Hemorrhagic and nonhemorrhagic stroke: diagnosis with diffusion-weighted and T2-weighted echo-planar MR imaging

PURPOSE: To determine if diffusion- and T2-weighted echo-planar magnetic resonance (MR) imaging can be used to detect acute hemorrhagic stroke and to differentiate hemorrhagic from nonhemorrhagic stroke. MATERIALS AND METHODS: A total of 118 examinations (diffusion- and T2-weighted MR imaging) in 19 patients with 27 nonhemorrhagic strokes and in six patients with seven hemorrhagic strokes were performed. The ratios of apparent diffusion coefficient and of signal intensity on T2-weighted MR images in lesions to those in contralateral control areas were calculated. RESULTS: Decreased ADC was shown in lesions of acute (0-3 days) hemorrhagic stroke, as well as in lesions of acute nonhemorrhagic stroke. Hypointense areas were seen on T2-weighted MR images in patients with acute hemorrhagic stroke, in contrast to normal to increased signal intensity in those with acute nonhemorrhagic stroke. Apparent diffusion coefficient tended to remain decreased in hemorrhagic stroke lesions even 100 days after onset, in contrast to the increased coefficient in nonhemorrhagic stroke lesions at the late chronic stage (31 days or older). CONCLUSION: Diffusion- and T2-weighted echo-planar MR imaging can be used to detect and distinguish between acute hemorrhagic and nonhemorrhagic stroke.     

The clinical application of diffusion weighted magnetic resonance imaging to acute cerebrovascular disorders]

Diffusion is a measure of motion freedom and is a sensitive parameter to characterize the tissue at the microscopic level. The methods of measuring in vivo diffusion by magnetic resonance imaging (MRI) have been based mainly on the addition of two motion-probing gradients (MPG) to the spin echo sequence to produce signal attenuation for the spins moving at random. The resultant MR images reflect the intravoxel incoherent motions (IVIM), which contain both water molecule diffusion and perfusion in the capillary network, and can be quantified by an apparent diffusion coefficient (ADC). Diffusion weighted MRI, acquired from IVIM MR imaging by the addition of the very strong MPG predicate water diffusion and anisotropy. High signal or reduced ADC can be observed in case of the slower diffusion. The anisotropy depends upon the orientation of the subjects and the gradients. Greater signal attenuation (faster diffusion) can be observed when the relative orientation of white matter tracts to the MPG is parallel as compared to that obtained with a perpendicular alignment. This anisotropy may preclude the detection or delineation of an ischemic lesion. Diffusion tensor trace has been designated to eliminate this anisotropy effect. In ischemic animal models, low signal (fast diffusion) and high signal (slow diffusion) have been noted in the vasogenic edema and cytotoxic edema, respectively. High signal appears only in case of cerebral blood flow below 15-20 ml/100 g per minute, a value identical to the threshold of tissue at high energetic metabolism and ion homeostasis. ADC value decreases following the cerebral vessel occlusion, or remains unchanged when collateral circulation develops. It has been speculated that reduction in ADC reflects the water shift from extracellular space to intracellular space due to the membrane permeability and/or intracellular osmolality increase. These results suggest that diffusion weighted MRI correlates well with the cell metabolism, and cytotoxic edema plays an important role in the acute cerebral stroke. In clinical setting of acute cerebral ischemia, diffusion weighted MRI may detect superacute infarction by showing high signal (slower ADC) over the 6 hours following the insult, whereas conventional MRI generally fails to do so. In chronic liquefied cerebral infarction, increased ADC, or attenuated signal are the most frequent findings, suggestive of an elevated diffusion. Therefore, diffusion weighted MRI improves early diagnosis of stroke and help differentiate acute from chronic stroke. One disadvantage of diffusion weighted MRI is motion artifact, which may be reduced by the introduction of a navigator echo to correct for the phase shift caused by the first imaging echo, or by the utility of ultrafast imaging technique, such as echo planar. Another shortcomings is the susceptibility artifact incorporating the diffusion weighted MRI. The eddy current may also result from the strong gradients, producing shiftlike artifact. Such artifacts can be compensated for by appropriate shaping of the current pulses sent into the gradient coils, or by use of shielded gradients. As with rapid progresses in perfusion imaging of ischemia penumbra, misery perfusion and luxury perfusion, new insight into the diffusion weighted MRI will be significant.     

Use of fluorescent in situ hybridization to detect aneuploidy in cervical dysplasia

An 8 year old girl with acute disseminated encephalomyelitis (ADEM) is described. Elevated serum antibody titers suggested recent Mycoplasma pneumoniae infection. T2-weighted image of magnetic resonance imaging (MRI) disclosed multiple lesions of high signal intensity in bilateral basal ganglia and thalami as well as in the white matter. Postcontrast T1-weighted image revealed an enhanced lesion in the deep white matter. She showed rapid clinical improvement in response to corticosteroid therapy. The lesions had disappeared completely on MRI performed 10 weeks after the onset. ADEM is believed to be a demyelinating disorder of probable autoimmune etiology. MRI findings in this case may support the hypothesis that the primary pathological event is vascular injury and demyelination occurs only as a secondary phenomenon.     

A case of adult type adrenoleukodystrophy with an acute onset and repeated episodes of ataxic dysarthria

We report a 30-year-old man with adult type adrenoleukodystrophy (ALD) who manifested an acute onset and repeated episodes of ataxic dysarthria. He noticed a moderate dysarthria after a high grade fever in February of 1995; however, two weeks later his symptom disappeared completely. Three months later, he noticed the dysarthria again and he was referred to our hospital for further examination. General physical findings on admission revealed a dark skin color, pigmentation of gingivae and reduced body hair. Neurologically he was normal except for a moderate ataxic dysarthria. Cranial T2-weighted MRI showed multiple high intensity lesions in the subcortical white matter of frontal lobe, bilateral peritrigonal white matter, splenium of the corpus callosum and bilateral cerebellar white matter. Only cerebellar lesions responsible for his symptom were enhanced on MRI after gadolinium administration. Initially we diagnosed him with multiple sclerosis (MS) based upon the clinical course and MRI findings, and then started corticosteroid treatment. His dysarthria was slightly improved after the treatment and bilateral gadolinium-enhanced lesions of cerebellar white matter on MRI disappeared. Multimodality evoked potentials such as short latency somatosensory evoked potentials, brainstem auditory evoked potentials and pattern-reversal visual evoked potentials, disclosed a prolonged central conduction time associated with bilaterally symmetric individual interpeak latencies. These findings, which supported diffuse and bilateral subclinical demyelinating lesions in the central nervous system, were unusual for MS; therefore his plasma very-long-chain fatty acids (VLCFA) were assayed for ALD. Finally, he was diagnosed with adult type ALD because of the high ratio of C26: 0/C22: 0 (0.075; normal 0.033). It is very difficult to clinically distinguish the early stage of adult type ALD especially in patients like this from MS. Therefore it is useful and important to evaluate not only the level of plasma VLCFA, but also to evaluate multimodality evoked potentials.     

Pre-and post-mortem MR imaging of unsuspected multiple sclerosis in a patient with Alzheimer's disease

A patient with the clinical diagnosis of Alzheimer's disease is presented in whom pre-mortem T2-weighted MRI revealed a periventricular white matter lesion. Postmortem T2 weighted MRIs of the formalin fixed brain revealed the same white matter lesion. Microscopically, classical Alzheimer changes were found and, unsuspectedly, the histopathological correlate of the white matter lesion proved to be an old, inactive, MS plaque. A similar lesion was discovered in the cervical myelum. These findings illustrate that T2-weighted post-mortem MRIs are highly comparable to pre-mortem images and that MRI is sensitive in detecting clinically silent white matter lesions. The histopathology of such lesions may also include MS plaques.     

An ERP study on visual spatial priming with peripheral onsets

The occlusion of the middle cerebral artery was used as an experimental acute stroke model in 30 cats. The diffusion of water was followed by diffusion-sensitized MRI between 1 and 15 h after induction of stroke. It is demonstrated that images representing the trace of the diffusion tensor provide a much more accurate delineation of affected area than images representing the diffusion in one direction only. The reason is that the strong contrast caused by the anisotropy and orientation of myelin fibers is completely removed in the trace of the diffusion tensor. The trace images show a small contrast between white and gray matter. The diffusion coefficient of white matter is decreased in acute stroke to approximately the same extent as gray matter. It is further shown that the average lifetime of water in extra and intracellular space is shorter than 20 ms both for healthy and ischemic tissue indicating that myelin fibers are permeable to water. The anisotropy contrast did not change before or after induction of stroke, nor after sacrifice. Together, these observations are consistent with the view that the changes in water diffusion during acute stroke are directly related to cytotoxic oedema, i.e., to the change in relative volume of intra- and extracellular spaces. Changes in membrane permeability do not appear to contribute significantly to the changes in diffusion.     

The apparent diffusion coefficient of water in gray and white matter of the infant brain

PURPOSE: The purpose was to obtain normal values of the apparent diffusion coefficient (ADC) in the infant brain and to compare ADC maps with T1- and T2-weighted images. METHOD: Diffusion was measured in nine infants with an ECG-gated SE sequence compensated for first-order motion. One axial slice at the basal ganglia level was investigated with the diffusion-encoding gradients in the slice-selection direction. RESULTS: On ADC maps, the corpus callosum and the optic radiations appeared dark before the onset of myelination, and the crus posterior of the internal capsule could be visualized before it appeared on T1- or T2-weighted images. In gray and white matter, the mean ADC ranged from 0.95 x 10(-9) to 1.76 x 10(-9) m2/s. In the frontal and occipital white matter, in the genu corporis callosi, and in the lentiform nucleus, the ADC decreased with increasing age. The cortex/white matter ratio of the ADC increased with age and approached 1 at the age of 30 weeks. CONCLUSION: ADC maps add information to the T1 and T2 images about the size and course of unmyelinated as well as myelinated tracts in the immature brain.     

MR identification of white matter abnormalities in multiple sclerosis: a comparison between 1.5 T and 4 T

BACKGROUND AND PURPOSE: Although MR spectroscopy and functional MR imaging of the brain have been successful at 4 T, conventional fast spin-echo imaging of the brain at 4 T has not been adequately evaluated. The purpose of this study was to compare the detection of white matter abnormalities in multiple sclerosis (MS) at 1.5 T and 4 T. METHODS: Fifteen patients with clinically definite MS were imaged at both 1.5 T and 4 T within a 1-week period. Comparison was made between fast spin-echo long-TR images at both field strengths. Pulse sequences were tailored to maximize resolution and signal-to-noise ratio in clinically relevant imaging times (< 7 min). Four interpreters independently reviewed the images obtained at both field strengths in separate sessions and evaluated them for lesion identification, size, characterization, and subjective resolution. Differences in interpretations at 1.5 T and 4 T were subsequently recorded. RESULTS: Images obtained at 4 T showed a mean of 88 more lesions as compared with images obtained at 1.5 T. All the lesions measured less than 5 mm and were typically aligned along perivascular spaces. Twenty-five consensually identified lesions on 4-T images were not seen at all on 1.5-T images. Moreover, 4-T images showed 56 additional consensually identified lesions, which were indistinct and seen only in retrospect on 1.5-T images. These lesions were frequently (n = 48) identified in large confluent areas of white matter signal intensity abnormality at 1.5 T. All observers also agreed that 4-T images subjectively enhanced the perception of normal perivascular spaces and small perivascular lesions. CONCLUSION: MR imaging at 4 T can depict white matter abnormalities in MS patients not detectable at 1.5 T through higher resolution with comparable signal-to-noise ratio and imaging times.     

Effects of diffusion anisotropy on lesion delineation in a rat model of cerebral ischemia

The effects of white and gray matter diffusion anisotropy on ischemic lesion delineation have been studied in the rat model of middle cerebral artery occlusion. Apparent diffusion coefficient (ADC) maps obtained by conventional pulsed gradient spin echo diffusion-weighted imaging (PGSE-DWI) were compared with maps of the trace of the diffusion tensor in both normal and occluded animals. Diffusion tensor trace maps were derived from the average of the ADC maps from three separate experiments with diffusion weighting along three orthogonal axes, and also from a single-scan method. A marked degree of diffusion anisotropy was observed in both cortical gray matter and white matter from ADC maps of the control animals. In the occluded animals, the systematic effects of anisotropy on ADC and lesion area influenced the delineation of the ischemic territory in the PGSE-DWI ADC maps. However, the two trace methods eliminated these effects and gave consistent ischemic lesion depiction, despite the use of differing diffusion times in the two measurements.     

Apparent diffusion coefficients in benign and secondary progressive multiple sclerosis by nuclear magnetic resonance

The diffusion characteristics of water in brain white matter were studied in patients with benign and secondary progressive multiple sclerosis (MS), and also in normal controls. In the MS patients, both lesions and normal-appearing white matter (NAWM) were examined to assess whether pathological differences might be evident from the diffusion behavior. A volume-selective technique was used to reduce data acquisition time and improve the reliability and precision of the measurements. This also allowed the time-dependence of apparent diffusion coefficients to be assessed. While lesions from both patient groups showed an elevated diffusion coefficient, no differences between the two groups were found. In addition, NAWM was elevated for both patient groups compared with the control group, although this was only statistically significant for patients with a benign disease course. The degree of elevation of the diffusion coefficient within the individual lesions measured was not related to the disability of the patient. Pathological differences between lesions in patients with different disease courses, if they exist, have not been detected in this study of brain water diffusion.     

A comparison of two oral ketamine-diazepam regimens for sedating anxious pediatric dental patients

A 62 year-old man was admitted with a right hemiparesis, sensory aphasia and right hemianopia which appeared on awakening. He was initially thought to have a stroke, but EEG showed diffuse slowing and both CT scan and MRI irregular white matter lesion suggesting a leucoencephalopathy. His neurological deficit regressed, and he was discharged after 2 weeks. He was readmitted 6 months later because of mental confusion. MRI revealed diffuse white matter lesions extending up to the frontal lobes, these were hyperintense on T2 weighted images and suggested the diagnosis of gliomatosis cerebri (GC). The patient became progressively comatose and died 6 weeks later. At autopsy the brain looked diffusely swollen with irregular greyish areas of the white matter of both centrum ovale and brain stem. On microscopic examination the cerebrum and brain stem were diffusely and asymmetrically infiltrated by numerous neoplastic glial cells without angiogenesis or disruption of architectonic boundaries. There were no mitoses nor necrosis. Many tumour cells were GFAP- and S100-positive. A high proportion of cells contained the leucocyte antigen Leu-7. This case of gliomatosis cerebri is compared to the 9 published cases of GC with an initial focal neurological deficit and to the 19 publications reporting MRI results. The controversial nosological boundaries and etiopathogenetic hypotheses of this peculiar neoplastic disease are discussed.     

Neurologic complications in a case of Werner syndrome

A 39 year old caucasian man was admitted in 1994 to the neurological department with a left pure motor hemiplegia that appeared suddenly. This patient showed typical features of Werner's syndrome. He had a hoarse voice, a diffuse muscle weakness and atrophy in the upper and lower limbs with chronic ulcers on the legs. His scalp and public hair were sparse. Cranial MRI revealed several lesions in the white matter, low signal intensity on T1 weighted images and high signal on T2 weighted images. Cerebrospinal fluid (CSF was inflammatory with hypercytosis and proteinorachia was 0.50 g/l with synthesis of IgG. Sural nerve biopsy revealed muscle atrophy and the loss of myelinated fibers. Thus, central and peripheral nervous systems were affected in this case.     

Osteochondritis dissecans of the femoral condyle in the growth stage

The site of lesion, spontaneous healing, onset mechanism, and magnetic resonance imaging findings of 51 knees in 38 patients with osteochondritis dissecans involving the femoral condyle in the growth stage were investigated. tercondylar site, and the remaining 1/4 were in other sites. Compared with those in the other sites, the lesions in a medial intercondylar site had a lower healing rate and required a longer time to heal. T2 weighted images of the lesions showed a progression from low signal areas to the appearance of a high signal line at the fragment to parent to bone interface, to a high signal double line at the interface and parent-bone surface, or to disappearance of the line. Magnetic resonance imaging often revealed discoid menisci or meniscal tears in patients with lesions in the lateral condyle, suggesting that endogenous forces play an important role in the onset of osteochondritis dissecans.     

Scientific role of German ophthalmology in the European telecommunication project OPHTEL]

We examined 21 patients aged 5 months to 19 years, on a 1.5 T magnet. T1-weighted spin-echo images, proton density and T2-weighted images with spin-echo and turbo spin-echo sequences, and contrast-enhanced magnetization transfer (MT) T1-weighted images were obtained in all cases. MT T1-weighted images were performed before injection in 9 patients. Subependymal nodules were found in 14, and cortical and subcortical tubers in 20 of the 21 patients. MT T1-weighted images showed tubers and subependymal nodules as higher signal than normal gray matter and revealed more tubers than conventional sequences in 11 cases. High signal intensity lesions of the white matter were found in 19 patients but were seen only on MT images in 9 cases. When MT images both before and after injection were available, tubers and white matter lesions were more easily recognised on unenhanced MT images because of their higher contrast.     

Neuroimaging and pathology of the spinal cord in compressive cervical myelopathy

Magnetic resonance imaging (MRI) has enabled us to see the spinal intramedullary pathology as differences in signal intensity. Intramedullary high intensity lesions were observed on T2-weighted MRI in patients with cervical spondylotic myelopathy (20.0%) and ossification of the posterior longitudinal ligament (OPLL) of the cervical spine (25.7%). The frequency of this findings was proportional to the clinical severity of myelopathy and degree of spinal cord compression. The pathophysiological basis of such signal abnormality was presumed to vary from acute edema to chronic myelomalacia. The intramedullary lesion on MRI is considered to be the main site of lesion responsible for the neurological symptom because of a good correlation between the neurological level and high intensity level. We found from nine autopsy cases of OPLL that there are distinct differences in severity and extent of pathological changes between the spinal cord with a boomerang-shaped cross-section and that with a triangular-shaped cross-section. In the boomerang-shaped cases, major pathological changes were restricted to the gray matter and the white matter was relatively well preserved. Secondary wallerian degeneration was restricted to the fasciclus cuneatus the fibers of which were derived from the affected segments. In the cases of a triangular shape, pathological changes were more severe, both white and gray matter were involved. There were severe pathological changes over more than one segment, and both descending degeneration of the lateral pyramidal tracts and ascending degeneration of the posterior column, including the fasciclus gracilis, were observed. In conclusion, it is clinically very important to understand the pathological basis of the compressed spinal cord on neuroimages.     

Complete transposition in a chick embryo demonstrated by scanning electron microscopy

The white matter lesions in a patient with late adult onset dentatorubropallidoluysian atrophy (DRPLA) were studied in detail by MRI using the fluid attenuation inversion recovery (FLAIR) technique. The patient was a 60 year old woman with a family history of DRPLA, in whom the number of CAG repeats in the DRPLA gene on chromosome 12 was expanded to 59 (normal allele 10). In addition to atrophy of the cerebral cortex, cerebellum, and pontomesencephalic tegmentum, the cerebral white matter and a part of the white matter tracts within the brainstem showed prominent high signal intensities on FLAIR images. These MR findings suggest that, in addition to the degeneration of the dentatorubral and pallidoluysian systems, the pathological process extends to the white matter in DRPLA. This could be important for differentiating DRPLA from other clinically similar diseases such as Machado-Joseph disease or Huntington's disease.     

Radiological diagnosis of viral encephalitis

Most of viral encephalitis may demonstrate no specific change on CT and MR images. Brain swelling, edema, abnormal density (CT) and abnormal intensity (MR) can be detected in herpes simplex encephalitis and enterovirus encephalitis (coxsackie, echo, polio). The common finding on CT and MRI in patients with HIV encephalopathy are atrophy, leukomalacia. Progressive multifocal leukoencephalopathy (PML) shows multifocal oval or round white matter T2-hyperintensities on MR images. Subacute sclerosing panencephalitis (SSPE) may present slight changes in the subcortical and periventricular white matter, as well as basal ganglia. Progressive disorder makes widespread T1-low, T2-high intensity area and atrophy. MRI of acute disseminated encephalomyelitis (ADEM) shows multifocal subcortical hyper intense foci on T2-weighted studies. The deep white matter, brainstem, thalamus and cerebellum can be affected. Most of ADEM lesions resolve. Imaging findings of acute lymphocytic meningitis by echovirus and coxsackievirus are usually normal.     

Diffusion and perfusion magnetic resonance imaging of the evolution of hypoxic ischemic encephalopathy in the neonatal rabbit

Hypoxic-ischemic encephalopathy (HIE) can result from neonatal asphyxia, the pathophysiology of which is poorly understood. We studied the acute evolution of this disease, using magnetic resonance imaging in an established animal model. HIE was induced in neonatal rabbits by a combination of common carotid artery (CCA) ligation and hypoxia. Serial diffusion and perfusion-weighted magnetic resonance images were acquired before, during, and after the hypoxic interval. Focal areas of decreased apparent diffusion coefficient (ADC) were detected initially in the cortex ipsilateral to CCA ligation within 62 +/- 48 min from the onset of hypoxia. Subsequently, these areas of decreased ADC spread to the subcortical white matter, basal ganglia (ipsilateral side), and then to the contralateral side. Corresponding perfusion-weighted images showed relative cerebral blood volume deficits which closely matched those regions of ADC change. Our results show that MRI diffusion and perfusion-weighted imaging can detect acute cell swelling post-hypoxia in this HIE model.     

Diffusion-weighted MR of acute cerebral infarction: comparison of data processing methods

BACKGROUND AND PURPOSE: Some investigators have proposed that either calculated diffusion trace images or apparent diffusion coefficient (ADC) maps, which require imaging with multiple diffusion sensitivities and/or postacquisition image processing, are essential for the accurate interpretation of diffusion-weighted images in acute stroke because of the possible pitfalls of regional diffusion anisotropy, magnetic susceptibility artifacts, and confounding T2 effects, all of which alter signal on diffusion-weighted MR images. The purpose of our study was to compare the sensitivity, specificity, and accuracy of simple, orthogonal-axis diffusion-weighted imaging for the diagnosis of early cerebral infarction with three other sets of postacquisition-processed images: isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace images. METHODS: Twenty-six consecutive adult patients with signs and symptoms consistent with a clinical diagnosis of early cortical and/or subcortical cerebral infarction and 17 control subjects were studied with multisection, single-shot, spin-echo echo-planar diffusion-weighted imaging at 1.5 T to generate a set of three orthogonal-axis diffusion-weighted images. Isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace (mean ADC) images were then generated off-line and all four sets of images were interpreted blindly by two neuroradiologists. RESULTS: The average sensitivity, specificity, and accuracy for the orthogonal-axis diffusion-weighted images were 98.1%, 97.1%, and 97.7%, respectively. The average sensitivity, specificity, and accuracy for isotropic diffusion-weighted images were 88.5%, 100%, and 93% respectively. The average sensitivity, specificity, and accuracy for diffusion trace-weighted images were 82.7%, 73.6%, and 79.1%, respectively. The average sensitivity, specificity, and accuracy for diffusion trace images were 50.0%, 85.3%, and 64.0%, respectively. CONCLUSION: Orthogonal-axis diffusion-weighted images have the highest sensitivity and accuracy and very high specificity for early cerebral infarction. Our data contradict the contention that quantitative diffusion maps, requiring imaging with multiple diffusion sensitivities and/or subsequent image processing, are necessary for clinical stroke imaging.     

Chronic carbon disulfide encephalopathy

To understand central nervous damage after long-term exposure to carbon disulfide (CS2), 10 patients who had polyneuropathy with various neuropsychiatric symptoms in a viscose rayon plant were studied. Clinical and laboratory examinations including electroencephalography (EEG), brain computed tomography (CT), brain magnetic resonance images (MRI), and carotid duplex sonography were carried out. Clinically, headache, unpleasant dreams, memory impairment, fatigue, anorexia and emotional lability were common in these patients while 2 patients had stroke episodes. EEGs were all normal. Brain CT scan showed mild cortical atrophy in 3 and low density lesions in the basal ganglia in 3. Brain MRI studies also disclosed mild cortical atrophy in 4 and multiple lesions involving the basal ganglia and corona radiata in 4. Carotid duplex sonography revealed mild atherosclerosis with plaques (< 20% stenosis) of extracranial vessels in 6. However there was no significant difference in flow velocities and flow volumes in the extracranial carotid arteries between patients and the normal controls. Interestingly, 2 patients had multiple brain lesions in the subcortical white matter but without strokes. In conclusion, encephalopathy with possible strokes may occur after chronic exposure to CS2, as well as polyneuropathy. The lesions usually involve the basal ganglia and subcortical white matter. Furthermore, MRI study may detect brain lesions particularly in the subcortical white matter areas before the occurrence of stroke.