What imaging can disclose about suspected stroke and its Tx

Knowledge of historic details of the event, the patient (eg, known atrial fibrillation), and findings on imaging can facilitate communication between the primary care physician and inpatient teams.

In the subacute setting, MR perfusion and MR angiography of the head and the neck are often performed to identify stenosis, dissection, and more subtle mimickers of cerebrovascular accident not ascertained on initial CT evaluation. These studies are typically performed well outside the window for thrombolysis or intervention.²⁶ No guidelines specifically direct or recommend this practice pattern. The superior sensitivity and cerebral blood flow mapping of MR perfusion and MR angiography might be useful for validating a suspected diagnosis of ischemic stroke and providing phenotypic information about AIS events.

Transcranial Doppler imaging relies on bony windows to assess intracranial vascular flow, velocity, direction, and reactivity. This information can be utilized to diagnose stenosis or occlusion. This modality is principally used to evaluate for stenosis in the anterior circulation (sensitivity, 70%-90%; specificity, 90%-95%).²⁰ Evaluation of the basilar, vertebral, and internal carotid arteries is less accurate (sensitivity, 55%-80%).²⁰ Transcranial Doppler imaging is also used to assess for cerebral vasospasm after subarachnoid hemorrhage, monitor sickle cell disease patients’ overall risk for ischemic stroke, and augment thrombolysis. It is limited by the availability of an expert technician, and therefore is typically reserved for unstable patients or those who cannot receive contrast.²⁰

Carotid duplex ultrasonography. A dynamic study such as duplex ultrasonography can be strongly considered for flow imaging of the extracranial carotids to evaluate for stenosis. Indications for carotid stenting or endarterectomy include 50% to 79% occlusion of the carotid artery on the same side as a recent transient ischemic attack or AIS. Carotid stenosis > 80% warrants consideration for intervention independent of a recent cerebrovascular accident. Interventions are typically performed 2 to 14 days after stroke.³³ Although this study is of limited utility in the hyperacute setting, it is recommended within 24 hours after nondisabling stroke in the carotid territory, when (1) the patient is otherwise a candidate for a surgical or procedural intervention to address the stenosis and (2) none of the aforementioned studies that focus on neck vasculature have been performed.

Conventional (digital subtraction) ­angiography is the gold standard for mapping cerebrovascular disease because it is dynamic and highly accurate. It is, however, typically limited by the number of required personnel, its invasive nature, and the requirement for IV contrast. This study is performed during intra-arterial intervention techniques, including stent retrieval and intra-arterial thrombolysis.²⁶

Impact of imaging on treatment

Imaging helps determine the cause and some characteristics of stroke, both of which can help determine therapy. Strokes can be broadly subcategorized as hemorrhagic or ischemic; recent studies suggest that 87% are ischemic.³⁴ Knowledge of the historic details of the event, the patient (eg, known atrial fibrillation, anticoagulant use, history of falls), and findings on imaging can contribute to determine the cause of AIS, and can facilitate communication and consultation between the primary care physician and inpatient teams.³⁵

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