Three weeks after femoral artery catheterisation, a patient has a pulsatile groin swelling. Colour Doppler shows a rounded collection adjacent to the common femoral artery with swirling internal flow producing red and blue areas side by side. Spectral sampling of the neck of the collection will most likely demonstrate which waveform?
- A Triphasic waveform with sharp reverse flow
- B Continuous low-resistance forward flow
- C To-and-fro waveform ✓
- D No detectable flow
Correct answer: C. To-and-fro waveform
Explanation
The swirling flow showing simultaneous red and blue colour is the yin-yang sign of a pseudoaneurysm. Because the sac fills during systole and empties back into the parent artery during diastole through the narrow neck, spectral Doppler at the neck shows the characteristic to-and-fro waveform: forward flow in systole and reversed flow in diastole. Continuous forward flow suggests an arteriovenous fistula, and a normal triphasic pattern belongs to an unremarkable native artery.
Reference: Brant and Helms Fundamentals of Diagnostic Radiology, 5th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.