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Urine Attenuation Ratio: A New CT Indicator of Renal Artery Stenosis

¹ Department of Radiology and Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul 110-744, Korea.
² Department of Radiology, Seoul National University Boramae Hospital, 425 Shindaebang-2-dong, Dongjak-gu, Seoul 156-707, Korea.

View larger version (92K): [in a new window]   Fig. 1A —33-year-old woman with unilateral renal artery stenosis (RAS) in left main renal artery. On pyelographic phase image, urine CT attenuation values of right (1)and left (02) renal pelves are 647.1 H and 2,131.6 H, respectively. Ratio is 3.29. This ratio reflects presence of functionally significant RAS in left side. Difference in attenuation between renal pelves was distinct on image obtained using wide window settings (window, 2,000 H; level, 300 H).

View larger version (113K): [in a new window]   Fig. 1B —33-year-old woman with unilateral renal artery stenosis (RAS) in left main renal artery. On subsequent intraarterial digital subtraction angiography image, focal grade 3 stenosis in left main renal artery is well visualized, which correlates exactly with grade of stenosis on CT angiography.

View larger version (112K): [in a new window]   Fig. 2A —31-year-old man with unilateral renal artery stenosis (RAS) in right main renal artery. On pyelographic phase image, urine CT attenuation values of right (01) and left (02) renal pelves are 2,470.0 H and 617.4 H, respectively. Ratio is 4.0. This ratio reflects presence of functionally significant RAS in right side. Difference in attenuation between both renal pelves was distinct on image obtained using wide window settings (window, 2,500 H; level, 350 H). Note multiple collateral vessels (arrows) in right renal hilum and retrocaval area.

View larger version (151K): [in a new window]   Fig. 2B —31-year-old man with unilateral renal artery stenosis (RAS) in right main renal artery. Intraarterial digital subtraction angiography shows total occlusion in right main renal artery (arrow) with extensive collateral formation including periureteric collaterals. Note early opacification of upper polar region in right kidney, which is supplied by intact segmental artery and accessory renal artery.

View larger version (107K): [in a new window]   Fig. 3A —35-year-old woman who is potential kidney donor. On pyelographic phase image, urine CT attenuation values of right (01) and left (02) renal pelves are 710.3 H and 689.9 H, respectively. Ratio is 1.03. Attenuations of both renal pelves were similar on image obtained using wide window settings (window, 1,730 H; level, 18 H).

View larger version (122K): [in a new window]   Fig. 3B —35-year-old woman who is potential kidney donor. Intraarterial digital subtraction angiography shows bilateral single renal arteries without stenosis.

View larger version (8K): [in a new window]   Fig. 4 —Receiver operating characteristic (ROC) curve analysis of urine CT attenuation ratio depending on presence of renal artery stenosis. Area under ROC curve was 0.948.

View larger version (150K): [in a new window]   Fig. 5A —Preoperative CT angiography (CTA) image shows urine CT attenuation values of right (01) and left (02) proximal ureters are 733.0 H and 378.2 H, respectively. Ratio is 1.94.

View larger version (128K): [in a new window]   Fig. 5B —Selective right renal arteriography shows grade 3 stenosis with poststenotic dilatation in single right main renal artery.

View larger version (144K): [in a new window]   Fig. 5C —Selective left renal arteriography shows complete obstruction in segmental branch of renal artery with multiple intrarenal collaterals. Left main renal artery appears to be normal. Note severe luminal irregularity and narrowing in infrarenal aorta.

View larger version (127K): [in a new window]   Fig. 5D —50-year-old man with syphilitic aortitis and bilateral renal artery stenosis (RAS). Postoperative CTA image obtained after aortoaortic bypass with reimplantation of right renal artery shows urine CT attenuation values of right (01) and left (02) proximal ureters are 670.2 H and 1,378.7 H, respectively. Difference of urine CT attenuation values between both sides was reversed when compared with that of preoperative CTA; ratio is 2.06.

View larger version (103K): [in a new window]   Fig. 5E —50-year-old man with syphilitic aortitis and bilateral renal artery stenosis (RAS). Coronal maximum-intensity-projection (MIP) image shows reimplanted right renal artery without stenosis. Left intrarenal arteries had significant stenosis and occlusion (not shown). Left main renal artery seems to be stenotic. However, degree of stenosis may be overestimated on MIP film compared with transverse scan. In this patient, followup intraarterial digital subtraction angiography was not performed.

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