Vessel tortuosity causing false positives in detecting renal artery stenosis on Doppler ultrasound

Color Doppler ultrasound (CDUS) is currently preferred to screen for renal artery stenosis (RAS); however, a wide range of sensitivities and specificities have been reported. We wanted to identify potential factors contributing to this wide range and to improve CDUS screening for RAS. We noted RAS was overcalled when the peak systolic velocity (PSV) was found in the mid-main renal artery, and we sought to determine whether this was a consistent source of error.

We reviewed the medical records of patients at Northshore University Healthsystems with a positive RAS examination by CDUS from 2009 to 2012, defined as a PSV greater than 200 cm/s and/or a renal artery-to-aorta ratio greater than 3.5. Patients were included who had an elevated PSV in the mid-main renal artery and had a confirmatory imaging study (angiography, magnetic resonance angiography, or computed tomography angiography).

Of the 16 arteries demonstrating a PSV in the mid-renal artery, 15 did not have significant stenosis on the subsequent study. The 1 true positive was a patient with fibromuscular dysplasia.

This study demonstrates a high false-positive rate (94%) when the PSV is in the mid-main renal artery. We suspect this pattern is due to the tortuous mid-main renal artery causing falsely elevated velocities that meet criteria for RAS. Fibromuscular dysplasia may also produce the same pattern and should be distinguished from vessel tortuosity. If the false-positive rate of Doppler ultrasound can be decreased, fewer patients will be subjected to an unnecessary follow-up study and possibly invasive procedures.