Diagnostic Ultrasound - Abdomen and Pelvis

Renal Artery Stenosis
Diagnoses: Urinary Tract
TERMINOLOGY
• Hemodynamically significant narrowing of renal arterial
lumen
IMAGING
• Poststenotic "jet" and turbulent flow on color Doppler US
○ Abnormally high peak systolic velocity with anglecorrected
spectral Doppler in main renal artery
immediately distal to stenosis
○ Peak systolic velocity in and immediately distal to
stenosis ≥ 180-200 cm/sec
○ Accurate Doppler angle ≤ 60° essential for velocity
measurements
• Diminished downstream systolic peaks
○ Abnormally low peak systolic velocity in arcuate arteries
with diminished resistive indices (RI)
○ Tardus et parvus waveform shape, late and small systolic
peaks
KEY FACTS
– Low resistive index < 0.5 (compare with other kidney)
due to dampened systolic peaks and normal diastolic
flow
– Prolonged acceleration time (time to peak systole) >
0.07 seconds
– Acceleration index (AI) < 3 m/s²
PATHOLOGY
• Atherosclerosis
○ Ostium or proximal 2 cm of renal artery
• Fibromuscular dysplasia
○ Most common mid or distal main renal artery
• Aortic dissection
• Aortic aneurysm (renal artery compression)
• Thromboembolism
• Other vasculitides
• Retroperitoneal fibrosis
• Trauma with renal artery dissection
(Left) Renal artery stenosis
and parvus tardus due to
aortic dissection are shown.
Note the prolonged
acceleration time ſt. (Right)
Spectral Doppler ultrasound in
another patient shows a peak
systolic velocity of 319 cm/sec
at location of aliasing,
consistent with high grade
stenosis. The renal:aortic ratio
was 4.0.
(Left) Transverse spectral
Doppler ultrasound in the
same patient illustrates
diminished systolic peaks and
resistive indices (RI) < 0.5
distal to the right renal artery
stenosis. (Right) Oblique
maximum intensity projection
from MRA shows duplicated
right renal arteries ſt, with
the more superior exhibiting a
significant stenosis st. It is
easy to envision why renal
artery duplication is often
missed with US and
complicates assessment of
intrarenal flow dynamics.
512