Whole-Brain Arterial Spin Labeling Perfusion MRI in Patients With Acute Stroke
Advanced neuroimaging is increasingly used in the emergency evaluation of patients with stroke to help differentiate true ischemic stroke from stroke mimics and to potentially offer a rationale to treat patients outside of the established intravenous treatment windows. As part of this regimen, tissue perfusion can be assessed by CT or MRI. However, the requirement for contrast dye application limits the clinical use of these techniques in patients with significant renal impairment. Hence, there is a great interest in developing perfusion techniques that do not require exogenous contrast agents. Arterial spin labeling (ASL) based MR-perfusion imaging measure cerebral perfusion without the need for intravenous contrast application but is challenging to implement in the clinical setting. In this issue of Stroke, Bokkers and colleagues compare pseudocontinuous ASL with background suppression with standard gadolinium-based dynamic susceptibility contrast (DSC) MR-perfusion imaging at 3.0 T. Of 105 patients with both ASL and DSC perfusion imaging, 64 (61%) had a clinically confirmed stroke. ASL and DSC perfusion imaging was interpretable in >95% of patients, respectively. A perfusion deficit was detected with DSC in 61% (n=39) of the 64 patients with confirmed stroke. ASL identified a perfusion deficit in 32 (82%) of the 39 patients with a deficit on DSC. The DSC-defined lesion volumes in patients without hypoperfusion on ASL were approximately 50% of those noted in patients with ASL-defined hypoperfused lesion (P<0.01). Twenty (31%) of the 64 patients with a confirmed stroke had a significant mismatch on DSC, and of these, 18 (90%) were also determined to have a mismatch on ASL. Although further development is required to reduce the false-negative rate in patients with small or subcortical strokes, this study highlights the clinical feasibility of ASL perfusion MRI. This technique holds great promise to inform on previously unavailable cerebral perfusion status in patients with contraindications to receiving CT or MRI contrast agents.
See p 1290.
Very Urgent Carotid Endarterectomy Confers Increased Procedural Risk
Benefit from carotid endarterectomy has been shown to be greatest within 2 weeks for symptomatic carotid stenosis. Strömberg and colleagues analyzed data of 2596 patients undergoing carotid endarterectomy from the prospective Swedish Vascular Registry (Swedvasc) to determine the procedural risk of carotid endarterectomy in relation to such early timing of surgery. They defined 4 subgroups depending on time to intervention: 0 to 2 days, 3 to 7 days, 8 to 14 days, and 15 to 180 days from last neurological event. Outcome measures were death, minor stroke (symptoms <1 week or minor dysfunction), or major (disabling) stroke within 30 days of surgery. Interestingly, the periprocedural risk was similar in patients treated within 14 days versus 15 to 180 days. There was a significantly higher risk of minor stroke (P<0.001) or the combined end point of mortality and any stroke (P<0.001) in patients undergoing carotid endarterectomy 0 to 2 days after the qualifying event compared with all other subgroups. However, there was no significant difference between subgroups when mortality (P=0.640) or major stroke (P=0.097) was analyzed alone. Multivariate analysis demonstrated increased perioperative complications when surgery was performed between 0 and 2 days (OR, 4.24; CI, 2.07–8.70; P<0.001) or 15 to 180 days (OR, 1.90; CI, 1.12–3.22; P<0.017), respectively. Interestingly, major stroke as the qualifying event, which some experts consider a contraindication, was not present in patients with early complications. Although limited because details regarding medical management, plaque and stenosis attributes, location and extent of infarcts as well as the cause of death were not provided, this study raises the important issue whether baseline characteristics (which may bias treating physicians toward immediate intervention) or increased brain vulnerability/plaque instability (as hypothesized by the authors) are the main contributing factors to the observed risk in very early operated patients.
See p 1331.
Mechanism of Ischemic Infarct in Spontaneous Cervical Artery Dissection
The mechanism underlying cerebral ischemia in the wake of carotid artery dissection may include intraluminal thrombus formation and/or mechanical narrowing of the luminal diameter resulting in embolism, hypoperfusion, or both. Accordingly, the optimal treatment should target the “true” etiology in each individual. Morel and colleagues sought to identify the most likely mechanism of stroke using cervical and cerebral imaging parameters in consecutive patients undergoing carotid artery dissection. They retrospectively analyzed 100 patients (mean age, 45 years) from a prospective database with carotid artery dissection who had an MRI-proven stroke attributable to carotid artery dissection and arterial imaging assessing the dissected vessel as well as the intracranial arteries. Interobserver agreement for interpretation of the various imaging modalities was high for each used modality (κ range, 0.84–0.91). According to the likely stroke etiology, patients were assigned to 3 groups: thromboembolic, hemodynamic, or mixed. An intracranial thrombus was seen in 57 patients; pial and perforating artery territory stroke was present in 96 patients; multiple diffusion-weighted imaging lesions were seen in 56 patients; and isolated watershed infarction was seen in 4 patients. Stroke was classified as thromboembolic in 85 of 100 patients, hemodynamic in 12 of 100 patients, and mixed in 3 of 100 patients. This suggests that stroke after carotid artery dissection is typically due to artery-to-artery embolism. It would be interesting to know what type of treatment was chosen as well as its timing relative to MRI. Based on the presented results, one might assume that anticoagulation should be the preferred treatment modality. However, as pointed out by the authors, clear superiority of such treatment has not been established in prior analyses. Hence, the current study is important because it provides a basis for future investigations evaluating efficacy of different treatment regimens in relation to the most likely (or feared) stroke etiology.
See p 1354.
- © 2012 American Heart Association, Inc.