How is a pseudoaneurysm diagnosed sonographically?
A pseudoaneurysm results from laceration of an artery, again most commonly seen in the groin following femoral artery puncture and in the kidney following percutaneous renal biopsy. On gray scale imaging, a pseudoaneurysm typically appears as an ovoid, hypoechoic collection adjacent to the artery. Color Doppler imaging then further distinguishes this hypoechoic collection from a more common postprocedural hematoma. A hematoma will have no detectable color Doppler flow, whereas a pseudoaneurysm demonstrates a characteristic “yin-yang” appearance of intraluminal swirling blood as blood flows into the pseudoaneurysm along one side and out along the other. Thus, one half of the pseudoaneurysm lumen is red and the other half is blue on color Doppler imaging. The characteristic spectral Doppler waveform of a pseudoaneurysm is a “to-and-fro” flow pattern at the pseudoaneurysm neck, as blood enters the pseudoaneurysm sac during systole and exits during diastole