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Biomedical subjects

D A Shewmon

Publications and source records attributed to D A Shewmon.

At least 55 records · Page 3Linked to original sources
PubMed1985

Seizures in an atelencephalic infant. Is the cortex essential for neonatal seizures?

Clinical and electrographic seizures were recorded in an infant with atelencephaly. Because the infant had no cerebral hemispheres, the ictal discharges were presumed to arise from the disorganized diencephalic derivatives that occupied the entire supratentorial space. The case provided strong support for the concept that, unlike epileptic seizures in older patients, some types of neonatal seizures may originate and propagate exclusively in subcortical structures. This may explain the striking dissociation between the electrographic and behavioral aspects of seizures occasionally observed in newborns, as well as the frequent intractability of such seizures to standard anticonvulsants.

Brain↗
PubMed1984

Off-line montage reformatting.

A method is described for off-line reformatting of recorded EEG data to any desired montage, gains, filter settings and paper speed. Thirty-two channels, including every scalp electrode, are recorded in a common referential montage and multiplexed onto videocassettes . Playback onto an EEG machine faithfully reproduces the original signals, so that any final montage may be specified at the EEG selector panel, with common mode rejection of the recording reference. The technique has proven especially useful in prolonged seizure monitoring and in the clarification of events which occur only rarely in the course of routine EEGs.

Child, Preschool↗
PubMed1981

Postischemic hypervascularity of infancy: a stage in the evolution of ischemic brain damage with characteristic CT scan.

One to 2 weeks after severe brain ischemia, four infants developed an unusual vascular lesion with a characteristic appearance on computed tomography that has not been reported previously. Restricted areas (most frequently the basal ganglia and thalamus) displayed increased attenuation, which enhanced further upon infusion of contrast medium. Autopsy of one infant revealed that the CT abnormality corresponded to an extremely dense neovascular network which had almost completely replaced the parenchyma in that region. We postulate that this pathological change is a stage in the organization of ischemic brain damage reflecting the infant's vascular plasticity. Thus, hypoxia induces marked capillary proliferation in regions of normally high metabolism and capillary density. The CT pattern may prove useful in predicting the location and extent of sequelae to perinatal asphyxia.

Asphyxia Neonatorum↗
PubMed1980

Delayed radiation necrosis of the brain contralateral to original tumor.

In a 23-year-old man, radiation necrosis developed in the left hemisphere after radiation of a right-sided intracranial tumor. Since normal tissue had to be resected around the tumor, the contralateral temporal lobe received the highest cumulative radiation dose for brain tissue. This report underscores the need for careful reconstruction of the radiation isodose distribution when considering the differential diagnosis of postradiation brain lesions.

Adult↗
PubMedDate not supplied

The probability of inevitability: the inherent impossibility of validating criteria for brain death or 'irreversibility' through clinical studies.

A great need persists for diagnostic criteria for both brain death in young children and irreversible loss of consciousness at all ages. This article examines the inferences derived from a hypothetical confirmatory study in which all of the N patients who fulfilled the criterion did in fact experience brain death (irreversibility). A Bayesian methodology proves that, for N in the range of a large clinical study, estimations of prior probabilities are, for all practical purposes, irrelevant to the calculation of the posterior probabilities. The risk of a false positive diagnosis for the next patient who meets the criterion is approximately 1/(N + 2). The chance of at least one false positive diagnosis among the next (N + 1) patients who meet the criterion is around 50 per cent. Thus, achievement of the requisite moral certainty of a declaration of death (irreversibility) necessitates an impossibly large N for the study. This does not mean that one cannot diagnose death, but rather that the validity of the diagnostic criteria must be self-evident on a priori grounds, and that confirmatory studies are necessarily either inadequate or superfluous.

Adult↗
PubMedDate not supplied

Electroencephalographic abnormalities in infants with hypoplastic left heart syndrome.

Electroencephalography (EEG) was performed on 16 neonates between 38-45 weeks conceptional age with hypoplastic left heart syndrome (HLHS). The findings were compared blindly with EEGs recorded from 16 infants with other congenital heart defects and 15 infants referred for EEGs with noncardiac diagnoses or problems. EEGs from HLHS infants demonstrated significantly decreased quiet sleep and increased indeterminate sleep, an abnormally discontinuous tracing in active and indeterminate sleep, and lack of response to stimulation. No significant differences were present in the amount of active sleep, sharp waves, focal slowing, or rhythmic theta activity. The distinctive abnormalities were unrelated to arterial blood gases or treatment with prostaglandin E at recording. Four HLHS infants had repeat recordings performed; there were serial increases in quiet sleep, decreases in indeterminate sleep, and improved continuity in all patients. Certain EEG abnormalities occur more frequently in infants with HLHS than in patients with other cardiac defects or noncardiac problems. These findings may result from the early onset of heart failure and abnormal cerebral perfusion due to hypoplasia of the ascending aorta and great arteries, conditions commonly associated with HLHS.

Aorta↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

Electrocorticographic confirmation of focal positron emission tomographic abnormalities in children with intractable epilepsy.

The relationship between focal disturbances of glucose utilization demonstrated by positron emission tomography (PET) and electrophysiologic abnormalities defined by intraoperative electrocorticography (ECoG) was studied in eight children (aged 13 months to 12 years) who underwent cortical resection because of intractable seizures. None of the children had pure temporal lobe epilepsy. Computed tomography (CT) and/or magnetic resonance imaging (MRI) were normal in four of the eight children. The scalp electroencephalogram (EEG) showed lateralized interictal epileptiform abnormalities in all eight and lateralized ictal onset in five of eight. In seven children, interictal PET showed focal hypometabolism; the eighth child had focal, ictal hypermetabolism. ECoG at the time of surgery showed epileptiform spiking, slowing, and/or suppression of normal background activity that in every case corresponded to the focus on PET scan. The ECoG findings support the notion that in children with epilepsy focal metabolic abnormalities on PET correspond to electrophysiologically abnormal areas of cortex, which are presumably also the epileptogenic regions. Such areas can appear normal on anatomic imaging studies (CT and MRI). When ictal scalp EEG data are ambiguous or contradictory, PET provides a less invasive means than chronic grid or depth electrode recording for evaluating whether a localized epileptogenic area exists.

Cerebral Cortex↗
PubMedDate not supplied

Neurosurgical treatment of refractory status epilepticus.

Refractory status epilepticus (RSE) is defined as status epilepticus that continues despite aggressive treatment. A 9.8-year-old boy with a past history of daily left focal motor seizures was transferred to University of California at Los Angeles (UCLA) Hospital in pentobarbital coma after 4 days in RSE. The RSE was treated with very high doses of all appropriate antiepileptic drugs (AEDs), alone and in combination. The pentobarbital was titrated to burst suppression on EEG, but whenever pentobarbital was decreased, the seizures recurred. An ictal positron tomography scan of glucose metabolism demonstrated a right frontal area of hypermetabolism corresponding to an epileptic focus on EEG and magnetic resonance lesion. Eight days after the boy was admitted to UCLA, the right frontal focus was surgically removed, with immediate control of the status epilepticus. Whereas before onset of RSE, he had daily focal seizures, the boy has been seizure-free postoperatively for greater than 1 year. Operative treatment should be considered in patients with RSE in whom a focus of seizure onset can be demonstrated and who are reasonably considered surgical candidates.

Child↗
PubMedDate not supplied

Surgery for intractable infantile spasms: neuroimaging perspectives.

Twenty-three infants and children underwent cortical resection (n = 15) or hemispherectomy (n = 8) for intractable infantile spasms. Infantile spasms were present at the time of surgery in 17 of the 23 patients; in six, spasms had evolved to other seizure types during surgical evaluation. Children with a remote history of infantile spasms were excluded from this study. Focal or hemispheric lesions were identified by magnetic resonance imaging in seven children; an additional two showed focal atrophy without a discrete lesion. Positron emission tomography (PET) showed lateralized or localized abnormalities of cerebral glucose utilization in all patients; in 14, PET was the only neuroimaging modality to identify the epileptogenic cortex. When this occurred, neuropathological examination of resected brain tissue typically showed malformative and dysplastic cortical lesions. Focal interictal and/or ictal electrographic abnormalities were present in all patients, and corresponded well with localization from neuroimaging. None of the patients were subjected to chronic invasive electrographic monitoring with intracranial electrodes. At follow-up (range 4-67 months; mean 28.3 months), 15 children were seizure-free, three had 90% seizure control, one had 75% seizure control, and four failed to benefit from surgery with respect to seizure frequency.

Brain↗
PubMedDate not supplied

Ictal patterns of cerebral glucose utilization in children with epilepsy.

To determine seizure propagation patterns, we analyzed ictal positron emission tomography (PET) studies of regional cerebral glucose utilization in 18 children (11 male and 7 female aged 2 weeks to 16 years) with epilepsy (excluding infantile spasms IS). Three major metabolic patterns were determined based on degree and type of subcortical involvement: Nine children had type I; asymmetric glucose metabolism of striatum and thalamus. Of these, the 7 oldest children showed unilateral cortical hypermetabolism (always including frontal cortex) and crossed cerebellar hypermetabolism. Two infants (aged < 1 year) had a similar ictal PET pattern but no cerebellar asymmetry, presumably owing to immaturity of corticopontocerebellar projections. Five children had type II, symmetric metabolic abnormalities of striatum and thalamus; this pattern was accompanied by hippocampal or insular cortex hypermetabolism, diffuse neocortical hypometabolism, and absence of any cerebellar abnormality. Four children had type III, hypermetabolism restricted to cerebral cortex. This classification can accommodate ictal PET and single photon emission computed tomography (SPECT) patterns described by other investigators. Future studies should be directed at the clinical relevance of this classification, particularly with regard to epilepsy surgery.

Adolescent↗
PubMedDate not supplied

The use of anencephalic infants as organ sources. A critique.

The recent abandonment of the only active US protocol for harvesting organs from anencephalic "donors" indicates both the practical and the ethical problems inherent in such an effort. Various data suggest that surprisingly few such organs would actually end up benefiting other children. Attempts to revise either the Uniform Anatomical Gift Act or the Uniform Determination of Death Act to allow organ removal from spontaneously breathing anencephalic infants face major ethical objections. Even if this posed no ethical problem in theory, the ultimate harm to society would not be offset by the good of the few surviving recipients of these organs. Furthermore, providing anencephalic infants with intensive care would tend to preserve the brain stem as effectively as the other organs, predictably rendering the occurrence of brain death unlikely. Thus, despite the great need for newborn organs, anencephalic infants are not as attractive a source as some had hoped.

Anencephaly↗