Stroke vs Aneurysm on Scans: How Doctors Spot the Difference Under Pressure

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Once the plain scan establishes whether blood is present, clinicians immediately transition the patient to CT angiography (CTA). By injecting an iodinated contrast agent through a peripheral intravenous line, clinicians turn the cerebral vascular tree visible under dynamic X-ray scanning. CTA bridges the gap between seeing the effect of vascular damage and identifying its precise anatomical cause.

In cases where the plain CT shows subarachnoid hemorrhage, CTA serves as the definitive anatomical roadmap for neurosurgeons. Most intracranial aneurysms arise at arterial branch points along the circle of Willis, a vascular ring at the base of the brain where hemodynamic stress is highest. The anterior communicating artery, posterior communicating artery, and the bifurcation of the middle cerebral artery account for the vast majority.

CTA reconstruction displays these structures in high-resolution three dimensions, exposing the precise morphology of the aneurysm: its neck width, dome diameter, aspect ratio, and whether secondary blebs (daughter sacs) are protruding from its walls. Identifying an irregular, multilobular dome confirms the exact site of rupture among patients who possess multiple incidental unruptured lesions.

If the non-contrast scan showed no bleeding, CTA plays the opposite role: hunting for large vessel occlusions (LVOs). Instead of looking for an abnormal bubble of blood protruding outward, the radiologist tracks the flow of contrast down major channels like the internal carotid or middle cerebral arteries, looking for an abrupt, square-edged stop where an embolus has blocked contrast flow entirely.