In which patients is diffusion-weighted magnetic resonance imaging most useful in routine stroke care?

BACKGROUND AND PURPOSE: Magnetic resonance (MR) diffusion-weighted imaging (DWI) has been used extensively in hyperacute cortical ischemic stroke, but its broader role in the assessment of patients presenting at later times after a wider variety of strokes has been less widely studied. METHODS: The authors assessed the clinical usefulness of DWI across a range of patients referred prospectively as either inpatients or outpatients. Detailed clinical information was collected. Diffusion (DWI) and T2-weighted images were read separately and blindly to clinical details. The presence of any infarct and its type were noted. RESULTS: In 153 stroke patients, imaged at a median of 2 days (range, 6 hours to 77 days) after stroke, recent infarcts were identified more often on DWI (70%) than on T2-weighted MRI (32%) in all severities of stroke. The proportion of scans on which relevant lesions were only seen on DWI was greatest among milder strokes due to small cortical or lacunar infarcts and among patients imaged later rather than earlier after the stroke. CONCLUSIONS: DWI is clinically useful up to several weeks after stroke, not just within the first few hours, and especially in patients with minor strokes.

What is the best imaging strategy for acute stroke?

OBJECTIVES: To determine the cost-effectiveness of computed tomographic (CT) scanning after acute stroke. To assess the contribution of brain imaging to the diagnosis and management of stroke, and to estimate the costs, benefits and risks of different imaging strategies in order to provide data to inform national and local policy on the use of brain imaging in stroke. DESIGN: A decision-analysis model was developed to represent the pathway of care in acute stroke using 'scan all patients within 48 hours' as the comparator against which to cost 12 alternative scan strategies. SETTING: Hospitals in Scotland. PARTICIPANTS: Subjects were patients admitted to hospital with a first stroke and those managed as outpatients. INTERVENTIONS: The effect on functional outcome after ischaemic or haemorrhagic stroke, tumours or infections, of correctly administered antithrombotic or other treatment; of time to scan and stroke severity on diagnosis by CT or MRI; on management, including length of stay, functional outcome, and quality-adjusted life years (QALYs), of the diagnostic information provided by CT scanning; the cost-effectiveness (cost versus QALYs) of different strategies for use of CT after acute stroke. MAIN OUTCOME MEASURES: Death and functional outcome at long-term follow-up; accuracy of CT and MRI; cost of CT scanning by time of day and week; effect of CT diagnosis on change in health outcome, length of stay in hospital and QALYs; cost-effectiveness of various scanning strategies. RESULTS: CT is very sensitive and specific for haemorrhage within the first 8 days of stroke only. Suboptimal scanning used in epidemiology studies suggests that the frequency of primary intracerebral haemorrhage (PICH) has been underestimated. Aspirin increases the risk of PICH. There were no reliable data on functional outcome or on the effect of antithrombotic treatment given long term after PICH. In 60% of patients with recurrent stroke after PICH, the cause is another PICH and mortality is high among PICH patients. A specific MR sequence (gradient echo) is required to identify prior PICH reliably. CT scanners were distributed unevenly in Scotland, 65% provided CT scanning within 48 hours of stroke, and 100% within 7 days for hospital-admitted patients, but access out of hours was very variable, and for outpatients was poor. The average cost of a CT brain scan for stroke was pounds 30.23 to pounds 89.56 in normal working hours and pounds 55.05 to pounds 173.46 out of hours. Average length of stay was greatest for severe strokes and those who survived in a dependent state. For a cohort of 1000 patients aged 70-74 years, the policy 'scan all strokes within 48 hours', cost pounds 10,279,728 and achieved 1982.3 QALYS. The most cost-effective strategy was 'scan all immediately' (pounds 9,993,676 and 1982.4 QALYS). The least cost-effective was to 'scan patients on anticoagulants, in a life-threatening condition immediately and the rest within 14 days'. CONCLUSIONS: In general, strategies in which most patients were scanned immediately cost least and achieved the most QALYs, as the cost of providing CT (even out of hours) was less than the cost of inpatient care. Increasing independent survival by even a small proportion through early use of aspirin in the majority with ischaemic stroke, avoiding aspirin in those with haemorrhagic stroke, and appropriate early management of those who have not had a stroke, reduced costs and increased QALYs.

The impact of delays in computed tomography of the brain on the accuracy of diagnosis and subsequent management in patients with minor stroke.

OBJECTIVES: To determine the proportion of haemorrhagic strokes misdiagnosed as infarcts on computed tomography (CT) in patients with mild stroke, and the implications for health care. METHODS: Patients with mild stroke presenting as inpatients or outpatients four or more days after stroke to our stroke service (catchment population 500 000) were recruited prospectively. They underwent detailed clinical examination and brain imaging with CT and magnetic resonance imaging (MRI) on the day of presentation. CT and MR images were examined independently to identify infarct, primary intracerebral haemorrhage, haemorrhagic transformation, or non-vascular lesion. RESULTS: In 228 patients with mild stroke (median time from stroke to scan 20 days), primary intracerebral haemorrhage was identified by CT in two patients (0.9%; 95% confidence interval (CI), 0.1% to 3.1%) and MRI in eight (3.5%; 1.5% to 6.8%). Haemorrhagic transformation was identified by CT in three patients (1.3%; 0.1% to 5.6%) and MRI in 15 (6.6%; 3.7% to 10.6%). The earliest time primary intracerebral haemorrhage was not identified on CT was 11 days. CONCLUSIONS: CT failed to identify 75% of primary intracerebral haemorrhages, equivalent to 24 patients per 1000 (95% CI, 14 to 37) with mild strokes. To detect haemorrhages reliably, CT would need to have been performed within about eight days. Rapid access to neurovascular clinics with same day CT brain imaging is required to avoid inappropriate secondary prevention. Increased public awareness of the need to seek urgent medical attention after stroke should be encouraged. MRI should be considered in late presenting patients.

Is diffusion imaging appearance an independent predictor of outcome after ischemic stroke?

BACKGROUND: MR diffusion-weighted imaging (DWI) in ischemic stroke can be quantified by calculating the apparent diffusion coefficient (ADC) or measuring lesion volume. OBJECTIVE: To clarify the association between DWI lesion parameters, clinical stroke severity at baseline, and the relationship with functional outcome. METHODS: Consecutive patients with stroke were categorized for stroke type (Oxford Community Stroke Project Classification [OCSP]) and severity (Canadian Neurologic Scale [CN Scale]) before DWI. The ratio of the trace of the apparent diffusion tensor in the ischemic lesion to the mirror image area in the contralateral hemisphere was calculated (r). The volume of the visible lesion on DWI was measured. Any visible lesion on T2-weighted imaging (T2WI) was noted. All assessments were blind to all other information. A blinded observer obtained a 6-month Rankin score. Univariate and multivariate analyses were performed to test for independent associations with outcome. RESULTS: In 108 patients, those with lower (i.e., more abnormal) r values had more severe strokes according to the CN Scale (p = 0.01) and the OCSP stroke type (p = 0.002), a large lesion on DWI (p = 0.05), a visible lesion on T2WI (p = 0.001), and poor 6-month functional outcome (p = 0.009). However, on logistic regression, neither r nor DWI lesion volume were independent predictors of 6-month outcome over and above age and stroke severity. CONCLUSION: The r is associated with functional outcome, but that is because it and DWI lesion volume are also associated with stroke severity. Although DWI lesion features are univariate surrogate outcome predictors, the authors were unable to show that they were independent outcome predictors in the current study. Differences between these and other results may be due to differences in study design, sample size, and case mix.

Systematic review of diffusion and perfusion imaging in acute ischemic stroke.

BACKGROUND AND PURPOSE: Recent advances in neuroimaging have raised hopes of early and accurate identification of ischemic brain and the discrimination of dead from salvageable tissue. We sought to determine whether the data published so far are enough to establish the roles of these techniques in everyday clinical practice. METHODS: A systematic review of studies of MR diffusion-weighted imaging (DWI), perfusion imaging (PI), or a combination of the two, in human stroke, excluding abstracts and case reports. One reviewer extracted information on the size of each study, its main purpose, methodological details, and results. RESULTS: We identified 47 studies of DWI, 18 studies of MR PI alone or in combination with another advanced imaging modality, and 19 studies of DWI and PI together. Although high proportions of the studies were prospective and gave good details of the imaging sequences used, the majority gave very limited details on patient selection and clinical characteristics or blinded imaging assessment. Pathophysiological changes were inferred from DWI/PI patterns that were not supported by other data. CONCLUSIONS: Despite considerable enthusiasm for and promise of these techniques, there is not sufficient information available in these studies to enable us to draw firm conclusions about the sensitivity and specificity of these techniques for identification of either ischemic lesions not visible by other means or salvageable tissue. Future studies should include larger numbers of carefully described patients, assess the contribution of DWI over and above other imaging, obtain follow-up at an appropriate time interval to determine accurate clinical and neuroradiological outcomes, and assess DWI/PI abnormality with reperfusion in randomized treatment trials. Investigators should also be encouraged to combine their individual patient data in meta-analyses to obtain a more robust assessment of the value of DWI and PI from larger sample sizes.

A study of the apparent diffusion coefficient of grey and white matter in human ischaemic stroke.

We examined whether there was any difference in the value, and temporal evolution, of the apparent diffusion tensor trace (ADC) in acute and subacute grey and white matter lesions. Thirty-seven patients underwent diffusion imaging once (up to 3 days), 15 patients were scanned twice (up to 7 days), and seven patients were scanned three times (up to 14 days) after stroke. Values of the ratio of ischaemic to contralateral ADC (ADCr) were reduced on average by 30% (p<0.001) in the whole hyperintense region up to 7 days post-ictus. No difference was seen between ADCr values of grey and white matter in individual subjects within the patient groups scanned up to 7 days. However, in the subgroup of patients scanned beyond 7 days, ADCr for grey matter rose significantly (p=0.02) from ADCr approximately 0.7 (< 7 days) to 0.95 (> or = 10 days). This increase did not occur in white matter whose ADCr remained fairly constant (ADCr approximately 0.7) over the time course of the study.

Admission plasma glucose and diabetes mellitus in elderly admissions to hospital.

Over 6 months, all admissions to three geriatric wards were studied to define an admission plasma glucose level (APG) that identified previously undiagnosed diabetes mellitus. Subjects with APG> or =7.0 mmol l(-1) had a modified oral glucose tolerance test (OGTT) when well before discharge if their dose of steroid and/or thiazide was constant, and they were neither terminally ill nor dead; excluded were 1 subject on reducing steroid doses, and 9 moribund admissions without APG. If the first 2 h OGTT result was > or =11.1 mmol l(-1), a second OGTT was performed 6 weeks later to fulfil 1985 WHO criteria. Subjects with APG<7.0 mmol l(-1) did not have OGTT. Seventy had a previous diagnosis of diabetes; scrutiny of records and OGTT refuted the diagnosis in 5, who were excluded from further analysis. Diabetes was only commonly found among those with APG> or =8.0 mmol l(-1), and the proportion was small until APG> or =13 mmol l(-1), although even then only 47% (95% CI 21-73%) had diabetes. Fourteen of 28 subjects with initial OGTT results suggesting diabetes were not diabetic on retesting. Inpatient mortality was higher if APG> or =7.0 (Odds ratio 2.82; CI 1.63-4.89) or the subject had known diabetes (Odds ratio 2.43; CI 1.15-4.97) compared to APG<7; there was no age or sex difference between these three groups. We conclude that, unless overtly diabetic, diagnosis of diabetes in elderly medical admissions needs later confirmation.