Is a CT head perfusion scan necessary when the tissue plasminogen activator (tPA) (Alteplase) window has expired?

From the Guidelines

You do not necessarily need to order a CT head perfusion scan if you’re out of the TNK window, but it may be valuable in evaluating mechanical thrombectomy candidacy for patients between 4.5-24 hours from symptom onset. The decision to perform a CT head perfusion scan should be guided by the patient's clinical presentation and your institution's stroke protocols 1. For patients within the TNK window, standard non-contrast CT imaging is sufficient to rule out hemorrhage, and CT angiography can be used to assess for large vessel occlusion if mechanical thrombectomy is being considered. However, for patients beyond the TNK window, perfusion imaging can help identify salvageable brain tissue (penumbra) and guide patient selection for late-window interventions 1. Key considerations include:

• The DAWN and DEFUSE 3 trials demonstrated the benefit of mechanical thrombectomy in selected patients with large anterior circulation vessel occlusion between 6 and 24 hours from last known normal, using clinical imaging mismatch and perfusion-core mismatch as eligibility criteria 1.
• Perfusion imaging can help identify the mismatch between infarcted core and potentially salvageable tissue, allowing for appropriate patient selection for late-window interventions.
• Standard supportive care, secondary prevention, and rehabilitation planning remain essential components of management regardless of reperfusion therapy eligibility. It is essential to strictly adhere to the eligibility criteria from the DAWN or DEFUSE 3 trials when selecting patients for mechanical thrombectomy beyond 6 hours from onset 1.

From the Research

CT Head Perfusion Scan Outside the TNK Window

• The decision to order a CT head perfusion scan outside the TNK (tissue plasminogen activator) window is complex and depends on various factors, including the patient's condition and the availability of other imaging modalities 2, 3.
• Studies have shown that CT perfusion imaging can be useful in selecting patients for mechanical thrombectomy, even outside the traditional TNK window 4, 5.
• However, the benefit of CT perfusion imaging in this context is still a topic of debate, and some studies have found that it may not significantly improve outcomes 3, 5.
• The use of automated CT perfusion imaging has been shown to be effective in identifying patients who may benefit from mechanical thrombectomy, with a sensitivity of 84% for identifying the infarct core 4.
• The cost-effectiveness of CT perfusion imaging in this context is also an important consideration, with some studies suggesting that it may be cost-effective for patients presenting at 6 to 24 hours after stroke symptom onset 4.

Key Findings

• CT perfusion imaging can be useful in selecting patients for mechanical thrombectomy outside the TNK window 4, 5.
• The benefit of CT perfusion imaging in this context is still a topic of debate 3, 5.
• Automated CT perfusion imaging has been shown to be effective in identifying patients who may benefit from mechanical thrombectomy 4.
• The cost-effectiveness of CT perfusion imaging in this context is an important consideration 4.

Imaging Modalities

• CT perfusion imaging is one of several imaging modalities that can be used to evaluate patients with acute ischemic stroke 2, 3.
• Other imaging modalities, such as diffusion-weighted MRI, may also be useful in this context 4.
• The choice of imaging modality will depend on the patient's condition and the availability of other imaging modalities 2, 3.