Diversity of ganglion cells in the mouse retina: Unsupervised morphological classification and its limits

The dendritic structures of retinal ganglion cells in the mouse retina were visualized by particle-mediated transfer of DiI, microinjection of Lucifer yellow, or visualization of green fluorescent protein expressed in a transgenic strain. The cells were imaged in three dimensions and the morphologies of a series of 219 cells were analyzed quantitatively. A total of 26 parameters were studied and automated cluster analysis was carried out using the k-means methods. An effective clustering, judged by silhouette analysis, was achieved using three parameters: level of stratification, extent of the dendritic field, and density of branching. An 11-cluster solution is illustrated. The cells within each cluster are visibly similar along morphological dimensions other than those used statistically to form the clusters. They could often be matched to ganglion cell types defined by previous studies. For reasons that are discussed, however, this classification must remain provisional. Some steps toward more definitive methods of unsupervised classification are pointed out.

fMRI temporal clustering analysis in patients with frequent interictal epileptiform discharges: comparison with EEG-driven analysis

Temporal clustering analysis (TCA) is an exploratory data-driven technique that has been proposed for the analysis of resting fMRI to localise epileptiform activity without need for simultaneous EEG. Conventionally, fMRI of epileptic activity has been limited to those patients with subtle clinical events or frequent interictal epileptiform EEG discharges, requiring simultaneous EEG recording, from which a linear model is derived to make valid statistical inferences from the fMRI data. We sought to evaluate TCA by comparing the results with those of EEG correlated fMRI in eight selected cases. Cases were selected with clear epileptogenic localisation or lateralisation on the basis of concordant EEG and structural MRI findings, in addition to concordant activations seen on EEG-derived fMRI analyses. In three, areas of activation were seen with TCA but none corresponding to the electro-clinical localisation or activations obtained with EEG driven analysis. Temporal clusters were closely coincident with times of maximal head motion. We feel this is a serious confound to this approach and recommend that interpretation of TCA that does not address motion and physiological noise be treated with caution. New techniques to localise epileptogenic activity with fMRI alone require validation with an appropriate independent measure. In the investigation of interictal epileptiform activity, this is best done with simultaneous EEG recording.

Studying spontaneous EEG activity with fMRI

The multifaceted technological challenge of acquiring simultaneous EEG-correlated fMRI data has now been met and the potential exists for mapping electrophysiological activity with unprecedented spatio-temporal resolution. Work has already begun on studying a host of spontaneous EEG phenomena ranging from alpha rhythm and sleep patterns to epileptiform discharges and seizures, with far reaching clinical implications. However, the transformation of EEG data into linear models suitable for voxel-based statistical hypothesis testing is central to the endeavour. This in turn is predicated upon a number of assumptions regarding the manner in which the generators of EEG phenomena may engender changes in the blood oxygen level dependent (BOLD) signal. Furthermore, important limitations are posed by a set of considerations quite unique to 'paradigmless fMRI'. Here, these issues are assembled and explored to provide an overview of progress made and unresolved questions, with an emphasis on applications in epilepsy.

Comparison of spike-triggered functional MRI BOLD activation and EEG dipole model localization

We studied six patients with localization-related epilepsy, frequent interictal epileptiform discharges, and positive spike-triggered blood oxygen level-dependent functional MRI (BOLD-fMRI) findings. EEG source analysis solutions based on 64-channel EEG recorded in a separate session outside the scanner were obtained using dipole models and compared to the BOLD localization. The BOLD and structural images were coregistered, allowing the measurement of distances between the generator models and BOLD activation(s) and structural lesion when present. In all cases dipole models could be found that explained a sufficient amount of the data and that were anatomically concordant with the BOLD localization. In the five cases with structural abnormality visible on T1 scans, the BOLD activation overlapped or was in close proximity to the abnormality. The overall mean distance between the main moving dipole and the center of the nearest BOLD activation was 3.5 and 2.2 cm for the negative and positive peaks, respectively, including one case of a deep BOLD activation, in which the distance was 5 cm. In conclusion, the degree of agreement between the BOLD and EEG source localization indicates that the combination of these two noninvasive techniques offers the possibility of advancing the study of the generators of epileptiform electrical activity.

Event-related fMRI with simultaneous and continuous EEG: description of the method and initial case report

We report on the initial imaging findings with a new technique for the simultaneous and continuous acquisition of functional MRI data and EEG recording. Thirty-seven stereotyped interictal epileptiform discharges (spikes) were identified on EEG recorded continuously during the fMRI acquisition on a patient with epilepsy. Localization of the BOLD activation associated with the EEG events was consistent with previous findings and EEG source modeling. The time course of activation was comparable with the physiological hemodynamic response function (HRF). The new methodology could lead to novel and important applications in many areas of neuroscience.

Spatio-temporal imaging of focal interictal epileptiform activity using EEG-triggered functional MRI

EEG-triggered, blood oxygen level-dependent functional MRI (BOLD-fMRI) was used in 24 patients with localization-related epilepsy and frequent interictal epileptiform discharges (spikes) to identify those brain areas involved in generating the spikes, and to study the evolution of the BOLD signal change over time. The location of the fMRI activation was compared with the scalp EEG spike focus and the structural MR abnormality. Twelve patients (50%) had an fMRI activation concordant with the EEG focus and structural brain abnormalities where present (n = 7). In 2 other patients, the fMRI activation was non-concordant with electroclinical findings. The remaining 10 patients (41.7%) showed no significant fMRI activation. These patients had significantly lower mean spike amplitudes compared to those with positive fMRI results (p = 0.03). The time course of the BOLD response was studied in 3 patients and this revealed a maximum signal change 1.5 to 7.5 sec after the spike. In conclusion, EEG-triggered fMRI can directly identify the generators of interictal epileptiform activity, with high spatial resolution, in selected patients with frequent spikes. The superior spatial resolution obtainable through EEG-triggered fMRI may provide an additional non-invasive tool in the presurgical evaluation of patients with intractable focal seizures.

A study of the relationship between participation in common leisure activities and seizure occurrence

OBJECTIVE

To investigate whether participation in a structured programme of fairly intensive leisure activities increased seizure occurrence.

MATERIAL AND METHODS

212 adults with medically-intractable epilepsy were closely monitored for seizure occurrence during an "activities day", i.e. a day consisting of various structured sessions of leisure pursuits (video game play, reading, word puzzles, television, physical exercise), and during other days of relative rest, whilst undergoing prolonged video EEG monitoring.

RESULTS

The relative risk of seizures did not differ significantly during activities days [0.71 (95% CL: 0.38 to 1.33)] compared with days of relative rest.

CONCLUSIONS

These findings fail to provide empirical support for the hypothesis that cognitive exertion has an adverse effect on seizure control.

Landmark-based morphometrics of the normal adult brain using MRI

We describe the application of statistical shape analysis to homologous landmarks on the cortical surface of the adult human brain. Statistical shape analysis has a sound theoretical basis. Landmarks are identified on the surface of a 3-D reconstruction of the segmented cortical surface from magnetic resonance image (MRI) data. Using publicly available software (morphologika) the location and size dependence of the landmarks are removed and the differences in landmark distribution across subjects are analysed using principal component analysis. These differences, representing shape differences between subjects, can be visually assessed using wireframe models and transformation grids. The MRI data of 58 adult brains (27 female and 15 left handed) were examined. Shape differences in the whole brain are described which concern the relative orientation of frontal lobe sulci. Analysis of all 116 hemispheres revealed a statistically significant difference (P < 0.001) between left and right hemispheres. This finding was significant for right- but not left-handed subjects alone. No other significant age, gender, handedness, or brain-size correlations with shape differences were found.

Functional MRI activation of individual interictal epileptiform spikes

We used spike-triggered functional MRI in a patient with localization-related epilepsy to determine whether individual (as opposed to averaged) focal interictal epileptiform discharges (spikes) were associated with hemodynamic changes detectable with blood oxygen level-dependent functional MRI (fMRI). It was found that 15 of 43 spikes (34.9%) were associated with significant focal fMRI activation. Single event-related fMRI of interictal spikes is feasible in selected patients, giving complementary information to that provided by averaged fMRI data.

Extrahippocampal temporal lobe atrophy in temporal lobe epilepsy and mesial temporal sclerosis

Visual inspection and volumetric analysis of MRIs allow mesial temporal sclerosis (MTS) to be reliably identified in patients with temporal lobe epilepsy. The presence of unilateral MTS ipsilateral to the side of habitual seizure onset is an indicator for the prognosis of good outcome after temporal lobe resection. There is evidence to suggest that widespread temporal lobe pathology, leading to atrophy, may be associated with MTS and such abnormal tissue may play an important role in epileptogenesis. We have analysed quantitatively the volumes of the mesial and lateral temporal lobe substructures in MRIs from 62 patients with intractable mesial temporal lobe epilepsy and in 20 normal controls. We found significant atrophy in these structures in patients, ranging from 8.3 to 18.4% compared with controls. The degree of atrophy in the extrahippocampal structures correlated with the degree of hippocampal atrophy, suggesting that a common process may be responsible. There was no correlation between the degree of atrophy in the extrahippocampal structures and the duration of epilepsy, a history of febrile convulsions or of generalized seizures. These findings suggest that there may be widespread pathological abnormalities in the temporal lobe associated with MTS. The importance of extrahippocampal atrophy to surgical outcome and whether it occurs in temporal lobe epilepsy not associated with MTS remain to be investigated.

Cardiac asystole in partial seizures

Literature review shows many anecdotal case reports of cardiac asystole in ictal recordings of partial seizures. We have reviewed our data from the last five years, of patients who are being assessed for epilepsy surgery and found 2 out of more than 1,500 complex partial seizures, recorded in 589 consecutive patients, showing a significant period of asystole (13 and 15 seconds). Our previous studies of cardiac and respiratory parameters during partial seizures showed that a central apnoea occurred in 39%. It is probable that sudden death during seizures is due to the interaction of both cardiac and respiratory irregularities. Although rare (occurrence < 0.15%), the possibility of cardiac asystole occurring in an epilepsy monitoring unit highlights the need for resuscitation equipment to be readily available and for trained nursing staff. Furthermore, it is important to recognize that the semiology of seizures may be affected by the consequences of secondary cardiac asystole.

Recovery of visual field constriction following discontinuation of vigabatrin

Epilepsy patients treated with vigabatrin may develop symptomatic or asymptomatic concentric visual field constriction due to GABA-associated retinal dysfunction. The prevalence and course of this side effect are not established yet; in previously reported adult patients the visual disturbances seem to be irreversible. We present two patients with a significant improvement of visual field constriction and retinal function after the discontinuation of vigabatrin. These findings suggest that vigabatrin-associated retinal changes are at least partly reversible in some patients, and that these patients may benefit significantly from a withdrawal of vigabatrin. Larger scale clinical studies are needed to identify predictive factors both for the occurrence and reversibility of vigabatrin-associated visual field defects.

Remote memory in epilepsy

PURPOSE

There is now a considerable amount of research relating to memory functioning in epilepsy. The majority of studies have focused on the retention of new information, and few reports have measured memory for past events. This study aims to redress this and measure the efficiency of remote memory in epilepsy.

METHODS

A remote memory questionnaire was prepared and administered to three groups of patients with epilepsy and a control group without epilepsy. The questionnaire assessed knowledge of public events that occurred between 1980 and 1991, inclusive. The epilepsy groups comprised 33 patients with temporal lobe epilepsy (TLE), 33 with extratemporal epilepsy (ExTE), and 10 with primary generalized epilepsy (PGE). Thirty control subjects were tested.

RESULTS

Patients with TLE performed significantly less well on the questionnaire than all other groups (p = 0.001), but no effect of laterality was recorded; patients with extratemporal or primary generalised epilepsy did not differ from controls. Performance on the questionnaire was not determined by verbal IQ, educational achievement, social class, or drug treatment, but was related to the number of generalised convulsions that had occurred since 1980. The strongest neuropsychological predictors of performance on this questionnaire were measures of verbal memory.

CONCLUSIONS

The study demonstrated weak memory for past events in patients with TLE, thereby providing evidence of a broader memory disturbance in this group than has been previously highlighted. A test of remote memory, such as the one designed for this study, is easy to administer and provides clinically important information not available from conventional neuropsychological tests.

Multimodal MR imaging: functional, diffusion tensor, and chemical shift imaging in a patient with localization-related epilepsy

PURPOSE

To demonstrate the integration of complementary functional and structural data acquired with magnetic resonance imaging (MRI) in a patient with localization-related epilepsy.

METHODS

We studied a patient with partial and secondarily generalized seizures and a hemiparesis due to a malformation of cortical development (MCD) in the right hemisphere by using EEG-triggered functional MRI (fMRI), diffusion tensor imaging (DTI), and chemical shift imaging (CSI).

RESULTS

fMRI revealed significant changes in regional blood oxygenation associated with interictal epileptiform discharges within the MCD. DTI showed a heterogeneous microstructure of the MCD with reduced fractional anisotropy, a high mean diffusivity, and displacement of myelinated tracts. CSI demonstrated low N-acetyl aspartate (NAA) concentrations in parts of the MCD.

CONCLUSIONS

The applied MR methods described functional, microstructural, and biochemical characteristics of the epileptogenic tissue that cannot be obtained with other noninvasive means and thus improve the understanding of the pathophysiology of epilepsy.

Seizures during video-game play and other common leisure pursuits in known epilepsy patients without visual sensitivity

PURPOSE

Some individuals who are negative to flash/pattern sensitivity have been reported to experience seizures while exposed to video games. This study seeks to examine systematically whether exposure to video-game material is a risk factor for seizures in patients with chronic epilepsy without visual sensitivity.

METHODS

Two hundred and twelve chronic epilepsy patients participated in the study. All were negative to rigorous flash and pattern sensitivity testing. They were randomly allocated to a video game-playing session or to a period of leisure (involving reading, physical exercise, puzzles, etc.) and then alternated between these activities for a fixed total of eight 45-min periods while undergoing video-EEG monitoring. The study ceased if the participant experienced a clinical seizure.

RESULTS

Twenty-five of 212 subjects experienced a seizure while participating in the study. Thirteen seizures occurred during periods of video-game play, and 12 during alternative leisure.

CONCLUSIONS

We have not identified a greater risk of seizures in patients with (not visually sensitive) epilepsy during video-game play compared with other common leisure pursuits. Furthermore, we exposed a large population (212 patients) mostly with severe epilepsy, mainly drug reduced and some sleep deprived, to prolonged video game-playing without observing a significant excess number of seizures. This finding provides strong support for the hypothesis that seizures during video game play in the >95% of the epilepsy population without visual sensitivity are most likely to represent a chance occurrence, although, as always, each individual should be carefully assessed.

EEG-triggered functional MRI of interictal epileptiform activity in patients with partial seizures

EEG-triggered functional MRI (fMRI) offers the potential to localize the generators of scalp EEG events, such as interictal epileptiform discharges, using a biological measurement as opposed to relying solely on modelling techniques. Although recent studies have demonstrated these possibilities in a small number of patients, wider application has been limited by concerns about patient safety, severe problems due to pulse-related artefact obscuring the EEG trace, and lack of reproducibility data. We have systematically studied and resolved the issues of patient safety and pulse artefact and now report the application of the technique in 24 experiments in 10 consecutive patients with localization-related epilepsy and frequent interictal epileptiform discharges (spikes or spike wave). At least two experiments were performed for each patient. In each experiment, 10- or 20-slice snapshot gradient-echo planar images were acquired approximately 3.5 s after a single typical epileptiform discharge (activation image) and in the absence of discharges (control image). Between 21 and 50 epileptiform discharges were sampled in each experiment. The significance of functional activation was tested using the t test at 95% confidence on a pixel-by-pixel basis. Six of the 10 patients showed reproducible focal changes of the blood oxygen level-dependent (BOLD) signal, which occurred in close spatial relationship to the maximum of the epileptiform discharges in the concurrent EEG. No reproducible focal BOLD signal changes were observed in the remaining four patients. In conclusion, EEG-triggered fMRI is now a sufficiently developed technique to be more widely used in clinical studies, demonstrating that it can reproducibly localize the brain areas involved in the generation of spikes and spike wave in epilepsy patients with frequent interictal discharges.

Analysis of temporal lobe resections in MR images

PURPOSE

The nature of the resection in surgery for intractable medial temporal lobe epilepsy is likely to be a principal factor determining seizure and neuropsychological outcome. However, there is no universally accepted system for describing the characteristics of individual resections to allow comparison between patients and patient groups treated at different institutions. We therefore developed a technique of volumetric analysis of temporal lobe resections.

METHODS

With comparison of coregistered pre- and postoperative, volumetric magnetic resonance imaging (MRI) scans in 10 subjects, the volumes of six temporal lobe substructures were determined by manual delineation in the pre- and post-operative images for each case, allowing the extent of resection to be determined.

RESULTS

The substructures and their extent of resection were measured with acceptable repeatability in each case.

CONCLUSIONS

We developed a reliable method for the quantitative description of temporal lobe resections. This will be of application in determining the relation between the anatomic nature of the resection in intractable epilepsy and the seizure and neuropsychological outcome.

Reproducible localization of interictal epileptiform discharges using EEG-triggered fMRI

We report preliminary experiences using fMRI triggered by EEG to localize the site of interictal epileptiform activity. EEG was recorded in the scanner and monitored on-line; the recording quality was good enough to allow the clear identification of spikes in the EEG. Snap-shot EPI was performed 2-4 s after an epileptiform discharge ('spike') or after at least 10 s of background activity ('rest') was observed. A pixel-by-pixel t-test was performed between the 'rest' and the 'spike' images to determine areas of significant activation. Significant activation was obtained in a patient with epilepsy. To assess the reliability and reproducibility of the technique, the patient was scanned on four separate occasions with similar areas being activated in all the studies, confirming the validity of the result.

Video-EEG telemetry: apparent manifestation of both epileptic and non-epileptic attacks causing potential diagnostic pitfalls

Video-EEG telemetry is often used to support the diagnosis of non-epileptic seizures (NES). Although rare, some patients may have both epileptic seizures (ES) and NES. It is crucially important to identify such patients to avoid the hazards of inappropriate anticonvulsant withdrawal. To delineate the electroclinical characteristics and diagnostic problems in this group of patients, we studied the clinical, EEG and MRI features of 14 consecutive patients in whom separate attacks, considered to be both NES and ES were recorded using video-EEG telemetry. Only two patients were drug-reduced during the telemetry. Most patients had their first seizure (ES or NES) in childhood (median age 7 years; range: 6 months-24 years); 8/14 patients were female. Brain MRI was abnormal in 10/14 patients. Interictal EEG abnormalities were present in all patients; 13/14 had epileptiform and 1/14 only background abnormalities. Over 70 seizures were recorded in these 14 patients: in 12/14 patients, the first recorded seizure was a NES (p < 0.001), and 7 of these patients had at least one more NES before an ES was recorded. Only 3/14 patients had more than 5 NES before an ES was recorded. Recording a small number of apparently NES in an individual by no means precludes the possibility of additional epilepsy. Particular care should be taken, and multiple (> 5) seizure recording may be advisable, in patients with a young age of seizure onset, interictal EEG abnormalities, or a clear, potential aetiology for epilepsy.

Supratentorial cavernous haemangiomas and epilepsy: a review of the literature and case series

OBJECTIVES

To characterise the clinical features and response to treatment of supratentorial cavernomas associated with epilepsy.

METHODS

A systematic review of the literature was carried out and a retrospective case series of patients with cavernoma diagnosed by MRI and/or histology was compiled. Patient selection biases in the literature review were reduced as far as possible by selection of unbiased publications.

RESULTS

In the literature, cavernomas were relatively less common in the frontal lobes. There were multiple cavernomas in 23% of cases. The main clinical manifestations were seizures (79%) and haemorrhage (16%). The annual haemorrhage rate was 0.7%. The outcome after excision was good with improvement in seizures in 92% of patients. In the case series the surgical outcome was less favourable, reflecting inclusion of a higher proportion of patients with intractable epilepsy. In both the literature review and the case series, outcome was poorer in cases with a longer duration of seizures at the time of surgery.

CONCLUSIONS

The good surgical results, particularly in cases treated earlier, and the significant cumulative haemorrhage rate, suggest that excision is the optimum treatment. However, these factors have not been examined prospectively and, despite the availability of several retrospective studies, the optimum treatment, particularly for non-intractable cases, will only be determined by a prospective study.

Surgical outcome in patients with epilepsy and dual pathology

High-resolution MRI can detect dual pathology (an extrahippocampal lesion plus hippocampal atrophy) in about 5-20% of patients with refractory partial epilepsy referred for surgical evaluation. We report the results of 41 surgical interventions in 38 adults (mean age 31 years, range 14-63 years) with dual pathology. Three patients had two operations. The mean postoperative follow-up was 37 months (range 12-180 months). The extrahippocampal lesions were cortical dysgenesis in 15, tumour in 10, contusion/infarct in eight and vascular malformation in five patients. The surgical approach aimed to remove what was considered to be the most epileptogenic lesion, and the 41 operations were classified into lesionectomy (removal of an extrahippocampal lesion); mesial temporal resection (removal of an atrophic hippocampus); and lesionectomy plus mesial temporal resection (removal of both the lesion and the atrophic hippocampus). Lesionectomy plus mesial temporal resection resulted in complete freedom from seizures in 11/15 (73%) patients, while only 2/10 (20%) patients who had mesial temporal resection alone and 2/16 (12.5%) who had a lesionectomy alone were seizure-free (P < 0.001). When classes I and II were considered together results improved to 86, 30 and 31%, respectively. Our findings indicate that in patients with dual pathology removal of both the lesion and the atrophic hippocampus is the best surgical approach and should be considered whenever possible.

Evidence for nodular epileptogenicity and gender differences in periventricular nodular heterotopia

OBJECTIVE

To determine whether clinical differences between the sexes seen in periventricular nodular heterotopia (PNH) have structural correlates on imaging.

BACKGROUND

PNH is the most common dysgenesis associated with hippocampal sclerosis (HS). Women with PNH have normal intellect; men may have mental retardation and other changes. Familial PNH, seen in women, is linked to Xq28-a region also abnormal in a sporadic male infant with PNH and retardation-suggesting sexual differences in gene expression. Epilepsy associated with PNH may be refractory to drugs, and surgery for associated HS does not stop seizures, suggesting intrinsic epileptogenicity of PNH.

METHODS

Quantitative MRI analysis was performed using established techniques for detecting subtle structural changes in 13 female patients (11 sporadic and two familial) and four male patients (sporadic).

RESULTS

There is structural heterogeneity in PNH, even in patients with bilateral PNH. On MRI, men have more cerebral abnormalities beyond PNH than control subjects or female patients (p < 0.005).

CONCLUSIONS

The findings support the concept of intrinsic epileptogenicity of PNH. There may be additional structural abnormalities relevant to seizure generation, especially in men. Structural heterogeneity, and widespread abnormalities, may need consideration when patients are referred for surgical treatment or when additional studies of patients with PNH are conducted.

Disproportion in the distribution of gray and white matter: neuropsychological correlates

OBJECTIVE

To examine the relationship between measures of disproportion in the regional distribution of gray and white matter and preoperative neuropsychological function in temporal lobe epilepsy patients with proved hippocampal sclerosis (HS).

BACKGROUND

Subtle cerebral structural disruption, not evident on routine inspection of high-resolution MRI, is associated with poor surgical outcome in patients with histologically proved HS. Preoperative global memory dysfunction is also associated with poor postoperative seizure control. The authors hypothesize that patients with HS and abnormal regional distributions of gray and white matter would show more diffuse neuropsychological deficits preoperatively than patients with isolated HS alone.

METHODS

A total of 28 adults with lateralized temporal lobe epilepsy and hippocampal volume loss measured on MRI were assessed preoperatively on neuropsychological tests of general intellect and the learning and recall of both verbal and nonverbal material. Quantitative MRI analysis of the regional distribution of gray and white matter was performed. Chi-square analyses were used to examine the relation between the presence or absence of cerebral abnormalities and preoperative performance on the neuropsychological tests.

RESULTS

A total of 15 of 28 patients had extrahippocampal abnormalities on quantitative MRI analysis. Thirteen patients had global memory impairment. Bilateral memory deficits were significantly associated with both the presence of cerebral abnormalities (p < 0.02) and poor postoperative seizure control (p < 0.05).

CONCLUSIONS

Disproportion in the regional distribution of gray and white matter in patients with HS may form the structural basis of global memory disturbance in a distinct group of patients with temporal lobe epilepsy.

Presurgical evaluation of patients with epilepsy and normal MRI: role of scalp video-EEG telemetry

When considering surgery for intractable partial seizures, even with high resolution MRI, some patients do not show structural abnormalities. The aim was to consider whether these patients were likely to proceed to surgical treatment after scalp video-EEG telemetry. All patients undergoing presurgical evaluation at the National Hospital for Neurology and Neurosurgery between 1995 and 1997 were reviewed and 40 were identified without definite MRI abnormalities. None of 40 disclosed a well localised epileptogenic zone concordant with other tests that would have allowed the patient to proceed directly to surgery. In five of the 40, evaluation led to a hypothesis that could be tested by intracranial studies; three proceeded to surgery. It is suggested that high quality MRI is performed first when surgical evaluation is undertaken and if negative the patient carefully counselled before proceeding with any investigations, as successful resective surgery is an unlikely outcome in such MRI negative cases.

Identifying homologous anatomical landmarks on reconstructed magnetic resonance images of the human cerebral cortical surface

Guided by a review of the anatomical literature, 36 sulci on the human cerebral cortical surface were designated as homologous. These sulci were assessed for visibility on 3-dimensional images reconstructed from magnetic resonance imaging scans of the brains of 20 normal volunteers by 2 independent observers. Those sulci that were found to be reproducibly identifiable were used to define 24 landmarks around the cortical surface. The interobserver and intraobserver variabilities of measurement of the 24 landmarks were calculated. These reliably reproducible landmarks can be used for detailed morphometric analysis, and may prove helpful in the analysis of suspected cerebral cortical structured abnormalities in patients with such conditions as epilepsy.

Autosomal dominant nocturnal frontal-lobe epilepsy: genetic heterogeneity and evidence for a second locus at 15q24

Autosomal dominant nocturnal frontal-lobe epilepsy (ADNFLE) is a recently identified partial epilepsy in which two different mutations have been described in the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (CHRNA4). An additional seven families are presented in which ADNFLE is unlinked to the CHRNA4 region on chromosome 20q13.2. Seven additional sporadic cases showed no evidence of defective CHRNA4. One of the families showed evidence of linkage to 15q24, close to the CHRNA3/CHRNA5/CHRNB4 cluster (maximum LOD score of 3.01 with D15S152). Recombination between ADNFLE and CHRNA4, linkage to 15q24 in one family, and exclusion from 15q24 and 20q13.2 in others demonstrate genetic heterogeneity with at least three different genes for ADNFLE. The CHRNA4 gene and the two known CHRNA4 mutations are responsible for only a minority of ADNFLE. Although the ADNFLE phenotype is clinically homogeneous, there appear to be a variety of molecular defects responsible for this disorder, which will provide a challenge to the understanding of the basic mechanism of epileptogenesis.

Identification of EEG events in the MR scanner: the problem of pulse artifact and a method for its subtraction

Triggering functional MRI (fMRI) image acquisition immediately after an EEG event can provide information on the location of the event generator. However, EEG artifact associated with pulsatile blood flow in a subject inside the scanner may obscure EEG events. This pulse artifact (PA) has been widely recognized as a significant problem, although its characteristics are unpredictable. We have investigated the amplitude, distribution on the scalp, and frequency of occurrence of this artifact. This showed large interindividual variations in amplitude, although PA is normally largest in the frontal region. In five of six subjects, PA was greater than 50 microV in at least one of the temporal, parasagittal, and central channels analyzed. Therefore, we developed and validated a method for removing PA. This subtracts an averaged PA waveform calculated for each electrode during the previous 10 s. Particular attention has been given to reliable ECG peak detection and ensuring that the average PA waveform is free of other EEG artifacts. Comparison of frequency spectra for EEG recorded outside and inside the scanner, with and without PA subtraction, showed a clear reduction in artifact after PA subtraction for all four frequency ranges analyzed. As further validation, lateralized epileptiform spikes were added to recordings from inside and outside the scanner: PA subtraction significantly increased the proportion of these spikes that were correctly identified and decreased the number of false spike detections. We conclude that in some subjects, EEG/fMRI studies will be feasible only using PA subtraction.

The detection and significance of subtle changes in mixed-signal brain lesions by serial MRI scan matching and spatial normalization

The purpose of this work is to detect and assess the significance of subtle signal changes in mixed-signal lesions based on serial MRI scan matching. Pairs of serially acquired T1-weighted volume MR images from 20 normal controls and seven patients with epilepsy were matched and difference images obtained. The precision and consistency of the registration were evaluated. The Gaussian noise level in the difference images was determined automatically. A structured difference filter was then used to segment structured (changed) voxels from the Gaussian noise. In the controls, the structured difference images were normalized into Talairach space, resulting in a structured noise map. The significance of changes in patients was assessed by spatial normalization and comparison with the structured noise map. The precision and consistency of the co-registration were < or = 0.06 mm with a registration success rate of 100%. The Gaussian noise level in the difference images was in the range 3.0-6.9. In the controls, an average of 1.6% of the brain voxels were classified as structured. Sine-based registration resulted in a reduction of < 1% in the amount of structure compared to linear interpolation. The structured noise map in controls showed high noise density in areas affected by image artefacts. We show examples of significant changes found in lesions which had been reported as unchanged on visual inspection. A novel quantitative approach has been presented for the detection and quantification of subtle signal changes in lesions. This method is of potential clinical value in the non-invasive characterization of signal change and biological behaviour of neoplastic lesions.

Cerebral activation in malformations of cortical development

Malformations of cortical development (MCD) are an important aetiology of localization-related epilepsy. Previous MRI and [11C]flumazenil PET studies have demonstrated widespread structural and neuroreceptor abnormalities beyond the region of MCD that is visually apparent on MRI. We investigated the ability of brain regions affected by MCD to participate in normal cognitive and motor tasks and compared the responses seen in such patients with those in normal subjects. We studied five patients known to have MCD affecting the occipital region and seven normal subjects using H2 (15)O PET whilst they were performing a visual attention task. We also studied five right-handed patients known to have MCD affecting the left frontal lobe and seven right-handed normal subjects, using H2 (15)O PET whilst they were performing a motor learning task with the right hand. The patient and normal control data were examined using statistical parametric mapping to determine the ability of the brain region affected by MCD to participate in the task and also to detect evidence for atypical organization of cortical function in association with the MCD. Eight of the ten patients with MCD showed significant alteration of relative regional cerebral blood flow during the task compared with 'rest' in the affected brain region. These regions included focally dysgenetic cortex, the cortex lining schizencephalic clefts, heterotopic bands, subependymal grey matter heterotopia, and the cortex overlying band and subependymal heterotopia. In addition there was a significant alteration in the overall activation pattern in five patients compared with the normal control groups; in all five patients this atypical organization involved regions of cortex that appeared entirely normal on MRI. We conclude that regions of MCD may participate in normal cognitive functions but widespread cortical atypical organization may be seen. These findings have implications for surgical planning in any such patients.

Effects of electrical stimulation on edema formation in different strains of rats

BACKGROUND AND PURPOSE

Although electrical stimulation (ES) is commonly used to curb edema formation, efficacy has been demonstrated in only one species of frog and one strain of rat. The purpose of this study was to determine whether different strains of rats respond differently to ES.

SUBJECTS AND METHODS

Feet of Sprague-Dawley, Zucker-Lean, and Brown Norway rats were injured in a uniform manner. One foot served as a control, and the other foot received four 30-minute exposures to cathodal high-voltage pulsed current at amplitudes 10% less than those required to induce visible muscle activity. Each treatment period was followed by a 30-minute rest period. Limb volumes were measured before and after trauma and after each treatment and rest period. Changes from pretrauma volumes were analyzed by repeated-measures analysis of variance.

RESULTS

Edema formation was curbed in Zucker-Lean and Brown Norway rats but not in Sprague-Dawley rats.

CONCLUSION AND DISCUSSION

The finding that two of the three strains of rats responded to ES suggests that some strains of rats may be suitable models for the study of edema. That frogs and rats respond to high-voltage pulsed current suggests that humans might respond similarly.

Musculoskeletal disorders in dentists

Occupational injuries involving musculoskeletal tissues are often related to repetitive movements of upper limbs and prolonged postures such as sitting and standing--activities common in dentistry. Surveys of the incidence of musculoskeletal disorders among dentists are few, but in Nebraska, 29 percent of more than 1,000 dentists reported symptoms of peripheral neuropathy in the upper limbs or neck. The Nebraskan dentists reported that crown and bridge work was most likely to evoke altered sensations in their upper limbs. Furthermore, since 47 percent of carpal tunnel syndrome cases in the general population are work-related and are often associated with repetitive motions, it is reasonable to suspect that dentists may be at risk for this musculoskeletal disorder. And, since it is estimated that 60 percent to 80 percent of adults will experience low back pain at one time or another, resulting in it being the second leading cause of absences from work in the general population, dental practitioners are most likely to be among those susceptible to this problem. This article focuses on two ailments afflicting dentists: carpal tunnel syndrome and low back pain.

Photosensitivity--better informing patients with epilepsy of their individual risk

Photosensitive epilepsy is relatively rare. However, a large proportion of individuals with epilepsy perceive that they are at an increased risk of a seizure whilst exposed to specific photic material. The difference between perceived and real risk may be due to inadequate education and misinformation. One half of the participants in the present survey could not recall being informed of the result of the 'gold standard' test for photosensitivity--intermittent photic stimulation during an electroencephalogram. Furthermore, approximately one-third of our sample were apparently given inaccurate and overcautious advice about their everyday exposure to photic material. Better information and advice is crucial to improve this situation in the future. The majority of people with epilepsy (>95%) who are not photosensitive can pursue activities that involve flickering or patterned light, encompassing educational, employment and leisure opportunities, without undue concern.

Circumstances of death in sudden death in epilepsy: interviews of bereaved relatives

OBJECTIVES

To study the circumstances of death in sudden death in epilepsy.

METHODS

Self referred bereaved relatives of patients with epilepsy who had died suddenly were interviewed with information obtained substantiated through other sources-namely, coroners' officers' reports, postmortem reports, previous medical records, and EEG reports.

RESULTS

Of 34 cases, 26 were classified as sudden unexpected deaths in epilepsy (SUDEP). Twenty four of 26 cases of SUDEP were unwitnessed. Evidence indicative or suggestive of a seizure was found in most. In 11 of 26 the position of the head was such that breathing could have been compromised. Cases included both localisation related and idiopathic primary generalised epilepsy. Only three were in remission at the time of death. Most relatives expressed the view that they would have preferred to have known that epilepsy could be fatal.

CONCLUSIONS

Although the deaths in question were largely unwitnessed, the available evidence suggested that most cases of SUDEP represented ictal or postictal seizure deaths, occurring in people with a history of generalised tonic clonic seizures, and in both primary generalised and localisation related epilepsy. These interviews highlight the needs of bereaved relatives and their sense of isolation in the face of an entirely unexpected and apparently unexplained loss.

A survey of epilepsy-patient perceptions of video-game material/electronic screens and other factors as seizure precipitants

The risk of seizures while playing video games in photosensitive (PS) individuals with epilepsy is well established. However, media reporting, game packaging and anecdotal advice of medical practitioners may have implicated a broader proportion of the epilepsy population, i.e. not just those with PS, to be at risk. By using a hospital outpatient survey this paper investigates the perceived risk of using video games and electronic screens among those individuals with epilepsy. More than a quarter of those surveyed indicated that they thought that a substantially greater proportion of people with epilepsy were at risk from this stimulus than the estimated real risk suggests. One in 13 perceived that every individual with epilepsy is at risk of a seizure as a result of playing video games. Our results also indicate that the proportion of individuals with epilepsy surveyed who saw themselves to be at risk from video games, is two to three times the estimated real risk. For many individuals seizures during video-game play will represent a chance occurrence without a causal link. It is essential that accurate information is passed on to every individual with epilepsy regarding their personal susceptibility to photic-induced seizures so that those who are not at increased risk may participate in relevant activities without undue concern.

Effect of high-voltage pulsed current and alternating current on macromolecular leakage in hamster cheek pouch microcirculation

BACKGROUND AND PURPOSE

Electrical stimulation (ES) is supposed to affect edema formation by inhibiting macromolecular leakage from microvessels. The purpose of the study was to determine the effects of various forms of ES on macromolecular leakage from microvessels.

SUBJECTS

Fifty-three hamsters were randomly assigned to one of seven groups: a control group (histamine only); groups that received histamine with cathodal high-voltage pulsed current (HVPC) at intensities of 90%, 50%, and 10% of visible motor threshold (VMT); groups that received anodal HVPC at intensities of 90% and 50% of VMT; and a group that received alternating current (AC) at 90% of VMT.

METHODS

Anesthetized animals were injected with fluorescein-labeled dextran. Macromolecular leakage was determined by computer analysis of fluorescence microscopy images for 5 minutes after treatment.

RESULTS

When compared with controls, leakage was less in groups treated with cathodal HVPC at 90% and 50% of VMT and anodal HVPC at 90% of VMT.

CONCLUSION AND DISCUSSION

Cathodal and anodal HVPC, but not AC, curb macromolecular leakage from the microvessels of histamine-treated hamsters. [Taylor K, Mendel FC, Fish DR, et al. Effect of high-voltage pulsed current and alternating current on macromolecular leakage in hamster cheek pouch microcirculation.

Recording of EEG during fMRI experiments: patient safety

The acquisition of electroencephalograms (EEG) during functional magnetic resonance imaging (fMRI) experiments raises important practical issues of patient safety. The presence of electrical wires connected to the patient in rapidly changing magnetic fields results in currents flowing through the patient due to induced electromotive forces (EMF), by three possible mechanisms: fixed loop in rapidly changing gradient fields; fixed loop in a RF electromagnetic field; moving loop in the static magnetic field. RF-induced EMFs were identified as the most important potential hazard. We calculated the minimum value of current-limiting resistance to be fitted in each EEG electrode lead for a representative worst case loop, and measured RF magnetic field intensity and heating in a specific type of current-limiting resistors. The results show that electrode resistance should be > or = 13 k(omega) for our setup. The methodology presented is general and can be useful for other centers.

Widespread cerebral structural changes in two patients with gelastic seizures and hypothalamic hamartomata

PURPOSE

We tested the hypothesis that widespread extralesional abnormalities of cerebral structure exist in association with apparently isolated hypothalamic hamartomata, providing a structural basis for the poor response of seizures to removal of the hamartoma or other apparently focal epileptogenic zones present.

METHODS

High-resolution magnetic resonance imaging (MRI) brain scans of 2 patients with hypothalamic hamartomata were quantified by determination of regional distribution and symmetry of distribution of cortical gray matter and subcortical matter volumes. The results were compared with normal ranges for the distribution of such tissues in 33 controls.

RESULTS

Both patients had abnormalities of distribution of gray and subcortical matter, whereas control subjects did not. These abnormalities were beyond the hamartoma itself, in areas of cerebrum that on visual inspection alone appeared completely normal.

CONCLUSIONS

Extralesional abnormalities of cerebral structure are present in the cerebrum of patients with hypothalamic hamartoma, as in most patients with other dysgeneses. These abnormalities may explain the poor outcome of epilepsy surgery in patients with this form of dysgenesis. These preliminary findings require further investigation.

Effects of cold water immersion on edema formation after blunt injury to the hind limbs of rats

OBJECTIVE

Despite the long history of using cryotherapy to control edema, we found no randomized, controlled studies providing evidence to substantiate this common clinical practice. The purpose of this study was to determine whether cold water immersion affects edema formation following blunt injuries in rats.

DESIGN AND SETTING

The feet of 16 rats were traumatized after hind limb volumes were determined. Four 30-minute treatments of cold water immersion (12.8 degrees C to 15.6 degrees C, 55 degrees F to 60 degrees F), interspersed with four 30-minute rest periods, began immediately after trauma to one randomly selected hind limb of each rat. The limb remained in a dependent position during all treatments, rest periods, and volumetric measurements.

SUBJECTS

Sixteen anesthetized Zucker Lean rats were used in the study.

MEASUREMENTS

Limb volumes were measured after each treatment and rest period for a total of 4 hours.

RESULTS

The volume of treated limbs was significantly smaller (p < .05) than the volume of untreated limbs after the first treatment and remained smaller throughout the experiment.

CONCLUSIONS

Immersing rat limbs in 12.8 degrees C to 15.6 degrees C (55 degrees F to60 degrees F) water immediately after blunt injury was effective in curbing edema formation.

Periventricular nodular heterotopia and intractable temporal lobe epilepsy: poor outcome after temporal lobe resection

We describe 5 women and 5 men with periventricular nodular heterotopia and electroclinical features suggestive of temporal lobe epilepsy, who were surgically treated for control of medically refractory seizures. Magnetic resonance imaging revealed bilateral periventricular nodular heterotopia in 7 of the 10 patients. Because of the lack of clear localization, 6 patients were studied with intracranial depth electrode recordings. Seizures were of hippocampal onset (3 patients), regional temporal lobe onset (2 patients), or occipital-temporal onset (1 patient). Anterior temporal lobectomy was performed in 6 patients; selective amygdalohippocampectomy, in 1; and anterior temporal lobectomy plus resection of the heterotopic tissue, in 3. None of the 9 patients followed for more than 12 months postoperatively were seizure free. Two patients were initially seizure free for approximately 18 months, but then seizures recurred. One patient had a major reduction in seizure frequency at a 39-month follow-up after most of the unilateral heterotopic tissue was included in the temporal resection. Temporal resection did not lead to a long-term favorable outcome in this group of patients with periventricular nodular heterotopia and epileptogenic discharges involving the temporal lobe. This suggests a more widespread disorder with epileptogenic activity possibly originating in or near the heterotopic tissue. The clinical and electrographic features of periventricular nodular heterotopia pointing to temporal lobe origin are misleading and temporal resection does not result in long-term cessation of seizures.

Correlation of widespread preoperative magnetic resonance imaging changes with unsuccessful surgery for hippocampal sclerosis

Despite meticulous preoperative assessment, about 30% of patients with refractory partial epilepsy due to hippocampal sclerosis fail to become seizure free after appropriate temporal lobe surgery. Perioperative complications, hippocampal remnants, and bitemporal disease do not account for all failures; extrahippocampal epileptogenic tissue must persist in some patients. Such dual pathology is detected on routine visual inspection of magnetic resonance images in about 15% of patients with hippocampal sclerosis, but most such patients are excluded from surgery. We postulated that some patients have occult extrahippocampal cerebral structural abnormalities (i.e., subtle dual pathology) and that the presence of these abnormalities would be associated with a poor surgical outcome. Quantitative postprocessing of preoperative magnetic resonance images from 27 patients subsequently proved to have hippocampal sclerosis demonstrated extrahippocampal structural abnormalities in 14, 10 of whom did not become seizure free, while 11 of 13 patients without such changes did become seizure free (chi2, p < 0.005). Such structural information may supplement clinical decision making in some patients being evaluated for epilepsy surgery and help to explain the biological basis of poor outcome from such surgery.

Somatosensory evoked potentials in adults with cortical dysgenesis and epilepsy

Cortical dysgenesis (CD) is a well-recognised cause of epilepsy, but its functional anatomy is not fully understood. We recorded cortical somatosensory evoked potentials (SEPs) in 13 adult patients with epilepsy and various CDs excluding diffuse gyral malformations as diagnosed by MRI. The CD involved the perirolandic/perisylvian region in 7 patients. Six patients had neurological signs but only 3 had sensory dysfunction (astereognosis). As compared with 12 control subjects, SEPs were considered definitely abnormal in 7 patients (including the 6 with neurological signs) and equivocally abnormal in 2. The abnormalities ranged from defects affecting single components to absence of all potentials of cortical origin in one patient with hemiparesis and astereognosis. In this case it appears that gross sensory function must have been mediated by subcortical structures or through diffuse cortical projections. The initial cortical potentials (N20/P20) were absent in 6 patients, 5 of whom had CD in zones involving or bordering on the primary sensory cortex. Parietal potentials following N20 were absent or attenuated in 4 patients and of abnormally wide distribution, spreading to frontal, midline and ipsilateral electrodes, in 3 frontal components following P20 were absent, attenuated, delayed or distorted by abnormal spread of the parietal activity in 5 patients. Five patients with unilateral CD showed definite or equivocal SEP abnormalities to stimulation of both arms, suggesting there may be more widespread disturbance of cortical organisation and/or synaptogenesis, beyond the resolution of present day neuroimaging.

Surgical treatment of patients with single and dual pathology: relevance of lesion and of hippocampal atrophy to seizure outcome

Modern neuroimaging can disclose epileptogenic lesions in many patients with partial epilepsy and, at times, display the coexistence of hippocampal atrophy in addition to an extrahippocampal lesion (dual pathology). We studied the postoperative seizure outcome of 64 patients with lesional epilepsy (median follow-up, 30 months) and considered separately the surgical results in the 51 patients with a single lesion and in the 13 who had dual pathology. In patients with a single lesion, 85% were seizure free or significantly improved (Engel's class I-II) when the lesion was totally removed compared with only 40% when there was incomplete resection (p < 0.007). All three patients with dual pathology who had both the lesion and the atrophic hippocampus removed became seizure free. In contrast, only 2 of the 10 patients with dual pathology undergoing surgery aimed at the lesion or at the hippocampus alone became seizure free (p < 0.05), although 4 of them showed significant improvement (Engel's class II). We conclude that the outcome in patients with single epileptogenic lesions is usually dependent upon the completeness of lesion resection. In patients with dual pathology, surgery should, if possible, include resection of both the lesion and the atrophic hippocampus.

Chronic encephalitis and epilepsy in adults and adolescents: a variant of Rasmussen's syndrome?

Chronic encephalitis and epilepsy (Rasmussen's encephalitis) is a rare progressive disorder of uncertain etiology that usually occurs in children, producing focal epilepsy, hemiparesis, and intellectual deterioration. We identified 13 patients in whom seizures developed in adolescence or adulthood with a pathologic picture of chronic encephalitis. The clinical characteristics were more variable than those occurring in children, with the patients falling into three groups: five patients developed seizures in adulthood, but otherwise showed many resemblances to the childhood form; five developed seizures in adolescence, with similar presentation but rather more benign course than in the younger patients; and three presented with clinical features initially suggestive of a tumor. Occipital onset to the seizures appeared to be more common than in the childhood form, and bilateral disease also occurred.