All of the efforts put into imaging the renal arteries will not be worthwhile if the treatments they subsequently direct do not bring improvements in patient outcome.
Although the results of endovascular therapy are technically impressive, at the time of writing, randomized controlled studies comparing pharmacological management with endovascular correction of RAS are keenly awaited. A meta-analysis of three small trials comparing angioplasty with best medical therapy alone has failed to give us a clear direction (14). The DRASTIC study (121) reported in early 2004 found that although there was a clear benefit from immediate angioplasty in patients with bilateral stenosis, it could be deferred in other patients unless they deteriorated clinically. Once again this study was small, with only 106 patients. Two other trials, STAR (122) and ASTRAL (123), are currently in progress in Europe. The largest of these, ASTRAL, will include 1000 patients (at the last report in late 2005, 600 patients had been enlisted). This trial should have the statistical power to conclusively prove or refute the value of treating RAS. They will use the objective end-points of renal preservation and hypertensive control, and the cost-effectiveness of the various investigations may be calculated. Only then will the case for early diagnosis or even screening or active case-finding become compelling. The main tools for diagnosis are likely to be MRA and CTA. However contrast-induced nephrotoxi-city is a major source of concern in this group of patients.
To summarize, RAS is an important cause of hypertension and renal failure, especially in patients with arterial disease in other vascular territories. Narrowing of the artery beyond 70% of its cross-sectional area is generally accepted to represent a significant stenosis. However, RAS may be clinically silent. Its prevalence runs
Table 11 Benefits and Limitations of the Different Imaging Modalities
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