A joint statement issued by the American Society of Neuroradiology, the American College of Radiology and the Society of NeuroInternational Surgery proposed a simple, pragmatic approach to determining an imaging strategy for stroke patients.
The article, written by Max Wintermark, MD, MAS, of the University of Virginia, Charlottesville, and more than a dozen colleagues from institutions across the U.S., was published online ahead of print Aug. 13 in the Journal of the American College of Radiology.
“The primary goal of imaging patients with acute stroke symptoms is to distinguish between hemorrhagic and ischemic stroke,” wrote the authors, who listed this as the initial step in their suggested imaging algorithm.
“If intraparenchymal hemorrhage is present, as occurs in 15 percent of all strokes, the imaging evaluation in the acute phase may include CTA [CT angiography] of the intracranial arteries for evaluation of an underlying vascular malformation or aneurysm.” Wintermark and colleagues added that MRI with and without contrast is sometimes also used to determine the presences of underlying amyloid angiopathy, multiple cavernous malformations, or septic emboli, but that the sensitivity of MRI may be limited in the acute phase by mass effect from the hematoma and complex signals of blood products.
For patients with ischemic stroke, the next step is to determine whether the patient is a candidate for intravenous (IV) tissue plasminogen activator (tPA). If the patient does not have intracranial hemorrhage and it’s within 4.5 hours from symptom onset, IV tPA has been shown to improve clinical outcomes.
“The presence of intracranial hemorrhage (excluding microbleeds) is an absolute contraindication to administering IV thrombolytic therapy,” wrote the authors. “The presence of a large acute hypodensity on NCCT [noncontrast CT] increases the risk for hemorrhagic transformation after thrombolytic therapy. This is considered a relative, not absolute, contraindication for IV tPA.”
If the patient is not a candidate for IV tPA, then physicians next should determine if endovascular therapy is to be considered. For endovascular therapy candidates, there are three major strategies. First is an immediate trip the angiography suite to assess vascular patency status on digital subtraction angiography. The second strategy leverages CTA, with or without perfusion imaging, to assess vascular patency and better characterize the site of occlusion before making treatment decisions. The final strategy utilizes MRI or MRA, possibly with diffusion- or perfusion-weighted techniques.
“There is currently no definitive evidence supporting one strategy over the other,” wrote Wintermark and colleagues. “Some believe that more imaging provides additional, clinically relevant information, whereas others are concerned about the time delay resulting from the additional imaging and the potential delay to recanalization it may cause.”
Finally, in patients who are not candidates for either IV or endovascular therapy, the focus of imaging becomes diagnosis, prevention of immediate complications and secondary prevention of future stroke. MRI takes preference here, but when that is unavailable, NCCT can be performed.
“A wide variety of imaging techniques have become available to assess vascular lesions and brain tissue status in patients with acute stroke. However, the practical challenge for physicians is to understand the multiple facets of these imaging techniques, including which imaging techniques to implement and how to optimally use them, given available resources at their local institutions.”