What does a CT brain image typically show in a pregnant patient who has suffered a stroke?

CT Brain Imaging Findings in Acute Ischemic Stroke

Non-contrast CT brain is the primary imaging modality for acute stroke evaluation and will show early ischemic signs in up to 94% of cases within the first 6-14 hours, including hyperdense artery sign, loss of gray-white matter differentiation, sulcal effacement, and hypodensity of deep structures. 1

Primary Purpose of Emergency CT

The three critical roles of CT imaging in acute stroke are: 2

• Exclude intracranial hemorrhage (absolute contraindication to thrombolytic therapy) 2
• Detect ischemic tissue changes to guide treatment decisions 2
• Exclude stroke mimics such as tumor, infection, or other non-vascular pathology 2

Specific Early CT Signs You Will See

Hyperdense Artery Sign

• Appears as a bright (hyperdense) middle cerebral artery indicating acute thrombus or embolus in the vessel 2, 1
• Present in approximately 22% of acute MCA strokes 3
• Never occurs in isolation—always accompanied by parenchymal changes in extended infarcts 3

Loss of Gray-White Matter Differentiation

• The normal sharp boundary between cortical gray matter and subcortical white matter becomes blurred or disappears 2, 1
• Indicates cytotoxic edema from ischemic injury 1
• Most prominent at the lateral margins of the insular cortex (loss of insular ribbon) and in the lentiform nucleus 2, 3
• Loss of insular ribbon is present in 59% of early MCA strokes and predicts large infarct size 3
• Attenuation of the lentiform nucleus occurs in 48% of cases and specifically predicts deep territory infarction 3

Sulcal Effacement

• Compression or disappearance of the normal CSF-filled sulci due to focal brain swelling 1
• Present in 69% of acute MCA strokes 3
• Specifically predicts superficial (cortical) infarction 3

Hypodensity of Brain Tissue

• Darker (hypodense) appearance of affected brain parenchyma compared to normal tissue 2, 1
• Frank hypodensity typically appears later (after 6-12 hours) but does not contraindicate thrombolytic therapy 2

Timing and Sensitivity Considerations

CT is relatively insensitive in the first 3-6 hours, showing abnormalities in less than 50% of patients initially with standard sequences. 1 However, when performed within the first 6-14 hours, early ischemic signs are detectable in up to 94% of cases. 1, 3

• CT performed before 6 hours may appear normal, particularly in the oldest patients (mean age 80 years) 3
• Posterior fossa strokes (brainstem and cerebellum) are particularly difficult to detect on CT due to beam-hardening artifact 2, 1
• Small cortical or subcortical lesions may not be visible on initial CT 2, 1

Critical Prognostic Thresholds

The One-Third MCA Territory Rule

Involvement of more than one-third of the MCA territory on early CT is a critical threshold that indicates: 1

• 8-fold increased risk of symptomatic hemorrhage after thrombolytic therapy 1
• Poor functional outcome regardless of treatment 2, 3
• Presence of two or three early signs (attenuation of lentiform nucleus, loss of insular ribbon, or sulcal effacement) predicts extended MCA infarct and poor outcome (p < 0.001) 3

Physician accuracy in detecting ischemia involving >1/3 MCA territory is approximately 70-80%, with variable reliability. 1

Imaging Protocol and Timing

For patients potentially eligible for rtPA: 1, 4

• Complete CT examination within 25 minutes of emergency department arrival 1, 4
• Interpretation within an additional 20 minutes (door-to-interpretation time of 45 minutes total) 1
• Subsequent CT scan should be obtained if the patient worsens neurologically, particularly to identify hemorrhagic transformation after rtPA administration 1, 4

What the Images Actually Show

On a non-contrast CT brain scan in acute ischemic stroke, you will see: 3, 5

1. A bright white artery (hyperdense MCA sign) in the Sylvian fissure if there is acute thrombus
2. Blurring or loss of the normal sharp edge between the gray cortex and white matter, particularly at the insula
3. Darkening (hypodensity) of the lentiform nucleus (putamen and globus pallidus) compared to the contralateral side
4. Flattening or disappearance of the cortical sulci due to swelling
5. Subtle hypodensity of the affected brain tissue compared to the normal side

Critical Pitfalls to Avoid

Do not delay thrombolytic therapy to obtain advanced imaging (MRI, CT perfusion, CT angiography) beyond non-contrast CT if the patient is otherwise eligible within the treatment window. 1, 4

A normal early CT does not exclude acute ischemic stroke—clinical assessment using the NIHSS remains paramount, and treatment decisions should be based on clinical presentation and time from symptom onset. 1, 4

Do not withhold thrombolytic therapy based solely on early ischemic changes (other than frank hypodensity), regardless of their extent, as intravenous fibrinolytic therapy is recommended even in the setting of early ischemic changes. 2

Extensive early changes (>1/3 MCA territory) increase hemorrhage risk but may not absolutely contraindicate thrombolysis in all protocols—this requires individualized risk-benefit assessment. 1

Avoid misinterpreting contrast enhancement in subacute infarcts (days to weeks later) as hemorrhagic conversion or tumor. 1