What is the role of ultrasonography in the workup of renal artery stenosis (RAS)?

Updated: Nov 02, 2020
  • Author: Bruce S Spinowitz, MD, FACP; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Renal ultrasonography scanning is performed frequently in patients with renal dysfunction. Ultrasonography scanning is an anatomic, not a functional, test. The only contribution to the entity of renal artery stenosis is a suggestion of the diagnosis when examination results indicate significant asymmetry of kidney size (ie, size discrepancy of >1.5 cm). Additionally, ultrasonography may be useful in detecting the presence of a solitary kidney, in which case, renal artery stenosis of that solitary kidney takes on more significant prognostic and therapeutic importance.

Duplex ultrasonographic scanning combines a B-mode ultrasonographic image with a pulse Doppler unit to obtain flow velocity data. The technique is noninvasive, relatively inexpensive, and can be used in patients with any level of renal function. The test is very sensitive and specific (98%); however, it is very labor intensive and technician-dependent. Thus, duplex ultrasonographic scanning may not be available in many medical centers.

Radermacher et al reported that the renal resistance index, calculated through the use of color Doppler ultrasonography, can be used to predict the outcome of invasive therapy  for renal artery stenosis.Patients with a resistance index (calculated as [1 - end-diastolic velocity divided by maximal systolic velocity] x 100) greater than 80, indicating small vessel and large vessel disease, were likely to have a poor response to angioplasty or surgery with respect to improvement in hypertension, renal function, or kidney survival. [16]


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