EEG features of focal malformations of cortical development

Recent advances in neuroimaging have allowed the detection and characterization of focal malformations of cortical developmental in a significant proportion of patients with epilepsy, many of whom were previously labelled as cryptogenic, allowing a better description of the associated electroencephalogram (EEG) features. Alpha activity is usually preserved, although superficial gyral abnormalities are often associated with overlying localized polymorphic delta activity, and occasionally abnormal fast activity. Most affected patients with epilepsy show interictal spikes. These are often broadly concordant with the structural abnormality but may show a wider anatomic distribution and be multifocal, or occasionally appear only in anatomically distant sites. In many patients the spikes are frequent and sometimes they occur continuously or in long trains. EEG findings are often stable over time, but some patients only show the development of slow wave changes or interictal spikes when followed serially for several years. A small proportion of patients with focal malformations of cortical development have EEG features mimicking idiopathic generalized epilepsy, and occasionally patients exhibit continuous generalized spike and slow wave activity in sleep. Electrocorticography studies confirm the often widespread nature of interictal spiking, but may also show highly epileptogenic patterns recorded directly from dysplastic cortex. The intrinsic epileptogenicity of areas of cortical developmental abnormalities has also been demonstrated by chronic intracranial studies and in vitro recordings of slices obtained from resected human dysplastic cortex. In this regard such developmental abnormalities are fundamentally different from acquired lesions such as tumors/vascular anomalies that usually exert their effects through changes in adjacent cortex.

Three-dimensional fractal analysis of the white matter surface from magnetic resonance images of the human brain

The convolutions of the cerebral cortex are difficult to describe and delineate. Our understanding of the development of the brain and its associated maldevelopment would be assisted by quantitative analysis of the cortex. Volumetric magnetic resonance (MR) imaging provides high-resolution anatomical data from which we can reconstruct the white matter as a three-dimensional object and extract its surface (the grey/white matter interface). Three-dimensional fractal analysis of this surface is a method of quantifying the surface complexity dependent upon the variation of the surface area under different scales of inspection. We estimate the fractal dimension of the white matter surface for each hemisphere and 10 coronal blocks of each hemisphere in 30 normal adult subjects. These values are tightly distributed and have been used to define a normal range of fractal dimensions. Abnormal fractal dimensions were found in 8/16 subjects with epilepsy and a gyral abnormality observed on routine MR imaging; and in 9/23 subjects with epilepsy and normal routine MR imaging. These analytical techniques offer additional information about the structure of the cortex in normal brains and about abnormalities of structure in subjects with suspected but unobserved structural abnormalities.

Startle provoked epileptic seizures:features in 19 patients

OBJECTIVES

To define the clinical characteristics of a group of patients with startle provoked epileptic seizures (SPES).

METHODS

Nineteen patients were identified during the course of a larger study of clinical seizure patterns. A witnessed seizure account was obtained in all patients; interictal EEG in 18, video-EEG-telemetry in eight, CT in 18, and high resolution MRI in eight.

RESULTS

The onset of SPES was in childhood or adolescence in 14 of 19 patients. It was preceded by exclusively spontaneous seizures in nine patients and SPES had been replaced by exclusively spontaneous seizures in two patients. Sudden noise was the main triggering stimulus and somatosensory and visual stimuli were also effective in some patients. The clinical seizure pattern involved asymmetric tonic posturing in 16 of 19 patients. Focal neurological signs were present in nine patients, mental retardation in six, and 10 were clinically normal. Ictal scalp EEG showed a clear seizure discharge in only one patient with a tonic seizure pattern; over the lateral frontal electrodes contralateral to the posturing limbs. Brain CT showed a porencephalic cyst in three patients, focal frontal atrophy in one, and generalised atrophy in one. Brain MRI was undertaken in five normal subjects and three neurologically impaired patients, six with normal CT. It showed a porencephalic cyst in one patient. In six patients, there were dysplastic lesions. They affected the lateral premotor cortex in three patients and the perisylvian cortex in three patients, one with bilateral perisylvian abnormality.

CONCLUSIONS

SPES are more frequent than is generally appreciated. They may be transient and occur relatively commonly without fixed deficit, by contrast with previous reports. The imaging abnormalities identified in those without diffuse cerebral damage suggest that SPES are often due to occult congenital lesions and that the lateral premotor and perisylvian cortices are important in this phenomenon.

Benzodiazepine receptors in focal epilepsy with cortical dysgenesis: an 11C-flumazenil PET study

Previous imaging studies using 11C-flumazenil in patients with mesial temporal lobe epilepsy and neocortical partial seizure disorders have found focal decreases in gamma-aminobutyric acid type A/benzodiazepine receptor binding. These studies used subjective visual assessment and a region of interest approach to quantitation. We performed three-dimensional, 11C-flumazenil positron emission tomography in 12 patients with cortical dysgenesis identified by high-resolution volumetric magnetic resonance imaging and in 26 normal subjects. Spectral analysis was used to produce a parametric image of 11C-flumazenil volume of distribution for each subject. Using volumetric normalization and statistical parametric mapping, we compared the entire brain volume of each patient with the brains of the normal group to produce maps of regions of abnormal 11C-flumazenil binding which were then rendered into the volumetric magnetic resonance images. This allowed a correlation of structure and function to be made. Of the 12 patients, 10 showed at least one region of abnormal 11C-flumazenil binding; the abnormal regions were frequently more extensive than were the lesions seen with magnetic resonance imaging. 11C-Flumazenil binding abnormalities were frequently seen in regions of cortex that had a normal magnetic resonance appearance. Lesions were characterized by increases in gamma-aminobutyric acid type A/benzodiazepine receptor availability, and by the decreases found in previous studies. These findings have implications for the neurobiology of seizure disorders associated with cortical dysgenesis and for the management of such patients if surgery is contemplated.

Bilateral hippocampal volume loss in patients with a history of encephalitis or meningitis

Volumetric analysis of high-quality magnetic resonance imaging (MRI) scans identifies asymmetric hippocampal atrophy in most patients with temporal lobe epilepsy. However, bilateral hippocampal atrophy can be missed by unnormalized volume measures. We considered two patient groups with temporal lobe epilepsy, one with a history of febrile convulsions (FC, n = 14) and one with a history of encephalitis or meningitis (E/M, N = 12), to compare the prevalence of bilateral volume loss between the groups. A volume normalization process defines a normal range of hippocampal volumes in control subjects (n = 32). Normalized volumes indicated that 11 of 14 subjects with a history of FC had unilateral hippocampal atrophy and 9 of 12 subjects with a history of E/M had bilateral hippocampal atrophy as compared with the controls. Visual assessments of unilateral hippocampal atrophy (n = 17) correlated well with measured unilateral volume loss (n = 14 ), but visual assessment of bilateral hippocampal atrophy (n = 3) correlated poorly with measured bilateral volume loss (n = 12). Mean age at seizure onset was lower in the FC group (7 years) than in the E/M group (13 years), but other clinical features were similar between the two groups. Hippocampal volume normalization is necessary to detect bilateral volume loss, which is common in patients with a history of encephalitis or meningitis.

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.

Apnoea and bradycardia during epileptic seizures: relation to sudden death in epilepsy

OBJECTIVE

To record non-invasively ictal cardiorespiratory variables.

METHODS

Techniques employed in polysomnography were used in patients with epilepsy undergoing EEG-video recording at a telemetry unit.

RESULTS

Apnoea (> 10, range > 10-63, mean 24 s) was seen in 20 of 47 clinical seizures (three secondary generalised, 16 complex partial, and one tonic) and 10 of 17 patients. Apnoea was central in 10 patients, but obstructive apnoea was also recorded in three of 10. Oxyhaemoglobin saturation (SpO2) dropped to less than 85% in 10 seizures (six patients). An increase in heart rate was common (91% of seizures). Bradycardia/sinus arrest was documented in four patients (mean maximum RR interval 5.36, range 2.8-8.6 s) but always in the context of a change in respiratory pattern.

CONCLUSION

Ictal apnoea was often seen. The occurrence of bradycardia in association with apnoea suggests the involvement of cardiorespiratory reflexes. Similar mechanisms may operate in cases of sudden death in epilepsy.

An analysis of clinical seizure patterns and their localizing value in frontal and temporal lobe epilepsies

The differentiation of frontal lobe epilepsy (FLE) and temporal lobe epilepsy (TLE) is a clinical problem of major theoretical and practical importance. Current electroclinical classification is based on retrospective studies of highly selected patients. When applied to the presurgical evaluation of patients, it has poor specificity. The current study adopts a different and prospective approach to the analysis of ictal clinical manifestations and their value in differentiating FLE and TLE. Two hundred and fifty-two patients with partial epilepsy were selected according to criteria of focal abnormality and imaging, ictal EEG or interictal EEG or highly focal clinical pattern. A witnessed seizure description was obtained for each of their habitual seizures and the sequence of manifestations encoded and entered into a statistical cluster analysis to form a clinical classification of the 352 seizures identified, which comprised 14 clinical groups. Neuroimaging abnormalities were measured, using a template technique, and graded 0-3 according to extent of involvement of each region in the lesion, using standard anatomical divisions. A chi 2 analysis of lesion location against seizure type was performed to assess the strength of association of seizure types with specific cerebral regions. The distribution of interictal EEG spikes and ictal EEG onsets were assessed qualitatively. An independent analysis was also performed, comparing clinical seizure manifestations associated with lesions restricted to either frontal or temporal lobes. Of the 14 clinical groups, four were predominantly related to temporal lobe abnormalities: fear/olfactory/gustatory; absence with no focal symptoms; experiential and visual. Within these groups, 45 out of 58 lesional cases involved the temporal lobes (P<<0.001). A minority of seizures in these groups were associated with frontal lesions and these seizures were significantly more likely to involve version/posturing, without an intervening absence phase, than the temporal cases (P<0.001). Two groups were related to perirolandic abnormalities; somatosensory and Jacksonian clonic with 22 out of 24 lesional cases involving this region (P<0.001). Two other groups were related to the frontal lobes; version/posturing and motor agitation. Early focal tonic activity or head turning were associated with lateral premotor lesions (P<0.001) and ictal and interictal EEG showed strong frontal predominance. Seizures characterized by general motor agitation were associated with lesions of the orbitofrontal (eight out of thirteen cases) and frontopolar (six out of thirteen cases) cortices (P<0.001). Location of interictal EEG spikes and ictal EEG onsets were generally consistent with lesion sites and where there were discrepancies, EEG localization tended to be more diffuse than lesion localization, rather than frankly discordant. Analysis of manifestations associated with pure frontal and pure temporal lesions supported the results of the cluster analysis and also showed a significant association of oro-alimentary automatisms with temporal lobe abnormalities. There were no consistent differences between groups with different localizations in terms of seizure frequency or other characteristics of seizure timing, although very high seizure frequencies were seen more often in association with frontal lesions. Only one combination of different seizure types in the same patient occurred with statistical significance: absence and generalized motor seizures and pseudo generalized epilepsy. The results of this study suggest that relatively few seizures can be localized reliably on clinical grounds and that even in those seizure types where there is a statistically significant association with specific cortical areas, an important minority do not share the same associations. Analysis of the seizure evolution as well as initial symptoms may be of value in localizing some cases, but even here wide variation occurs...

The demonstration of gyral abnormalities in patients with cryptogenic partial epilepsy using three-dimensional MRI

BACKGROUND

Despite the use of high-resolution magnetic resonance imaging (MRI) in the demonstration of structural abnormalities underlying chronic partial epilepsy, a significant proportion of MRI scans in such cases still appear normal when viewed conventionally as two-dimensional images, especially in extratemporal epilepsies.

OBJECTIVES

To increase the yield of MRI in patients with extratemporal epilepsies. To examine specific regions of three-dimensional surface renderings of the cerebral hemispheres.

DESIGN

Postprocessing of volumetric MRI data was used to detect abnormalities of gyration that may not be seen otherwise.

SETTING

Scans were obtained at a hospital clinical imaging facility.

PARTICIPANTS

Sixty-four subjects were studied: 33 controls, 15 patients with hippocampal sclerosis (as disease controls), and 16 patients with cryptogenic partial epilepsy that on clinical grounds was extratemporal.

MAIN OUTCOME MEASURES

Gyral patterns were evaluated for abnormality by visual comparison between subjects.

RESULTS

Inspection of the routine two-dimensional images had failed to demonstrate relevant underlying neocortical abnormality in any of the patients' scans. Three-dimensional reconstruction revealed abnormal gyral patterns in the frontal lobe convexity in seven of the 16 cryptogenic clinically extratemporal cases. Macrogyria was revealed in one case and increased gyral complexity with altered disposition was seen in six cases. Similar gyral patterns were not seen in any subjects from the other groups.

CONCLUSION

Three-dimensional analysis of volumetric MRI data can reveal structural abnormality that is not visible when the data are viewed as two-dimensional images only.

Sudden death in epilepsy: a study of incidence in a young cohort with epilepsy and learning difficulty

Sudden death, often seizure related, may occur in patients with epilepsy. Population-based incidence is probably on the order of 1:1,000/year. The incidence is much higher in selected groups, however. We wished to establish the incidence of sudden unexpected death (SUD) in a young cohort with severe epilepsy and learning difficulties. The study cohort included 310 pupils with epilepsy enrolled at a special residential school between April 1970 and April 1993. The follow-up period totaling 4,135 person-years included a period of residence at the school as well as time after leaving. Age and sex standardized overall mortality ratio was 15.9 [95% confidence interval (CI) 10.6-23.0], with 20 of 28 deaths considered epilepsy related. An incidence of sudden death cases of 1:295/year was noted. All 14 sudden deaths occurred when the pupils were not under the close supervision of the school and most were unwitnessed, which has implications for prevention.

Quantitative hippocampal MRI and intractable temporal lobe epilepsy

OBJECTIVES

To evaluate and compare T2 relaxometry and volumetrics of hippocampus in the presurgical evaluation of patients with intractable temporal lobe epilepsy (TLE), and to correlate these quantitative MRI measures with the pathology of the resected hippocampus.

PATIENTS

Forty patients with intractable TLE who underwent presurgical evaluation and subsequent temporal lobe surgery.

MAIN OUTCOME MEASURES

Hippocampal T2 (HCT2), volumes of hippocampi and hippocampal volume ratio (HCVR) (volume of hippocampus with higher HCT2 divided by volume of hippocampus with lower HCT2), and qualitative pathology.

RESULTS

Thirty-two patients had hippocampal sclerosis, three patients had end-folium sclerosis, one patient had amygdala sclerosis, and four patients had a foreign tissue lesion in the temporal lobe. HCT2 (R/L) correlated inversely with the ratio of hippocampal volumes (R/L) (r = -0.91; p < 0.0001). A high T2 signal in an atrophic hippocampus was characteristic of hippocampal sclerosis. All patients with hippocampal sclerosis had an HCVR below control values, and only one of these had an HCT2 in the normal range. HCVR produced one false-positive result. The patients with end-folium sclerosis had normal HCT2 and HCVR. The patient with amygdala sclerosis had a normal hippocampus on qualitative and quantitative assessment. Of the four patients with a lesion, one had a mildly increased HCT2 and one had mild volume asymmetry. Hippocampal volume asymmetry could be reliably detected on visual inspection of the MRI with an HCVR of 0.85 or less, and an increase of HCT2 with a T2 of 115 msec or higher.

CONCLUSION

Quantitative MRI combining HCT2 and HCVR is a reliable method for diagnosing hippocampal sclerosis noninvasively. End-folium sclerosis and amygdala sclerosis should be considered in patients with intractable TLE and negative findings on MRI studies, including quantitative measures of the hippocampus.

Frequency and characteristics of dual pathology in patients with lesional epilepsy

We studied 167 patients who had identifiable lesions and temporal or extratemporal partial epilepsy. Pathology included neuronal migration disorders (NMDs) (48), low-grade tumors (52), vascular malformations (34), porencephalic cysts (16), and gliotic lesions as a result of cerebral insults early in life (17). MRI volumetric studies using thin (1.5- or 3-mm) coronal images were performed in all patients and in 44 age-matched normal controls. An atrophic hippocampal formation (HF), indicating dual pathology, was present in 25 patients (15%). Abnormal HF volumes were present in those with lesions involving temporal (17%) but also extratemporal (14%) areas. Age at onset and duration of epilepsy did not influence the presence of HF atrophy. However, febrile seizures in early childhood were more frequently, although not exclusively, found in patients with hippocampal atrophy. The frequency of hippocampal atrophy in our patients with low-grade tumors (2%) and vascular lesions (9%) was low. Dual pathology was far more common in patients with NMDs (25%), porencephalic cysts (31%), and reactive gliosis (23.5%). Some structural lesions, such as NMDs, are more likely to be associated with hippocampal atrophy, independent of the distance of the lesion from the HF. In other types of lesions, such as vascular malformations, dual pathology was found when the lesion was close to the HF. A common pathogenic mechanism during pre- or perinatal development may explain the occurrence of concomitant mesial temporal sclerosis and other structural lesions because of either (1) associated developmental abnormalities or (2) predisposition to prolonged febrile convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

High resolution magnetic resonance imaging in adults with partial or secondary generalised epilepsy attending a tertiary referral unit

In the past the underlying structural abnormalities leading to the development of chronic seizure disorders have usually only been disclosed by histological examination of surgical or postmortem material, due to their often subtle nature that was beyond the resolution of CT or early MRI. The MRI findings in 341 patients with chronic, refractory epilepsy attending The National Hospital for Neurology and Neurosurgery and Chalfont Centre for Epilepsy are reported. Studies were performed on a 1.5 Tesla scanner with a specific volumetric protocol, allowing the reconstruction of 1.5 mm contiguous slices throughout the whole brain. Direct visual inspection of the two dimensional images without the use of additional quantitative measures showed that 254/341 (74%) were abnormal. Twenty four (7%) patients had more than one lesion. The principal MRI diagnoses were hippocampal asymmetry (32%), cortical dysgenesis (12%), tumour (12%), and vascular malformation (8%). Pathological confirmation was available from surgical specimens in 70 patients and showed a very high degree of sensitivity and specificity for the different entities. The advent of more widely available high resolution MRI should make it possible to identify the underlying pathological substrate in most patients with chronic partial epilepsy. This will allow a fundamental reclassification of the epilepsies for both medical and surgical management, with increasing precision as new methods (both of acquisition and postprocessing) are added to the neuroimaging battery used in clinical practice.

Incidence of photosensitive epilepsy: a prospective national study

We undertook a prospective nationwide study to determine the incidence of photosensitive epilepsy (PE). Virtually all EEG departments in Great Britain (providing approximately 90% coverage of all EEGs performed on people with newly diagnosed seizures) screened cases referred to them over a 3 month period and identified all new cases of epilepsy (defined as one or more recognised seizures) whose first EEG showed a photoparoxysmal response (PPR) on intermittent photic stimulation (IPS). 191 cases were identified, 143 of whom had type 4 PPRs (generalised spike and wave on IPS) on their first EEG. The annual incidence of cases of epilepsy with type 4 PPRs on their first EEG was conservatively estimated to be 1.1 per 100,000, representing approximately 2% of all new cases of epilepsy. When restricted to the age range 7-19 years, the annual incidence rose to 5.7 per 100,000-approximately 10% of all new cases of epilepsy presenting in this age range. To ascertain if there was a significant seasonal variation in PE, 5 EEG departments (which together contributed 15% of cases in the first study period) were visited during a second 3 month study period to identify all new cases of epilepsy with type 4 PPRs on their first EEG. No significant seasonal variation in incidence between summer and winter was found.

Widespread cerebral structural changes in patients with cortical dysgenesis and epilepsy

Cerebral cortical dysgenesis (CD), as revealed by MRI is the second commonest cause of medically refractory chronic partial epilepsy. Surgical treatment is often disappointing in these cases. This has been attributed to the probable diffuse nature of the condition but proof of this in the human brain is lacking. We have quantitatively analysed MRI scans of 30 neurologically normal control subjects and 18 patients with CD, examining the regional distribution of grey and subcortical matter volumes. In 15 out of the 18 patients, we have demonstrated abnormalities of this distribution beyond the margins of the visualized lesion. Nine out of 10 patients with dysgenetic lesions visualized only in one hemisphere had volumetric abnormality in the apparently normal contralateral hemisphere. These abnormalities were not visible on reinspection of the MRI scans. Such abnormalities were not found in 10 patients with isolated hippocampal sclerosis (HS) although the history of generalized seizure activity and duration of epilepsy did not differ between the two groups of patients. Thus there is evidence for the existence of extensive structural disorganization outside visually identified focal lesions in the brains of patients with CD and chronic partial epilepsy. This disruption is not due to the effects of the epilepsy and must instead be associated with its cause. Possible mechanisms producing the abnormalities are discussed. The methodology described may be applied to other cortical diseases.

Demonstration of thalamic activation during typical absence seizures using H2(15)O and PET

BACKGROUND

The EEG correlate of absence seizures is 3-Hz, generalized spike-wave activity. Depth electrode recordings in animal models suggest that spike-wave activity oscillates within thalamocortical circuits, but the site of the primary abnormality is uncertain. The aim of the present study was to determine whether there is a selective increase in blood flow in the thalamus during absence seizures and, if so, whether it precedes the appearance of spike-wave activity on scalp EEG.

METHODS

Using PET, regional cerebral blood flow (rCBF) was measured in eight patients with idiopathic generalized epilepsy in whom typical absence seizures were induced by voluntary hyperventilation. Each patient was studied up to 12 times, with an intravenous bolus injection of H2(15)O followed by a 90-second scan. The distribution of rCBF during absence seizures and in the 30 seconds before an absence seizure were compared with the distribution of rCBF when absence seizures did not occur.

RESULTS

There was a mean global 14.9% increase in blood flow in association with typical absence seizures and, on top of the global increase, a focal increase in thalamic blood flow of 3.9 to 7.8%. There were no significant focal changes in rCBF in the 30 seconds before the onset of spike-wave activity on the EEG.

CONCLUSION

This study provides evidence for the key role of the thalamus in the pathogenesis of absence seizures but was unable to show that it is the site of initiation of the seizures.

Cortical dysgenesis: serial EEG findings in children and adults

Cortical dysgenesis (CD) is becoming increasingly recognised as a cause of epilepsy in otherwise cryptogenic cases. We describe the serial EEG findings in 22 patients with focal/localised CD. The EEGs covered a minimum period of 5 years in each case (median = 13 years, range: 5-30 years), beginning in childhood. Median age at seizure onset was 3 years (range: 3 weeks-10 years, n = 21). The EEG was normal in the one patient, a 6 year old, who did not have epilepsy. Background rhythms appropriate for age were preserved in the majority of patients (18/22). Slow activity localised to the area of CD was seen in 11 patients; in 3 patients, this did not appear until the second decade of life. Epileptiform discharges were seen in at least one EEG in 20 patients: these were continuous or near-continuous (6 patients) or occurred recurrently in short runs (6 patients). In 6 patients, these discharges appeared only after the second decade of life and in 11 patients, they became more widespread over time. In the remaining patients, the EEG changes did not evolve. Sleep failed to produce new abnormalities (n = 15). None of the patients showed EEG features characteristic of lissencephaly or evolution to the Lennox-Gastaut syndrome. Even in this selected cohort of patients who had undergone serial clinical EEGs, the EEG abnormalities in focal/localised CD appeared relatively stable and showed only moderate changes over time. CD must be included in the differential diagnosis of any patient who presents with localised slow activity on EEG.

Abnormalities of gyration, heterotopias, tuberous sclerosis, focal cortical dysplasia, microdysgenesis, dysembryoplastic neuroepithelial tumour and dysgenesis of the archicortex in epilepsy. Clinical, EEG and neuroimaging features in 100 adult patients

Cerebral cortical dysgenesis (CD) is a heterogeneous disorder of cortical development and organization commonly associated with epilepsy, with a variety of subtypes. We reviewed the clinical, EEG and neuroimaging features in 100 adult patients with CD. There were 39 men and 61 women with a median age of 27 years (range 15-63 years). All patients were referred because of medically refractory epilepsy. Median age at seizure onset was 10 years (range 3 weeks to 39 years); in 30 patients, onset was in adulthood. The epilepsy was classified as generalized in 16 patients and localization-related in 84. Of the latter, the epileptic syndromes in decreasing frequency were frontal (32%), temporal (31%), parietal (14%) and occipital (7%). Only 15% of patients had a history of status epilepticus. Prenatal/perinatal problems were reported in 32 patients but these were severe in only four: exposure to drugs (three) and infection (one) during the first trimester. Delayed developmental milestones were seen in 10%, mental retardation in 9%, additional congenital abnormalities in 4% and neurological deficits in 14% of patients. Diagnosis of CD was based on neuroimaging in 70, pathology in four and both methods in the remaining 26. The following subcategories were identified: agyria/diffuse macrogyria (four patients), focal macrogyria (16), focal polymicrogyria (one), focal macrogyria/polymicrogyria associated with a cleft (11), minor gyral abnormalities (seven), subependymal grey matter heterotopia (20), bilateral subcortical laminar grey matter heterotopia (eight), tuberous sclerosis (five), focal cortical dysplasia/microdysgenesis (seven) and dysembryoplastic neuroepithelial tumours (DNT) (21). Sixty-eight percent of patients had normal CT and 19 out of 36 patients had normal previous conventional MRI. MRI-based hippocampal volume measurements in 47 patients revealed ratios (smaller: larger hippocampus) of < 0.90 in 16, 0.90-0.94 in 14 and > or = 0.95 in 17 patients. EEGs were normal in only five patients. Alpha rhythm was preserved in 78 patients, including one patient with bilateral posterior macrogyria. Localized polymorphic slow activity was present in 43 patients. Five of 68 patients with focal/unilateral CD had only bilateral independent/synchronous spiking and 14 out of 32 with diffuse/bilateral CD only focal/unilateral spiking. In 60 patients with nondiffuse CD or with abnormal gyration or DNT, the epileptiform abnormalities were less extensive than coextensive with the lesion in 28, more extensive than and overlapped the lesion in 18 and remote from the lesion in five; nine patients did not have epileptiform abnormalities. There was poor correlation between the epileptic syndromes and EEG abnormalities and the location/extent of CD as defined by MRI and pathology.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzodiazepine-GABAA receptor binding during absence seizures

The role of benzodiazepine (BZD)-gamma-aminobutyric acidA (GABAA) receptors in the pathogenesis of absence seizures is uncertain. In this study, we examined the effect of absence seizures on the binding of flumazenil to the BZD binding site of the GABAA receptor. Five patients with idiopathic generalized epilepsy (IGE) were studied at rest and during absence seizures with [11C]flumazenil and positron emission tomography (PET). Normalized regional cerebral time-activity curves from the resting and ictal scans were compared with each other and with computed simulations showing the effects of changes in cerebral blood flow (CBF) and [11C]flumazenil binding. No evidence was found for a change in [11C]flumazenil binding with absence seizures. This result, together with those of a recent study showing no abnormality of [11C]flumazenil binding interictally in patients with childhood and juvenile absence epilepsy (JAE) does not support a primary role for the BZD binding site of the GABAA receptor in the pathogenesis of absence seizures.

First seizures associated with playing electronic screen games: a community-based study in Great Britain

Active surveillance by virtually all electroencephalographic departments throughout Great Britain identified 118 patients who had a first seizure while playing an electronic screen game during two 3-month periods. Patients were divided into Group A (46 patients)--those for whom there was thought to be a definite causal relationship (type 4 photoparoxysmal response); Group B (25 patients)--those for whom there was a probable causal relationship (types 1-3 photoparoxysmal response, clinical evidence of photosensitivity, subsequent recurrent seizures on repeat exposure to electronic screen games, and/or occipital spikes in the resting electroencephalogram); and Group C (47 patients)--those for whom there was no apparent causal relationship. The number of patients in Group C did not exceed that expected by the chance occurrence of two common events (playing electronic screen games and incidence of epilepsy). Most (103/118) of the patients were in the age range of 7 to 19 years. Within this age group the annual incidence of first seizures triggered by playing electronic screen games (Groups A and B combined) was estimated to be 1.5/100,000.

Incidence of sudden unexpected death in an adult outpatient cohort with epilepsy at a tertiary referral centre

Overall mortality, incidence of sudden unexpected death, and cause of death were determined in 601 adult outpatients with epilepsy at a tertiary referral centre. The patients were followed up from 1990 to 30 June 1993. There were 24 deaths among the 601 patients (1849 patient years) with a standardised mortality ratio of 5.1 (95% confidence interval 3.3-7.6) of which 14 were related to epilepsy. Underlying disease of which epilepsy was a symptom accounted for four deaths only. An incidence of sudden deaths (including seizure related) was of the order of 1:200/year. In conclusion, excess mortality in chronic epilepsy is more likely to be related to the epilepsy itself than to underlying pathology. The relatively high incidence of sudden deaths found in this hospital based cohort has important implications for patient management.

High-voltage pulsed current: its influence on diameters of histamine-dilated arterioles in hamster cheek pouches

Results from five independent studies from our laboratory indicate that cathodal high-voltage pulsed current (HVPC) significantly curbs posttraumatic edema formation in several animal models. Conversely, anodal HVPC did not curb edema formation. The mechanism by which HVPC reduces edema formation is unknown. We hypothesize that HVPC causes a decrease in local blood flow by active vasoconstriction of arterioles. Because we had previously observed positive effects with cathodal HVPC but not anodal HVPC, we further hypothesized that cathodal but not anodal HVPC would reduce diameters of histamine-dilated arterioles. Changes in diameters of resistance arterioles (5 to 30 microns internal diameter) were measured directly in cheek pouches of anesthetized hamsters, using in vivo video microscopy. Three minutes after superfusion with the inflammatory mediator (histamine) was begun, sensory-level HVPC at 120pps was applied concurrently for 30 minutes. Five animals received cathodal HVPC and five received anodal HVPC. Four other animals received 30-minute treatments of both cathodal and anodal HVPC in random order. Three control animals received histamine without HVPC for 30 minutes. Diameter changes of one arteriole from each cheek pouch was measured every 20 seconds throughout the treatment period. One-way analysis of variance (ANOVA) with repeated measures showed that diameters of histamine-dilated controls varied little over 30 minutes, and that adding cathodal HVPC did not significantly alter diameters of arterioles superfused with histamine. However, applying anodal HVPC to histamine-dilated arterioles significantly reduced arteriolar diameters. These results do not support the hypothesis that cathodal HVPC curbs edema formation by increasing arteriolar tone in the injured area.

Management and outcome of severe Guillain-Barré syndrome

Seventy-nine patients with Guillain-Barré syndrome admitted to a neurological intensive therapy unit (ITU) between 1985 and 1992 were studied retrospectively. The mean age was 49.8 years (range 16-86) and the time between the first neurological symptom and admission to ITU was 10.2 days (0-62). Admission was precipitated by a combination of respiratory failure requiring ventilatory support (73.4%), bulbar weakness (57.0%), autonomic features (11.4%) and general medical factors (10.1%). Specific treatments included plasma exchange (65.8%), intravenous immunoglobulin (13.9%) and methylprednisolone/placebo (12.7%). Significant complications included lower respiratory tract infections (45.6%), hyponatraemia (25.3%), dysautonomia (19.0%), urinary tract infection (12.7%) and cognitive disturbances (8.9%). Four patients (5.1%) died during the acute illness. Duration of nadir correlated with duration of ventilation, duration of ITU stay and outcomes at 3 months, 6 months and 1 year. However, time to nadir, an indicator of rapidity of deterioration, did not correlate with any outcome. The low mortality in this series of acutely ill and severely disabled patients suggests that specialized intensive therapy units continue to have an important role in the management of acutely ill patients with Guillain-Barré syndrome.

Magnetic resonance imaging in partial epilepsy: additional abnormalities shown with the fluid attenuated inversion recovery (FLAIR) pulse sequence

Thirty six patients with a history of partial epilepsy had MRI of the brain performed with conventional T1 and T2 weighted pulse sequences as well as the fluid attenuated inversion recovery (FLAIR) sequence. Abnormalities were found in 20 cases (56%), in whom there were 25 lesions or groups of lesions. Twenty four of these lesions were more conspicuous with the FLAIR sequence than with any of the conventional sequences. In 11 of these 20 cases, lesions thought to be of aetiological importance were only seen with the FLAIR sequence. In eight this was a solitary lesion. In the other three, an additional and apparently significant lesion (or lesions) was only seen with the FLAIR sequence when another lesion had been identified with both conventional and FLAIR sequences. The 11 additional lesions or groups of lesions were seen in the hippocampus, amygdala, cortex, or subcortical and periventricular regions. No lesion was found with any pulse sequence in 16 (44%) of the original group of 36 patients. In the eight cases where a lesion was seen only with the FLAIR sequence, localisation was concordant with the electroclinical features. Two of the eight patients with solitary lesions seen only on the FLAIR sequence underwent surgery, after which there was pathological confirmation of the abnormality identified with imaging. In one patient with a congenital cavernoma, the primary lesion was best seen with a contrast enhanced T1 weighted spin echo sequence. In this selected series, the FLAIR sequence increased the yield of MRI examinations of the brain by 30%.

Methods for normalization of hippocampal volumes measured with MR

PURPOSE

To investigate the use of six cerebral measures as correlates for hippocampal volumes and, therefore, to enable normalized absolute hippocampal volumes to be calculated via two correction processes.

METHODS

Hippocampal volumes and six cerebral measures were estimated from MR data in 20 control subjects. Three of these measures (the cranial volume, the cerebral volume, and the midsagittal cranial area) were then applied to a group of 32 control subjects, and regression analysis was performed to investigate the linear relationship between hippocampal volume and each measure. Division of hippocampal volume by cerebral measure and correction via a covariance calculation enabled corrected absolute hippocampal volumes to be determined for 32 control subjects and 23 patients with temporal lobe epilepsy.

RESULTS

Correction processes reduced the variance in absolute hippocampal volumes in control subjects and enabled abnormally small absolute volumes to be defined. Of 11 patients with unilateral volume ratio abnormalities, 8 had unilateral abnormally small absolute hippocampal volumes. Of 12 patients with normal volume ratios, 4 had bilateral abnormally small absolute hippocampal volumes.

CONCLUSION

Correction processes can define absolute hippocampal volumes for correlation studies and may enable identification of unsuspected bilateral hippocampal volume loss.