Hemodynamically significant narrowing of renal artery (RA)

Poststenotic “jet” and turbulent flow on color Doppler

• ○
  

  Abnormally high peak systolic velocity with angle-corrected spectral Doppler in main RA immediately distal to stenosis

  
  
• ○
  

  Peak systolic velocity in and immediately distal to stenosis ≥ 180-200 cm/s

Diminished downstream systolic peaks

• ○
  

  Abnormally low peak systolic velocity in arcuate arteries with diminished resistive indices

  
  
• ○
  

  Tardus et parvus waveform shape

  
  
  
  
  • –
    

    Low resistive index < 0.5 due to dampened systolic peaks and normal diastolic flow

    
    
  • –
    

    Acceleration time (time to peak systole) > 0.07 s

    
    
  • –
    

    Acceleration index < 3 m/s²

  
  
  
  
• ○
  

  These downstream effects are very different from poststenotic high-velocity jet

Ultrasound may be used for screening, followed by contrast-enhanced MRA or CTA

DSA may be needed for accurate fibromuscular dysplasia diagnosis in distal RA, hilar branches due to higher spatial resolution

Atherosclerosis: Ostium or proximal 2 cm of RA

Fibromuscular dysplasia: Mid or distal main RA

Aortic dissection or aneurysm (RA compression)

Thromboembolism

Other vasculitides

Retroperitoneal fibrosis

Trauma with RA dissection

Scanning in decubitus or oblique position in coronal plane through posterior axillary line will allow improved Doppler evaluation of segmental arteries

Evaluation of RA ostium can be best achieved via epigastric window; use superior mesenteric artery or renal vein as landmarks; if this window is obscured by bowel gas, left lateral decubitus position with probe in sagittal orientation from below ribs may be used

Right RA can be seen arising from aorta via longitudinal transhepatic view; by angling probe, both RAs can be seen arising from aorta in this view, creating “banana peel” view, which demonstrates both RA origins in 1 image