Characterization of renal artery stenoses based on magnetic resonance renal flow and volume measurements

The benefits of percutaneous angioplasty of renal artery stenosis is not known. In an attempt to better define the patient subgroup most likely to benefit from a revascularization procedure, the relationship between renal arterial morphology, blood flow volume, and renal volume was investigated using magnetic resonance (MR) techniques.

Analysis was based on arterial flow volume and renal volume measurements of 130 kidneys in 65 patients with clinically suspected renal vascular disease. Significant renal arterial stenosis (RAS), documented by contrast-enhanced three-dimensional MR angiography, compromised blood supply to 31 kidneys. Renal volume measurements were related to the body mass index to derive the renal volume index (RVI). The RVI of 72 kidneys in 36 patients without evidence of RAS or severe renal insufficiency was used as a standard of reference to differentiate normal-volume from reduced-volume kidneys.

Eighteen out of 31 RAS kidneys were significantly reduced in volume (3.08 +/- 0.75); the volume of the remaining 13 kidneys was within one standard deviation of the normal reference value. Flow volumes in kidneys with RAS were significantly reduced compared with kidneys without RAS (91.56 vs. 279.15 ml/min). Based on the RFI values (RFI = flow volume/renal volume), there was only minimal overlap between normal volume kidneys with RAS (0.73 +/- 0.34) and kidneys without RAS (2.02 +/- 0.59). RFI values of small volume kidneys with RAS (1.55 +/- 0.47), on the other hand, overlapped with both groups.

Normal volume kidneys with impaired arterial flow caused by RAS can be differentiated from those without based on a flow index (RFI). These data suggest the existence of a critical cut-off value (flow index <1.2 ml/min per cm3 of renal tissue) beyond which the renal parenchyma starts shrinking.