Noninvasive assessment of renal artery stenosis

Noninvasive diagnostic methods for evaluation of renal arteries continue to improve. Contrast arteriography is the reference standard to which other techniques are compared, and preoperative arteriography before operative or endovascular therapy remains the practice standard. However, noninvasive examination methods have supplanted arteriography as a screening test for renal artery occlusive disease, and they allow more selective use of the invasive technique. ACE inhibitor-enhanced renal scintigraphy has improved on the sensitivity of standard renal scintigraphy, but several investigators found it still lacks when significant renal dysfunction is present. A positive scan implies the renal artery lesion is functionally significant and is predictive of a response to therapy. Although ACE inhibitor-enhanced renal scintigraphy can detect significant renal artery disease, it can neither localize the arterial lesion nor can it characterize the severity of the stenosis. Renal scintigraphy therefore lacks utility as a method to follow progression of the arterial disease. Magnetic resonance and helical CT imaging are advanced technologies that acquire axial imaging data, but with advanced software and powerful image processing hardware, the anatomic information can be represented in multiple planes or with three-dimensional reconstructions. The anatomic information provided is not limited to the renal arteries, but can define relationships to the surrounding anatomy. Validation studies from several institutions suggest that although these methods for renal artery assessment may be sufficiently accurate for screening use, they remain relatively expensive and are just now becoming more widely available. Not all patients can be studied. Helical CT scanning requires a relatively large intravenous contrast dose, which is undesirable in patients with renal insufficiency, and it seems to underestimate severity of some renal artery stenoses. MRA is impractical or unsafe for patients with claustrophobia, cardiac dysrhythmias, pacemakers, certain types of metallic implants or clips, or for seriously ill patients requiring monitoring. Duplex scanning is both sensitive and specific. It is the least expensive of the available diagnostic modalities, and it is completely safe and noninvasive. Not only is the presence of a renal artery lesion detectable, the severity of the stenosis can be categorized and its hemodynamic significance or renal blood flow can be evaluated. Renal artery duplex scanning is the optimal method for renal artery assessment when it is available from a validated vascular laboratory. However, this last point is the key. The utility of the study is entirely dependent on the skill and experience of the examining technologist. Other drawbacks to duplex scanning include the fact that to yield the "whole picture" of the anatomy and pathology requires a mental synthesis. Real-time scanning generates a series of images and flow data that must be interpreted with a understanding of how the scan was performed. Clinical circumstances, local expertise, equipment availability, costs, and other important considerations will factor into the decision-making process of planning a work-up for suspected renal artery stenosis. The noninvasive diagnostic technologies continue to advance, and as new methods are validated, the need for arteriography may be further lessened.