When should a CT scan be repeated and what are the expectations after thrombolysis (tissue plasminogen activator (tPA)) for ischemic stroke?

CT Scan Timing and Expectations After Thrombolysis for Ischemic Stroke

A repeat CT or MRI brain scan should be done 24 hours after thrombolysis to assess for hemorrhagic transformation and infarct progression, regardless of the patient's clinical status. 1

Timing of Follow-up Imaging

• A repeat CT or MRI brain scan should be performed 24 hours after the initial stroke event in patients treated with thrombolysis, even if the patient is clinically stable 1
• For patients who experience clinical deterioration (worsening neurological status, severe headache, acute hypertension, nausea, or vomiting), emergency CT scanning should be performed immediately 1
• Neurological assessments should be performed every 15 minutes during the tPA infusion, every 30 minutes for the next 6 hours, then hourly until 24 hours after treatment 1

What to Expect on Follow-up Imaging

Normal Findings

• Resolution or stability of initial ischemic changes 1
• No evidence of hemorrhagic transformation 1

Abnormal Findings to Look For

• Hemorrhagic transformation, which occurs in approximately 15% of cases 2
• Infarct progression 1
• Cerebral edema with or without mass effect 3
• Contrast staining that may mimic hemorrhage (particularly if CTA or CTP was performed during initial evaluation) 4

Clinical Implications of Follow-up Imaging

• The 24-hour follow-up CT scan is required before starting anticoagulants or antiplatelet agents for secondary stroke prevention 1
• Findings on the 24-hour CT scan impact acute management in approximately 7-12% of patients 2, 3
• Management changes may include:
  • Delaying antiplatelet therapy in cases of hemorrhagic transformation 1
  • Need for neurosurgical intervention (rare, approximately 0.3% of cases) 2
  • Adjustments to blood pressure management 3
  • Extended monitoring or hospitalization 3

Risk Factors for Abnormal Findings on Follow-up Imaging

• Advanced age 2, 3
• Higher stroke severity (NIHSS score) 2, 3
• Mechanical thrombectomy in addition to thrombolysis 2
• Atrial fibrillation 2
• Elevated admission blood glucose (≥140 mg/dL) 3

Special Considerations

• Dual-energy CT (DECT) may help differentiate contrast staining from true hemorrhage in patients who received contrast during initial imaging (CTA/CTP), potentially changing the radiological diagnosis in approximately 10% of cases with suspected hemorrhage 4
• Recent research suggests that routine follow-up imaging may not be necessary for all patients, particularly those with low NIHSS scores who remain clinically stable 5, 2
• The 24-h CT score can help stratify patients' risk for clinically relevant findings: NIHSS score 5-15 (+3 points); NIHSS score ≥16 (+5 points); age <75 years (+1 point); admission glucose ≥140 mg/dL (+1 point) 3
  • Low risk (score ≤4): 4.3% have clinically relevant findings
  • Medium risk (score 5): 11.3% have clinically relevant findings
  • High risk (score ≥6): 21.4% have clinically relevant findings

Pitfalls and Caveats

• Contrast staining from prior CTA/CTP can mimic hemorrhage on follow-up CT, potentially leading to unnecessary delays in antiplatelet therapy 4
• Relying solely on clinical examination without follow-up imaging may miss asymptomatic hemorrhagic transformation 1
• Delay in obtaining follow-up imaging may postpone initiation of secondary stroke prevention measures 1
• Current guidelines still recommend routine 24-hour imaging despite emerging evidence questioning its necessity in all patients 1, 5