[Extrarenal ultrasound and color Doppler: renal artery stenosis]

There is a long term interest in noninvasive Doppler (Duplex Doppler, Color Doppler) methods to screen patients with reno-vascular hypertension resistant to medical therapy. Doppler criteria for the diagnosis of renal artery stenosis in native kidneys vary (peak systolic velocity exceeding 100 cm/sec; RAR (Renal Aortic Ratio) exceeding 3.5; Doppler shift frequency exceeding 6-8 KHz; dampened peripheral waveform; lack of signal in complete occlusion). When the vessels are adequately visualized (about 40% of cases) sensitivity and specificity are quite good (80-90%). In the transplanted kidney Doppler diagnosis of renal artery is easier (diagnostic accuracy about 90%). The diagnostic criteria have been well codified (Doppler shift of 7.5 KHz at an insonating frequency of 3 MHz).