRI). A repeat 18FDG PET brain scan 1 year later showed a significant bilateral decreased uptake of glucose in the putamen and the head of the caudate nucleus as well as a decreased uptake in the frontal lobes. On MRI, there was atrophy and watershed infarcts in the basal ganglia, explaining the loss of glucose uptake. These results reflect a selective vulnerability of the basal ganglia, their functional derangement, and ultimate degeneration.

Paroxysmal tonic upgaze: a reappraisal of outcome

Paroxysmal tonic upgaze (PTU) of childhood is a distinctive neuro-ophthalmological syndrome of unknown etiology and pathogenesis that is characterized by episodes of sustained upward deviation of the eyes, often with incomplete downward saccades on attempted downgaze. It is generally regarded as having a benign outcome. We observed 16 children with PTU, from 10 months to 11 years from onset (mean, 5.4 years), to study the natural history and possible etiology. Five cases were from two unrelated families. Onset of PTU occurred either during or after an intercurrent infection or vaccination in 5 children. No antecedent was identifiable in the rest. PTU had completely resolved in 10 children (62%) (mean age at offset, 2.5 years), whereas 2 children intermittently manifest a modified form of the disorder. At follow-up, 11 children (69%) had developmental delay, intellectual disability, or language delay and 9 (56%) had ocular motility problems other than PTU. Only 3 children (19%) had normal development and neurological findings. PTU is a heterogeneous syndrome with respect to associations and outcome and may simply be an age-dependent manifestation of a variety of disorders affecting corticomesencephalic control of vertical eye movement. This disorder may be an early sign of more widespread neurological dysfunction.

Radiological findings in developmental delay

This article reviews the neuroimaging findings in patients with nonsyndromic mental retardation and global developmental delays. The frequency and type of abnormal neuroimaging findings in this patient population are discussed. Specifically addressed are the issues of which patients should have neuroimaging studies in light of (in the vernacular) "cost-benefit" analysis. The extension of these studies to "milder" developmental delays, and other neurodevelopmental disorders are also discussed.

Glucose metabolism in the human cerebellum: an analysis of crossed cerebellar diaschisis in children with unilateral cerebral injury

Using high-resolution positron emission tomography (PET), we have recently described the normal pattern of glucose utilization in 11 anatomical regions of the human cerebellum. In the present study, we evaluated the phenomenon of crossed cerebellar diaschisis in 40 patients (mostly children) with unilateral cerebral injury sustained at various periods of brain development. Diaschisis refers to a functional impairment at a remote site following injury to an anatomically connected area of brain and, presumably due to a loss of afferent input to the remote site. Of the 40 patients, 11 had sustained their cerebral injury prenatally, 7 in the perinatal period (+/- 24 hours of birth), and 22 postnatally (1 day to 15 years). Crossed cerebellar hypometabolism was seen in 22 patients; symmetric cerebellar metabolism was found in 16 subjects. The presence of crossed cerebellar hypometabolism was typically associated (75% of cases) with a postnatal injury, while symmetric cerebellar metabolism was seen only in patients with injury occurring prior to 4 weeks of age (13 of the 16 had prenatal or perinatal insults). A third pattern of cerebellar metabolism, consisting of paradoxical crossed cerebellar hypermetabolism, was seen in two patients; both had sustained their cerebral injury at 4 months of age. These findings suggest the presence of considerable plasticity, which is dependent on age at injury, in the cerebrocerebellar pathway of developing brain.

Agyria-pachygyria: cerebral perfusion studies by 99mTc-HMPAO SPECT [corrected]

Cerebral perfusion was investigated in three patients with agyria-pachygyria by using 99mTc-HMPAO SPECT in order to study the distribution of blood flow. Diffuse cortical hypoperfusion was found in all three infants. The visual cortex was not identifiable in two of the cases. The basal ganglia and cerebellum were prominent by their normal high activity, while tracer uptake was very low in the thalamus. The possible role of improper development of interneuronal connections and abnormal vascular pattern in background of the perfusion defect is discussed.

Glucose metabolism in the human cerebellum: anatomical-functional correlations

Functional maturation of human cerebellar structures was previously difficult to evaluate with positron emission tomography (PET) because of scanner resolution. Only vermis and cerebellar hemispheres could be reliably identified with 2-deoxy-2[18F]fluoro-D-glucose (FDG) PET. In the present study, we have used a new high resolution PET system, the Siemens EXACT-HR, to study, in depth, the patterns of glucose metabolism in various cerebellar structures. Due to the orientation of the cerebellar fissures which are important landmarks, the largest number of regions could be identified when the cerebellar regions were displayed on coronal planes. The high resolution PET images, together with magnetic resonance imaging (MRI) data and standard atlases, now allow identification of the following cerebellar structures: anterior vermis, posterior vermis, dentate nucleus, anterior lobe, posterior quadrangular lobule, superior semilunar lobule, inferior semilunar, gracile, and biventer lobules, tonsil, and cerebellar white matter. These cerebellar regions are displayed in an atlas format together with magnetic resonance images to allow easy identification. The present study is a prerequisite for detailed PET analyses of cerebellar metabolism in children with diseases of the cerebellum.

Hemispherectomy for intractable seizures in children: a report of 58 cases

Fifty-eight children who underwent anatomical, functional, or modified anatomical hemispherectomy for intractable seizures from 1986 to 1995 were evaluated for seizure control, motor function, and complications. Age at surgery ranged from 0.3 to 17.3 years (median 2.8 years). Twenty-seven anatomical, 27 functional, and 4 modified anatomical hemispherectomies were performed. Seizure control and motor function in the 50 patients with more than 1 year follow-up revealed a 90% or better reduction in seizure frequency in 44/50 (88%) overall: 19/22 (86%) anatomical, 23/26 (89%) functional, and 2/2 modified anatomical. Motor function of the preoperatively hemiparetic extremities was improved or unchanged postoperatively in 38/50 (76%) of the patients. Complications included one intraoperative death, one late death from shunt obstruction managed elsewhere, late postoperative seizure breakthrough requiring reoperation and further disconnection in 5/27 functional hemispherectomy patients, mild cerebrospinal fluid infections in 3/27 anatomical hemispherectomy patients, and hydrocephalus requiring shunting in 3/27 functional hemispherectomy patients. A review of the literature and comparison of techniques is presented.

Infantile spasms: III. Prognostic implications of bitemporal hypometabolism on positron emission tomography

Positron emission tomography (PET) of brain glucose utilization is highly sensitive in detecting focal cortical abnormalities in patients with infantile spasms even when the computed tomographic (CT) and magnetic resonance imaging (MRI) scans are normal. Of 110 infants with spasms evaluated for potential surgical intervention during an 8-year period, we encountered 18 infants (7 males, 11 females; age range, 10 mo to 5 yr) with a common metabolic pattern on positron emission tomography (PET) consisting of bilateral hypometabolism in the temporal lobes. CT and MRI scans did not reveal any focal abnormalities in the 18 infants. Video-electroencephalographic monitoring indicated either bilateral or multifocal epileptogenicity, or failed to show any epileptic focus, so that none of the 18 infants were considered candidates for resective surgery. These patients were then enrolled in a prospective study aimed at determining long-term outcome in the presence of bilateral temporal PET hypometabolism. Analysis of outcome in 14 of the 18 subjects (follow-up period, 10 mo to 10 yr 5 mo; mean, 3 yr 11 mo +/- 2 yr 4 mo [SD]) revealed the following: (1) all had severe developmental delay and had failed to gain significant milestones; (2) language development had been minimal or absent; (3) 10 of the 14 met the DSM-IV criteria for autistic disorder. Our findings indicate that patients with infantile spasms and bitemporal glucose hypometabolism on PET comprise a relatively homogeneous group and are typically not candidates for cortical resection. The long-term outcome of these infants is particularly poor and the majority are autistic.

Usefulness of [18F]fluorodeoxyglucose positron emission tomography in pediatric epilepsy surgery

We sought to analyze our experience with pediatric epilepsy surgery patients to determine the place of [18F]fluorodeoxyglucose (FDG) positron emission tomography (FDG-PET) in the preoperative evaluation of such children relative to chronic invasive intracranial monitoring. Fifty-six children who received an interictal FDG-PET as part of a phase 1 epilepsy surgery evaluation were compared with 44 children who did not have this study in a retrospective analysis of 100 patients accrued over a 4-year period. There was no significant difference between the two groups of children in terms of age or follow-up or was there a significant difference between the FDG-PET group and the no-FDG-PET group in regard to the numbers of children who had surgery, the type of procedure done, whether chronic invasive intracranial monitoring was performed, or outcome. The hypometabolic area demonstrated on interictal FDG-PET was concordant with that of the epileptogenic zone as mapped out with ictal recordings from subdural electrodes in 2 of 13 patients in whom a complete data set was available for comparison. In the other 11 children there was either poor agreement between interictal FDG-PET and ictal electrocorticographic data or the interictal FDG-PET was normal in the face of an epileptogenic focus which was successfully mapped by invasive electrophysiologic techniques and excised. We conclude that one cannot exclude a child with intractable partial seizures from surgical consideration because the interictal FDG-PET is normal; nor is there sufficient correlation between the interictal hypometabolic area on FDG-PET and the epileptogenic zone in terms of anatomic location and size to justify forgoing chronic invasive intracranial monitoring in children with intractable partial seizures being evaluated for epilepsy surgery unless there is absolute concordance between all neuroimaging, clinical, and video-electroencephalographic data.

Etiologic classification of infantile spasms in 140 cases: role of positron emission tomography

The classification of infantile spasms into symptomatic, cryptogenic, and idiopathic subgroups depends on clinical examination and available diagnostic technology. Positron emission tomography (PET) of glucose utilization is a powerful tool in detecting brain malformations (particularly cortical dysplasia) in infants with spasms. We analyzed etiologic data from 140 such infants, 78 girls and 62 boys, ages 2 months to 4 years 10 months (mean, 17 months). All had been evaluated extensively in one of two major medical centers. It should be emphasized that our referral population is biased toward infants with intractable spasms who fail to show a structural lesion. Seven patients had neurocutaneous syndromes, two had chromosomal abnormalities, two had inborn errors of metabolism, and one each had craniosynostosis or Menkes syndrome. Computed tomography and/or magnetic resonance imaging detected lesions in another 29 infants (20.7%) who did not have a specific disease or syndrome. Without the benefit of PET, the total number of symptomatic cases was 42 (30.0%). One infant, classified as idiopathic, had normal development and PET. In 97 cryptogenic cases, PET uncovered unifocal abnormalities in 30 and multifocal abnormalities in 62. Diffuse PET abnormalities, which did not provide specific etiologic information, were seen in three infants. Another two infants had normal PET scans. Thus, with the benefit of PET, the number of symptomatic cases rose dramatically from 42 (30.0%) to 134 (95.7%). The majority of unifocal and multifocal abnormalities on PET are believed to represent dysplastic lesions.

The place of the EEG and imaging in the management of seizures

Images

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.

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.

Adrenoleukodystrophy: cortical hypoperfusion demonstrated with 99mTc-HMPAO SPECT

Regional cerebral blood flow was investigated in an 8-year-old boy with adrenoleukodystrophy by single photon emission computed tomography. The use of 99mTc-hexamethylpropylene amine oxime revealed markedly reduced blood flow in the occipital, parietal, and temporal cortical gray matter, in addition to the anticipated reduction in white matter. The area with a decreased blood flow was more extensive than that detected by x-ray computed tomography.