Stroke patients

At the other extreme are those acute stroke patients who have no visible arterial occlusion whatsoever, presumably because their infarcts were due to lesions in small arteries that cannot be imaged, or because an embolus in a large proximal artery has broken up spontaneously. Several smdies (again using catheter angiography rather than CTA) have shown that such patients generally enjoy relatively favorable outcomes. 

FIGURE 2.6 Dynamic susceptibility contrast imaging. Axial images of the brain are acquired repeatedly, in this case every 1.5 seconds. As a bolus of intravenously injected contrast material enters the brain, first arteries, then brain parenchyma, and finally veins demonstrate a transient loss of signal intensity. In this acute stroke patient, hypoperfusion of the left middle cerebral artery territory results in delayed arrival of the contrast bolus and prolonged stasis of contrast within the tissue. 

These studies raise the possibility that, one day, imaging-based treatment protocols may allow for intravenous thrombolysis in patients well outside of the now-accepted 3-hour window, provided they demonstrate substantial diffusion-perfusion mismatch. Such protocols could allow for treatment of a vastly larger number of patients than are currently treated. It has been estimated that only 1-7% of acute stroke patients currently receive thrombolytic medication, and that, in up to 95% of cases, they are ineligible because they present outside of the 3-hour time window. As many as 80% of patients who present 6 hours after stroke onset may demonstrate a significant diffusion-perfusion mismatch. "... 

Arnold M, Nedeltchev K, Brekenfeld C, Fischer U, Remonda L, Schroth G, Mattie H. Outcome of acute stroke patients without visible occlusion on early arteriography. Stroke 2004 35 1135-1138. 

Smith AM, Grandin CB, Duprez T, Mataigne F, Cosnard G. Whole brain quantitative CBF, CBV, and MTT measurements using MRI bolus tracking implementation and application to data acquired from hyperacute stroke patients. J Magn Reson Imaging 2000 12 400-410. 

Cho A-H, Lee DH, Kim JS, Choong GC, Kwon SU, Suh DC, Choi J, Chun S-B, Kim SJ, Kang D-W. MRI-Based thrombolysis in acute stroke patients with unclear onset time is safe and feasible Stroke 2006 37 634 (abstract, American Stroke Association International Stroke Conference 2006). 

Barber PA, Zhang J, Demchuk AM, Hill MD, Buchan AM. Why are stroke patients excluded from TPA therapy An analysis of patient eligibility. Neurology 2001 56 1015-1020. 

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