We describe adapting a Limited Stroke Protocol of unenhanced MRI pulse sequences (including diffusion-weighted images to diagnose recent cerebral infarction and TOF MR angiography to detect large intracranial vessel stenosis/occlusion), for hospital inpatients and the Emergency Room patients with suspected recent ischemic stroke. Although this abbreviated, targeted limited MRI protocol may be challenging in subtle diagnosis, it improves patient access, enables image-guided decision-making, and results in rapid throughput.
Clinical Question:
Limited Stroke Protocol is designed to rapidly determine whether acute neurological symptoms are caused by recent cerebral infarction (on DWI) and whether there is large intracranial vessel stenosis/occlusion (on MRA): the results will determine primary treatment and secondary prevention of ischemic stroke.Impact:
Ischemic stroke is a major cause of mortality and morbidity, and MRI can be a viable alternative to current best practice using computed tomography (CT) for decision-making. Patients who may benefit include those with acute (thrombolysis candidates within 6 hours of ictus) or subacute stroke (who do not qualify for therapeutic time window). This latter subgroup, which comprise a much larger proportion of patients in a typical referral hospital casemix can potentially benefit from improved access to image-guided decision-making, particularly from the Emergency Room (ER).Approach:
We use a Limited Stroke Protocol, which comprises an abbreviated unenhanced MRI pulse sequence that includes diffusion-weighted images, T2-weighted images, gradient-recalled echo images, and time-of-flight MR angiography. The Limited Stroke Protocol study is available on a 24 hour on-demand basis for all inpatients and ER patients with clinical diagnosis of Ischemic stroke. This allows improved access to clinical decision-making in selected patients, who might otherwise undergo initial CT, followed by delayed full MRI protocol. The key differences between the Limited Stroke Protocol and CT-based techniques include improved sensitivity to acute ischemic infarction and Circle of Willis occlusion without requiring contrast media injection, stroke subtyping (into large vessel, small vessel and cardioembolic causes), and potentially faster throughput and decreased average length of hospital stay.Gains and Losses:
Potential pitfalls include misdiagnosis of non-ischemic conditions that show increased signal intensity on DWI that may mimic ischemic stroke (common misdiagnosis included lymphoma, encephalitis). Failure of limited sequence MRI to detect and diagnose subtle subarachnoid hemorrhage and meningitis may also be risks. Changing referral patterns and unintended consequences include broadening of the clinical suspicion of ischemic stroke to include transient ischemic attack, dizziness and altered mental status; these have the potential to change systems-based practice, with both advantages and disadvantages.Preliminary Data:
Hyperintensity on DWI with very high contrast-to-noise ratio is superior to more subtle low density of acute ischemic stroke on CT.