International Stroke Conference
February 6–8, 2019
Kat Dakay, DO
Much discussion has taken place about the role of advanced imaging in patient selection for mechanical thrombectomy. In this symposium, Dr. Marc Fisher, Editor-in-Chief of Stroke, moderated a lecture series focused on what imaging to perform in order to select patients for thrombectomy. The lectures were given by Dr. Fisher, Dr. Bruce Campbell (Melbourne Brain Institute, University of Melbourne), Dr. Michael Hill (University of Calgary), Dr. Maarten Lansberg (Stanford), and Dr. Pooja Khatri (University of Cincinnati).
Some themes that came up in the four lectures:
Advanced neuroimaging such as MR perfusion or CT perfusion can help make thrombectomy decisions, and may be especially important in patients presenting in the extended time window as per DAWN and DEFUSE.
- Dr. Lansberg discussed how CT perfusion can extend the time window, and identify patients who may be a high risk for hemorrhage.
- He also cited a meta-analysis titled “Neurons Over Nephrons” published in 2017 that dispelled the notion that CTA/CTP was associated with acute renal injury to help alleviate concerns regarding iodinated contrast exposure.
CT brain is a fast and informative test; however, the ASPECTs score is limited in its ability to predict lesion volume. It may be falsely low and exclude a good thrombectomy candidate, as Dr. Lansberg demonstrated in a patient example; however, it can also be spuriously benign and fail to show an early large infarct in a patient with poor collaterals.
- Dr. Fisher elucidated how various factors can affect the ASPECTs score, including how the images are acquired by the CT scanner itself, high inter-rater variability, and confounding factors (such as edema, leukoaraiosis, and artifacts).
- Dr. Hill made the point that the non contrast CT may be enough to exclude some patients at high likelihood of harm from thrombectomy, e.g., hemorrhage or very large infarct (though they may require other considerations, such as neurosurgical consultation in the case of malignant MCA infarction).
There is a lot of variability between what imaging different centers and physicians utilize for thrombectomy patient selection, especially with regards to inter-hospital transfers and the extended time window.
- Dr. Fisher discussed a study in which neurologists were given several theoretical scenarios of patients with acute stroke, all with varying time from LKW, transfer status, and clinical features. There was substantial heterogeneity between physicians with regards to what imaging they would pursue.
- Dr. Campbell spoke about the limited data regarding repeating neuroimaging in patients transferred from a PSC to a CSC, but that collaterals may influence concerns about risk of deterioration in these patients.
Consider the question you are trying to answer with neuroimaging, and try to use the fastest test that will help you answer that question.
- One point raised by Dr. Hill was that the decisions that a primary stroke center (PSC) versus a comprehensive stroke center may need to make are different, and that may impact imaging. For a PSC, the question is often which patients require transfer to a CSC. For the CSC, once the presence of a large vessel occlusion has been established, the concern may be to rule out a malignant infarction or hemorrhagic transformation that may have occurred in the time elapsed between initial imaging and transfer.
- For inter-hospital transfers, it may be prudent to ask oneself, what findings on repeat neuroimaging would change your mind about a patient’s candidacy for thrombectomy? Would a repeat non-contrast head CT be sufficient (e.g., to rule out hemorrhage), or is further imaging to evaluate concerns for an enlarging core required?
- The amount of elapsed time between transfer from the PSC to CSC may affect the decision to repeat neuroimaging upon arrival to the CSC.
We need to keep in mind center-specific limitations and variables when considering neuroimaging in acute stroke.
- Dr. Khatri highlighted the resources required to perform vessel and perfusion neuroimaging, and that the imaging resources available to smaller community hospitals may be limited compared to the imaging protocols highlighted in many of the thrombectomy trials and available to comprehensive stroke centers. She spoke about the importance of considering those factors when determining what imaging to perform prior to transfer to a CSC and working collaboratively with surrounding centers.
All in all, what struck me most about this symposium was that although we have a growing amount of data, there is a lot of practice variability in advanced neuroimaging and that neuroimaging decisions are tied into many other factors. One especially pertinent factor is the pre-hospital triage system and how patients with severe stroke ultimately end up at a CSC (whether it is bypass, drip and ship, mobile stroke, or another iteration). I can envision how CSCs that receive patients from a large geographical area and multiple hospitals with longer transfer times would have different protocols and neuroimaging needs than CSCs covering smaller geographical areas in which bypass may be more feasible and transfers may be less frequent. A theme throughout many of the lectures was to consider the time cost of repeating imaging, balanced with the additional information the physician may gain from it. Though many diverse, compelling viewpoints were articulated in this symposium, it is clear that we are all striving for the goal of treating patients as safely and as quickly as possible.