Diagnosis of acute brain-stem infarcts using diffusion-weighed MRI

There are many reports on acute cerebral infarcts diagnosed by diffusion-weighted MRI (DWI), but few describe brain-stem infarcts diagnosed by this method. Using the apparent diffusion coefficient (ADC), we studied 18 consecutive patients with brain-stem infarcts who underwent DWI during the acute phase. We calculated and compared the ADC ratio (lesion ADC/contralateral ADC) in 10 patients with brain-stem and 23 with supratentorial cortical infarcts examined within 24 h of the onset of stroke. Ischaemic brain-stem lesions were detected in all 15 patients who underwent DWI more than 3 h after the onset, but not in two who had DWI within 3 h of the onset; their ADC ratio was more than 0.95. ADC ratios in patients with brain-stem infarcts decreased as the interval between onset and DWI increased; the decrease was slower than in patients with supratentorial cortical infarcts.     

Persistent high signal on diffusion-weighted MRI in the late stages of small cortical and lacunar ischaemic lesions

Diffusion-weighted imaging (DWI) is very sensitive to early brain infarcts. However, the late stages have been insufficiently studied. Infarcts in small vessel disease are often multiple and of different ages, and differentiation between new and old lesions might be difficult. We have therefore studied the change with time in DWI of small (< 3 ml) ischaemic lesions. We imaged 21 patients with an acute lacunar syndrome and a lesion visible on early DWI. They all had three MRI examinations 12-58 h (early), 7-16 and 54-144 days after the onset of stroke; 10 patients with high DWI signal on the third examination had a fourth examination 12-28 months after the stroke. MRI was performed at 1.5 T, using echo-planar DWI with 7 b-values from 0 to 1200 x 10(6) s/m2 and conventional T2-weighted imaging. After 7-16 days 18 of 21 lesions gave high signal on DWI, and 12/16 measurable lesions had a decreased apparent diffusion coefficient (ADC). After 54-144 days ten lesions still gave high DWI signal and two still had an ADC below normal. On the fourth examination there was no remaining high DWI signal and all ADC were higher than normal.     

Transient detection of early wallerian degeneration on diffusion-weighted MRI after an acute cerebrovascular accident

We report three patients with a cerebrovascular accident studied serially by MRI, including diffusion-weighted imaging (DWI). In case 1, DWI 1 day after the onset of left frontoparietal cortical infarcts showed no abnormal signal in the left corticospinal tract. DWI 12 days after onset showed high signal in the corticospinal tract, interpreted as early wallerian degeneration. This had disappeared by 22 days after onset. In case 2, DWI obtained 7 days after the onset of a right internal capsule lacunar infarct showed high signal from the right corticospinal tract in the brainstem, which was less marked 15 days after onset. In case 3, MRI on postnatal day 7 showed a cerebral haemorrhage in the right corona radiata and high signal from the right corticospinal tract on DWI. The latter disappeared by day 23. DWI shows early wallerian degeneration; transient signal abnormalities within 2 weeks of stroke should not be mistaken for new ischaemic lesions.     

Silent embolism in diagnostic cerebral angiography: detection with diffusion-weighted imaging

Angiography has known and documented risks of neurological events. We prospectively studied 20 patients who underwent diagnostic cerebral angiographic examinations and diffusion-weighted MRI (DWI). Eighteen patients had DWI before and after their angiogram, whereas two patients had a DWI only after their angiogram (DWI was normal in both of these patients). No clinical neurological deficits were detected in any of our patients after angiography, but in three of 20 patients there was a new hyperintense signal abnormality found on DWI. Diffusion-weighted MRI provides an objective means of detecting both clinical and subclinical neurological events. Diffusion-weighted imaging might therefore provide an easier method of assessing complication rates in cerebral angiography by reducing the number of patients required for meaningful statistical analysis.     

Diffusion-weighted imaging in ischaemic stroke: a follow-up study

Diffusion-weighted (DWI) echo-planar (EPI) MRI has been used for imaging acute ischaemic stroke. We used DWI and conventional spin-echo (SE) MRI to study the dynamics of ischaemic human stroke. We examined 30 patients (mean age 57.5 years, range 27–82 years, median 57 years) with a diagnosis of stroke. They were examined in the acute (120 min to 47 h, mean 15.3 h), subacute (8 days) and chronic (2–3 months) stages of ischaemia using clinical scores and MRI. Imaging was performed on an 1.5-T imager. Anisotropic DWI with diffusion gradients in all three axes, an isotropic tensor trace pulse DWI sequence and SE MRI were used. In all patients both DWI sequences showed a decrease in the apparent diffusion coefficient (ADC) in the acute stage, even when SE images did not reveal signal abnormalities. Clinical features correlated with lesion site but not size. The ADC was initially 19.6–43 % less than that of nonischaemic tissue and increased to normal after 7 days in conventionally treated patients and after 2–5 days in patients who underwent intra-arterial fibrinolysis. In the chronic stage the ADC rose by up to 254.4 %. In patients who did not undergo fibrinolysis DWI changes correlated with the final infarct size (P < 0.05). It was possible to differentiate acute from chronic ischaemic lesions. We conclude that DWI is a sensitive and practicable tool for detecting early cerebral ischaemia. It is possible to predict in the acute stage the final size of an infarct. DWI may be helpful for clinical decisions and for monitoring therapy. Received: 1 March 1999/Accepted: 13 July 1999     

Patterns of complications of neonatal and infant meningitis on MRI by organism: a 10 year review

Introduction

Imaging of meningitis in neonates and infants is not routine, but is frequent for complications. Aside from tuberculosis and herpesvirus, imaging findings related to most responsible pathogens are thought to be nonspecific, but few studies exist. We reviewed the imaging features of complicated meningitis in infants and neonates at our hospital in the past decade, hypothesizing that patterns of complications might be more specific than previously recognized.

Methods

10 yr retrospective review of magnetic resonance imaging (MRI) and microbiology data for all neonates (age <30 d) and infants (age <1 yr) imaged for possible complications of meningitis at a tertiary children's hospital.

Results

We had 63 patients (25 neonates, 38 infants). The 3 most common pathogens were streptococcal species (n = 32, mean age 4.7 mo), E. coli (n = 9, mean 1.2 mo), and herpes simplex virus (n = 4). The most common findings were meningeal enhancement (78% of those given IV contrast), infarct (52%), subdural collection (35%), and ventriculomegaly (32%). E. coli presented much more frequently with ventriculomegaly (64% vs. 22%) than streptococcal species. Extensive infarcts were typical of streptococcal meningitis (13/32, 41%) and rarely seen with other organisms (2/31, 6%, p = 0.001). All 3 cases of Serratia meningitis had large parenchymal abscesses, and 2/4 cases of meningococcus had occipital cortical necrosis.

Conclusion

Although overlap was present, each organism responsible for neonatal/infant meningitis produced an identifiable pattern of complications on MRI. Recognising these patterns can help the radiologist suggest possible diagnosis and influence early management.     

Diffusion-weighted MRI for monitoring neurovascular interventions

Carotid stenting is increasingly considered as treatment for carotid artery disease. A reliable noninvasive method is desirable for assessing the safety of the procedure. Diffusion-weighted MRI (DWI) is sensitive to early brain ischaemia which becoming widely available and might therefore serve this purpose. We prospectively studied 19 patients referred for investigation of carotid artery disease by echo-planar whole-brain DWI before and within 24 h of stenting. The images obtained at a high b value were examined by two independent blinded reviewers for new high-signal areas consistent with ischaemia. We found that 15 patients had no new changes after stenting. One patient showed enlargement of a posterior watershed lesion after the procedure, which correlated with an increase in neurological deficit. Three other patients had presumed small embolic infarcts on DWI; two were asymptomatic and one had weakness at the hand that corresponded to an embolic infarct with a lesion on DWI in the hand notch. There were no false- positive or -negative results on DWI, when compared to clinical findings. DWI is thus a new method that can demonstrate neurologically silent or asymptomatic infants. It can be used to help to assess the safety and efficacy of neurovascular intervention. Received: 30 January 1999/Accepted: 12 July 1999     

CNS vasculitis and vasculopathy: efficacy and usefulness of diffusion-weighted echoplanar MR imaging

This pictorial essay illustrates the usefulness of diffusion-weighted imaging (DWI) on various vasculitis or vasculopathies, including systemic lupus erythematosus (SLE), Beh?et's disease, Churg-Strauss disease, primary angitis of the central nervous system (PACNS), giant cell arteritis, infectious vasculitis, sickle cell disease, drug-induced vasculopathy and hypertensive vasculopathy. DWI proves to detect small and active ischemic changes not visible on conventional MRI, and it clearly discriminates cytotoxic from vasogenic edema in patients with cerebral vasculitis or vasculopathy. DWI seems useful in assessing the treatment and patient outcome.     

常规MRI及DWI在新生儿低血糖脑损伤评估中的初步研究

目的:分析妊娠期糖尿病母亲分娩的足月低血糖新生儿脑损伤的常规磁共振和磁共振扩散加权成像(DWI)的特征。方法:随机回顾性分析妊娠期糖尿病母亲所分娩的足月低血糖新生儿48例,对患儿行动态血糖检测、常规MRI及DWI检查。对照分析血糖水平与影像学特征之间的关系。结果:常规MRI显示脑内异常信号8例(16.7%,8/48),11例(18.8%,11/48)DWI显示脑内异常信号,病灶部位均以顶、枕叶为著。反复发作性低血糖的脑损伤发生率高于短暂性低血糖(P0.05)。有症状低血糖患儿比无症状低血糖患儿的脑损伤发生率高,两者差异有统计学意义(P0.05)。结论:新生儿低血糖持续时间和程度与脑损伤密切相关,MRI特别是DWI对新生儿低血糖脑损伤可作出早期诊断和预后评估。     

Clinical single-shot diffusion-weighted MRI of the human brain on a short-bore medium-field imager

Diffusion-weighted MRI (DWI) is becoming important for assessment of acute stroke. Until recently single-shot DWI required expensive technology such as echo-planar imaging (EPI) available only at some research sites. A new medium-field (1.0 T) short-bore MR imager has been developed with which DWI data sets can be acquired. We prospectively studied 169 patients on this 1.0 T commercial system. After conventional imaging, DWI was performed with a single-shot multi-slice sequence with b values 0 an 900 s/mm², and with the gradients switched in three directions. The apparent diffusion coefficients were calculated with online calculation software. There were 50 patients with totally normal MRI, and 17 had strokes, these strokes were detected as areas of high signal on the images at a maximal b value. There was a drop in the ADC in ischaemic regions: in subacute infarcts, the values were between 0.41 and 0.531 × 10^{− 3} mm²/s. In old infarcts the ADC was 1.15 × 10^{− 3} mm²/s. Cerebrospinal fluid (CSF) gave low signal whereas areas in the brain had more intermediate intensities (CSF: 3.00; deep white matter: 0.75, cortical grey matter: 0.80, basal ganglia (thalamus): 0.70 and cerebellar white matter: 0.65 × 10^{− 3} mm²/s. Anisotropy was detected as areas of restricted diffusion along the tracts. These preliminary data show that DWI can be aquired successfully on a medium-field short-bore system. This should allow the technique to be implemented at more sites, therefore facilitating the diagnosis of acute stroke and rendering early intervention feasible. Received: 22 February 1999 Accepted: 27 April 1999     

Diffusion-weighted MRI of subdural and epidural empyemas

We reviewed diffusion-weighted images (DWI) from eight patients with subdural and four with epidural empyemas to assess the possibility of differentiating between these lesions by DWI. The signal intensities of the empyemas on DWI, and maps of the apparent diffusion coefficient (ADC) were analysed in seven patients. In seven of the eight patients with subdural empyema, the lesions appeared as areas of high signal. The ADC maps confirmed that these areas were the result of restricted diffusion. (In the remaining patient, the lesion showed a mixture of high and low signal.) The epidural empyemas contained areas of low signal in all four patients; part of the empyema was isointense or gave high signal in two. DWI may be an adjunct to conventional sequences for differentiating between subdural and epidural empyemas.     

扩散加权成像在早期诊断早产儿局灶性脑白质损伤及其预后的价值

目的探讨扩散加权成像(DWI)在早期诊断早产儿局灶性脑白质损伤(punctate white matter damage,PWMD)及其预后的价值。资料与方法搜集PWMD早产儿39例资料。患儿均在生后两周内进行头部MR、DWI(b=1000s/mm2)扫描且被确诊为PWMD。随访患儿头部MRI及生长发育情况。观察患儿早期DWI上病灶的数量、形状、分布;观察随访期病灶演变及对临床预后的影响。结果早期DWI上PWMD病灶数量<3个13例,3～10个10例,>10个16例;早期DWI上病灶呈簇状22例(簇状病灶组),呈线状11例(线状病灶组),呈混合型6例(混合型病灶组)。病灶分布只位于侧脑室旁者9例,只位于侧脑室后角旁者13例,位于半卵圆中心、侧脑室旁、后角、前角旁等部位者17例。随访0.6～22个月后,簇状病灶组22例头部MRI示病灶吸收消失,未见异常信号灶。20例智力发育指数(mental development index,MDI)>80,神经运动发育指数(psychomotor devel-opment index,PDI)>80,2例语言发育障碍,MDI<69,PDI>80;线状病灶组7例头部MRI出现...     

Analysis of central nervous system vasculitis with diffusion-weighted imaging and apparent diffusion coefficient mapping of the normal-appearing brain

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) is a novel method of studying the brain that creates tissue contrast secondary to water diffusion. Central nervous system (CNS) vasculitis is a rare inflammatory disease that continues to be difficult to diagnose and evaluate with MR imaging. DWI with apparent diffusion coefficient (ADC) analysis may demonstrate abnormalities within the brain that would otherwise be undetected by conventional imaging, thus aiding in the diagnosis and evaluation of patients with CNS vasculitis. MATERIALS AND METHODS: A retrospective analysis was performed of patients who were diagnosed with CNS vasculitis and had undergone DWI. A total of 15 patients who had DWI with b = 1000 were analyzed. Regions of interest were drawn in the anterior, central, and posterior regions of white matter (WM) at 3 levels. Regions of interest were also drawn bilaterally in the caudate heads, putamina, thalami, posterior internal capsules, and the cerebellar WM. ADC values were measured and compared with 15 healthy controls who were matched for age, sex, and MR imaging scanner. RESULTS: There was a significant increase in the ADC values (P<.00625) for the anterior WM, central WM, thalami, and posterior internal capsules in patients with CNS vasculitis. CONCLUSION: Diffuse increase in water diffusion was present in the normal-appearing brain in patients with CNS vasculitis, and these abnormalities were not demonstrated by conventional MR imaging sequences. The detection and quantification of ADC abnormalities may provide useful diagnostic information for patients with CNS vasculitis.     

MRI findings of Wernicke encephalopathy revisited due to hunger strike

BACKGROUND AND PURPOSE: The purpose of this study was to determine the characteristic magnetic resonance imaging (MRI) findings among a group of patients who presented with Wernicke encephalopathy (WE) due to the neurological complications of a long-term hunger strike (HS). METHODS: MRI studies also including the fluid-attenuated inversion recovery (FLAIR) sequence and diffusion-weighted imaging (DWI) of six male patients with WE aged from 25 to 38 years (mean age 31 years) were evaluated. RESULTS: In all subjects, T2-weighted sequences, FLAIR and DWI revealed a signal hyperintensity within the posteromedial thalami and surrounding the third ventricle. In particular, on coronal images, the hyperintense areas around the third ventricle showed a suggestive "double wing" configuration. We observed an increased signal on proton-density and T2-weighted images in the mamillary bodies of three patients. Four patients demonstrated additional hyperintensities within the periaqueductal region and/or the tectal plate. At least one lesion area in five of six patients demonstrated contrast enhancement. CONCLUSION: The consistent imaging findings of our study suggest that MRI is a reliable means of diagnosing WE. Acute WE is sometimes underdiagnosed, yet early diagnosis and treatment of WE is crucial in order to avoid persistent brain damage. MRI, including postcontrast T1-weighted imaging, DWI beneath standardized T2-weighted imaging, and FLAIR sequences may prove to be a valuable adjunct to clinical diagnosis and to provide additional information in acute and/or subacute WE.     

Serial diffusion-weighted imaging in MELAS

Clinical features of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) resemble those of cerebral infarcts, but the pathogenesis of infarct-like lesions is not fully understood. To characterise these infarct-like lesions, we studied two patients with MELAS using diffusion-weighted (DWI) MRI before and after stroke-like episodes and measured the apparent diffusion coefficient (ADC) in the new infarct-like lesions. These gave high signal on DWI and had much higher ADC than normal-appearing regions. The ADC remained high even 30 days after a stroke-like episode then decreased in lesions, with or without abnormality as shown by conventional MRI. We speculate that early elevation of ADC in the acute or subacute phase reflects vasogenic rather than cytotoxic edema. The ADC of the lesions, which disappeared almost completely with clinical improvement, returned to normal levels, which may reflect tissue recovery without severe damage. To our knowledge, this is the first study of DWI in MELAS. Received: 13 September 1999/Accepted: 7 January 2000     

Predicting final infarct size using acute and subacute multiparametric MRI measurements in patients with ischemic stroke

PURPOSE: To identify early MRI characteristics of ischemic stroke that predict final infarct size three months poststroke. MATERIALS AND METHODS: Multiparametric MRI (multispin echo T2-weighted [T2W] imaging, T1-weighted [T1W] imaging, and diffusion-weighted imaging [DWI]) was performed acutely (<24 hours), subacutely (three to five days), and at three months. MRI was processed using maps of apparent diffusion coefficient (ADC), T2, and a self-organizing data analysis (ISODATA) technique. Analyses began with testing for individual MRI parameter effects, followed by multivariable modeling with assessment of predictive ability (R(2)) on final infarct size. RESULTS: A total of 45 patients were studied, 15 of whom were treated with tissue plasminogen activator (tPA) before acute MRI. The acute DWI and DWI-ISODATA mismatch lesion size, and the interactions of ADC, T2, and T2W imaging lesion with tPA remained in the final multivariable model (R(2) = 70%). A large acute DWI lesion or DWI < ISODATA lesion independently predicted increase in the final infract size, with predictive ability 68%. Predictive ability increased (R(2) = 83%) when subacute MRI parameters were included along with acute DWI, DWI-ISODATA mismatch, and acute T2W image lesion size by tPA treatment interaction. Subacute DWI > acute DWI lesion size predicted an increased final infarct size (P < 0.01). CONCLUSION: Acute-phase DWI and DWI-ISODATA mismatch strongly predict the final infarct size. An acute-to-subacute DWI lesion size change further increases the predictive ability of the model.     

The value of diffusion-weighted imaging for prediction of lasting deficit in acute stroke: an analysis of 134 patients with acute neurologic deficits

Acute stroke is one of the three major causes of death and disability in the United States. Now that new, and possibly effective therapy is becoming available, accurate, rapid diagnosis is important to provide timely treatment, while avoiding the risk of complications from unnecessary intervention. Our objective was to test the hypothesis that use of echo-planar (EPI) diffusion-weighted imaging (DWI) is more accurate than conventional T₂ weighted MRI in predicting progression to stroke in patients with acute ischemic neurologic deficits. We studied 134 patients presenting with acute neurologic deficits to a community hospital emergency room with both conventional MRI and DWI within 72 h of the onset of the acute deficit. We found DWI significantly more sensitive to permanent neurologic deficit at discharge (sensitivity 0.81) than conventional MRI (sensitivity 0.41). When available, DWI should be considered for routine use in patients being imaged for acute stroke. Received: 21 January 2000 Accepted: 7 October 2000     

Presidential address

Introduction The aim of this prospective study was to analyse small band-like cortical infarcts after subarachnoid haemorrhage (SAH) using magnetic resonance imaging (MRI) with reference to additional digital subtraction angiography (DSA). Methods In a 5-year period between January 2002 and January 2007 10 out of 188 patients with aneurysmal SAH were evaluated (one patient Hunt and Hess grade I, one patient grade II, four patients grade III, two patients grade IV, and two patients grade V). The imaging protocol included serially performed MRI with diffusion- and perfusion-weighted images (DWI/PWI) at three time points after aneurysm treatment, and cerebral vasospasm (CVS) was analysed on follow-up DSA on day 7±3 after SAH. Results The lesions were located in the frontal lobe (n=10), in the insular cortex (n=3) and in the parietal lobe (n=1). The band-like infarcts occurred after a mean time interval of 5.8 days (range 3–10 days) and showed unexceptional adjacent thick sulcal clots. Seven out of ten patients with cortical infarcts had no or mild CVS, and in the remaining three patients DSA disclosed moderate (n=2) or severe (n=1) CVS. Conclusion The infarct pattern after aneurysmal SAH includes cortical band-like lesions. In contrast to territorial infarcts or lacunar infarcts in the white matter which develop as a result of moderate or severe proximal and/or distal vasospasm visible on angiography, the cortical band-like lesions adjacent to sulcal clots may also develop without evidence of macroscopic vasospasm, implying a vasospastic reaction of the most distal superficial and intraparenchymal vessels.     

Asymptomatic choroid plexus cysts in the lateral ventricles: an incidental finding on diffusion-weighted MRI

We assessed the role of diffusion-weighted imaging (DWI) in the detection of choroid plexus cysts. We reviewed more than 1000 patients who had undergone MRI in a 1-year period. We reviewed echo-planar DWI with b=1000 s/mm(2), acquired at 1.0 tesla, for any difference in signal intensity which might indicate choroid plexus cysts. On conventional images, all cystic lesions were isointense with cerebrospinal fluid, and 72 cysts could not be identified. On DWI, 90 rounded high-signal foci were detected in 58 patients; 64 cysts were bilateral. Focal ventricular expansion due to large cysts was observed in nine cases. DWI were found to show choroid plexus cysts undetected within the cerebrospinal fluid on conventional images.     

Application of transcranial Doppler sonography in children with acute neurologic events due to primary cerebral and West Nile vasculitis

We describe the use of serial transcranial Doppler studies to evaluate neurovascular disease in three girls presenting with acute stroke due to primary cerebral vasculitis (n = 2) and West Nile vasculitis (n = 1). Correlation of abnormal findings on transcranial Doppler sonography was compared with those of MR angiography and conventional angiography in each child. All three girls had left middle cerebral artery infarcts on MR imaging, with an abnormal left middle cerebral artery detected by MR angiography, conventional angiography, and transcranial Doppler sonography in each child. In all three cases, findings of the transcranial Doppler sonography, MR imaging, and catheter angiography were concordant.