Weighing the evidence on DWI: caveat emptor

Acute Stroke Imaging for Thrombolytic Therapy – An Update

More than ten years after its approval intravenous thrombolysis with rtPA still is the only approved therapy for acute ischemic stroke. In this review we aim to give an up-to-date overview of acute stroke imaging within and outside of approved indications for thrombolysis. We discuss the potential applications of modern CT techniques such as CT angiography and perfusion CT as well as stroke MRI for the selection-based treatment of acute ischemic stroke. Recent publications regarding diagnostic strength as well as new randomized trials and larger prospective but open studies are reviewed and discussed. Finally we present a suggestion for the selection of patients for thrombolysis within and beyond the 3-hour time window in the form of an institutional algorithm prioritizing according to present evidence and pathophysiological reasoning.

The Evolving Role of Advanced MR Imaging as a Management Tool for Adult Ischemic Stroke: A Western-European Perspective

New and more advanced diagnostic imaging techniques for acute stroke triage have the potential to not only improve the quality of care but also reduce health care costs. Although sufficiently large and methodologically sound studies with regard to cost effectiveness of MR imaging are lacking, the overall impression is that MR imaging has revolutionized not only the diagnosis but also the open and investigational management of neurologically ill patients.

Therapeutic time window of thrombolytic therapy following stroke

Stroke is the third leading cause of death after myocardial infarction and cancer and the leading cause of permanent disability and of disability-adjusted loss of independent life-years in Western countries. Thrombolysis is the treatment of choice for acute stroke within 3 hours after symptom onset. Treatment beyond the 3-hour time window has not been shown to be effective in any single trial; however, meta-analyses suggest a somewhat less but still significant effect within 3 to 6 hours after stroke. It seems reasonable to apply improved selection criteria that would allow one to differentiate patients with a relevant indication for thrombolytic therapy from those who do not have one. We present an overview of a diagnostic approach to acute stroke management that allows the clinician to individualize patient management based on pathophysiologic reasoning and not rigid time windows established by randomized controlled trials. Therefore, this review concentrates on giving the reader an integrated knowledge of the current status of thrombolytic therapy in stroke and then develops a treatment algorithm based on pathophysiologic information rendered by a multiparametric stroke magnetic resonance imaging protocol.

An update on thrombolytic therapy for acute stroke

PURPOSE OF REVIEW

Stroke is the third leading cause of death after myocardial infarction and cancer, and is the leading cause of permanent disability and disability-adjusted loss of independent life-years in western countries. Thrombolysis is the treatment of choice for acute stroke within 3 h after the onset of symptoms. We present an overview of a diagnostic approach to acute stroke management that allows the individualization of patient management based on pathophysiological reasoning and not rigid time windows established by randomized controlled trials.

RECENT FINDINGS

This review concentrates in the first part on giving the reader an integrated knowledge of the current status of thrombolytic therapy in stroke, and in the second part develops a treatment algorithm based on pathophysiological information rendered by a multiparametric stroke magnetic resonance imaging protocol.

SUMMARY

Thrombolysis is an effective therapy for ischemic stroke, whether performed intravenously within 3 h or intra-arterially within 3-6 h. Meta-analyses have provided evidence of an effect of intravenous thrombolysis beyond the 3 h time window, especially when improved selection criteria such as modern magnetic resonance imaging protocols are applied. Sadly, thrombolysis is still underused. Positive results from studies currently underway may encourage more centers to offer this therapy to an increasing number of stroke patients, and thereby reduce the considerable socioeconomic burden of stroke.

MRI-guided therapy in acute stroke

Stroke is the third leading cause of death after myocardial infarction and cancer and the leading cause of permanent disability and of disability-adjusted loss of independent life-years in Western countries. Thrombolysis is the treatment of choice for acute stroke within 3 h after onset of symptoms. Treatment beyond the 3-h time window has not been shown to be effective in any single trial, however, meta-analyses suggest a somewhat less but still significant effect within 3 to 6 h after stroke. It seems reasonable to apply improved selection criteria that allow the differentiation of patients with a relevant indication for thrombolytic therapy from those who have not. An overview of a diagnostic approach to acute stroke management that allows patient management individualization based on pathophysiological reasoning and not rigid time windows, established by randomized controlled trials is presented. Therefore, this review concentrates in the first part on giving the reader an integrated knowledge of the current status of thrombolytic therapy in stroke, and in the second part, develops a treatment algorithm based on pathophysiological information rendered by a multiparametric stroke magnetic resonance imaging protocol.

Imaging-Based Decision Making in Thrombolytic Therapy for Ischemic Stroke

Background— Thrombolysis is the treatment of choice for acute stroke within 3 hours after symptom onset. Treatment beyond the 3-hour time window has not been shown to be effective in any single trial; however, meta-analyses suggest a somewhat lesser but still significant effect within 3 to 6 hours after stroke. It seems reasonable to apply improved selection criteria that allow differentiation between patients with and without a relevant indication for thrombolytic therapy.

Summary of Review— The present literature on imaging in stroke has been thoroughly reviewed, covering Doppler ultrasound (DU), arteriography, CT, and MRI and including modern techniques such as perfusion CT, diffusion- and perfusion-weighted MRI (DWI, PWI), CT angiography and MR angiography (CTA, MRA), and CTA source image analysis (CTA-SI). The authors present their view of a comprehensive diagnostic approach to acute stroke, which challenges the concept of a rigid therapeutic time window.

Conclusions— Information about the presence or absence of a vessel occlusion, whether by means of DU, CTA, or MRA, is essential before recombinant tissue plasminogen activator is given in the 3- to 6-hour time window. Clear demarcation of the irreversibly damaged infarct core and the ischemic but still viable and thus salvageable tissue at risk of infarction as seen on DWI/PWI/MRA or alternatively CT/CTA/CTA-SI should be obtained before thrombolysis is initiated within 3 to 6 hours. Once these advanced techniques are used, the therapeutic time window can be extended with acceptable safety. However, comprehensive informed consent is mandatory, especially when thrombolytic therapy is considered beyond established time windows.

CT and diffusion-weighted MR imaging in randomized order: diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke

BACKGROUND AND PURPOSE

Diffusion-weighted MRI (DWI) has become a commonly used imaging modality in stroke centers. The value of this method as a routine procedure is still being discussed. In previous studies, CT was always performed before DWI. Therefore, infarct progression could be a reason for the better result in DWI.

METHODS

All hyperacute (<6 hours) stroke patients admitted to our emergency department with a National Institutes of Health Stroke Scale (NIHSS) score >3 were prospectively randomized for the order in which CT and MRI were performed. Five stroke experts and 4 residents blinded to clinical data judged stroke signs and lesion size on the images. To determine the interrater variability, we calculated kappa values for both rating groups.

RESULTS

A total of 50 patients with ischemic stroke and 4 patients with transient symptoms of acute stroke (median NIHSS score, 11; range, 3 to 27) were analyzed. Of the 50 patients, 55% were examined with DWI first. The mean delay from symptom onset until CT was 180 minutes; that from symptom onset until DWI was 189 minutes. The mean delay between DWI and CT was 30 minutes. The sensitivity of infarct detection by the experts was significantly better when based on DWI (CT/DWI, 61/91%). Accuracy was 91% when based on DWI (CT, 61%). Interrater variability of lesion detection was also significantly better for DWI (CT/DWI, kappa=0.51/0.84). The assessment of lesion extent was less homogeneous on CT (CT/DWI, kappa=0.38/0.62). The differences between the 2 modalities were stronger in the residents' ratings (CT/DWI: sensitivity, 46/81%; kappa=0.38/0.76).

CONCLUSIONS

CT and DWI performed with the same delay after onset of ischemic stroke resulted in significant differences in diagnostic accuracy. DWI gives good interrater homogeneity and has a substantially better sensitivity and accuracy than CT even if the raters have limited experience.

Heterogeneity affecting outcome from acute stroke therapy: making reperfusion worse

BACKGROUND

Stroke patients are heterogeneous not only with respect to etiology but also in terms of preexisting clinical conditions. Approximately one fifth of patients with acute stroke are hyperglycemic and/or have had a recent infectious or inflammatory condition. Summary of Review-- Experimental research indicates that these factors can alter and accelerate the evolution of stroke and reperfusion injury, although these effects are complex and some may have a favorable impact. Both conditions involve activation of inflammatory and reactive oxygen mechanisms. In addition, hyperglycemia has concomitant deleterious vascular and metabolic effects that worsen infarct size and encourage hemorrhagic transformation in reperfusion models. Clinical data are less extensive but in general support an adverse impact on outcome.

CONCLUSIONS

After examining these data in detail, we concluded that the presence of these clinical conditions could assist in identification of those at increased risk for complications of reperfusion therapy. Furthermore, consideration of these factors may provide a rational basis for combination therapy and improve the clinical relevance of experimental stroke models.