Post-Puncture Pseudoaneurysm: Ultrasound Criteria and Measurements

Clinical Task

A post-puncture pseudoaneurysm is a localized cavity with blood flow outside the artery lumen, maintaining communication with the artery through a neck. For the ultrasound diagnostician, the key task is not limited to the phrase 'pseudoaneurysm present': it is necessary to prove arterial communication, describe the neck anatomy, and assess conditions for treatment. The updated AIUM Practice Parameter for Peripheral Arterial Ultrasound, 2025 considers peripheral arterial ultrasound as an examination that adapts to the clinical question and includes B-mode, color, and spectral Doppler.

After catheterization, the femoral artery puncture area is more frequently examined, but the same approach applies to radial, brachial, and other accessible peripheral arteries. It is important to simultaneously exclude alternatives: non-vascular hematoma, true aneurysm, arteriovenous fistula, active bleeding, and impaired distal blood flow.

Minimal Scanning Protocol

The examination is performed from the original artery to the area of tenderness, swelling, or pulsating mass. B-mode determines hematoma, fluid or mixed cavity, thrombotic masses, depth of location, and relation to the skin. Color Doppler is used to search for blood flow within the cavity and communication with the artery. Spectral Doppler is mandatory in the neck, as this is where the diagnostic bidirectional flow is recorded.

Settings should allow visualization of low-velocity and turbulent flow without excessive suppression of the color signal. Minimal probe pressure is required: strong compression can temporarily reduce blood flow in the neck and lead to a false-negative conclusion. In complex hematomas, it is useful to scan in longitudinal and transverse planes, tracing the artery proximally and distally to the defect.

Ultrasound Criteria for Pseudoaneurysm

The diagnosis is based on a combination of morphology and Doppler signs. B-mode may show an anechoic or heterogeneous cavity near the artery, but alone it does not distinguish a pseudoaneurysm from a hematoma. Color Doppler reveals blood flow in the cavity, often with bidirectional coding due to turbulence. This sign is often called 'yin-yang,' but it is not a standalone definitive criterion without neck visualization.

The most specific sign for post-puncture pseudoaneurysm is the 'to-and-fro' spectral signal in the neck. In one phase of the cardiac cycle, blood enters the cavity from the artery, and in another, it partially returns from the cavity to the artery. Therefore, the spectral Doppler sample volume should be placed precisely in the communication channel, not in the center of the sac, where the spectrum may be chaotic and less interpretable.

Neck: What Must Be Described

The neck is the main focus before choosing treatment. The protocol specifies the source artery, point of origin, neck length, neck width, and course direction. If the neck is short, wide, tortuous, or poorly separated from the cavity, this should be explicitly reflected in the conclusion, as such features affect the possibility of compression, thrombin injection, and surgical tactics.

Spectral Doppler in the neck is documented with an image showing the characteristic bidirectional signal. Angle correction may be challenging due to turbulence and a short channel, so it is more important to confirm the phasic flow and the localization of the sample volume. The description of the neck should not be replaced solely by peak velocity: the AIUM parameter for peripheral arteries does not set treatment velocity thresholds for post-puncture pseudoaneurysm.

Pseudoaneurysm Cavity: Measurements Before Treatment

The cavity is measured in three orthogonal directions: longitudinal, transverse, and anteroposterior. The active part with blood flow and the thrombosed part, if distinguishable, are described separately. It is important not to include the entire surrounding hematoma without blood flow in the 'active chamber' size: for interventional planning, these are different entities.

If the cavity is multi-chambered, the number of chambers should be described, their connections, and the presence of a single or multiple necks. In partial thrombosis, the protocol records the residual lumen with blood flow, the thickness/location of thrombotic masses descriptively, and the proximity of active flow to the skin. In follow-up studies, comparison is made in the same planes and with the same components: overall hematoma, active cavity, neck.

Artery, Vein, and Distal Blood Flow

AIUM emphasizes that peripheral arterial ultrasound should be clinically directed and document significant vascular findings. In post-puncture complications, this means assessing the artery proximally and distally to the pseudoaneurysm: patency, local wall defect, thrombosis, dissection, stenotic compression by hematoma. None of these points replace pseudoaneurysm diagnosis, but each can change further tactics.

The adjacent vein is examined to exclude arteriovenous fistula and venous thrombosis or compression. In a fistula, the vein receives pulsating arterialized flow, and a low-resistance spectrum may appear in the feeding artery. If a fistula is combined with a pseudoaneurysm, the conclusion should describe both components, not choose one diagnosis.

What to Write in the Conclusion

The conclusion should be suitable for the physician who will perform compression, puncture treatment, or surgery. The optimal wording includes localization, source artery, cavity dimensions, neck dimensions, presence of 'to-and-fro,' partial thrombosis, hematoma, vein condition, and distal flow. If the study is limited by pain, dressing, obesity, gas in soft tissues, or inability to compress with the probe, this is indicated separately.

Example: 'In the projection of the common femoral artery puncture, a post-puncture pseudoaneurysm is determined: cavity with blood flow, partially thrombosed; a neck from the anterior artery wall is visualized, bidirectional 'to-and-fro' flow is recorded in the neck. No signs of arteriovenous fistula obtained. Distal arterial blood flow preserved.' Specific dimensions are added from measurements performed in this study.

What Not to Write as an Ultrasound Criterion

Phrases like 'pulsating hematoma' or 'probable pseudoaneurysm' are insufficient without Doppler confirmation of communication with the artery. Color filling of the cavity without a spectrum in the neck is also weaker than full documentation of 'to-and-fro.' Do not specify a treatment size threshold as a universal rule unless set by a local protocol or a specialized treatment document: AIUM 2025 is a parameter for performing and documenting peripheral arterial ultrasound, not an algorithm for choosing a post-puncture pseudoaneurysm treatment method.

It is also undesirable to mix the size of the hematoma and the size of the active pseudoaneurysm into one number. For dynamics after compression or thrombin, it is crucial to distinguish the absence of flow in the cavity, residual blood flow in the chamber, preservation of the neck, and changes in the surrounding hematoma.