[Color-Doppler of the renal arteries at their origin. Technical-methodologic problems]

Steno-obstructive diseases of the renal arteries affect mainly the ostium and the proximal vessels. The Doppler US study of the renal arteries can be troublesome on account of their depth, reduced caliber and considerable anatomical variability in their origin, course and number. Recent color-Doppler techniques have helped partially overcome these limitations relative to the identification of both vessels and stenoses. The technique for the visualization of the renal arteries requires supine transverse epigastric, coronal and transcaval scans to obtain a good beam angle. The stenosis can be recognized by the phenomena of turbulence and blood flow acceleration that elicit a typical yellow-green or white color variance, according to the different units. Spectral analysis allows monitoring of spectral broadening, velocity/frequency increase in systolic peak and increase in aortic-renal ratio. Stenoses can be quantified by calculating the stenosis index. The major limitation to the clinical use of color-Doppler US to study steno-obstructive diseases of the renal arteries is the high incidence of supplemental vessels (25-30% of the patients) and early bifurcations of the main branch. Thus, a correct and accurate imaging technique designed to search supplemental vessels plays a major role in decreasing the number of false negatives. Captopril renal scintigraphy is more sensitive than color-Doppler US in the identification of renin-dependent hypertension, but Doppler US is definitely better at detecting stenoses < 60% which may lead to chronic renal insufficiency.