West Nile virus infection: MR imaging findings in the nervous system

BACKGROUND AND PURPOSE: West Nile virus (WNV) infection is an ongoing seasonal epidemic. We correlated the MR imaging findings with the clinical presentations and outcomes of WNV infection. METHODS: We reviewed 14 brain and three spinal MR images: nonenhanced and contrast-enhanced T1-weighted images (T1WIs) and T2-weighted images (T2WIs), nonenhanced fluid-attenuated inversion recovery (FLAIR) images (11 patients) and enhanced FLAIR images (three patients), with diffusion-weighted (DW) images and apparent diffusion coefficient maps. WNV infection was diagnosed by means of enzyme-linked immunosorbent assay with a plaque reduction neutralization test. We also correlated the MR findings with the clinical presentation, course, and outcome to determine their prognostic importance. RESULTS: MR imaging findings included: 1) normal (five patients); 2) DW imaging-only abnormalities in the white matter, corona radiata, and internal capsule (four patients); 3) hyperintensity on FLAIR images and T2WIs in the lobar gray and white matter, cerebellum, basal ganglia, thalamus and internal capsule, pons and midbrain (three patients); 4) meningeal involvement (two patients); and 5) spinal cord, cauda equina, and nerve root involvement (three patients). All patients with finding 1 and all but one with finding 2 recovered completely. Two patients with finding 3 died. Those with finding 4 or 5 had residual neurologic deficits that were severe or moderate to severe, respectively. CONCLUSION: Patients with normal MR images or abnormalities on only DW images had the best prognosis, while those with abnormal signal intensity on T2WI and FLAIR images had the worst outcomes. No definite predilection for any specific area of the brain parenchyma was noted.     

Thalamic involvement in sporadic Creutzfeldt-Jakob disease: a diffusion-weighted MR imaging study

BACKGROUND AND PURPOSE: Recent neuropathologic research suggests thalamic involvement in sporadic Creutzfeldt-Jakob disease (sCJD), which has been disregarded in imaging studies. Diffusion-weighted (DW) MR imaging has the highest sensitivity for the detection of signal intensity (SI) abnormalities in CJD. We hypothesized that pathologic changes in the thalamus in sCJD can be detected by using a subtle analysis of DW MR imaging. METHODS: Six sCJD patients and nine healthy controls were examined with a 1.5-T system by using DW single-shot spin-echo echo planar (b = 0, 1000 s/mm(2)), T2-weighted turbo spin-echo, and fluid-attenuated inversion recovery sequences. One patient was examined serially (3, 4, and 8 months after onset of symptoms). MR images were reviewed for SI changes in the striatum, hippocampus, mediodorsal thalamic nucleus (MD), and pulvinar thalami. Apparent diffusion coefficients (ADCs) were measured in these areas. RESULTS: All sCJD patients showed increased SI on DW images in the striatum bilaterally. ADCs in these areas were significantly reduced. Four of six sCJD patients showed increased SI on DW images in the pulvinar thalami, whereas ADCs were significantly reduced in all patients (mean ADC +/- SEM: in patients with SI changes, 701 +/- 38; in patients without SI changes, 684 +/- 37; in controls, 853 +/- 15 [P <.0001]). No patient showed SI changes in the MD on DW images, whereas ADCs were significantly reduced in all (664 +/- 28 as compared with 800 +/- 24 in controls [P =.0011]). Serial measurements in one sCJD patient showed ADC reduction in the pulvinar thalami preceding the SI changes on DW images. CONCLUSION: A quantitative analysis of DW images with ADC measurements shows slight MR imaging changes in the thalamus in sCJD when abnormal SI may not be present.     

Pattern of cortical changes in sporadic Creutzfeldt-Jakob disease

BACKGROUND AND PURPOSE: High cortical signal intensity on diffusion-weighted (DW) or fluid-attenuated inversion recovery (FLAIR) images is increasingly described in sporadic Creutzfeldt-Jakob disease (sCJD). The aim of this study was to assess the extent and location of high cortical signal intensity, to investigate whether DW or FLAIR is superior in showing changes in cortical signal intensity, and to find out whether the distribution of the signal intensity changes is random or follows a common pattern. MATERIALS AND METHODS: We analyzed FLAIR and DW MR imaging scans of 39 patients with sCJD for hyperintense cortical signal intensity. We compared the sensitivity of the DW and FLAIR scans. We correlated the extent and location of the cortical signal intensity changes with concomitant changes in deep gray matter and the genotype of codon 129 of the prion protein gene. RESULTS: There was high signal intensity in the insula, the cingulate gyrus, and the superior frontal gyrus in 95%. The cortical areas near the midline also frequently showed the abnormal signal intensity (precuneus 87%, paracentral lobe 77%). The precentral and postcentral gyri were affected less frequently (41% and 28%, respectively). The DW MR imaging showed the cortical changes more effectively than FLAIR. There was no correlation between the distribution of changes and additional signal alterations in deep gray matter or the genotype of codon 129. CONCLUSION: The distribution of cortical signal intensity abnormalities in patients with sCJD follows a common pattern, affecting mainly the cortical areas near the midline, the insula, cingulum, and the superior frontal cortex. DW imaging is superior to FLAIR in the detection of cortical high signal intensity.     

Arterial hyperintensity on fast fluid-attenuated inversion recovery images: a subtle finding for hyperacute stroke undetected by diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging is generally acknowledged to be more sensitive in detecting acute stroke than is conventional MR imaging. Our purpose in the present study was to evaluate the utility of fast fluid-attenuated inversion recovery (FLAIR) MR imaging compared with that of diffusion-weighted MR imaging for the diagnosis of hyperacute stroke. METHODS: We reviewed patient records and cerebral MR images from all patients in a 13-month period from whom diffusion-weighted and fast-FLAIR imaging were obtained within 6 hours after symptom onset (n = 11). Special attention was paid to the presence or absence of arterial hyperintensity on FLAIR images and abnormally high-signal regions on diffusion-weighted images in the affected vascular territories. RESULTS: Arterial hyperintensity was found in eight of 11 patients, all of whom had embolic or thrombotic infarctions with middle cerebral arterial (MCA) distribution. Arterial hyperintensity was negative in the remaining three patients; the vascular territories were the posterior circulation region in two of these patients and the MCA region in one, and the types of infarction in these same patients were lacunar in two and embolic in one. Regions with high-signal diffusion abnormalities relevant to the patients' symptoms were found in 10 of 11 patients. One patient showed no diffusion abnormalities but the presence of arterial hyperintensity in the affected MCA territory on the initial MR examination, and manifested embolic infarction along with arterial hyperintensity on the initial FLAIR image. CONCLUSION: Although diffusion-weighted MR imaging is highly sensitive to stroke, diffusion-weighted MR imaging alone may not rule out a possible infarction. Arterial hyperintensity on FLAIR images can precede diffusion abnormalities and may provide a clue to the early detection of impending infarction.     

Diffusion abnormality of deep gray matter in external capsular hemorrhage

BACKGROUND AND PURPOSE: To our knowledge, diffusion abnormality of the unaffected deep gray matter during striatocapsular hemorrhage has not been previously described in the literature. We report the presence of the diffusion abnormality separated from hematoma in patients with external capsular (lateral striatocapsular) hemorrhage and suggest the plausible mechanisms of diffusion signal intensity change. METHODS: We retrospectively reviewed MR images in 28 consecutive patients with spontaneous striatocapsular hemorrhage and evaluated signal intensity changes at sites separated from the hemorrhage and the lesions on diffusion-weighted (DW) images. Apparent diffusion coefficients (ADCs) of the lesions were measured, and volume changes in the deep gray matter were assessed at follow-up. RESULTS: On DW images, hyperintensity of deep gray matter was found in nine patients (25%). In all patients with DW imaging abnormality, the hemorrhage was located in the external capsule, and the interval from hemorrhagic ictus to MR imaging study was 8-54 days. Hyperintensity of the deep gray matter was seen in the caudate (n = 8), putamen (n = 7), thalamus (n = 5), and substantia nigra (n = 2). Mean relative ADC ratios of the diffusion abnormality were 0.76 +/- 0.10 in the caudate, 0.79 +/- 0.07 in the putamen, and 0.85 +/- 0.11 in the thalamus. DW imaging abnormality disappeared with mild atrophy in two patients who underwent follow-up imaging. CONCLUSION: External capsular hemorrhage may be uncommonly accompanied by diffusion abnormality in the striatum or thalamus at follow-up, and the lesion should not be misdiagnosed as new-onset infarction. Secondary neuronal degeneration may play an important role in the development of diffusion abnormality.     

Fluid-attenuated inversion-recovery MR imaging in acute and subacute cerebral intraventricular hemorrhage.

BACKGROUND AND PURPOSE: Fluid-attenuated inversion-recovery (FLAIR) MR imaging may show subarachnoid hemorrhage (SAH) with high sensitivity. We hypothesized that the FLAIR technique is effective and reliable in the diagnosis of cerebral intraventricular hemorrhage (IVH). METHODS: Two observers evaluated the 1.5-T MR fast spin-echo FLAIR images, T1- and T2-weighted MR images, and CT scans of 13 patients with IVH and the FLAIR images of 40 control subjects. RESULTS: IVH appeared bright on the FLAIR images obtained during the first 48 hours and was of variable appearance at later stages. FLAIR MR imaging detected 12 of 13 cases of IVH; no control subjects were falsely thought to have IVH (92% sensitivity, 100% specificity). However, IVH could not be fully excluded in the third ventricle (20%, n = 8) or in the fourth ventricle (28%, n = 11) on some control images because of CSF pulsation artifacts. Two cases had CT-negative IVH seen on FLAIR images. One case had FLAIR-negative IVH seen by CT. Although the sensitivities of conventional MR imaging (92%) and CT (85%) were also high, FLAIR imaging showed IVH more conspicuously than did standard MR imaging and CT in 62% of the cases (n = 8). FLAIR was as good as or better than CT in showing IVH in 10 cases (77%). FLAIR images showed all coexisting SAH. CONCLUSION: FLAIR MR imaging identifies acute and subacute IVH in the lateral ventricles with high sensitivity and specificity. In cases of subacute IVH, conventional MR imaging complements FLAIR in detecting IVH. The usefulness of the FLAIR technique for detecting third and fourth ventricular IVH may be compromised by artifacts. Blood hemoglobin degradation most likely causes the variable FLAIR appearance of IVH after the first 48 hours.     

Intracranial epidermoid cysts: diffusion-weighted, FLAIR and conventional MR findings

PURPOSE: To compare diffusion-weighted echo-planar imaging (DW) with spin-echo (SE), and fluid-attenuated inversion recovery (FLAIR) sequences in the evaluation of epidermoid cysts (ECs), and to evaluate T2 shine-through effect. MATERIALS AND METHODS: Fifteen patients were imaged prospectively in two different 1.5 T magnetic resonance (MR) units with standard head coils with SE, FLAIR and DW echo planar imaging sequences. The qualitative and quantitative assessments were performed by two radiologists in consensus. Apparent diffusion coefficient (ADC) values were obtained from all ECs. Exponential DW images are obtained in 11 cases to eliminate T2 shine-through effects. The results are analyzed with variance analysis (ANOVA) and Bonferroni t method. RESULTS: FLAIR sequence was superior to T1- and T2-weighted sequences in showing ECs. In 13 cases, the borders of the lesions could be delineated from the surrounding structures with only DW imaging where ECs were markedly hyperintense. The ADC values of ECs are significantly lower than CSF (P < 0.001), and significantly higher than deep white matter (P < 0.01). On exponential DW images, ECs had similar intensity with brain parenchyma showing that the real cause of the hyperintensity of the lesions on trace images is the enhanced T2 effect of the tissue. CONCLUSION: FLAIR sequence is superior to the conventional MR sequences in demonstrating the ECs and DW imaging is superior to other MR sequences in delineating the borders of the ECs. Exponential DW images had shown that the hyperintensity in the trace images are caused by increased T2 effect of the lesion rather than the decrease in ADC values.     

Sulcal hyperintensity on fluid-attenuated inversion recovery mr images in patients without apparent cerebrospinal fluid abnormality

OBJECTIVE: Failure to suppress cerebrospinal fluid (CSF) signal intensity (sulcal hyperintensity) on fluid-attenuated inversion recovery (FLAIR) images has been reported in patients with abnormal CSF, such as those with meningitis and subarachnoid hemorrhage. Our study investigates the clinical history and MR findings associated with sulcal hyperintensity on FLAIR images in patients without apparent CSF abnormality. SUBJECTS AND METHODS: Three hundred consecutive MR imaging examinations were prospectively screened for patients with sulcal hyperintensity on FLAIR images. Nine patients with clinical, CT, or laboratory evidence suggesting abnormal CSF were excluded. The distribution of sulcal hyperintensity on FLAIR images and associated abnormal enhancement were evaluated. The presence of the "dirty CSF" sign (mild increase in CSF signal on unenhanced T1-weighted images or mild decrease on T2-weighted images) in the corresponding hyperintense sulcus was also assessed. RESULTS: Twenty-six (8.9%) of the 291 patients had sulcal hyperintensity (16 focal, 10 diffuse) associated with 18 masses (6.1%) and eight vascular abnormalities (2.7%). Sulcal hyperintensity was frequently associated with the dirty CSF sign (69.2%) and abnormal contrast enhancement (overall, 96.2%; 88.5%, leptomeningeal; 53.8%, vascular enhancement). CONCLUSION: Our study shows that sulcal hyperintensity on FLAIR imaging can occur in patients without apparent CSF abnormality. Its frequent association with mass effect, vascular disease, abnormal vascular enhancement, and dirty CSF sign suggests that an increase in blood pool, a small amount of protein leakage, and the "flow-entering" phenomenon of the congested blood may contribute to sulcal hyperintensity on FLAIR images.     

Creutzfeldt-Jakob disease: comparative analysis of MR imaging sequences

BACKGROUND AND PURPOSE: MR imaging has played an increasingly important role in the diagnosis of Creutzfeldt-Jakob disease (CJD) since basal ganglia abnormalities on T2-weighted images have been described; thus, the aim of our study was to compare the value of different MR images in the diagnosis of CJD. METHODS: One hundred fifty-seven patients with CJD underwent MR imaging examinations. Ninety-two patients were neuropathologically confirmed, and 65 were clinically classified as having CJD through the CJD Surveillance Unit (probability of 95%). There was no standardized MR imaging protocol; thus, the examinations included 143 T2-weighted, 43 proton attenuation (PD)-weighted, 84 fluid-attenuated inversion recovery (FLAIR), and 44 diffusion-weighted images (DWI). The MR images were reviewed for pathologic changes of the basal ganglia, thalamus, and cerebral cortex. RESULTS: Cortical abnormalities were present in 70 patients (45%) and were visible in 80% (35/44) of all available DWI examinations. The basal ganglia were affected in 94 patients (60%), in particular in the caudate nucleus; the most sensitive sequences were DWI (64%) and PD-weighted (63%). A thalamic involvement was more frequently diagnosed on PD-weighted images (19%) and DWI (14%) than on FLAIR or T2-weighted images. CONCLUSION: PD-weighted images and DWI showed better results in the diagnosis of signal intensity changes in the basal ganglia compared with T2-weighted or FLAIR images; however, in the diagnosis of cortical changes, DWI was clearly superior. Our data suggest that DWI is the most sensitive MR imaging technique in the diagnosis of CJD.     

Increased signal in the subarachnoid space on fluid-attenuated inversion recovery imaging associated with the clearance dynamics of gadolinium chelate: a potential diagnostic pitfall

BACKGROUND AND PURPOSE: Hyperintense CSF in the subarachnoid space (SAS) on fluid-attenuated inversion recovery (FLAIR) imaging has been reported in numerous pathologic conditions, including subarachnoid hemorrhage, meningitis, meningeal carcinomatosis, superior sagittal thrombosis, adjacent tumors, status epilepticus, and stroke. It has also been reported in otherwise healthy patients undergoing anesthesia with supplemental oxygen. We present a series of 11 patients with hyperintense CSF signal intensity in the SAS on FLAIR imaging after previous administration of gadolinium chelate. MATERIALS AND METHODS: Head MR images of patients who had a prior gadolinium-enhanced body, spine, or brain MR imaging and who had increased signal intensity in the SAS on FLAIR images were prospectively and retrospectively reviewed. Correlation was made with the clinical and laboratory findings. RESULTS: Eight of the 11 patients had negative findings on lumbar punctures. Seven patients had either chronic renal insufficiency or acute renal failure, but the remaining 4 had normal renal function. Nine patients had no other significant intracranial abnormalities, and 2 patients had acute infarcts remote from the CSF hyperintensity. One patient had follow-up studies at 24 and 48 hours, documenting resolution of the CSF hyperintensities. CONCLUSION: Given the sharp rise in volume of contrast-enhanced MR imaging studies, it is inevitable that some patients will have undergone a contrast-enhanced MR imaging 24-48 hours before an MR imaging of the brain. The neuroradiologist should be aware that previous administration of gadolinium chelate can cause increased signal intensity in the SAS on FLAIR imaging in patients with or without a history of renal insufficiency and without abnormalities known to disrupt the blood-brain barrier.     

Acute methotrexate neurotoxicity: findings on diffusion-weighted imaging and correlation with clinical outcome

BACKGROUND AND PURPOSE: Acute lymphocytic leukemia (ALL) is a common malignancy of childhood treated with methotrexate (MTX), which is associated with acute neurotoxicity. We evaluated diffusion-weighted (DW) and conventional MR images in children with ALL and acute MTX-induced neurotoxicity, with clinical correlation. METHODS: Five patients aged 12-15 years underwent fluid-attenuated inversion recovery (FLAIR), T2-weighted fast spin-echo and gradient-echo, T1-weighted gadolinium-enhanced spin-echo, and DW imaging within 24 hours of symptom onset. Records were reviewed for the temporal relationship to MTX administration, strokelike symptoms, and neurologic outcome. RESULTS: Six strokelike events were temporally related to intrathecal MTX given 6-11 days before symptom onset. FLAIR images showed abnormal hyperintensity in the callosal splenium in one patient but were otherwise normal. Diffusion abnormalities were frontoparietal in three events and frontal in one; nonfluent aphasia was seen in all. Bilateral frontoparietal diffusion abnormalities were associated with bilateral upper-extremity weakness, right-sided hemiparesis, or left-sided hemiparesis (one patient each); one patient had mild facial droop. Unilateral precentral subcortical diffusion abnormality was associated with contralateral motor deficit and ipsilateral upper-extremity sensory loss. Strokelike symptoms resolved rapidly and were not associated with other signs of encephalopathy. Subsequent intrathecal MTX administration was not associated with recurrence in four patients. CONCLUSION: Diffusion abnormalities in acute MTX neurotoxicity indicated cerebral dysfunction but not necessarily overt structural injury to the cerebrum. Subsequent demyelination or gliosis could not be predicted on the basis of diffusion abnormalities. A single strokelike episode with diffusion abnormalities should not necessarily prompt modification of potentially curative chemotherapeutic regimens.     

West Nile virus meningoencephalitis: MR imaging findings

BACKGROUND AND PURPOSE: Reports of MR imaging in West Nile virus (WNV) meningoencephalomyelitis are few and the described findings limited. The purpose of this study was to review the spectrum of MR imaging findings for WNV meningoencephalomyelitis and investigate whether any of the findings correlates with clinical presentation of flaccid paralysis. METHODS: We reviewed the MR imaging findings of 17 patients with confirmed WNV encephalitis and/or myelitis. MR imaging brain studies were evaluated for location of signal intensity abnormalities, edema, hydrocephalus, or abnormal enhancement. MR imaging spine studies were evaluated for signal intensity abnormalities in cord and/or enhancement. RESULTS: Retrospective review of the MR imaging studies of 17 patients was performed by 2 neuroradiologists. Eleven of 16 brain MR images demonstrated abnormalities. Eight (50%) patients had abnormal studies related to meningoencephalitis. All 8 patients had abnormal findings in the deep gray matter and/or brain stem; 2 had additional white matter abnormalities. Three patients with abnormal MR studies of the spine had extremity weakness on examination. The imaging findings included abnormal signal intensity more pronounced in the ventral horns and/or enhancement around the conus medullaris and cauda equina. One patient had additional abnormalities in the pons. CONCLUSION: Abnormal MR imaging findings in patients with WNV meningoencephalomyelitis are nonspecific but not uncommon. Anatomic areas commonly affected are basal ganglia, thalami, mesial temporal structures, brain stem, and cerebellum. Extremity weakness or flaccid paralysis corresponds to spinal cord/cauda equina abnormalities.     

Role of fluid-attenuated inversion recovery in the diagnosis of meningitis: comparison with contrast-enhanced magnetic resonance imaging

OBJECTIVE: Fluid-attenuated inversion recovery (FLAIR) has shown promise in the detection of subarachnoid space disease. The exact role of FLAIR in the diagnosis of meningitis has not been established. The purpose of this study was to evaluate FLAIR in the detection of meningitis in comparison with contrast-enhanced T1-weighted images (T1WI) in a blinded-reader study. We describe hyperintense sulci (HS) on FLAIR sequence in meningitis in relation to cerebrospinal fluid (CSF) protein and effective echo time (TE). METHODS: Two observers blinded to clinical information reviewed magnetic resonance (MR) images of patients with the diagnosis of meningitis and those of age-matched controls. The diagnosis was confirmed from chart review and CSF results. FLAIR images were obtained with 2 different TE values of 120 milliseconds and 150 milliseconds. FLAIR changes were correlated with CSF protein concentration and contrast-enhanced T1WI. RESULTS: Twenty-eight MR images of meningitis patients were reviewed. There were 23 abnormal MR images including 16 abnormal FLAIR scans with hyperintense sulci and 23 with leptomeningeal enhancement on contrast-enhanced T1WI. HS on FLAIR correlated with leptomeningeal enhancement on contrast-enhanced T1WI. Four viral and 1 bacterial meningitis had normal MR images (FLAIR and postcontrast TIWI). Two different TE values were used: 120 milliseconds (n = 15) and 150 milliseconds (n = 13). All patients with effective TE of 150 milliseconds. and CSF protein of more than 132 mg/dL had hyperintense sulci whereas patients with effective TE of 120 milliseconds and CSF protein of 257 mg/dL or more had HS. CONCLUSIONS: The sensitivity of contrast-enhanced T1WI was higher than FLAIR. HS on FLAIR correlated with contrast enhancement on T1WI. However, the sensitivity of FLAIR depends on CSF protein concentration threshold for (CSF hyperintensity) for a given effective TE. FLAIR cannot replace contrast-enhanced T1WI in diagnosing meningitis.     

Posterior reversible encephalopathy syndrome: utility of fluid-attenuated inversion recovery MR imaging in the detection of cortical and subcortical lesions

BACKGROUND AND PURPOSE: Posterior reversible encephalopathy syndrome (PRES) is typically characterized by headache, altered mental functioning, seizures, and visual loss associated with imaging findings of bilateral subcortical and cortical edema with a predominantly posterior distribution. Our goal was to determine whether fluid-attenuated inversion recovery (FLAIR) imaging improves the ability to detect subtle peripheral lesions of PRES, as compared with conventional MR techniques. METHODS: Sixteen patients with clinical and imaging findings consistent with PRES were studied. Thirteen patients had undergone transplantation and had cyclosporin A neurotoxicity. Fast-FLAIR images were compared with spin-echo proton density- and T2-weighted images. RESULTS: FLAIR imaging improved diagnostic confidence and conspicuity of the T2 hyperintense lesions of PRES, typically in the subcortical white matter of the parietooccipital regions bilaterally. On all 23 abnormal MR studies, FLAIR was judged superior to proton density- and T2-weighted images for the detection of PRES in the supratentorial brain. In a mean of 6.7 of 23 studies, FLAIR findings prompted a raise in the grade of disease severity. FLAIR also showed cortical involvement in 94% of patients with PRES and in a mean of 46% of the total lesion burden. In four cases, subtle lesions were virtually undetectable without FLAIR. Brain stem or cerebellar disease was encountered in 56% of patients. CONCLUSION: FLAIR improves the ability to diagnose and detect subcortical and cortical lesions in PRES as compared with proton density- and T2-weighted spin-echo images. We therefore believe that FLAIR should be performed in patients with suspected PRES to allow more confident recognition of the often subtle imaging abnormalities.     

The magnetic resonance imaging appearances of the brain in acute carbon monoxide poisoning

AIMS: To describe the magnetic resonance imaging (MRI) appearances of the brain in acute carbon monoxide poisoning, the commonest cause of accidental poisoning in Europe and the U.S.A. To attempt to correlate the imaging findings with patient outcome as an aid to prognosis. MATERIALS AND METHODS: Brain MRI was performed on 19 consecutive patients, who had sustained acute carbon monoxide poisoning, as soon as possible after their referral to the regional Hyperbaric Unit at the Royal Hospital, Haslar. All patients were unconscious on arrival, and had received at least one treatment with hyperbaric oxygen by the time of first MR. The imaging findings were analysed independently by two experienced MR radiologists, with a third radiologist arbitrating on discrepant results. RESULTS: Thirteen male and six female patients, age range 21-70 years (mean 38.7 years) underwent MR an average of 35.6 h (range 6-126 h) following presentation at the referring centre. MR (at 0.5T) revealed abnormalities in the following areas: globus pallidus (n = 12); other basal ganglia [ n = 5: entire lentiform (globus pallidus and putamen), putamen alone, caudate nucleus, thalamus]; white matter (n = 6: periventricular, subcortical, other); cerebral cortex (n = 5), either localized or general; medial temporal lobe in the region of the hippocampus (n = 4). The majority of the patients with hyperintensity in the region of the hippocampus (n = 3) had no other area of cortical involvement. Two patients showed abnormalities in the cerebellum. Normal appearances were seen on the initial MR in seven patients. CONCLUSION: The appearances of the brain following acute CO poisoning are varied, and have previously been the subject of case reports or small studies, most of which have have addressed the delayed sequelae of this condition. This study, the first large series undertaken in the acute phase, confirms that, although the globus pallidus is the commonest site of abnormality in the brain, the effects of CO poisoning are widespread. The extent of damage correlates with clinical outcome, and therefore aids management and prognosis.     

Brain: gadolinium-enhanced fast fluid-attenuated inversion-recovery MR imaging

PURPOSE: To determine the clinical utility of gadolinium-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain by comparing results with those at gadolinium-enhanced T1-weighted MR imaging with magnetization transfer (MT) saturation. MATERIALS AND METHODS: In 105 consecutive patients referred for gadolinium-enhanced brain imaging, FLAIR and T1-weighted MR imaging with MT saturation were performed before and after administration of gadopentetate dimeglumine (0.1 mmol per kilogram of body weight). Pre- and postcontrast images were evaluated to determine the presence of abnormal contrast enhancement and whether enhancement was more conspicuous with the FLAIR or T1-weighted sequences. RESULTS: Thirty-nine studies showed intracranial contrast enhancement. Postcontrast T1-weighted images with MT saturation showed superior enhancement in 14 studies, whereas postcontrast fast FLAIR images showed superior enhancement in 15 studies. Four cases demonstrated approximately equal contrast enhancement with both sequences. Six cases showed some areas of enhancement better with T1-weighted imaging with MT saturation and other areas better with postcontrast fast FLAIR imaging. Superficial enhancement was typically better seen with postcontrast fast FLAIR imaging. CONCLUSION: Fast FLAIR images have noticeable T1 contrast making gadolinium-induced enhancement visible. Gadolinium enhancement in lesions that are hyperintense on precontrast FLAIR images, such as intraparenchymal tumors, may be better seen on T1-weighted images than on postcontrast fast FLAIR images. However, postcontrast fast FLAIR images may be useful for detecting superficial abnormalities, such as meningeal disease, because they do not demonstrate contrast enhancement of vessels with slow flow as do T1-weighted images.     

Assessment of transient ischemic attack with diffusion- and perfusion-weighted imaging

BACKGROUND: Diagnosing TIA can be difficult, since evidence of brain ischemia is habitually lacking on CT and conventional MR imaging. It has been suggested that patients with acute brain infarction on neuroimaging should be considered stroke cases instead of TIA, regardless of duration of symptoms, implying that optimal diagnostic methods need to be utilized. We therefore postulated that perfusion-weighted MR imaging (PW imaging) would be useful in the diagnosis of TIA. METHODS: Retrospective analysis of 22 patients with reversible neurologic symptoms lasting less than 24 hours, assessed with DW and PW imaging. RESULTS: MR imaging was abnormal in 15 patients (68%): 12 had abnormal DW imaging, four had both DW and PW imaging defects (all with a mismatch) and three had an isolated PW imaging abnormality. There were no differences in symptom duration, stroke etiology or cardiovascular risk factors between patients with abnormal MR imaging and those with unremarkable scan. Patients with mismatch were more likely to need conventional angiography or other cerebrovascular procedures. CONCLUSION: The combined use of DW imaging and PW imaging provided evidence of brain ischemia in most patients with clinical diagnosis of TIA. Prospective studies using follow-up MR imaging are required to determine the outcome of affected tissue, as well as the clinical implications of DW-PW imaging abnormalities.     

Brain imaging findings in pediatric patients with sickle cell disease

PURPOSE: To determine prevalence of imaging abnormalities in the brain of children with sickle cell disease (SCD) and to identify clinical and methodological factors that influence prevalence estimate. MATERIALS AND METHODS: Magnetic resonance (MR) imaging and MR angiographic findings for 185 patients with SCD examined at St Jude Children's Research Hospital since 1993 were reviewed. At least two readers independently reviewed images. Standard MR imaging criteria were used to identify lacunae, loss of white matter volume, encephalomalacia, or leukoencephalopathy. Patients were assigned grades to indicate limited or extensive abnormalities. Standard MR angiographic criteria were used to identify arterial tortuosity (limited vasculopathy) and stenosis or occlusion (extensive vasculopathy). Findings were evaluated as a function of patient clinical status (including stroke) and diagnosis. Recent methods (T1- and T2-weighted MR imaging plus fluid-attenuated inversion recovery [FLAIR] at 3-mm section thickness) were compared with older methods (T1- and T2-weighted MR imaging without FLAIR at 5-mm section thickness). RESULTS: At mean age of 10 years, overall prevalence of infarction, ischemia, or atrophy in patients with SCD was 44% (82 of 185), and prevalence of vasculopathy was 55% (102 of 185), without evidence of a significant referral bias. Twenty-six of 27 patients with clinical stroke had abnormal findings at imaging, but even if patients with stroke were excluded, 35% (56 of 158) had a "silent infarction" (MR imaging-visible injury without clinical stroke), and 49% (78 of 158) had abnormal findings at MR angiography. Patients with clinically severe disease had more abnormalities at MR imaging (P <.001) and MR angiography (P <.004) than did patients with milder disease. Severe vasculopathy was more prevalent in patients with hemoglobin SS than in those with hemoglobin SC (P <.001). Recent imaging methods showed more abnormalities than did older methods (P <.01). With newer methods, 43% (29 of 67) of patients had extensive abnormalities, whereas with older methods, 28% (33 of 116) had extensive abnormalities. CONCLUSION: Prevalence of ischemic brain injury in pediatric patients with SCD is substantially higher than was previously reported, in part because of improvements in imaging methods.     

Magnetoencephalographically directed review of high-spatial-resolution surface-coil MR images improves lesion detection in patients with extratemporal epilepsy

PURPOSE: To determine whether (a) interictal magnetoencephalographic (MEG) epileptiform activity corresponds to anatomic abnormalities at magnetic resonance (MR) imaging, (b) high-spatial-resolution MR imaging depicts lesions in regions without MEG spike activity, (c) MEG-directed review of high-spatial-resolution MR images enables detection of abnormalities not apparent on conventional MR images, and (d) MEG information results in a greater number of diagnosed lesions at re-review of conventional MR images. MATERIALS AND METHODS: Twenty patients with neocortical epilepsy were evaluated with MEG, conventional brain MR imaging with a head coil, and high-spatial-resolution MR imaging with either a surface coil (n = 17) or a high-spatial-resolution birdcage coil (n = 3). Abnormal MEG foci were compared with corresponding anatomic areas on conventional and high-spatial-resolution MR images to determine the presence (concordance) or absence (discordance) of anatomic lesions corresponding to foci of abnormal MEG activity. RESULTS: Forty-four epileptiform MEG foci were identified. Twelve foci (27%) were concordant with an anatomic abnormality at high-spatial-resolution MR imaging, and 32 foci (73%) were discordant. Results of high-spatial-resolution MR imaging were normal in eight patients, and 23 lesions were detected in the remaining 12 patients. Twelve lesions (52%) were concordant with abnormal MEG epileptiform activity, and 11 (48%) were discordant (ie, there was normal MEG activity in the region of the anatomic abnormality). At retrospective reevaluation of conventional MR images with MEG guidance, four occult gray matter migration lesions that had initially been missed were observed. An additional patient with MEG-concordant postoperative gliosis was readily identified with high-spatial-resolution MR images but not with conventional MR images. CONCLUSION: Review of MEG-localized epileptiform areas on high-spatial-resolution MR images enables detection of epileptogenic neocortical lesions, some of which are occult on conventional MR images.     

增强后液体衰减反转恢复序列MRI在颅内肿瘤诊断中的应用

目的 评价增强后液体衰减反转恢复序列（FLAIR）在颅内肿瘤诊断中的应用价值。方法 104例颅内肿瘤，经手术、病理证实共有病灶124个。分别行增强前、后T1WI和FLAIR扫描。由2名有经验的放射科医生对所有病例进行评价。评价内容包括：增强例数、增强病灶个数及强化病灶部位；对比度及增强率；病变大小和范围。结果行统计学分析。结果 104例中，增强后FLAIR（CEFLAIR）成像、增强SE T1WI（CET1WI）均显示98例有强化。CEFLAIR成像检出了117个强化灶，CE T1W1检出了120个。4个病灶仅在CEFLAIR显示而CET1WI未显示。另有7个病灶仅在CET1WI显示而CEFLAIR未显示。两者之信噪比（SNR）差异无统计学意义（t=1．10，P=0．270），脑灰白质对比度（GMC）、对比噪声比（CNR）及强化率（CER）差异均有统计学意义（t值分别为2．46、7．10、9．67，P值分别为0．015、0．000、0．000）。在显示病灶大小上，CEFLAIR成像明显大于CET1WI（t=4．13，P=0．000），在病灶范围上，有62例CEFLAIR成像较CET1WI大。CEFLAIR成像对位于脑沟、凸面、侧脑室旁及侧脑室内病灶的检出优于CET1WI，而对大脑半球及第四脑室内的病灶的显示不如CET1WI。结论 CEFLAIR成像与CET1WI比较，强化病灶数，两者无明显差别，强化程度CET1WI明显高于CEFLAIR成像，但两者对不同部位病灶的显示有明显差异，CEFLAIR成像显示病灶大小和范围明显大于CET1WI。两种序列相互补充，建议将CEFLAIR成像序列列为增强后常规序列。