Acute occlusion of the middle cerebral artery: early evaluation with triphasic helical CT--preliminary results

Multimodal CT techniques for cerebrovascular and hemodynamic evaluation of ischemic stroke: occlusion, collaterals, and perfusion

Neuroimaging of cerebrovascular status and hemodynamics has vastly improved our understanding of stroke mechanisms and provided information for therapeutic decision-making. CT techniques are the most commonly used techniques due to wide availability, rapid acquisition and acceptable tolerance. Numerous multimodal CT techniques have been developed in the last few years. We summarize and explain the various multimodal CT acquisition techniques within three categories based on the scanning mode, namely static mode (single-phase CTA), multiple static mode (multi-phase CTA) and continuous mode (CT perfusion and dynamic CTA). Post-processing methods based on different acquisition modes are also introduced in an easy manner by focusing on the information extracted and products generated. We also describe the applications for these techniques along with their advantages and disadvantages.

Accuracy of Non-Enhanced CT in Detecting Early Ischemic Edema Using Frequency Selective Non-Linear Blending

Purpose

Ischemic brain edema is subtle and hard to detect by computed tomography within the first hours of stroke onset. We hypothesize that non-enhanced CT (NECT) post-processing with frequency-selective non-linear blending (“best contrast”/BC) increases its accuracy in detecting edema and irreversible tissue damage (infarction).

Methods

We retrospectively analyzed the NECT scans of 76 consecutive patients with ischemic stroke (exclusively middle cerebral artery territory—MCA) before and after post-processing with BC both at baseline before reperfusion therapy and at follow-up (5.73±12.74 days after stroke onset) using the Alberta Stroke Program Early CT Score (ASPECTS). We assessed the differences in ASPECTS between unprocessed and post-processed images and calculated sensitivity, specificity, and predictive values of baseline NECT using follow-up CT serving as reference standard for brain infarction.

Results

NECT detected brain tissue hypoattenuation in 35 of 76 patients (46.1%). This number increased to 71 patients (93.4%) after post-processing with BC. Follow-up NECT confirmed brain infarctions in 65 patients (85.5%; p = 0.012). Post-processing increased the sensitivity of NECT for brain infarction from 35/65 (54%) to 65/65 (100%), decreased its specificity from 11/11 (100%) to 7/11 (64%), its positive predictive value (PPV) from 35/35 (100%) to 65/69 (94%) and increased its accuracy 46/76 (61%) to 72/76 (95%).

Conclusions

This post-hoc analysis suggests that post-processing of NECT with BC may increase its sensitivity for ischemic brain damage significantly.

Thrombus Length Estimation on Delayed Gadolinium-Enhanced T1

BACKGROUND AND PURPOSE

Previous studies revealed a close relationship between thrombus length and recanalization rate after intravenous thrombolysis (IVT). As a novel approach, we prospectively adjusted the order of sequence acquisition to obtain delayed gadolinium-enhanced T1 (dGE-T1) and thereby assess thrombus length on dGE-T1 to evaluate its predictive value for recanalization after IVT.

METHODS

We reviewed prospectively collected clinical and imaging data from acute ischemic stroke patients with middle cerebral artery occlusion who underwent multimodal magnetic resonance imaging before and 24 hours after IVT. Perfusion-weighted imaging was performed followed by conventional T1. We measured thrombus length on dGE-T1 and examined its association with middle cerebral artery recanalization.

RESULTS

Of the included 74 patients, the median age was 66 years and 28 (37.8%) were women. Thrombus length was 8.18±4.56 mm on dGE-T1, which was an acceptable predictor for no recanalization (odds ratio, 1.196; 95% confidence interval, 1.015-1.409; P=0.033), with a receiver-operator characteristic of 0.732 (95% confidence interval, 0.619-0.845; P=0.001). The optimal cut-off point was identified at 6.77 mm, which yielded a sensitivity of 77.8%, a specificity of 57.9%, and an odds ratio of 4.81 (95% confidence interval, 1.742-13.292; P=0.002). Moreover, no one achieved recanalization after IVT when length of thrombus exceeded 14 mm on dGE-T1.

CONCLUSIONS

The dGE-T1, obtained by simply adjusting scanning order in multimodal magnetic resonance imaging protocol, is a useful tool for thrombus length estimation and middle cerebral artery recanalization prediction after IVT.

Magnetic resonance imaging versus computed tomography for detection of acute vascular lesions in patients presenting with stroke symptoms

BACKGROUND

Magnetic resonance imaging (MRI) is increasingly used for the diagnosis of acute ischaemic stroke but its sensitivity for the early detection of intracerebral haemorrhage has been debated. Computed tomography (CT) is extensively used in the clinical management of acute stroke, especially for the rapid exclusion of intracerebral haemorrhage.

OBJECTIVES

To compare the diagnostic accuracy of diffusion-weighted MRI (DWI) and CT for acute ischaemic stroke, and to estimate the diagnostic accuracy of MRI for acute haemorrhagic stroke.

SEARCH STRATEGY

We searched MEDLINE and EMBASE (January 1995 to March 2009) and perused bibliographies of relevant studies for additional references.

SELECTION CRITERIA

We selected studies that either compared DWI and CT in the same patients for detection of ischaemic stroke or examined the utility of MRI for detection of haemorrhagic stroke, had imaging performed within 12 hours of stroke onset, and presented sufficient data to allow construction of contingency tables.

DATA COLLECTION AND ANALYSIS

Three authors independently extracted data on study characteristics and measures of accuracy. We assessed data on ischaemic stroke using random-effects and fixed-effect meta-analyses.

MAIN RESULTS

Eight studies with a total of 308 participants met our inclusion criteria. Seven studies contributed to the assessment of ischaemic stroke and two studies to the assessment of haemorrhagic stroke. The spectrum of patients was relatively narrow in all studies, sample sizes were small, there was substantial incorporation bias, and blinding procedures were often incomplete. Amongst the patients subsequently confirmed to have acute ischaemic stroke (161/226), the summary estimates for DWI were: sensitivity 0.99 (95% CI 0.23 to 1.00), specificity 0.92 (95% CI 0.83 to 0.97). The summary estimates for CT were: sensitivity 0.39 (95% CI 0.16 to 0.69), specificity 1.00 (95% CI 0.94 to 1.00). The two studies on haemorrhagic stroke reported high estimates for diffusion-weighted and gradient-echo sequences but had inconsistent reference standards. We did not calculate overall estimates for these two studies. We were not able to assess practicality or cost-effectiveness issues.

AUTHORS' CONCLUSIONS

DWI appears to be more sensitive than CT for the early detection of ischaemic stroke in highly selected patients. However, the variability in the quality of included studies and the presence of spectrum and incorporation biases render the reliability and generalisability of observed results questionable. Further well-designed studies without methodological biases, in more representative patient samples, with practicality and cost estimates are now needed to determine which patients should undergo MRI and which CT in suspected acute stroke.

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Cerebral Angiography in the Assessment of Acute Cerebral Ischemia: Guidelines and Recommendations

Catheter-based cerebral angiography remains an essential tool for evaluating patients with acute cerebral ischemia. Noninvasive vascular imaging techniques have yet to achieve the accuracy and wide availability necessary for this purpose. Angiography is rarely indicated when patients present within the short 3-hour time window for treatment with intravenous alteplase. For the many patients who present later in their course, however, angiography is useful for the accurate evaluation of the cerebral vasculature. In addition, angiography serves as the foundation for the endovascular therapies that may be performed to treat acute ischemic stroke beyond the 3-hour time window.

Anatomy and functionality of leptomeningeal anastomoses: a review

BACKGROUND

This review seeks to provide a structured presentation of existing knowledge of leptomeningeal anastomoses from anatomic and functional points of view and to identify problems and possible research directions to foster a better understanding of the subject and of stroke mechanisms.

SUMMARY OF REVIEW

Available data show that leptomeningeal anastomoses may be important in understanding stroke mechanisms and that leptomeningeal anastomoses play an important role in penumbra outcome. However, the literature shows no consensus between statements on the existence of leptomeningeal anastomoses and compensatory capacity.

CONCLUSIONS

By analyzing the available literature and identifying the factors that contribute to this confusion, we found that variability and the functional consequences thereof are important but that quantitative data are lacking. Moreover, vascular remodeling is an issue to consider.

Use of CT angiography in patient selection for thrombolytic therapy

It has been shown that thrombolytic therapy can improve clinical outcome in some patients with acute cerebral ischemia. These patients have been reported to be characterized by certain clinical and imaging findings, mainly with non-contrast enhanced computed tomography (CT). Our purpose in this study was to find out whether CT angiography (CTA) information about the status of the cerebral vessels is helpful in the selection of patients who may benefit the most from thrombolytic therapy for acvte cerebral ischemia. CTA was prospectively performed in 15 consecutive patients (6 women and 9 men; age range 44-83 years) with moderate or severe symptoms of hyperacute cerebral ischemia. The clinical manifestations of the patient's condition and the findings on CTA were analyzed. Three-dimensionally reconstructed CTA images of diagnostic quality could be obtained for all 15 patients. Of the 15 patients 14 had a vessel occlusion identified on CTA, which was consistent with and/or helpful for making the clinical diagnosis in all 14 cases; one patient had an aneurysm of the anterior communicating artery without detectable hemorrhage on CTA. Although a thrombolytic agent was not given because of CTA evidence of intracranial aneurysm, the patient nevertheless developed a massive subarachnoid hemorrhage during hospitalization. Ischemic symptoms reversed after CTA and before the initiation of thrombolytic therapy in 2 patients whose CTAs showed occlusion of secondary branch of the middle cerebral artery (MCA). CTA can provide important information before the initiation of thrombolytic therapy. Identification both of the occluded vessel and of an intracranial aneurysm is feasible with the use of CTA, which is particularly important if the intracranial aneurysm is a potential contraindication to thrombolytic therapy. Occlusion of a secondary branch of the MCA and internal carotid artery occlusion are valuable prognostic predictors.

Multiphasic perfusion computed tomography in hyperacute ischemic stroke: comparison with diffusion and perfusion magnetic resonance imaging

PURPOSE

The purpose of this study was to compare multiphasic perfusion computed tomography (CT) with diffusion and perfusion magnetic resonance imaging (MRI) in predicting final infarct volume, infarct growth, and clinical severity in patients with hyperacute ischemia untreated by thrombolytic therapy.

METHOD

Multiphasic perfusion CT was performed in 19 patients with ischemic stroke within 6 hours of symptom onset. Two CT maps of peak and total perfusion were generated from CT data. Diffusion-weighted imaging (DWI) and perfusion MRI were obtained within 150 minutes after CT. Lesion volumes on CT and MRI were compared with final infarct volume and clinical scores, and mismatch on CT or MRI was compared with infarct growth.

RESULTS

The lesion volume on the CT total perfusion map strongly correlated with MRI relative cerebral blood volume (rCBV), and that on the CT peak perfusion map strongly correlated with MRI relative cerebral blood flow (rCBF) and rCBV (P < 0.001). The lesion volume on unenhanced CT or DWI moderately correlated with final infarct volume, but only lesion volume on unenhanced CT weakly correlated with baseline clinical scores (P = 0.024). The lesion volumes on the CT peak perfusion map and MRI rCBF similarly correlated with final infarct volume and clinical scores and more strongly than those on mean transit time (MTT) or time to peak (TTP). DWI-rCBF or CT mismatch was more predictive of infarct growth than DWI-MTT or DWI-TTP mismatch.

CONCLUSION

Multiphasic perfusion CT is useful and of comparable utility to diffusion and perfusion MRI for predicting final infarct volume, infarct growth, and clinical severity in acute ischemic stroke.

Multiphasic perfusion CT in acute middle cerebral artery ischemic stroke: prediction of final infarct volume and correlation with clinical outcome

Objective

To assess the utility of multiphasic perfusion CT in the prediction of final infarct volume, and the relationship between lesion volume revealed by CT imaging and clinical outcome in acute ischemic stroke patients who have not undergone thrombolytic therapy.

Materials and Methods

Thirty-five patients underwent multiphasic perfusion CT within six hours of stroke onset. After baseline unenhanced helical CT scanning, contrast-enhanced CT scans were obtained 20, 34, 48, and 62 secs after the injection of 90 mL contrast medium at a rate of 3 mL/sec. CT peak and total perfusion maps were obtained from serial CT images, and the initial lesion volumes revealed by CT were compared with final infarct volumes and clinical scores.

Results

Overall, the lesion volumes seen on CT peak perfusion maps correlated most strongly with final infarct volumes (R²=0.819, p<0.001, slope of regression line=1.016), but individual data showed that they were less than final infarct volume in 31.4% of patients. In those who showed early clinical improvement (n=6), final infarct volume tended to be overestimated by CT peak perfusion mapping and only on total perfusion maps was there significant correlation between lesion volume and final infarct volume (R²=0.854, p=0.008). The lesion volumes depicted by CT maps showed moderate correlation with baseline clinical scores and clinical outcomes (R=0.445-0.706, p≤0.007).

Conclusion

CT peak perfusion maps demonstrate strong correlation between lesion volume and final infarct volume, and accurately predict final infarct volume in about two-thirds of the 35 patients. The lesion volume seen on CT maps shows moderate correlation with clinical outcome.

CT angiography in the rapid triage of patients with hyperacute stroke to intraarterial thrombolysis: accuracy in the detection of large vessel thrombus

PURPOSE

The purpose of this work was to evaluate the accuracy of CT angiography (CTA) for the detection of large vessel intracranial thrombus in clinically suspected hyperacute (<6 h) stroke patients.

METHOD

Forty-four consecutive intraarterial thrombolysis candidates underwent noncontrast CT followed immediately by CTA. Axial source and two-dimensional collapsed maximum intensity projection reformatted CTA images were rated for the presence or absence of large vessel occlusion. Five hundred seventy-two circle-of-Willis vessels were reviewed; arteriographic correlation was available for 224 of these.

RESULTS

Sensitivity and specificity for the detection of large vessel occlusion were 98.4 and 98.1%; accuracy, calculated using receiver operating characteristic analysis, was 99%. Mean time for acquisition, reconstruction, and analysis of CTA images was approximately 15 min.

CONCLUSION

CTA is highly accurate for the detection and exclusion of large vessel intracranial occlusion and may therefore be valuable in the rapid triage of hyperacute stroke patients to intraarterial thrombolytic treatment.

Treatment of acute ischemic stroke

Acute ischemic stroke is the third leading cause of death in the United States and the leading cause of adult disability. The direct and indirect costs of stroke care exceed $51 billion annually. In 1996, the US Food and Drug Administration approved the first treatment for acute ischemic stroke, intravenous tissue plasminogen activator. Later that year, the National Institute of Neurologic Disorders and Stroke (a branch of the National Institutes of Health) convened a consensus conference on the Rapid Identification and Treatment of Acute Ischemic Stroke, setting goals for stroke care in the United States. Since then, it has become imperative that emergency physicians understand the pathophysiology of stroke, the basis and rationale for treatment, and the therapeutic approaches. This article reviews the state of the art of acute stroke treatment, its foundation, as well as its future.

Diagnostic evaluation of stroke

Diagnostic testing in patients with ischemic stroke serves many purposes, including confirmation of the diagnosis and providing clues as to possible causes. Evaluation of the cerebral vasculature, the heart, the blood coagulation system, and selected other diagnostic tests may point to a mechanism of stroke which helps determine treatment and prognosis. With the recent advent of acute interventions for ischemic stroke, diagnostic testing is now an important component in the emergency management of stroke. In this article, the authors will review the standard approach to diagnostic testing for patients with ischemic stroke or transient ischemic attack, and new developments in neuro-imaging and their use in acute stroke assessment.

Recent advances in imaging of cerebrovascular disease

The recent advances made in CT and MR imaging have led to increased accuracy in making a number of diagnoses in the emergency room setting. Increasingly, radiologists are asked to perform these studies and accurately interpret the findings, which often have a dramatic impact on triaging and treatment of the patient. Future trials need to address further the relative merits of each of the techniques outlined previously in specific settings. In addition, given the increasing number of means of obtaining diagnostic information, cost effectiveness studies are needed to better formulate an appropriate algorithm for each diagnosis.

Neurovascular applications of CT angiography

CT angiography, which has important advantages over both MR and ultrasound, is rapidly becoming an important modality for noninvasive evaluation of the neurovasculature. This article discusses CT angiography techniques for imaging the neurovasculature, including spiral acquisition protocols and image processing techniques, with a focus on the use of volume rendering for three-dimensional visualization. The clinical results for CT angiography of the cervical carotid arteries, intracranial aneurysms, arteriovenous malformations, and emerging work in the evaluation of acute stroke are reviewed. Important areas of ongoing research also are described.