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Difficulty: MediumInterpreting Imaging Results

A 68-year-old woman is brought to the emergency department by emergency medical services at 07:30 due to sudden neurological deficits. Her husband reports that they went to bed at 22:00 the previous night, at which time she was at her baseline. Upon waking at 07:00, she was found to have dense right-sided weakness and severe difficulty speaking. On examination, her blood pressure is 165/90 mmHg, heart rate is 88/min, and oxygen saturation is 98% on room air. Neurologic examination reveals right-sided hemiplegia, a right facial droop, and expressive aphasia. The clinical team activates the acute stroke protocol for a suspected 'wake-up' ischemic stroke. Arrange the following imaging modalities and confirmatory protocols in the most appropriate sequential order for the diagnostic workup and management of this patient, from first to last.

  1. 1Non-contrast computed tomography (NCCT) of the head
  2. 2Computed tomography angiography (CTA) of the head and neck
  3. 3Magnetic resonance imaging (MRI) of the brain with diffusion-weighted (DWI) and fluid-attenuated inversion recovery (FLAIR) sequences
  4. 4Endovascular digital subtraction angiography (DSA)

Answer

The correct sequential order for evaluating a wake-up stroke is: NCCT of the head, CTA of the head and neck, MRI of the brain with DWI/FLAIR sequences, and finally Endovascular DSA.
The standard imaging sequence for a wake-up stroke prioritizes speed and sequential exclusion of contraindications based on consecutive interpretations. Non-contrast CT is strictly the first step to rule out hemorrhage. CT angiography immediately follows to detect large vessel occlusions. Because the exact time of symptom onset is unknown in a wake-up stroke, tissue viability must be assessed. This is effectively done by interpreting an MRI for a DWI-FLAIR mismatch (presence of acute ischemia on DWI without corresponding hyperintensity on FLAIR), which determines if intravenous thrombolysis is safe and indicated. Finally, if a large vessel occlusion is found and salvageable tissue is present, the patient proceeds to the neurointerventional suite for digital subtraction angiography and mechanical thrombectomy.

Step-by-Step Solution

1
Rule out intracranial hemorrhage
Perform Non-contrast CT of the head.
Hemorrhage is an absolute contraindication to thrombolytic and endovascular therapies; NCCT is the fastest modality for this.
2
Identify potential large vessel occlusion
Perform CT Angiography of the head and neck.
Detects proximal occlusions (e.g., MCA M1 segment) that may benefit from endovascular mechanical thrombectomy.
3
Assess tissue viability and estimate stroke timeline
Perform MRI of the brain with DWI and FLAIR.
A DWI-FLAIR mismatch indicates the stroke likely occurred within the last 4.5 hours, identifying patients who may safely receive thrombolytics despite an unknown onset time.
4
Confirm occlusion and perform intervention
Perform Endovascular Digital Subtraction Angiography.
Provides definitive diagnostic confirmation of the vascular anatomy and allows for simultaneous mechanical thrombectomy.

Key Concept

Step-wise imaging evaluation of wake-up strokes requires sequentially ruling out hemorrhage, identifying large vessel vascular occlusion, determining tissue viability via perfusion or DWI-FLAIR mismatch, and finally performing therapeutic angiography.
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Interpreting Imaging Results

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