Which ultrasound finding describes a puncture-site pseudoaneurysm?

• A. A pulsatile, anechoic mass with a neck to the artery
• B. A non-pulsatile, hyperechoic lesion with no communication to the artery
• C. A pulsatile mass with continuous forward flow into the artery
• D. A pulsatile, anechoic or hypoechoic sac with a communication neck to the arterial lumen and to-and-fro flow at the neck on color Doppler

Answer: (D)

The key finding here is a puncture-site pseudoaneurysm, which forms when blood escapes through a puncture in the artery but is contained by surrounding tissue, creating a sac that remains in communication with the arterial lumen through a narrow neck. On ultrasound, this appears as a pulsatile sac that is typically anechoic or hypoechoic. The telltale feature is the connection neck to the arterial lumen with bidirectional or to-and-fro flow at the neck on Doppler, reflecting blood moving into the sac during systole and back into the artery during diastole. Color Doppler often shows this swirling flow within the sac, sometimes described as the yin-yang sign. This combination—pulsatile, fluid-filled sac + a neck connecting to the artery + to-and-fro flow at the neck—best identifies a puncture-site pseudoaneurysm and distinguishes it from simple hematomas or other vascular lesions. The other options lack the essential neck communication and bidirectional flow.