When should a follow-up scan be done after an ischemic stroke?

Timing of Follow-up Imaging After Ischemic Stroke

A follow-up CT or MRI scan should be performed 24 hours after an ischemic stroke, even if the patient is clinically stable, particularly for patients who received thrombolytic therapy. 1

Initial Imaging Timeline

• Initial brain imaging (CT or MRI) must be performed within 30 minutes of hospital admission for all acute stroke patients 2
• For patients who are candidates for thrombolytic therapy, the goal is to complete CT examination within 25 minutes of arrival at the emergency department, with interpretation within an additional 20 minutes (door-to-interpretation time of 45 minutes) 2
• Most patients should initially be admitted to monitored stroke unit beds for a minimum monitoring phase of 24 hours 2

Follow-up Imaging Recommendations

Standard Follow-up Timing

• A repeat CT or MRI brain scan should be performed at 24 hours after initial stroke event or thrombolytic therapy, regardless of clinical stability 1
• For patients with intracerebral hemorrhage, follow-up CT scans at approximately 6 and 24 hours after onset appear adequate to exclude hemorrhagic expansion and document final hemorrhage volume 2
• The 24-hour follow-up CT scan is required before starting anticoagulants or antiplatelet agents for secondary stroke prevention 1

Special Circumstances for Earlier Imaging

• For patients who experience clinical deterioration, emergency CT scanning should be performed immediately 1
• Neurological assessments should be performed every 15 minutes during tPA infusion, every 30 minutes for the next 6 hours, then hourly until 24 hours after treatment 1
• Beyond the first 24 hours, serial imaging is generally guided by the clinical picture of the patient 2

What to Expect on Follow-up Imaging

• Resolution or stability of initial ischemic changes is the desired outcome 1
• No evidence of hemorrhagic transformation is a favorable finding 1
• Infarct progression may be observed and is an abnormal finding 1
• About one-quarter of acute stroke cases with an initially negative head CT will have evidence of acute/subacute infarction on follow-up MRI within 1-2 days 2

Clinical Value of Follow-up Imaging

• Follow-up imaging helps confirm the diagnosis of acute ischemic stroke, which may improve patient education and adherence to prevention regimens 2
• MRI with diffusion-weighted imaging is particularly helpful in evaluating patients with low-risk TIA and mild neurological symptoms 2
• For posterior circulation strokes, a follow-up MRI may be appropriate to confirm diagnosis even when initial MRI is negative 2
• Follow-up imaging can detect complications such as hemorrhagic transformation, which may necessitate delaying antiplatelet therapy 1

Pitfalls and Caveats

• 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
• After the first 3 hours of stroke onset, the odds of detecting CT ischemic changes increase significantly with time, making timing of follow-up imaging important 3
• X-ray hypoattenuation on CT within the first 6 hours is highly specific (85%) for irreversible ischemic brain damage 4

Imaging Modality Selection for Follow-up

• CT head without IV contrast is usually preferred for follow-up due to its quick repeatability and ease of comparison to prior examinations 2
• MRI is more accurate for detecting chronic intracerebral hemorrhage and small intraventricular hemorrhages 2
• There is no role for IV contrast in CT evaluation of evolving or subacute infarct, as contrast enhancement within previously undocumented subacute infarcts can cause confusion with other brain lesions 2