Published online before print March 27, 2003, doi: 10.1161/01.STR.0000065109.19932.8B
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(Stroke. 2003;34:835.)
© 2003 American Heart Association, Inc.
Letters to the Editor |
CTA Source Images in Acute Stroke
The Calgary Stroke Program, Department of Clinical Neurosciences, University of Calgary, Foothills Hospital, Calgary, Canada
To the Editor:
In their abstract, Schramm et al, describe lesions seen on CT angiography source images (CTA-SI) as "demarcation of irreversible infarct."1 We believe this description is inaccurate and have several comments regarding the utility and future study of CTA-SI.
First, CTA-SI gives direct information about flow of contrast into the tissues and not about the viability of tissue. The inference that hypointense tissue is "irreversible infarct" may be time dependent. Irreversible damage may have occurred in most cases with clear hypointensity on CTA-SI at late time points after stroke onset, but this may not necessarily be true in the very early phase of infarct evolution. In Table 1, the authors report six cases in which the size of the area of CTA-SI hypointensity is bigger than the abnormal area of hyperintensity seen on the MR diffusion weighted image which was obtained following the CT. It has yet to be proven that volumes delineated on CTA-SI imply irreversibly damaged tissue in all cases and the relationship with time from stroke onset has not been clarified.
Second, in the displayed examples, the areas delineated by the CTA-SI are distinctly obvious on the baseline non-contrast CT. Scales for assessing the baseline non-contrast CT, such as ASPECTS are available to supply the same information.2 ASPECTS has excellent reliability and prognostic capability.3 Where the lesion is clearly seen on the baseline CT, there appears to be no advantage to CTA-SI. Indeed, because time is so critical,4 even ten minutes delay to complete the CT angiogram may be disadvantageous by delaying the application of thrombolysis. Because of the learning curve in appreciating the signs of ischemia on the non-contrast CT scan, some observers may still benefit from a CTA-SI scan.
Our experience with CTA-SI is promising. CTA-SI shows great potential where the baseline non-contrast CT scan looks normal (ASPECTS score of 10), a situation that tends to occur at early time points after stroke onset. If such a patient has an occlusion on CTA and no "black hole" regions of low flow of contrast (CTA-SI) into the tissue, they would seem ideal candidates for reperfusion strategies. But if no occlusion is present on CTA or a large "black hole" is revealed such reperfusion strategies might provide no added benefit. This stratification of patients by CTA-SI is a clear testable hypothesis for a clinical trial.
Clinicians on the front lines of hyperacute stroke treatment must balance the added expense of time required to perform CTA/CTA-SI with the new information this imaging provides. Clearly not all acute stroke patients need such imaging and delays in therapy are to be discouraged. The patient with a disabling stroke, a hyperdense artery sign and a favorable non-contrast CT scan appearance within 3 hours of symptom onset needs no further imaging to make a treatment decision. Acute neurovascular imaging is an evolving area with improving methods and much debate. What is definitely clear is that CT remains an important tool for hyperacute stroke that will not easily be displaced by other modalities such as MRI.
References
1. Schramm P, Scheillinger PD, Fiebach JB, Heiland S, Jansen O, Knauth M, Hacke W, Sartor K. Comparison of CT and CT Angiography source images with diffusion-weighted imaging in patients with acute stroke within 6 hours after onset. Stroke. 2002; 33: 2426–2432.
2. Pexman JHW, Barber PA, Hill MD, Sevick RJ, Demchuk AM, Hudon ME, Hu WY, Buchan AM. Use of the Alberta Stroke Program Early CT Score (ASPECTS) for assessing CT scans in patients with acute stroke. Am J Neuroradiol. 2001; 22: 1534–1542.
3. Barber PA, Demchuk AM, Zhang J, Buchan AM, for the ASPECTS Study Group. Validity and reliability of a quantitative computed tomographic score in predicting outcome of hyperacute stroke before thrombolytic therapy. Lancet. 2000; 355: 1670–1674.[CrossRef][Medline] [Order article via Infotrieve]
4. Marler JR, Tilley BC, Lu M, Brott TG, Lyden PC, Grotta JC, Broderick JP, Levine SR, Frankel MP, Horowitz SH, Haley EC, Lewandowski CA, Kwiatkowski TP. Early stroke treatment associated with better outcome: the NINDS rt-PA stroke study. Neurology. 2000; 55: 1649–1655.
Departments of Neuroradiology and Neurology, Medical School, University Heidelberg, Heidelberg, Germany
Response
We would like to thank Dr Hill et al for their interest and their comments. Obviously, this group is very experienced in the use of CTA-SI and their potential in the early hours of acute stroke. We agree that CTA-SI provide information about the flow of contrast medium into the brain tissue and not directly about the viability of tissue. As a surrogate parameter and by their correlation with DWI, however, they are a reliable predictor for the infarct core.
Hill et al consider the time delay caused by CT angiography, which can be disadvantageous in the first hours of acute stroke. No time should thus be spent for unnecessary neurovascular imaging that could dangerously delay treatment. We certainly agree that not every patient with acute stroke needs additional CTA imaging, eg, patients with a large and well demarcated MCA infarction. Also, the ASPECTS score may be helpful.1,2 While the HMCAS highly correlates with occlusion of the proximal MCA,3,4 it renders limited information regarding distal M1 or M2 occlusions.
We believe that the additional few minutes needed for CT angiography are well compensated by the benefit of the additional information. We also believe that the vascular information obtained from the CTA-SI justifies the additional examination time with a reasonable cost-value ratio. While the experts may not need CTA-SI (and this is clearly a matter of debate), less experienced observers benefit from a CTA-SI analysis; in most instances the expert is not available 24 hours a day.
Hill et al emphasize that CT as an important tool in stroke imaging will not easily be displaced by MRI. We want to point out, though, that several recent studies have consistently shown that especially within the first 6 hours of acute stroke DWI is superior to non-contrast CT. The combination of CT, CTA and CTA-SI is superior to non-contrast CT alone,5 however DWI should be considered as the present gold standard for the imaging assessment in acute stroke.6
In keeping with the scientific progress, the optimum diagnostic tools should be applied to improve patient management.7 Thus, we suggest that regarding the narrow time window either stroke CT (non-contrast CT, CTA, CTA-SI) or stroke MRI (DWI, PWI, MRA, T2, T2*), depending on availability, should be used for imaging in hyperacute stroke. An efficient stroke team can perform this diagnostic workup without a dangerous loss of time.8
References
1. Pexman JHW, Barber PA, Hill MD, Sevick RJ, Demchuk AM, Hudon ME, Hu WY, Buchan AM. The methodology of assessing CT scans in the acute stroke patient using ASPECTS. Am J Neuroradiol. 2001; 22: 1534–1542.
2. Barber PA, Demchuk AM, Zhang J, Buchan AM, for the ASPECTS Study Group. Validity and reliability of a quantitative computed tomographic score in predicting outcome of hyperacute stroke before thrombolytic therapy. Lancet. 2000; 355: 1670–1674.[CrossRef][Medline] [Order article via Infotrieve]
3. von Kummer R, Meyding-Lamade U, Forsting M, Rosin L, Rieke K, Hacke W, Sartor K. Sensitivity and prognostic value of early CT in occlusion of the middle cerebral artery trunk. AJNR Am J Neuroradiol. 1994; 15: 9–15;discussion 16–18.
4. Bozzao L, Angeloni U, Bastianello S, Fantozzi LM, Pierallini A, Fieschi C. Early angiographic and CT findings in patients with hemorrhagic infarction in the distribution of the middle cerebral artery. AJNR Am J Neuroradiol. 1991; 12: 1115–1121.[Abstract]
5. Schramm P, Schellinger PD, Fiebach JB, Heiland S, Jansen O, Knauth M, Hacke W, Sartor K. Comparison of CT and CT angiography source images with diffusion-weighted imaging in patients with acute stroke within 6 hours after onset. Stroke. 2002; 33: 2426–2432.
6. Fiebach JB, Schellinger PD, Jansen O, Meyer M, Wilde P, Bender J, Schramm P, Jüttler E, Oehler J, Hartmann M, et al. 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. Stroke. 2002; 33: 2206–2210.
7. Röther J, Schellinger PD, Gass A, Siebler M, Villringer A, Fiebach JB, Fiehler J, Jansen O, Kucinski T, Schoder V, et al. Effect of intravenous thrombolysis on MRI parameters and functional outcome in acute stroke <6h. Stroke. 2002; 33: 2438–2445.
8. Schellinger PD, Fiebach JB, Jansen O, Heiland S, Steiner T, Ryssel H, Pohlers O, Hacke W, Sartor K. Feasibility and practicality of stroke MRI in hyperacute cerebral ischemia. AJNR Am J Neuroradiol. 2000; 21: 1184–1189.
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