Colour Doppler ultrasound in renal artery stenosis: Intrarenal waveform analysis

Renal artery stenosis (RAS) is the commonest secondary cause of hypertension and may result in renal ischaemia with resultant renal failure. Recent studies have suggested that colour Doppler ultrasound, with spectral analysis of the intrarenal waveforms, can identify those patients with a significant RAS. A prospective study was performed in which colour Doppler ultrasound was compared with angiography in 73 patients (143 kidneys) presenting for renal angiography. Colour Doppler ultrasound was unsuccessful in 16% of kidneys due to a combination of technical failures and small kidney size. Accessory renal vessels were present in 14% of kidneys on angiography but none was detected by ultrasound. Of the 120 kidneys that had both examinations, no significant difference in intrarenal pulsatility or resistive index was noted between the angiographically stenosed and normal arteries. There were significant differences for intrarenal peak and end diastolic velocities, and acceleration time and index. Of these measurements, acceleration time was the best indicator of RAS. The probability of detecting a high grade RAS in an individual patient did not reach 90% until the acceleration time was prolonged to more than 0.12 s. Intrarenal colour Doppler ultrasound is not a general screening test for RAS and it should be reserved for selected patient groups where the incidence of disease is high. Patients with prolonged acceleration times of more than 0.12 s have a high likelihood of at least 70% RAS and should proceed directly to angiography.