Renal Doppler, Renal Artery Stenosis, and Renovascular Hypertension

Abstract

There are two methods of duplex evaluation for renal artery stenosis (RAS): (a) direct interrogation of the main renal artery and (b) indirect duplex evaluation of the distal renal arterial tree (distal main renal artery, segmental or interlobar branches of the renal artery). Direct and indirect methods have comparable sensitivity (low 90% range) and specificity (mid-90% range) for detection of ≥ 60% RAS. Direct interrogation requires that the entire length of both renal arteries be evaluated and is plagued by a relatively high technical failure or incomplete examination rate, long examination times, and difficulties in measuring accurate velocities due to suboptimal angles of incidence. Indirect evaluation, on the other hand, is technically successful in the vast majority of cases and less time consuming than direct interrogation. We recommend the indirect method for initial evaluation, but direct interrogation whenever the indirect evaluation is equivocal or abnormal. Although less demanding than direct methods, indirect duplex methods still require a thorough understanding of Doppler principles and meticulous technique. Direct interrogation criteria for ≥ 60% RAS are (a) renal artcry-to-aortic ratio (RAR) of ≥ 3.5 or (b) peak systolic velocity (PSV) ≥ 180 cm/s in association with poststenotic turbulence. Indirect parameters to diagnose ≥ 60% diameter RAS include acceleration time (AT) <.07 s, acceleration index (Al)<2.78 kHz/s2/MHz, acceleration (ACC)<3 m/s2, absence of the normal early systolic peak (ESP), difference in resistivity index between the ipsilateral and contralateral kidney (RID) <—5, and marked asymmetry in the shape of waveforms between the right and left kidneys or between upper-h mid-, and lower portions of one kidney. We found pattern recognition for loss of ESP the most expedient and sensitive parameter for 60% diameter RAS (91% sensitivity. 96% specificity). Limitations of indirect Doppler methods include insensitivity for 50% diameter RAS, inability to distinguish severe stenosis from occlusion, and insensitivity for stenosis in an accessory or segmental renal artery. In addition, bilateral indirect Doppler abnormalities may be due to occlusive disease proximal to the renal arteries (i.e., aortic coarctation) rather than bilateral RAS. Duplex sonography is useful to assess the effectiveness of revascularization procedures, [percutaneous transluminal angioplasty (PTA). stent placement, surgical graft placement]. After successful revascularization, indirect Doppler parameters return to normal immediately. Their failure to return to normal indicates a poor technical result and also predicts a poor blood pressure response to treatment. Patients with indirect Doppler abnormalities have higher systolic and diastolic blood pressures than subgroups of hypertensive patients who have a ≥ 10% of RAS based on clinical selection criteria.