When is a repeat cranial CT scan recommended in a patient with ischemic stroke, particularly those with uncontrolled hypertension, diabetes, hyperlipidemia, or taking anticoagulant medications such as warfarin (International Normalized Ratio (INR)) or novel oral anticoagulants like apixaban (Factor Xa inhibitor) or rivaroxaban (Factor Xa inhibitor)?

Repeat Cranial CT Scan in Ischemic Stroke

Routine 24-Hour Follow-Up Imaging

All patients with ischemic stroke should undergo repeat CT or MRI brain scan at 24 hours after the initial stroke event or thrombolytic therapy, regardless of clinical stability. 1, 2 This mandatory follow-up scan serves multiple critical purposes: excluding hemorrhagic transformation, confirming infarct evolution, and determining safety for initiating anticoagulant or antiplatelet therapy for secondary stroke prevention. 1, 2

Emergency Repeat CT Indications

Immediate repeat CT scanning is required for any neurological deterioration, regardless of the time since initial imaging. 3, 4, 1 Specific triggers include:

• Decline in level of consciousness or change in Canadian Neurological Scale score by ≥1 point 3
• Worsening NIHSS score by ≥4 points from baseline 3
• New or progressive neurological deficits suggesting hemorrhagic conversion or infarct expansion 4, 1
• Signs of increased intracranial pressure including progressive headache, nausea, vomiting, or cranial nerve palsies 4

Special Considerations for High-Risk Patients

Patients on Anticoagulation (Warfarin, Apixaban, Rivaroxaban)

Patients taking anticoagulants require the mandatory 24-hour follow-up CT before resuming any antithrombotic therapy. 1, 2 The risk of hemorrhagic transformation is elevated in anticoagulated patients, making this imaging checkpoint non-negotiable for treatment decisions. 5, 6

Patients Receiving Thrombolysis

For patients treated with IV tPA, perform repeat CT at 24 hours even if clinically stable, and immediately for any deterioration. 1 During tPA infusion and the subsequent 24 hours, neurological assessments should occur every 15 minutes during infusion, every 30 minutes for 6 hours post-treatment, then hourly until 24 hours. 1 Any clinical worsening mandates emergency CT to exclude symptomatic intracranial hemorrhage. 1

Cerebellar Stroke Patients

Cerebellar infarction requires more intensive monitoring with lower threshold for repeat imaging. 4 High-risk features on initial CT include:

• Hypodensity affecting ≥2/3 of cerebellar hemisphere 4
• Compression or displacement of 4th ventricle 4
• Obstructive hydrocephalus 4
• Brainstem displacement or basal cistern compression 4

For cerebellar strokes with high-risk features, perform clinical assessments every 1-2 hours and consider repeat CT within 24-48 hours even if stable, as approximately 20% develop mass effect requiring surgical intervention. 4

Patients with Uncontrolled Hypertension, Diabetes, or Hyperlipidemia

These comorbidities increase hemorrhagic transformation risk but do not change the fundamental imaging algorithm: mandatory 24-hour follow-up CT and immediate imaging for any clinical deterioration. 3, 1 The presence of these risk factors should lower your threshold for obtaining emergency repeat imaging when subtle clinical changes occur. 3

Monitoring Framework Prior to Repeat Imaging

Hourly neurological assessments are the minimum standard for acute stroke patients, with more frequent monitoring (every 15-30 minutes) for those receiving thrombolysis or with high-risk features. 3, 1 Blood pressure should be monitored at least hourly, with more frequent checks as clinical condition requires. 3

Critical Pitfalls to Avoid

• Never delay imaging when clinical deterioration occurs - signs of brainstem compression appear late and can lead to sudden respiratory arrest, particularly in cerebellar strokes 4
• Do not rely solely on clinical examination to exclude hemorrhagic transformation, as asymptomatic hemorrhage can occur 1
• Do not start anticoagulants or antiplatelet agents before obtaining the 24-hour follow-up CT scan 1, 2
• Do not use contrast-enhanced CT for routine surveillance, as enhancement can mimic hemorrhagic conversion 4

Imaging Modality Selection

Noncontrast CT is the preferred modality for repeat imaging due to quick repeatability, ease of comparison to prior examinations, and superior sensitivity for detecting hemorrhagic transformation and mass effect. 4, 2 MRI is more accurate for detecting small hemorrhages but should not delay urgent clinical decisions. 2