Brain distortions in patients with primarily generalized tonic-clonic seizures

Increases in GFAP immunoreactive astrocytes in the cerebellar molecular layer of young adult CBA/J mice

Background

CBA/J mice are standard experimental animals in auditory studies, and age-related changes in auditory pathways are well documented. However, changes in locomotion-related brain regions have not been systematically explored.

Results

We showed an increase in immunoreactivity for glial fibrillary acidic protein (GFAP) in the cerebellar molecular layer associated with Purkinje cells in mice at 24 weeks of age but not in the younger mice. Increased GFAP immunoreactivity appeared in the form of clusters and distributed multifocally consistent with hyperplasia of astrocytes that were occasionally associated with Purkinje cell degeneration. Three out of 12 animals at 16 and 24 weeks of age exhibited pre-convulsive clinical signs. Two of these 3 animals also showed increased GFAP immunoreactivity in the cerebellum. Rotarod behavioral assessments indicated decreased performance at 24 weeks of age.

Conclusions

These results suggest minimal to mild reactive astrocytosis likely associated with Purkinje cell degeneration in the cerebellum at 24 weeks of age in CBA/J mice. These findings should be taken into consideration prior to using this mouse strain for studying neuroinflammation or aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-021-00100-5.

EEG-LORETA endophenotypes of the common idiopathic generalized epilepsy syndromes

OBJECTIVE

We tested the hypothesis that the cortical areas with abnormal local EEG synchronization are dissimilar in the three common idiopathic generalized epilepsy (IGE) phenotypes: IGE patients with absence seizures (ABS), juvenile myoclonic epilepsy (JME) and epilepsy with generalized tonic-clonic seizures exclusively (EGTCS).

PATIENTS AND METHODS

Groups of unmedicated ABS, JME and EGTCS patients were investigated. Waking EEG background activity (without any epileptiform potentials) was analyzed by a source localization method, LORETA (Low Resolution Electromagnetic Tomography). Each patient group was compared to a separate, age-matched group of healthy control persons. Voxel-based, normalized broad-band (delta, theta, alpha, and beta) and very narrow band (VNB, 1Hz bandwidth, from 1 to 25Hz) LORETA activity (=current source density, A/m(2)) were computed for each person. Group comparison included subtraction (average patient data minus average control data) and group statistics (multiple t-tests, where Bonferroni-corrected p<0.05 values were accepted as statistically significant).

RESULTS

Statistically not significant main findings were: overall increased delta and theta broad band activity in the ABS and JME groups; decrease of alpha and beta activity in the EGTCS group. Statistically significant main findings were as follows. JME group: bilaterally increased theta activity in posterior (temporal, parietal, and occipital) cortical areas; bilaterally increased activity in the medial and basal prefrontal area in the 8Hz VNB; bilaterally decreased activity in the precuneus, posterior cingulate and superior parietal lobule in the 11Hz and 21-22Hz VNBs. ABS group: bilaterally increased theta activity emerged in the basal prefrontal and medial temporal limbic areas. Decreased activity was found at 19-21Hz in the right postcentral gyrus and parts of the right superior and medial temporal gyri. EGTCS group: decreased activity was found in the frontal cortex and the postcentral gyrus at 10-11Hz, increased activity in the right parahippocampal gyrus at 16-18Hz.

DISCUSSION

Increased theta activity in the posterior parts of the cortex is the endophenotype for JME. Increased theta activity in the fronto-temporal limbic areas is the endophenotype for ABS. Statistically not significant findings might indicate diffuse biochemical abnormality of the cortex in JME and ABS.

SIGNIFICANCE

EEG-LORETA endophenotypes may correspond to the selective propensity to generate absence and myoclonic seizures in the ABS and JME syndromes.

Correlation between quantitative EEG and MRI in idiopathic generalized epilepsy

The objective of this study was to investigate the relationship between the focal discharges sometimes observed in the electroencephalogram of patients with idiopathic generalized epilepsies and subtle structural magnetic resonance imaging abnormalities. The main hypothesis to be assessed is that focal discharges may arise from areas of structural abnormality which can be detected by quantitative neuroimaging. Focal discharges were used for quantitative electroencephalogram source detection. Neuroimaging investigations consisted of voxel-based morphometry and region of interest volumetry. For voxel-based morphometry, volumetric MRI were acquired and processed. The images of each patient were individually compared with a control group. Statistical analysis was used to detect differences in gray matter volumes. Region of interest-based morphometry was automatically performed and used essentially to confirm voxel-based morphometry findings. The localization of the focal discharges on the electroencephalogram was compared to the neuroimaging results. Twenty-two patients with idiopathic generalized epilepsies were evaluated. Gray matter abnormalities were detected by voxel-based morphometry analysis in 77% of the patients. There was a good concordance between EEG source detection and voxel-based morphometry. On average, the nearest voxels detected by these methods were 19 mm (mm) apart and the most statistically significant voxels were 34 mm apart. This study suggests that in some cases subtle gray matter abnormalities are associated with focal epileptiform discharges observed in the electroencephalograms of patients with idiopathic generalized epilepsies.

Characteristic Distribution of Interictal Brain Electrical Activity in Idiopathic Generalized Epilepsy

PURPOSE

To demonstrate the anatomic localization of the cortical sources of the interictal EEG activity in human idiopathic generalized epilepsy (IGE).

METHODS

Multiple cortical and hippocampal sources of the interictal spontaneous EEG activity were investigated by low-resolution electromagnetic tomography in 15 untreated IGE patients and in 15 healthy controls. EEG activity (current density) in four frequency bands (delta: 1.5-3.5 Hz, theta: 3.5-7.5 Hz, alpha: 7.5-12.5 Hz, beta: 12.5-25.0 Hz) was computed for 2,397 voxels. Voxel-by-voxel group comparison was done between the patient and the control group. Voxels with p < 0.01 differences (between the two groups) were correlated with cortical anatomy.

RESULTS

Areas of significantly increased or decreased activity were characterized by their anatomical extension and the frequency bands involved. Five areas of bilaterally increased activity were found: rostral part of the prefrontal cortex (delta, theta); posterior part of the insula (delta); hippocampus and mediobasal temporal cortex (all frequency bands); medial parietooccipital cortex (theta, alpha, beta); dorsal and polar parts of the occipital cortex (alpha). Bilaterally decreased delta, theta, alpha activity was found in the majority of the frontal and anterior parietal cortex on the lateral surface, and in parts of the medial surface of the hemispheres. The area of decreased beta activity was less extensive. The right lateral and laterobasal temporal cortex showed decreased delta, theta, alpha, and beta activity, while its left counterpart only showed decreased delta and alpha activity in a limited part of this area.

CONCLUSIONS

(1) Pathological interictal EEG activity is not evenly distributed across the cortex in IGE. The prefrontal area of increased activity corresponds to the area that is essential in the buildup of the ictal spike-wave paroxysms (absence seizures). The existence of the posterior "center of gravity" of increased EEG activity in IGE was confirmed. The frontal area of decreased activity might be related to the cognitive deficit described in IGE patients. (2) Increased activity in a lot of ontogenetically older areas (including the hippocampi) and decreased activity in the majority of the isocortex is a peculiar pattern that argues for a developmental hypothesis for IGE.

Are absences truly generalized seizures or partial seizures originating from or predominantly involving the pre-motor areas?

In both the current (1981) ILAE Classification of Epileptic Seizures and the recently Proposed Diagnostic Scheme for People with Epilepsy and Epileptic Seizures, typical absence seizures are defined as generalized seizures, implying widespread subcortical and cortical neuronal involvement from onset with impairment of consciousness as the clinical hallmark. Clinical observations from three patients and clinical and experimental data from the literature suggest, however, that: (1) consciousness is retained in many typical absences; (2) the true hallmark of these seizures is arrest of motor initiation due to disturbance of pre-motor area frontal-lobe function; (3) typical absences and partial seizures from these areas may show similar clinical and EEG features and involve the same neuronal circuits. The neuronal system primarily involved in these seizures consists of a relatively limited cortico-thalamo-cortical circuit, including the reticular thalamic nucleus, the thalamocortical relay and the predominantly anterior and mesial frontal cerebral cortex, with the cortex probably acting as the primary driving site. Typical absences thus should not be classified or defined as generalized seizures, particularly since neuropathological and imaging studies increasingly argue for localized structural abnormalities, even in idiopathic or primary generalized epilepsy. These observations further highlight the intrinsic weaknesses of the current classification system for seizures and support further adaptations of the diagnostic system currently under development.

Brain imaging in idiopathic generalized epilepsies

While it is generally accepted that there is no neuroimaging abnormality in idiopathic generalized epilepsy (IGE), image processing and quantitative magnetic resonance imaging (MRI) studies suggest that there may be subtle structural abnormalities. Magnetic resonance spectroscopy indicates neuronal dysfunction with differing abnormalities in the IGE subsyndromes, and high concentrations of glutamate and glutamine have been inferred in the frontal lobes, and low gamma-aminobutyric acid levels in the occipital lobe. Studies of cerebral blood distribution at the time of absences have given complex results. The general consensus is of an increase in the thalamus and broad decreases in the neocortex, reflecting a suppression of neuronal activity, but with some increases, that may indicate focal areas of activation. Positron emission tomography (PET) ligand studies with an opioid tracer have inferred neocortical release of endogenous opioids at the time of serial absences. In combination with neurophysiological methods, PET studies with specific ligands have the potential to clarify the functional anatomy and neurochemical circuits that underlie IGE.

Distribution of Spatial Complexity of EEG in Idiopathic Generalized Epilepsy and Its Change After Chronic Valproate Therapy

The objective of this study was to investigate the global and regional spatial synchrony of the EEG background activity, and to assess the effect of chronic valproate therapy on spatial synchrony. 15 idiopathic generalized epilepsy (IGE) patients were examined and compared to 16 normal controls. Resting EEG with 19 channels was investigated before and during chronic administration of valproate (VPA). Omega, a single-valued measure of spatial covariance complexity, was calculated to assess the degree of spatial synchrony of EEG. Furthermore, a new parameter was defined to characterize the distribution of spatial synchrony (Antero-Posterior Complexity Ratio, APCR). Global Omega complexity was significantly lower in IGE compared to controls, while regional complexity showed significant differences only in the anterior region: the IGE group showed lower complexity. APCR was significantly lower in IGE. VPA therapy (1) lowered the global complexity, (2) increased regional complexity in the anterior region, but decreased it in the posterior region, and (3) increased APCR. In IGE lower complexity, i.e. enhanced spatial synchrony, was found, especially in the anterior cortical area. VPA modified the distribution of spatial synchrony in IGE patients towards that of normal controls, although the effect is not identical with full normalization of cortical bioelectric activity. Whether the observed change of spatial synchrony distribution may reflect the normalizing effect of valproate on the brain state is worth further investigation.

Imaging idiopathic generalized epilepsy

It has been traditionally held that there is no radiological abnormality in patients with idiopathic generalized epilepsy (IGE). Sophisticated image processing and quantitative magnetic resonance imaging (MRI) studies suggest that, in some cases, there may be a subtle structural abnormality. Magnetic resonance spectroscopy indicates neuronal dysfunction with differing patterns of abnormality in the IGE sub-syndromes, and high levels of glutamate and glutamine have been suggested in the frontal lobes, and low GABA levels in the occipital lobe. Studies reflecting cerebral blood flow at the time of absences have given complex results. The principal consensus is of an increase in the thalamus and broad decreases in the neocortex, reflecting a suppression of neuronal activity, but with the possibility of some increases, that could perhaps reflect focal areas of neuronal activation. PET ligand studies with an opioid tracer have implied neocortical release of endogenous opioids at the time of serial absences. In combination with high time-resolution neurophysiological methods, static and dynamic PET studies with specific ligands have the potential to elucidate the functional anatomy and neurochemical circuits that under-lie IGE.

Epilepsy

PURPOSE OF REVIEW

The purpose of this review is to consider the current and potential role of neuroimaging from an epilepsy perspective, and to illustrate that by combining appropriate imaging techniques, neuroimaging can contribute greatly to elucidating the basic mechanisms of the various forms of epileptic disorders.

RECENT FINDINGS

New magnetic resonance imaging sequences (magnetization transfer imaging) and positron emission tomography ligands (serotonergic system) were biologically validated in large groups of patients with localization-related epilepsies. Investigations in genetically determined homogenous patient populations (PAX6, juvenile myoclonic epilepsy) have strengthened the link between genetic defects and neuropathological targets (anterior commissure, thalamus). Magnetic resonance spectroscopy and electroencephalogram-triggered functional magnetic resonance imaging provided converging evidence for a key role of the thalamus in the generation of generalized seizures. The role of functional magnetic resonance imaging in identifying eloquent areas of cortex and its relationship to structural lesions, in particular malformations of cortical development, has been further elucidated. Longitudinal magnetic resonance imaging studies reported progressive volume loss after febrile convulsions and in active epilepsy.

SUMMARY

Neuroimaging is essential for improving the efficacy and safety of therapeutic, in particular, surgical procedures. Investigations of larger, more homogenous genetic disorders and longitudinal rather than cross-sectional neuroimaging studies have advanced our knowledge about the cause and effect of epileptic disorders, and will ultimately link defects in molecular genetics with specific neuropathological targets.

Neuropsychological aspects of type of epilepsy and etiological factors in adults

Whether certain types of epilepsies and etiologies are related to profiles of cognitive impairment is of interest for diagnostics and treatment. The dichotomy between generalized and focal epilepsies (mesial temporal lobe, frontal lobe, parietal, and occipital lobe epilepsies) is considered. Then the most frequent etiologies are discussed. We conclude that specific associations between neuropsychological deficits and type of epilepsy and etiology are rather exceptions. However, knowledge of the type of epilepsy and pathology provides eminent information to evaluate the nature of deficits, to estimate chances of functional recovery, to provide rehabilitation recommendations, and to support decisions about treatment options.

MRS shows syndrome differentiated metabolite changes in human-generalized epilepsies

OBJECTIVE

While it is generally accepted that the thalamo-cortical loop is abnormal in idiopathic generalized epilepsy (IGE), it is uncertain whether this loop is similarly affected among different IGE syndromes. We recently demonstrated reduced frontal lobe levels of N-acetyl aspartate (NAA) in patients with juvenile myoclonic epilepsy (JME). The present follow-up study investigates if similar or other types of changes exist in subjects with pure primarily generalized tonic clonic epilepsy (GTCS).

METHOD

Twenty patients with GTCS, 26 patients with JME, and 10 matched healthy controls were investigated with quantitative single voxel MR spectroscopy (MRS) measurements of NAA, choline (Cho), creatine (Cr), and myo-inositol (mI) at 1.5 T scanner. The voxels were placed over the right cerebellum, right thalamus, prefrontal, occipital cortex, and over a spherical phantom above the subject's head.

RESULTS

Patients with JME had reduced frontal lobe NAA (mmol/l) in relation to controls (9.8 +/- 1.1 vs. 10.8 +/- 0.7, P = 0.01), as well as GTCS patients (9.8 +/- 1.1 vs. 10.6 +/- 0.7, P = 0.007), whose values were normal. Patients with GTCS, on the other hand, showed significantly lower thalamic NAA than controls (9.7 +/- 1.0 vs. 10.8 +/- 0.9, P = 0.002), and both groups of patients had reduced thalamic Cho, and mI; [CHO: 2.0 +/- 0.4 (control) vs. 1.61 +/- 0.3 (JME) P = 0.001, and vs. 1.57 +/- 0.3 (GTCS) P = 0.0005; MI: 4.8 +/- 1.5 (control) vs. 3.3 +/- 1.4 (JME) P = 0.003, and vs. 3.2 +/- 1.5 (GTCS), P = 0.002]. No other regional changes were observed.

CONCLUSION

The present MRS data emphasize the involvement of thalamus in IGE. They also show partly differentiated alterations within the thalamo-cortical loop in JME vs. GTCS. The various clinical expressions of IGE may, thus, be associated with more localized neuroanatomical substrates than generally believed.

Achados tomográficos em 1000 pacientes consecutivos com antecedentes de crises epilépticas

Analizamos retrospectivamente as tomografias computadorizadas (TC) de crânio de 1000 pacientes consecutivos, com história clínica de crises epilépticas classificadas do ponto de vista clínico em generalizadas (CG) e parciais (CP). Nossos resultados mostraram a presença de CG em 70,7% dos pacientes, sendo 57,1% do sexo masculino e 42,9% do sexo feminino e, CP em 29,3%, sendo 60,0% do sexo maculino e 40,0% do sexo femninino. As faixas etárias de maior incidência foram entre 0 a 10 (31,0%) e 11 a 20 (21,8%) anos nos pacientes com CG e 0 a 10 (24,5%), 21 a 30 (16,7%) e 31 a 40 anos (18,4%) nos pacientes com CP. Os resultados tomográficos no grupo com CG foram: normais (48,8%) e alterados em 51,2%, sendo esses achados definidos como calcificações/cisticercose (14,0%), neurocisticercose/cistos (9,6%) hidrocefalia (4,4%), infarto (4,2%), indefinido (4,0%), tumor (2,5%) entre outros (12,5,%). Nos pacientes com CP os exames tomográficos foram normais em 37,4%, alterados em 62,7%, tendo os diagnósticos de neurocisticercose/cistos (12,2%), calcificações/cisticercose (11,2%), tumor (10,5%), indefinido (8,1%), infarto (5,4%), hidrocefalia (3,7%) e outros (11,6%). Salientamos a importância da TC em pacientes com epilepsia, particularmente para o diagnóstico de neurocisticercose.

Causes of epilepsies: insights from discordant monozygous twins

Whereas some patients with epilepsy have known acquired or genetic causes, in many the cause is unknown. By analyzing monozygotic twins, discordant for epilepsy, subtle etiological factors may be detected. We analyzed 12 monozygotic, discordant twins for factors explaining discordancy. These factors were presence of major clinical risk factors, presence of possibly epileptogenic lesions on brain magnetic resonance imaging (MRI), and quantitative brain volume abnormalities. Major risk factors, with associated acquired lesions were found in 4 of 12 twins. An MRI lesion without a major risk factor was found in a further 4 of 12 twins. Two of these had unilateral malformations of cortical development, 1 had bilateral periventricular heterotopia, and 1 had focal atrophy. Significant twin-twin differences in MRI volumes without obvious MRI lesions or major risk factors were found in 2 of 12 twins. Both had larger volumes than their co-twins, and idiopathic generalized epilepsy. No clinical or MRI findings accounting for discordance for epilepsy were found in 2 of 12 twins. In 10 of 12 pairs a clinical or MR correlate of epilepsy was found; some of those were subtle and only apparent by twin-twin comparison. They may be due to occult acquired factors, such as prenatal insults, or to genetic abnormalities resulting from postfertilization genetic processes.

EEG frequency profiles of idiopathic generalised epilepsy syndromes

The objective of this study was to investigate EEG frequency profiles (topographic distribution of spectral power data) in well-defined idiopathic generalised epilepsy (IGE) syndromes: juvenile absence epilepsy (JAE), juvenile myoclonic epilepsy (JME), epilepsy with grand mal seizures on awakening (EGMA), and in the unified 'common IGE' (CIGE) group of these patients.

METHODS

Absolute and relative (percent) power values were computed from waking EEG activity by Fast Fourier Transform (FFT). Each patient group was compared to an age-matched group of healthy control persons.

RESULTS

There was a general tendency for diffuse (absolute and relative) delta-theta-alpha power excess and relative beta power deficit in all IGE groups as compared to controls. Statistically significant (P</=0.05) bilateral absolute power differences were: fronto-parietal delta and diffuse theta (in JAE), frontal delta (in JME) and frontal alpha (in EGMA). Statistically significant (P</=0. 05) relative power differences were: frontal delta, diffuse theta, fronto-centro-parietal beta (in JAE), frontal delta and beta (in JME) and fronto-central alpha (in EGMA). The CIGE group showed power alterations of the same type but differences were statistically more significant than in the other patient groups.

CONCLUSION

Absolute power findings were interpreted as enhanced neuronal synchrony in the 0.5-12.0 Hz frequency range together with the tendency of decreasing synchrony in faster (12.5-32.0 Hz) frequencies. Corresponding shifts in relative power were interpreted as reflecting dysfunction of cortical regions. The authors hypothesise that these IGE frequency profiles reflect widespread cortical dysfunction essentially common to all the investigated IGE syndromes.

MR spectroscopy shows reduced frontal lobe concentrations of N-acetyl aspartate in patients with juvenile myoclonic epilepsy

PURPOSE

Neuropsychological studies suggest frontal lobe dysfunctions in patients with juvenile myoclonic epilepsy (JME). In this study we investigated whether an underlying mechanism could be a regional neuronal damage not visible with structural magnetic resonance (MR), but detectable with magnetic resonance spectroscopy (MRS).

METHODS

The study included 15 patients with JME and 10 matched healthy controls. Quantitative single voxel MRS was conducted at 1.5 Tesla by using a STEAM sequence (TR/TE/TM = 6,000/30/13.7 ms). The voxels were placed over the right cerebellum, right thalamus, and the prefrontal and occipital cortex. The quantitation included fitting of transmitter gain, and correction for partial volume of cerebrovascular fluid. LC-Model was used for estimation of the absolute concentrations of total N-acetyl aspartate (NAA), cholines, total creatine, and myoinositol.

RESULTS

Patients with JME had significantly reduced prefrontal concentrations of NAA in relation to controls (9.1 +/- 1.0 vs. 10.2 +/- 0.8 mM; p = 0.031 after Bonferroni correction). The other regions showed normal NAA values, as did the other metabolites.

CONCLUSIONS

The observed reduction in NAA levels suggests a prefrontal neuronal lesion in patients with JME.

Abnormal cerebral structure in juvenile myoclonic epilepsy demonstrated with voxel-based analysis of MRI

MRI scans of patients with idiopathic generalized epilepsy (IGE) are normal on visual assessment. Using an interactive anatomical segmentation technique and volume-of-interest measurements of MRI, we showed recently that patients with IGE had significantly larger cortical grey matter than control subjects. Further, 40% of individual patients with juvenile myoclonic epilepsy (JME), a syndrome of IGE in adolescence, had significant abnormalities of cerebral structure. In this study, we applied the automated and objective technique of statistical parametric mapping (SPM) to the analysis of structural MRI from 20 patients with JME and 30 control subjects. The cortical grey matter of each individual JME patient and the group of JME patients was contrasted with that of the group of 30 normal subjects. The voxel-based SPM comparison between the group of JME patients and the control subjects showed an increase in cortical grey matter in the mesial frontal lobes of the patients. Analysis of individual patients revealed significant abnormalities of cortical grey matter in five out of 20 JME patients, four of whom had been shown to have widespread abnormalities using the previous volume of interest technique. These findings indicate a structural cerebral abnormality in JME, with involvement of mesiofrontal cortical structures.

Voxel-by-voxel comparison of automatically segmented cerebral gray matter--A rater-independent comparison of structural MRI in patients with epilepsy

Quantitative evaluation of MRI in patients with epilepsy can give more information than qualitative assessment. Previously developed volume-of-interest-based methods identified subtle widespread structural changes in the neocortex beyond the visualized lesions in patients with malformations of cortical development (MCD) and hippocampal sclerosis (HS) and also in MRI-negative patients with juvenile myoclonic epilepsy (JME). This study evaluates a voxel-based automated analysis of structural MRI in epilepsy. After fully automated segmentation of cerebral gray matter from structural T1-weighted, high-resolution MRI scans, we applied the automated and objective technique of statistical parametric mapping (SPM) to the analysis of gray matter of 35 control subjects, 10 patients with partial seizures and MCD, 10 patients with left temporal lobe epilepsy (TLE) and HS, 10 patients with left TLE and normal MR quantitation of the hippocampus, and 20 patients with JME. At a corrected threshold of P < 0.05, significant abnormalities were found in 3/35 controls; in all 10 patients with MCD, 6 of whom had additional lesions beyond the margins of the visualized abnormalities; in 2/10 TLE patients with HS; in 2/10 MRI-negative TLE; and in 4/20 JME patients. Group comparisons between control subjects and HS patients identified the affected left temporal lobe with an increase in gray matter in the posterior temporal lobe, but did not identify hippocampal atrophy. The group of MRI-negative TLE patients showed no abnormalities compared with control subjects. Group comparison between control subjects and JME patients identified a mesial frontal increase in gray matter. The SPM-based voxel-by-voxel comparison of gray matter distribution identified MCD and abnormalities beyond the visualized lesion in individual MCD patients. The method did not reliably identify HS in individual patients or identify abnormalities in individual MRI-negative patients with TLE or JME in a proportion larger than the chance findings in the control group. Using group comparisons, structural abnormalities in the neocortical gray matter of patients with TLE and HS were lateralized to the affected temporal lobe. In patients with JME as a group, an increase in gray matter was localized to the mesial frontal area, corroborating earlier quantitative MRI findings.