CT Angiography in Stroke and Cerebral Atrophy
Role in Acute Stroke
CT angiography (CTA) is a rapid, highly accurate first-line vascular imaging modality for detecting large vessel occlusions in acute stroke, with sensitivity and specificity of 92-100% and 82-100% respectively, making it essential for identifying candidates for endovascular thrombectomy. 1
Primary Indications in Acute Stroke
CTA should be performed emergently in suspected acute stroke to identify large vessel occlusions (LVO) that may benefit from endovascular therapy up to 24 hours from symptom onset. 1
CTA provides critical information about vessel patency, occlusion location, clot length, and collateral circulation—all of which independently predict clinical outcome and guide treatment decisions. 2, 3
The examination should cover the entire cerebrovascular axis from aortic arch to vertex, as this identifies additional stenoses, occlusions, and other clinically significant findings that impact management. 1, 4
Technical Advantages
CTA can be obtained rapidly (within minutes) using standard CT equipment available at most emergency departments, making it more accessible than MRI for acute triage. 1, 5
CTA source images provide estimates of cerebral blood volume and can detect ischemic regions with sensitivity similar to MRI diffusion-weighted imaging, though MRI remains superior for smaller lesions and posterior fossa strokes. 1
The accuracy of CTA approaches or exceeds digital subtraction angiography for detecting large vessel occlusions, with agreement rates of 98-99% when compared to other imaging modalities. 1, 5
Specific Stroke Applications
For anterior circulation strokes, CTA reliably identifies internal carotid artery terminus occlusions, proximal and distal M1 segment occlusions, and M2 branch occlusions—critical information for endovascular treatment planning. 1
CTA should be performed within 24 hours of hospitalization or 48 hours of symptom onset in patients with minor stroke who are candidates for carotid endarterectomy or stenting, due to high early recurrent stroke risk. 1
Multiphase CTA can assess collateral circulation quality, which predicts tissue salvageability and clinical outcomes independent of other factors. 6, 3
Role in Delayed/Subacute Stroke
In late-presenting strokes (beyond acute treatment window), CTA remains useful for identifying underlying intracranial atherosclerosis and steno-occlusive disease, though the urgency is reduced and MRA can provide similar information. 1
CTA is valuable for secondary stroke prevention workup, detecting carotid stenosis and other vascular pathology that requires intervention. 1
Important Caveat
- CTA may overestimate the degree of carotid stenosis, particularly with significant carotid calcification—in these cases, carotid duplex ultrasound provides more accurate stenosis quantification. 1
Role in Cerebral Atrophy
CTA has no role in the primary diagnosis or management of cerebral atrophy, as atrophy is a parenchymal finding best assessed on non-contrast CT or MRI. 1
When CTA May Be Relevant
In patients with vascular dementia or vascular cognitive impairment (where atrophy coexists with vascular disease), CTA can detect intracranial stenoses or occlusions, though vascular imaging is not required for diagnosis—clinical criteria and evidence of end-organ brain damage on standard imaging suffice. 1
For patients with atrophy and suspected mixed vascular-degenerative dementia, non-contrast CT adequately demonstrates both atrophy and white matter changes without need for CTA. 1
Surveillance Imaging After Stroke
Non-contrast CT is the preferred modality for surveillance of established strokes to monitor for hemorrhagic conversion, mass effect, and herniation—contrast administration serves no role and may cause diagnostic confusion. 1
Specific Surveillance Scenarios
CT perfusion may be used for surveillance when known vascular lesions are present (such as complete carotid occlusion) to assess hemodynamic effects, though this does not improve outcomes when used to select patients for revascularization. 1
Cerebral angiography is reserved for select cases where non-invasive imaging findings are indeterminate or when detecting early progression of steno-occlusive disease. 1
Key Pitfalls to Avoid
Never order CT with IV contrast for acute or subacute stroke evaluation—contrast enhancement in subacute infarcts mimics hemorrhagic conversion or aggressive lesions, causing diagnostic confusion. 1
Do not rely solely on CTA for quantifying carotid stenosis when heavy calcification is present—obtain carotid duplex ultrasound for accurate stenosis measurement. 1
Recognize that CT significantly underestimates small vessel disease burden compared to MRI—if clinical symptoms suggest more extensive disease than CT shows, obtain MRI for definitive assessment. 7
CTA should ideally be performed within 1 hour of non-contrast CT in acute stroke to avoid interval hemorrhagic or ischemic changes that would alter treatment eligibility. 1