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Biomedical subjects

D C Reutens

Publications and source records attributed to D C Reutens.

At least 19 recordsLinked to original sources
PubMed1998

Morphometric analysis of the temporal lobe in temporal lobe epilepsy.

PURPOSE: Using high-resolution magnetic resonance imaging (MRI), we examined the temporal neocortex and the underlying white matter in patients with unilateral temporal lobe epilepsy (TLE) and in control subjects. METHODS: The images of 27 patients and 42 control subjects were registered into stereotaxic space, corrected for image intensity inhomogeneity, and automatically segmented into gray matter, white matter, and cerebrospinal fluid (CSF) over a predetermined extent of the temporal lobe. The surface between the gray matter and CSF was extracted, indices of curvature (IOC) of the surface were calculated, and a frequency histogram of the IOC was obtained. RESULTS: There was significant bilateral reduction in the total volume of the temporal lobe and in the volume of gray matter. White matter volume was significantly reduced only in the temporal lobe ipsilateral to the seizure focus. There were significant changes in the position and amplitude of peaks in the frequency histogram of the IOC. CONCLUSIONS: The volume of gray matter was negatively correlated with duration of epilepsy, suggesting that neocortical changes may be a consequence of seizures. Changes in the frequency histogram of the IOC suggested an additional alteration in the surface morphology of the temporal lobe in TLE, possibly related to sulcal widening.

Adolescent↗
PubMed1998

Regional lumped constant differences and asymmetry in fluorine-18-FDG uptake in temporal lobe epilepsy.

UNLABELLED: To date, there has been no satisfactory explanation for the observation that interictal uptake of the glucose analog [18F]fluorodeoxyglucose (FDG) is consistently reduced in the temporal lobe ipsilateral to the seizure focus in patients with temporal lobe epilepsy. We examined the hypothesis that regional differences in tracer uptake in temporal lobe epilepsy reflect regional differences in the lumped constant (lambda). METHODS: In 9 control subjects and 10 patients with temporal lobe epilepsy, we obtained regional estimates of lambda by expressing lambda in terms of transfer coefficients for FDG and parameters which are likely to remain constant throughout both the brain and under different functional states. RESULTS: In the patients, lambda was lower in the temporal lobe ipsilateral to the epileptic focus (0.53 +/- 0.06; p < 0.005) than in the contralateral temporal lobe (0.56 +/- 0.06). Interside differences in lambda were highly correlated with asymmetry in tracer uptake. Furthermore, the use of regional estimates of lambda reduced the asymmetry in estimated rCMRglc in patients with temporal lobe epilepsy but not in controls. CONCLUSION: In these patients, a change in tracer uptake may not indicate a change in glucose consumption of corresponding magnitude, raising the possibility that in at least some patients with temporal lobe epilepsy, the term hypometabolism does not accurately describe reductions in tracer uptake.

Adult↗
PubMed1998

Signal-enhancing switched protocols to study higher-order cognitive tasks with PET.

UNLABELLED: We tested the effectiveness of a switched protocol when it is used to detect signals that result from the study of a higher-order cognitive task with PET. Using language tasks that have been studied extensively in our laboratories, we compared the signal-to-noise ratio (S/N) and statistical significance of the activation signals detected in PET images of regional cerebral blood flow (rCBF), obtained using a standard activation protocol, and of activity concentration, obtained using a switched protocol. METHODS: Four volunteers were studied with PET while they were performing synonym-generation and word-repetition tasks (activation and baseline tasks, respectively). Each volunteer had three activation/baseline and three baseline/ activation scans. Data for each scan were collected in two frames (60 and 120 sec long). During the first 60 sec, data were collected using a standard activation protocol. Subjects then switched tasks, and acquisition continued for 120 sec. Two images were obtained from each scan: an rCBF image using the first frame and an activity-concentration image using both frames. Images were transformed into Talairach space, subtracted and averaged within and across subjects. Parametric t-statistic images were generated for each protocol, and the magnitude and significance of the activation signals yielded by the two acquisition methods were compared. RESULTS: All the activation foci detected using measurements of rCBF were detected when the switched protocol was used; this protocol, in addition, yielded better S/N values. The cognitive component introduced by task-switching in switched protocols did not yield extra statistically significant foci. In single subjects, the average improvement in the signal significance from regions of activation, at a 95% confidence level, was between 6% and 25%. When scans were averaged across subjects, the switched protocol yielded improvements in signal statistical significance of up to 38%. CONCLUSION: We present evidence suggesting that switched protocols can be used to study higher-order cognitive tasks and that they yield activation foci with S/N values that are greater than those of equivalent foci detected using an rCBF protocol. Switched protocols appear to be easy to apply to the testing of higher-order cognitive functions. However, the extra cognitive requirement of switching tasks during data acquisition may be a limiting factor when switched protocols are used to study memory processes.

Adult↗
PubMed1997

Results of surgical treatment in temporal lobe epilepsy with chronic psychosis.

The combination of psychosis and refractory temporal lobe epilepsy is not rare. However, patients with chronic interictal psychosis and refractory epilepsy are rejected from many epilepsy surgery programmes purely on psychiatric grounds. It is often assumed that disturbed behaviour will prevent adequate preoperative evaluation or that the patients are unable to provide informed consent for preoperative investigations and for surgery. The observation that the psychosis usually does not improve after operation and fears of an exacerbation of psychosis with post-surgical seizure remission, analogous to 'forced normalization', are further deterrents to surgery in these patients. We describe five patients with the dual diagnoses of medically intractable temporal lobe epilepsy and chronic psychosis who underwent temporal lobe resection. The patients were able to provide informed consent and were easily managed during preoperative investigation. Seizure outcome has been excellent in all. Neither temporal lobe resection nor remission of seizures influenced the nature or evolution of the psychosis. Subjectively the patients functioned better in activities of daily living and freedom from seizures improved integration into psychiatric treatment facilities. With appropriate psychiatric intervention, patients with chronic psychosis and refractory epilepsy can participate in presurgical investigation successfully, and can undergo surgery uneventfully.

Adult↗
PubMed1997

Cerebral [15O] water clearance in humans determined by positron emission tomography: II. Vascular responses to vibrotactile stimulation.

When used to measure blood flow, water leaves a residue in the vascular bed, which may contribute to the calculation of increased blood flow during functional activation of brain tissue. To assess the magnitude of this contribution with the two-compartment positron emission tomography (PET) method, we mapped the water clearance (K1) of the brain as an index of cerebral blood flow (CBF) and the apparent vascular distribution of nonextracted H2 15O (Vo). The latter map represented mainly the cerebral arterial and arteriolar volume. We also prepared subtraction maps (delta K1, delta Vo) of the response to vibrotactile stimulation of the fingertips of the right hand of six normal volunteers. Using magnetic resonance (MR) images of all subjects, the data were rendered into Talairach's stereotaxic coordinates and the averaged subtraction images (activation minus baseline) merged with the corresponding averaged MRI image. The delta K1 map revealed the expected response in the primary sensory hand area; the delta Vo response was located about 13 mm more anteriorly, close to the central fissure, most likely reflecting changes of the arteries feeding the primary sensory hand area. We conclude that cerebral perfusion and cerebrovascular responses to vibrotactile stimulation may occur in disparate locations that can be identified separately by using the two-compartment method.

Brain↗
PubMed1997

L-arginine infusion increases basal but not activated cerebral blood flow in humans.

Nitric oxide is a potent vasodilator. Infusion of its precursor, L-arginine, results in increased cerebral blood flow (CBF) in experimental animals. We examined the effects of L-arginine infusion on CBF in humans using positron emission tomography and the quantitative H2(15)O method. Six subjects received 500 ml of 0.9% NaCl solution, and six subjects received an infusion of L-arginine (16.7 mg/kg/min; 500 mg/kg). Before and after the i.v. infusion, paired CBF measurements were performed at baseline and with vibrotactile stimulation of the right hand. In scans performed without vibrotactile stimulation, mean whole-brain CBF increased from 34.9 +/- 3.7 ml 100 g-1 min-1 to 38.2 +/- 4.4 ml 100 g-1 min-1. (9.5%; p < 0.005) after L-arginine infusion. The temporal pattern of CBF changes differed from that of plasma growth hormone and insulin levels and of arterial pH. In contrast, in the saline group, mean whole-brain CBF did not change significantly (35.8 +/- 5.9 ml 100 g-1 min-1 to 35.9 +/- 6.4 ml 100 g-1 min-1; 0.3%). Vibrotactile stimulation produced significant focal increases in CBF, which were unaffected by L-arginine infusion. L-arginine infusion was associated with an increase in plasma L-citrulline, a byproduct of nitric oxide synthesis.

Adult↗
PubMed1996

Reliability of visual inspection for detection of volumetric hippocampal asymmetry.

Volumetric measurement of the hippocampus is of use in localisation of lesions causing focal epilepsy and in lateralisation of epilepsy due to mesial temporal sclerosis. However, it is time consuming and requires specialised equipment. Hence, we compared volumetric measurement with visual detection of hippocampal asymmetry by five trained observers. MRI studies of 19 neurologically normal subjects and of 34 consecutive patients with epilepsy and hippocampal volume ratios below the lowest normal value were employed. Agreement between visual and quantitative diagnoses was 59% for all subjects (kappa = 0.38) and 65% for those with volumetric hippocampal asymmetry. Disagreements in visual and volumetric lateralisation of hippocampal asymmetry were relatively uncommon. Visual estimates of the extent of hippocampal involvement and the observers' confidence in the diagnosis influenced the accuracy of visual inspection. However, discordance in diagnoses occurred even when confidence in the visual diagnosis was high. Reliable visual detection occurred for hippocampal volume ratios below 0.7, suggesting that visual determination of hippocampal asymmetry is of greatest clinical value in the lateralisation of seizure foci in patients already selected for the presence of intractable temporal lobe epilepsy. Volumetric measurements are particularly important if hippocampal asymmetry is used for seizure localisation in groups of patients with temporal or extratemporal epilepsy.

Adolescent↗
PubMed1996

Cerebral [15O]water clearance in humans determined by PET: I. Theory and normal values.

When used to measure blood flow in the brain, water leaves a residue in the vascular bed that influences the estimation of blood flow by current methods. To assess the magnitude of this influence, we developed a two-compartment model of blood flow with separate parameters for transport and vascular distribution of brain water. Maps of the water clearance, K1 into brain tissue, separated from the circulation by a measurably resistant blood-brain barrier (BBB), were generated by time-weighted integration. Depending on the validity of the assumptions underlying the two-compartment model presented here, the maps revealed a significant overestimation of the clearance of water when the vascular residue was ignored. Maps of Vo, the estimate of the apparent vascular distribution volume of tracer H2(15)O, clearly revealed major cerebral arteries. Thus, we claim that the accumulation of radioactive water in brain tissue also reflects the volume of the arterial vascular bed of the brain.

Body Water↗
PubMed1995

Intractable partial epilepsy following low-dose scalp irradiation in infancy.

We report the development of intractable epilepsy in 3 patients treated with irradiation to "strawberry" scalp nevi in infancy. Low-dose radiation was used (12 and 13 Gy in 2 of the patients). The clinical evolution suggested a recognizable and distinctive postradiation syndrome. There was concordance between the site of radiation as shown by localized alopecia, the clinical features of the partial seizures, and electrographic abnormalities. The clinical picture was unlike delayed cerebral radiation necrosis of adulthood, which is not thought to occur at doses below 50 Gy, in 2-Gy fractions. Neurological deficits were not progressive and in 2 patients there was no evidence of parenchymal injury on cranial magnetic resonance imaging scanning. These differences suggest pathogenetic differences to cerebral radiation injury of adulthood, probably relating to the interaction between nervous system development, individual susceptibility, and the low doses of radiation employed.

Adolescent↗
PubMed1995

Morphometry in temporal lobe epilepsy.

We demonstrate a method for quantitating changes in volume and morphology of the temporal lobe in epilepsy. The temporal lobes of 10 neurologically normal subjects and six subjects with well defined left-sided mesial temporal epilepsy were studied. From high resolution T1-weighted magnetic resonance images, the grey and white matter were manually segmented over a predetermined extent. The volumes of the grey and white matter were determined. Using the segmented images, the grey matter/CSF surface and the white matter/grey matter surface were reconstructed, allowing estimates of the surface area and calculation of indices of curvature for the two surfaces. The index of curvature was calculated for each vertex of a polygonal mesh that was fitted to the surfaces. An index of grey matter thickness (grey matter volume/white matter surface area) was also calculated. There was a significant bilateral decrease in the total volume (p < .01), grey matter volume (p < .001) and grey matter thickness index (p < .05) in epileptic subjects. In addition, there was a bilateral decrease in white matter surface area (p < .05) and a small left-sided decrease in white matter volume (p < .05) in epileptic subjects. The average distributions of indices of curvature for both surfaces differed significantly (p < .05) between normal and epileptic subjects. In the grey matter/CSF surface of normal subjects, a large peak corresponding to surface concavity was present. The amplitude of this peak was significantly lower in epileptic subjects (p < .05 for the right hemisphere; p < .001) for the left hemisphere).

Adult↗
PubMed1995

Idiopathic generalized epilepsy of adolescence: are the syndromes clinically distinct?

Juvenile myoclonic epilepsy, juvenile absence epilepsy, and epilepsy with generalized tonic-clonic seizures (GTCS) on awakening are the three syndromes of idiopathic generalized epilepsy of adolescent onset currently included in the classification of epilepsy syndromes of the International League Against Epilepsy (ILAE). Although they differ in their predominant seizure types, the syndromes share several clinical features, thus giving rise to questions of phenotypic overlap and purity. We studied the clinical features of 101 patients with idiopathic generalized epilepsy beginning in adolescence. A standardized interview was used to elucidate seizure phenomenology, precipitants, frequency, and response to treatment. Groups defined by seizure type were compared and their similarities examined. The group with myoclonic but not absence seizures (21 patients) corresponded to the ILAE syndrome of juvenile myoclonic epilepsy, whereas those with absences but not myoclonus (37 patients) resembled juvenile absence epilepsy. Twenty-six patients shared the features of juvenile myoclonic epilepsy and juvenile absence epilepsy. Epilepsy with GTCS on awakening was not a specific syndromic entity; 10 patients had this seizure type alone. Seven patients were without a syndromic diagnosis. In these patients only GTCS occurred, but neither on awakening nor in the evening period of relaxation. We conclude that whilst syndromes of idiopathic generalized epilepsy of adolescence can be recognized, the current classification does not include all patients. In addition, the boundaries between the syndromes are indistinct, suggesting underlying neurobiological, possibly genetic, relationships.

Adolescent↗
PubMed1994

Late-onset drop attacks in temporal lobe epilepsy: a reevaluation of the concept of temporal lobe syncope.

We report the clinical, radiologic, and EEG features of six patients with temporal lobe drop attacks (TLDA), all of whom underwent temporal resection. Postoperative follow-up of at least 1 year was available in all. TLDA were never the first manifestation but followed the onset of epilepsy after a long delay ranging from 7 to 43 years (mean, 24.4 years). Seizures were of unilateral temporal origin. In one patient, stereo EEG recording of TLDA showed rapid spread of the ictal discharge away from the temporal lobe in less than 1 second. Postoperatively, three patients were seizure free; one has had no TLDA but experiences sporadic auras; another, despite a reduction of more than 50%, continues to have complex partial seizures and TLDA; and the sixth has had sporadic secondarily generalized seizures upon reduction of antiepileptic medication. In conclusion, drop attacks may occur in temporal lobe epilepsy, usually long after the onset of epilepsy. They lead to increased disability and suggest a rapid spread of the ictal discharge and possible involvement of the pontine reticular formation rather than the presence of bitemporal foci or an extratemporal origin.

Adult↗
PubMed1993

Magnetic stimulation of the brain in generalized epilepsy: reversal of cortical hyperexcitability by anticonvulsants.

Observations on experimental models suggest that diffuse cortical hyperexcitability is an important abnormality in the generalized epilepsies. We used the threshold for transcranial magnetic stimulation as an index of motor cortical excitability in 89 neurologically normal control subjects and 56 patients with idiopathic generalized epilepsy (20 untreated and 36 chronically treated with anticonvulsants). Magnetic stimulation was repeated in 10 patients after valproate monotherapy had been commenced and in 23 control subjects. The threshold intensity was significantly lower in the untreated patients (46 +/- 5% [mean +/- 95% confidence interval]) than in the control subjects (56 +/- 2%). Treated patients had significantly higher thresholds (64 +/- 4%) than did untreated patients and control subjects. A significant increase in threshold intensity (8 +/- 2%) occurred in patients retested after starting valproate; there was no significant change in retested control subjects (-1 +/- 2%). Threshold intensity was positively correlated with plasma valproate levels (rs = 0.37). The findings suggest that cortical excitability is increased in idiopathic generalized epilepsy and is reduced following anticonvulsant treatment. Transcranial magnetic stimulation is of use in examining the pathophysiology of generalized epilepsy. Furthermore, changes in threshold intensity in response to anticonvulsant treatment may prove useful in guiding therapy.

Adolescent↗
PubMed1993

The influence of changes in the intensity of magnetic stimulation on coil output.

We measured the peak voltage induced in a sensing loop by a Magstim 200 magnetic stimulator. Coil output varied little for repeated stimulation at the same intensity over a wide range of coil output. In contrast, the first stimulus immediately after a change in intensity was of larger amplitude and showed greater variability than subsequent stimuli. The effect was seen for changes in intensity of 5% and 60% and was greater for reductions than for increases in stimulation intensity. Stimulation immediately after a reduction in intensity from 100% to 40% resulted in peak induced voltages as high as those recorded for repeated stimulation at 43% of maximum coil output. Increased coil output following changes in stimulation intensity may affect measurement of the threshold old for motor cortical stimulation. The effect of a change in intensity could be minimized by delaying stimulation for at least 30 s or discarding the first stimulus after the change.

Brain↗
PubMed1993

Localised neuronal migration disorder and intractable epilepsy: a prenatal vascular aetiology.

Localised neuronal heterotopias are an increasingly recognised cause of intractable focal epilepsies. The aetiology of these circumscribed disorders of neuronal migration is often unknown although in some instances proximity to areas of prenatal infarction suggests that severe ischaemia was responsible. A patient is described with intractable complex partial seizures associated with heterotopic grey matter and cerebral hypoplasia confined to the territory of the left posterior cerebral artery; the left hippocampus was spared. Angiography showed a normal left anterior choroidal artery but a hypoplastic left posterior cerebral artery, implicating prenatal ischaemia without frank infarction as the aetiology of the malformation.

Adult↗