Subacute sclerosing panencephalitis findings at MR imaging, diffusion MR imaging, and proton MR spectroscopy

A case of subacute sclerosing panencephalitis in a 2-year-old boy is reported. In addition to asymmetric lesions in the parietotemporal lobes, right thalamus, and globus pallidus, symmetric patterns were notable in the brain stem, middle cerebellar pedincles, and dentate nuclei. Proton MR spectroscopy revealed markedly decreased N-acetylaspartate peaks and normal choline and myo-inositol levels in the lesions. Diffusion MR imaging revealed an elevated diffusion pattern manifested with high apparent diffusion coefficient values (1.14-1.60 x 10(-3) mm(2)/s) compared with those in normal-appearing brain tissue (0.65-1.00 x 10(-3) mm(2)/s) and subtle high signal intensity characteristics on diffusion-weighted images obtained at b = 1000 s/mm(2).     

Neuro-Behcet''s disease: diffusion MR imaging and proton MR spectroscopy

We herein report the case of a 53-year-old woman with Behcet's disease and an acute T2-hyperintense lesion in left side of the pons. Echo-planar "trace" diffusion MR imaging revealed high signal intensity changes at the lesion site on b = 1000 s/mm(2) images, initially suggesting restricted diffusion. On corresponding apparent diffusion coefficient maps, however, the lesion had high signal intensity and high apparent diffusion coefficient values (1.22 x 10(-3) mm(2)/s), compared with the contralateral normal side of the pons (0.86 x 10(-3) mm(2)/s) and compared with the normal temporal white matter (0.80 x 10(-3) mm(2)/s). This was consistent with the presence of increased diffusion, hence vasogenic edema. Proton MR spectroscopy excluded acute infarction. This particular pattern (high signal intensity on b = 1000 s/mm(2) images in association with high apparent diffusion coefficient values) likely represented the acute inflammatory process associated with disrupted brain-blood barrier in the fulminant form of neuro-Behcet's disease. Follow-up examinations 相似文献   

Acute carbon monoxide poisoning: diffusion MR imaging findings

During the acute stage of carbon monoxide poisoning, diffusion MR images obtained at b=1000 s/mm2 revealed high signal intensity lesions in the white matter, consistent with restricted diffusion. Low apparent diffusion coefficient values (0.18-0.34 x 10(-3) mm2/s) were noted in the affected white matter regions. Follow-up MR imaging performed 16 days later revealed disappearance of white matter lesions, suggesting that during the acute stage of carbon monoxide poisoning, white matter can be more sensitive than gray matter to ischemia.     

Mitochondrial encephalomyopathy: comparison of conventional MR imaging with diffusion-weighted and diffusion tensor imaging: case report

Summary: Conventional MR imaging, MR spectroscopy, diffusion-weighted imaging, and diffusion tensor imaging were performed in a 5-month-old male patient with mitochondrial encephalomyopathy. On conventional T2-weighted MR images, symmetric, confluent high signal intensity was found in the temporoparietal white matter. A large lactate peak and decreased N-acetylaspartate were found in this region on proton MR spectroscopic images. Diffusion-weighted imaging showed increased apparent diffusion coefficient, representing vasogenic edema. Diffusion tensor imaging revealed decreased anisotropy, consistent with injury to the oligodendro-axonal unit. A muscle biopsy specimen revealed an isolated complex III enzyme respiratory chain deficiency. Diffusion-weighted and diffusion tensor imaging are valuable techniques for the characterization of hyperintense lesions on T2-weighted MR images in cases of mitochondrial encephalomyopathy.     

Diffusion-weighted MR imaging in patients with phenylketonuria: relationship between serum phenylalanine levels and ADC values in cerebral white matter

PURPOSE: To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU). MATERIALS AND METHODS: Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3-44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3-33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation. RESULTS: Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 micromol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = -0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = -0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005). CONCLUSION: Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 micromol/L).     

Megalencephalic leukoencephalopathy with subcortical cysts in an adult: quantitative proton MR spectroscopy and diffusion tensor MRI

A 37-year-old macrocephalic woman was investigated for increasing gait disturbance due to longstanding spasticity and ataxia. MRI showed widespread bilateral increase in signal from cerebral white matter on T2-weighted images. Numerous subcortical cysts were visible in anterior-temporal and parietal regions. These clinical and neuroradiological features are those of megalencephalic leukoencephalopathy with subcortical cysts (MLC), a recently delineated white-matter disease with onset in childhood. Quantitative localised proton MR spectroscopy of white matter revealed marked reduction of N-acetylaspartate, creatine, and choline with normal values for myo-inositol, consistent with axonal loss and astrocytic proliferation. Diffusion tensor imaging showed an increased apparent diffusion coefficient and reduced anisotropy in affected white matter pointing to reduced cell density with an increased extracellular space. These findings are in line with histological changes alterations known to occur in MLC.     

Canavan disease: diffusion magnetic resonance imaging findings

A 15-month-old boy with Canavan disease is reported in whom a restricted diffusion pattern on diffusion magnetic resonance imaging (MRI) (high signal on b = 1,000 mm2/s images and low apparent diffusion coefficient [ADC] values) was evident in the affected regions of the brain, including the peripheral white matter, globi pallidi, thalami, brainstem, dorsal pons, and dentate nuclei. The ADC values at these regions ranged from 0.42 to 0.56 x 10(-3) mm2/s compared with the normal ADC values from the uninvolved deep frontal white matter (0.68-0.92 x 10(-3) mm2/s). The known histopathologic features in Canavan disease include edematous and gelatinous brain tissue associated with diffuse vacuolization. Considering these and the diffusion MRI findings in this patient, it is likely that existence of a gel (gelatinous) state rather than the usual sol state of water molecules in the affected brain regions accounted for the restricted diffusion pattern in Canavan disease.     

Metachromatic leukodystrophy: diffusion MR imaging findings

Herein the case of a 10-month-old boy with metachromatic leukodystrophy is reported. Diffusion MR imaging performed with an echo-planar trace sequence revealed a cytotoxic edema-like pattern (high signal intensity on b = 1000 s/mm(2) images and low apparent diffusion coefficient values) in the affected white matter in the absence of an ischemic condition. This finding was unchanged at a 6-month follow-up, as revealed by diffusion MR imaging. A gradient-echo diffusion sequence, reverse fast imaging in steady-state precession, revealed hyperintense changes at the corresponding regions. It is likely that the cytotoxic edematous pattern (restricted diffusion pattern) reflected restriction of mobility of the water molecules within abnormal portions of the myelin sheath, because impaired myelin breakdown and reutilization are known features of metachromatic leukodystrophy.     

High-b-value diffusion-weighted MR imaging of adult brain: image contrast and apparent diffusion coefficient map features

BACKGROUND AND PURPOSE: Recent improvements in MR gradient technology allow significant increases in diffusion weighting without prohibitive signal-to-noise degradation. The purpose of our investigation was to establish normative references for the signal intensity characteristics and apparent diffusion coefficient values of the adult brain at high b values. METHODS: Fifty adults underwent diffusion-weighted single-shot spin-echo echo-planar MR imaging. Isotropic diffusion-weighted images were obtained with b values of 0, 1,000, 2,000, 2,500, 3,000, and 3,500 s/mm2. Qualitative assessments were made in multiple regions of interest in gray and white matter. Three apparent diffusion coefficient maps were generated for each of six patients with a 2-point technique at a b value of 0 and at b values of 1,000, 2,000, and 3,000 s/mm2. RESULTS: Increasing b values result in a progressive decrease in the gray to white matter signal intensity ratio. Isointensity between gray and white matter results at b values between 1,000 and 2,000 s/mm2. At b values greater than 2,000, the gray-white pattern reverses relative to the usual b value of 1,000. Apparent diffusion coefficient values were shown to decrease with increasing b values. CONCLUSION: Attention to the reversal of gray-white contrast and the dependence of apparent diffusion coefficient on the b value are important in avoiding erroneous assignment of pathologic abnormalities to normal regions. This study provides the normative data for future diffusion investigations performed at high b values.     

Phenylketonuria: diffusion magnetic resonance imaging and proton magnetic resonance spectroscopy

Two patients with phenylketonuria are reported with white matter lesions. Diffusion magnetic resonance (MR) imaging revealed restricted diffusion patterns (high signal) on b = 1000 s/mm2 images associated with low apparent diffusion coefficient values ranging between 0.44 x 10-3 mm2/s and 0.56 x 10-3 mm2/s. On proton MR spectroscopy obtained in 1 of the patients, a prominent peak resonating at approximately 3.80 ppm was consistently present attributable to the peak rising from the alpha-proton of the phenylalanine molecule.     

Diffusion-weighted MR imaging of pyogenic ventriculitis

OBJECTIVE: The purpose of this study was to describe the features of pyogenic ventriculitis (ventricular empyema, pyocephalus) on diffusion-weighted MR imaging. CONCLUSION: Markedly increased signal intensity of dependent intraventricular fluid on diffusion-weighted MR imaging and an apparent diffusion coefficient that is less than that of normal cerebral white matter indicate restricted water diffusion in purulent fluid and suggest the diagnosis of pyogenic ventriculitis.     

Diffusion-weighted MR imaging in hypertensive encephalopathy: clues to pathogenesis.

PURPOSEHypertensive encephalopathy, a complex of cerebral disorders, including headache, seizures, visual disturbances, and other neurologic manifestations, is associated with a variety of conditions in which blood pressure rises acutely. It has been ascribed to either exuberant vasospasm with ischemia/infarction or breakthrough of autoregulation with interstitial edema. Diffusion-weighted MR imaging may be used to determine whether the edema in hypertensive encephalopathy is cytotoxic or vasogenic in origin.METHODSDiffusion-weighted imaging was performed using the double line scan diffusion imaging technique on a 1.5-T MR system. Seven patients with hypertensive encephalopathy were imaged within 1 day of the onset of their symptoms. Apparent diffusion coefficient maps as well as low and high b-factor images were acquired. The two-tailed paired Student''s t-test was used to compare the apparent diffusion coefficients in edematous brain regions with those of normal white matter.RESULTSIn all cases the apparent diffusion coefficient maps of the patients with hypertensive encephalopathy showed increased signal in regions corresponding to increased T2 signal on standard T2-weighted (low b-factor) images. Quantitative apparent diffusion coefficients in regions of abnormal T2 signal were 1.36 +/- 0.14 microm2/ms, compared with 0.80 +/- 0.05 microm2/ms in normal white matter. Diffusion-weighted (high b-factor) T2-weighted images did not show abnormal signal.CONCLUSIONDiffusion-weighted MR imaging shows that the edema in hypertensive encephalopathy is of vasogenic origin and does not represent ischemia or infarction. This finding may have therapeutic implications.     

Metachromatic leukodystrophy. Diffusion MR imaging and proton MR spectroscopy

Metachromatic leukodystrophy is characterized by dysmyelination caused by a deficiency of arylsulfatase-A. In a 17-month-old boy with metachromatic leukodystrophy, an echo-planar diffusion MR sequence revealed a restricted diffusion pattern in the deep white matter, manifested by high-signal on b = 1000 s/mm² images, and low ADC values (0.56 × 10^-3 mm²/s). Proton MR spectroscopy revealed a marked decrease in choline, a metabolite related to myelin turnover. These observations consisting of a restricted diffusion pattern on diffusion MR imaging, and decreased choline peaks on proton spectroscopy, likely represented dysmyelination in metachromatic leukodystrophy.     

Proton MR spectroscopic and diffusion tensor brain MR imaging in X-linked adrenoleukodystrophy: initial experience

PURPOSE: To compare conventional magnetic resonance (MR) imaging, proton MR spectroscopic imaging, and diffusion tensor (DT) MR imaging findings in patients with X chromosome-linked adrenoleukodystrophy (X-ALD). MATERIALS AND METHODS: Multisection proton MR spectroscopy and DT imaging were performed in 11 patients with X-ALD and in 11 healthy control subjects. Quantitative measures of N-acetylaspartate (NAA), choline, and creatine values and of isotropic apparent diffusion coefficient (IADC) and fractional anisotropy (FA) were obtained from coregistered regions of interest. DT imaging and metabolic parameters were compared by using regression analysis. In addition, differences in DT imaging and metabolite measurements between normal- and abnormal-appearing white matter on conventional MR images were evaluated by using a nonparametric (Mann-Whitney) test. RESULTS: A strong logarithmic relationship between NAA value and FA (r = 0.64, P <.001) and an inverse logarithmic relationship were found between NAA value and IADC (r = -0.69, P <.001). Creatine and choline values correlated poorly with IADC and FA. In the normal-appearing white matter of asymptomatic patients, the NAA value was 17% lower than that in the healthy control subjects (P =.016), whereas no significant difference in DT imaging measures was seen in these regions. CONCLUSION: In patients with X-ALD, MR spectroscopic imaging can depict abnormalities in white matter that have a normal appearance on both conventional MR and DT images; this finding suggests that it may be the most sensitive technique for detecting early abnormalities of demyelination or axonal loss in patients with X-ALD.     

Diffusion weighted MR: principles and clinical use in selected brain diseases

PURPOSE: To define the principles and technical bases of diffusion weighted MR imaging of the brain and report our experience in the evaluation of selected brain disorders including age-related ischemic white matter changes (leukoaraiosis), neoplastic and infective cysts and wallerian degeneration. MATERIAL AND METHODS: Between May 1999 and June 2000 we examined seventeen patients: 10 patients with leukoaraiosis and deterioration of cognitive and motor function, 5 patients with focal cystic lesions (one anaplastic astrocytoma, one glioblastoma, one metastasis from squamous cell lung carcinoma, one pyogenic abscess and one case with cerebral tubercolosis) and 2 patients with wallerian degeneration (one with post-hemorrhagic degeneration of right corticospinal tract and one with post-traumatic degeneration of left optic tract). All patients underwent a standard cranial MR examination including SE T1-, proton density, T2-weighted, FLAIR and diffusion weighted images. Post-contrast T1-weighted sequences were also obtained in the patients with cystic lesions. Diffusion weighted images were acquired with double shot echoplanar sequences. Diffusion sensitizing gradient along the x, y and z axes and b values ranging 800 to 1200 s/mm2 were used. For each slice a set of three orthogonal diffusion "anisotropic" images, an "isotropic" image and a standard T2-weighted image were reconstructed. Postprocessing included generation of the apparent diffusion coefficient maps and of the "trace" image that reflects pixel by pixel the diffusional properties of water particles only. Values of mean diffusivity within regions of interest were computed in the "trace" image and compared with those obtained in contralateral brain areas. In patients with leukoaraiosis the diffusivity in posterior periventricular white matter was compared with that measured in 10 age-matched control subjects without leukoaraiosis. RESULTS: In patients with leukoaraiosis the areas of increased periventricular signal intensity on T2-weighted images showed a significantly higher (p < 0.001) diffusivity (mean values 124.7 +/- 21.3 x 10(-5) mm2/s) as compared to control subjects (mean values 85 +/- 7 x 10(-5) mm2/s). Diffusion weighted images in 2 patients revealed the presence of a small focal area of increased signal and reduced diffusivity in "trace" images consistent with recent ischemic lesion. In neoplastic cystic lesions the central necrotic/cystic content was always hypointense on diffusion weighted images and showed increased diffusivity on "trace" images. On the other hand the central necrotic content of the pyogenic brain abscess was hyperintense and showed low diffusivity. In patients with wallerian degeneration diffusion weighted images and "trace" images demonstrated loss of anisotropy and increased diffusivity in the affected white matter tract relative to the contralateral. DISCUSSION: The increased diffusivity observed in areas of leukoaraiosis and the identification of subclinical acute ischemic lesions by diffusion weighted images might be more useful than standard MR sequences for monitoring the disease progression. Diffusion weighted images allow differentiation of the different parts of focal cystic lesions (edema, solid and cystic/necrotic portion) and are useful to differentiate pyogenic brain abscess from necrotic tumors. In patients with wallerian degeneration the loss of anisotropy and the increase of diffusivity values in the affected tract are probably related to myelin breakdown and allow better recognition of the affected tract relative to standard MR images. CONCLUSIONS: Diffusion weighted MR imaging can be performed during a standard cranial MR examination and add useful clinical information in several brain disorders besides acute ischemic stroke.     

Evolution of lesions in Susac syndrome at serial MR imaging with diffusion-weighted imaging and apparent diffusion coefficient values

BACKGROUND AND PURPOSE: Susac syndrome is a rare disorder consisting of encephalopathy, hearing loss, and retinal arteriolar occlusions. The purpose of this study was to evaluate the evolution of lesions in this disease by using serial MR imaging with diffusion-weighted imaging (DWI) and apparent diffusion coefficients (ADCs). Abnormalities in the nonlesional white matter (NLWM) were also analyzed. METHODS: Serial MR and DWI findings in two patients with Susac syndrome were reviewed retrospectively. ADCs of the lesions and the NLWM were compared with values of the corresponding anatomical regions in 16 control subjects. RESULTS: T2-weighted images, DWIs, and fluid-attenuated inversion-recovery (FLAIR) images demonstrated diffuse small hyperintense lesions predominantly involving the corpus callosum, white matter, cerebral cortex, and deep gray structures. During the whole course in the two patients, 437, 295, and 113 lesions were depicted on FLAIR images, T2-weighted images, and DWIs, respectively. With the aggravation and mitigation of the clinical symptoms, the size and number of the lesions changed over time. Of 65 lesions with measured ADCs, six had restricted ADCs (5.29-6.91 x 10(-4) mm(2)/s), and 29 had elevated ADCs (8.02-13.5 x 10(-4) mm(2)/s). With disease progression, ADCs in the NLWM changed from normal to elevated; this corresponded to the diffuse signal-intensity change seen in the white matter. CONCLUSION: FLAIR imaging is the most sensitive sequence for detecting lesions of Susac syndrome. DWI is useful in demonstrating the heterogeneous nature of lesions, depicting occult abnormalities in the white matter, elucidating underlying pathologic processes, and conducting patient follow-up.     

Diffusion-weighted echoplanar MR imaging of the salivary glands

OBJECTIVE: We determined the apparent diffusion coefficients of normal and dysfunctional salivary glands. SUBJECTS AND METHODS: A diffusion-weighted single-shot spin-echo type of echoplanar MR imaging was performed on the parotid or submandibular glands, or both, in 36 healthy subjects, 20 patients with Sj?gren's syndrome, and six patients with sialoadenitis. The apparent diffusion coefficient of the salivary gland was calculated using two b factors (b = 500 and 1,000 sec/mm(2)). RESULTS: The apparent diffusion coefficient was lower in the parotid glands (0.28 x 10(-3) mm(2)/sec) than that of the submandibular glands (0.37 x 10(-3) mm(2)/sec). The apparent diffusion coefficient was increased in sialoadenitis, whereas it decreased with abscess formation. The apparent diffusion coefficients of the parotid glands in patients with Sj?gren's syndrome correlated with the salivary flow rates but not with the sialographic gradings of the glands. We also found a correlation of the decreases in apparent diffusion coefficients with the severity of gland damage as assessed on T1-weighted MR images. CONCLUSION: Diffusion-weighted echoplanar MR imaging may reveal diseased states of the salivary glands.     

Apparent diffusion coefficient determination in normal fetal brain: a prenatal MR imaging study

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging studies of normal brain development have focused on premature babies who were free of focal lesions on conventional MR images. The condition of prematurity, however, is dissimilar to intrauterine life. We sought to establish normal values of fetal brain apparent diffusion coefficient (ADC) to highlight its abnormal changes in pathologic conditions and to obtain information about normal brain development. METHODS: We measured the ADC, in utero, by using an echo-planar three-axes diffusion-sensitized sequence (b factor, 0 and 600 s/mm(2)), in frontal and occipital white matter and basal ganglia gray matter of 15 fetuses. Their gestational ages ranged from 22 to 35 weeks, and the postnatal MR images or sonograms revealed normal brain. RESULTS: Mean ADC value was 1.96 +/- 0.1 micro m(2)/ms (SD) in frontal white matter, 1.95 +/- 0.1 micro m(2)/ms in occipital white matter, and 1.56 +/- 0.1 micro m(2)/ms in basal ganglia. A significant negative correlation between ADC and gestational age was found for basal ganglia, whereas only a trend was present for frontal white matter. CONCLUSION: Although moderately higher, the ADC determinations we obtained are consistent with those reported in the literature in postnatal studies performed in premature babies.     

van der Knaap syndrome: MR imaging findings including FLAIR, diffusion imaging, and proton MR spectroscopy

A patient is reported with diffuse leukoencephalopathy associated with cystic degeneration of the white matter of the brain (van der Knaap syndrome). The changes were studied by fluid attenuated inversion recovery (FLAIR), and diffusion-weighted MR imaging. The FLAIR sequence revealed suppressed signal of the cysts, and widespread high-signal white matter changes associated with thinned cortices. On diffusion-weighted MR imaging, apparent diffusion coefficient (ADC) values ranged from 3.0 × 10^–3 to 2.7 × 10^–3 mm²/s in the temporal cysts, similar to that of CSF. The ADC values within the parenchyma ranged between 2 × 10^–3 and 2.1 × 10^–3 mm²/s, a value falling between normal parenchyma and cerebrospinal fluid, compared with a control group of three healthy subjects. The changes were also evaluated by proton MR spectroscopy, and were compared with a control group of 12 cases. Magnetic resonance spectroscopy revealed apparently increased NAA/Cr ratios in most parts of the brain. The NAA/Cho ratios were either high or low, and the Cho/Cr ratios were increased or normal in different regions. Received: 27 October 1999; Revised: 9 December 1999; Accepted: 20 December 1999     

Parenchymal abnormalities associated with cerebral venous sinus thrombosis: assessment with diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: The common entity cerebral venous sinus thrombosis is associated with the poorly characterized imaging finding of parenchymal abnormalities; diffusion-weighted imaging has offered some insight into these manifestations. We assessed the relationship between the diffusion constant from apparent diffusion coefficient (ADC) maps in patients with cerebral venous thrombosis (CVT) with follow-up imaging findings and clinical outcome. METHODS: We evaluated the medical records and T2-weighted MR images of 13 patients with CVT complicated by intraparenchymal abnormality. Diffusion-weighted (DW) images and ADC maps were evaluated for increased, decreased, or unchanged signal intensity and were compared with signal intensity of contralateral, normal-appearing brain. In addition, ADCs were obtained in nine pixel regions of interest in abnormal regions in eight of the 13 patients. RESULTS: Eight patients had superficial CVT, and five had superficial and deep CVT. CVT of deep veins was associated with deep gray nucleus and deep white matter abnormalities, whereas superficial CVT was associated with cortical and subcortical abnormalities. Twenty-four nonhemorrhagic lesions were identified in 10 of 13 patients on the basis of follow-up imaging findings. Four patients without seizures had lesions with decreased diffusion that appeared hyperintense on follow-up T2-weighted images, three patients with seizures had lesions with decreased diffusion that resolved, and seven patients had lesions with increased diffusion that resolved. Three of 10 patients had more than one lesion type. No difference was noted in mean ADCs for lesions with decreased diffusion that resolved compared with lesions with decreased diffusion that persisted. CONCLUSION: DW imaging in these patients disclosed three lesion types: lesions with elevated diffusion that resolved, consistent with vasogenic edema; lesions with low diffusion that persisted, consistent with cytotoxic edema in patients without seizure activity; and lesions with low diffusion that resolved in patients with seizure activity. This information may be important in prospectively determining severity of irreversible injury and in patient treatment.