What are the signs of ischemic stroke on a CT (computed tomography) brain scan?

Early CT Signs of Ischemic Stroke

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

Primary CT Findings in Acute Ischemic Stroke

Hyperdense Artery Sign

• Hyperdense middle cerebral artery (MCA) sign appears as increased density of the MCA on non-contrast CT, reflecting acute arterial occlusion by thrombus 2, 3
• This sign occurs in approximately 13-22% of acute MCA strokes and is never found in isolation—it is always associated with other parenchymal signs in extended infarcts 3, 4
• The hyperdense artery sign frequently disappears on follow-up CT and indicates embolic occlusion 4

Early Parenchymal Changes

The most clinically significant early CT signs include:

• Loss of gray-white matter differentiation: Loss of the normal contrast between cortical gray matter and subcortical white matter, indicating cytotoxic edema 1

• Attenuation of the lentiform nucleus (ALN): Hypodensity or decreased attenuation of the basal ganglia structures, present in approximately 48% of early scans and significantly associated with subsequent deep infarction 3, 4

• Loss of the insular ribbon (LIR): Obscuration of the normal gray-white interface in the insular cortex, seen in 59% of early cases and associated with large infarct size 2, 3

• Hemispheric sulcal effacement (HSE): Compression or loss of visualization of cortical sulci due to focal brain swelling, present in 41-69% of cases and significantly associated with superficial infarction 3, 4

Mass Effect and Edema

• Focal or diffuse brain swelling manifests as compression of cerebrospinal fluid (CSF) spaces and sulcal effacement 1
• Midline shift may be present in approximately 5% of early cases, indicating significant mass effect 3
• CT evidence of early edema or mass effect within 3 hours is associated with an 8-fold increase in risk of symptomatic hemorrhage after thrombolytic therapy 1

Clinical Significance and Prognostic Value

Extent of Early Changes

• Involvement of more than one-third of the MCA territory on early CT is a critical threshold 1
• In patients receiving thrombolysis within 3 hours, extensive early changes (>1/3 MCA territory) were not independently associated with increased adverse outcomes in one analysis, though European trials showed increased hemorrhage risk when treatment was given within 6 hours 1
• Physician accuracy in detecting ischemia involving >1/3 MCA territory is approximately 70-80%, with variable reliability and reproducibility 1

Predictive Value of Multiple Signs

• The presence of two or three early parenchymal signs (ALN, LIR, or HSE) is significantly associated with extended MCA infarction and poor outcome 3
• Early parenchymal abnormalities predict subsequent infarct extension and hemorrhagic transformation 2
• However, some studies suggest early CT signs cannot reliably predict outcome in all patient populations 5

Timing and Sensitivity Considerations

Time-Dependent Detection

• CT is relatively insensitive for detecting acute ischemia in the first hours, showing abnormalities in less than 50% of patients initially with standard sequences 1
• Early CT abnormalities are detectable in 94% of cases when performed within 6-14 hours, with mean detection time of 6.4 hours 3
• CT scans performed earliest (mean 4.5 hours) and in oldest patients (mean age 80.1 years) are more likely to be normal 3
• Sensitivity of early CT for cerebral infarction ranges from 57% to 94%, with 100% specificity 4, 3

Limitations

• CT is less sensitive for small cortical or subcortical lesions, particularly in the posterior fossa (brainstem and cerebellum) 1, 6
• Non-contrast CT does not reliably demonstrate irreversibly damaged brain tissue in the hyperacute stage 7

Practical Imaging Protocol

Timing Requirements

• Complete CT examination within 25 minutes of emergency department arrival, with interpretation within an additional 20 minutes (door-to-interpretation time of 45 minutes) for rtPA candidates 1
• No contrast administration is necessary for initial evaluation unless CT angiography is planned 1

Follow-up Imaging

• Subsequent CT is obtained if the patient worsens neurologically and is especially helpful for identifying hemorrhagic transformation following rtPA administration 1
• Non-contrast CT is more sensitive for evaluating the extent of ischemic changes on follow-up imaging than in the hyperacute setting 1
• CT is preferred for surveillance due to quick repeatability and ease of comparison to prior examinations 1

Critical Pitfalls to Avoid

• Do not delay thrombolytic therapy to obtain advanced imaging beyond non-contrast CT if the patient is otherwise eligible 1
• Recognize that a normal early CT does not exclude acute ischemic stroke—clinical assessment remains paramount 1, 3
• Avoid misinterpreting contrast enhancement in subacute infarcts as hemorrhagic conversion or other aggressive lesions 1
• Be aware that extensive early changes (>1/3 MCA territory) increase hemorrhage risk but may not absolutely contraindicate thrombolysis in all protocols 1