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Difficulty: HardInterpreting Imaging Results

A 72-year-old woman is brought to the emergency department at 07:00 by emergency medical services. Her husband found her awake but with profound right-sided weakness and an inability to speak when they woke up at 06:30. She was last known well at 22:30 the previous night. On presentation, her blood pressure is 165/90 mm Hg and her heart rate is 88/min and irregularly irregular. Neurologic examination reveals global aphasia, a right facial droop, and right hemiplegia (NIH Stroke Scale score of 18).

Arrange the following neuroimaging modalities and interventional procedures in the most appropriate step-wise sequence for evaluating this patient for acute reperfusion therapy.

  1. 1Non-contrast computed tomography (NCCT) of the head
  2. 2Computed tomography angiography (CTA) of the head and neck
  3. 3Computed tomography perfusion (CTP) imaging of the brain
  4. 4Transcatheter digital subtraction angiography (DSA) of the cerebral vasculature

Answer

The correct sequence is Non-contrast CT of the head, followed by CTA of the head and neck, then CTP of the brain, and finally DSA of the cerebral vasculature.
The evaluation of late-window or wake-up stroke follows a strict protocol based on the DAWN and DEFUSE-3 trial criteria. The interpretation of each imaging modality serves as a necessary gatekeeper for the subsequent step. First, a Non-contrast CT (NCCT) must be interpreted to exclude intracranial hemorrhage. Without this step, administering contrast is contraindicated. Second, a CT Angiography (CTA) is interpreted to identify a proximal large vessel occlusion (LVO) that could be targeted for clot retrieval. Third, because the patient was last known well >6 hours ago, a CT Perfusion (CTP) scan must be interpreted to calculate the ischemic core volume and the surrounding salvageable penumbra. Finally, if the mismatch criteria are favorable, the patient is taken for Digital Subtraction Angiography (DSA) for mechanical thrombectomy.

Step-by-Step Solution

1
Rule out intracranial hemorrhage
Non-contrast computed tomography (NCCT) of the head
NCCT is the fastest and most reliable initial modality to exclude hemorrhage, which is an absolute contraindication to all reperfusion therapies.
2
Identify a target for endovascular intervention
Computed tomography angiography (CTA) of the head and neck
Once hemorrhage is excluded, interpretation of the CTA is necessary to detect a proximal large vessel occlusion (LVO) amenable to mechanical thrombectomy.
3
Assess tissue viability and mismatch
Computed tomography perfusion (CTP) imaging of the brain
Because the patient is in an extended time window (wake-up stroke, >6 hours), CTP interpretation is required to prove a favorable ratio of salvageable penumbra to unsalvageable ischemic core.
4
Perform definitive diagnostic and therapeutic intervention
Transcatheter digital subtraction angiography (DSA) of the cerebral vasculature
After non-invasive imaging criteria are met, DSA provides dynamic visualization and serves as the conduit for mechanical thrombectomy.

Key Concept

In patients with acute ischemic stroke of unknown time of onset or >6 hours from last known well, the imaging algorithm requires a step-wise interpretation starting with NCCT (to rule out hemorrhage), followed by CTA (to identify large vessel occlusion), and CTP (to identify salvageable mismatch), before proceeding to DSA for mechanical thrombectomy.
Estimated Time:1m 30s
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Interpreting Imaging Results

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