What does a pseudoaneurysm look like on CT?

How Pseudoaneurysms Appear on CT Scans

When evaluating vascular complications, radiologists often rely on computed tomography (CT) to identify abnormalities like pseudoaneurysms. Unlike true aneurysms, which involve all three layers of the arterial wall, pseudoaneurysms—sometimes called "false aneurysms"—form when blood leaks through a tear in the artery and becomes contained by surrounding tissues.

On unenhanced CT scans, a pseudoaneurysm typically presents as a rounded structure with low attenuation. This appearance reflects the presence of flowing blood within the sac that communicates with the injured artery. Because there's no contrast administered at this stage, the structure stands out due to its density relative to surrounding tissues.

However, the appearance can vary. If the pseudoaneurysm has partially clotted, areas of hyperdensity may appear due to thrombosis within the sac. Similarly, adjacent hemorrhage from recent rupture can mimic or mask the lesion, complicating diagnosis. In such cases, contrast-enhanced CT becomes essential, highlighting the classic "contrast blush" that confirms active arterial leakage and recanalization.

Common sites include the femoral artery (especially after catheter-based procedures), the splenic artery following pancreatitis, and the popliteal artery in trauma cases. Early detection is crucial, as untreated pseudoaneurysms carry risks of rupture, distal embolization, or continued bleeding.

While CT provides a strong initial assessment, correlation with clinical history—such as recent surgery, trauma, or infection—is key. When in doubt, further evaluation with CTA (CT angiography) or ultrasound with Doppler can confirm the diagnosis and guide intervention.