ABSTRACT
Renal artery stenosis (RAS) has long been recognized as a potentially reversible cause of hypertension (1). It is also an important cause of renal impairment, especially in the elderly. However, there is also a further large reservoir of asymptomatic or unrecognized RAS. For example, postmortem studies have found various degrees of renal artery narrowing in previously normotensive patients (2). Thus some cases of RAS are clinically unimportant in the patient’s lifetime, because it does not always produce a detrimental effect. The contemporary dilemma is the diagnosis of all cases of significant RAS without the misdiagnosis of clinically unimportant arterial stenosis. This demands a test of high specificity and of equally high sensitivity, a demand common with many other screening or quasi-screening scenarios. Furthermore, an ideal test should not only have a high diagnostic accuracy but also should be able to grade the stenosis. The ‘‘gold’’ or reference standard for the diagnosis of RAS is the renal arteriogram (Fig. 1), ideally with the measurement of the intra-arterial pressure gradient across the stenosis to grade its physiological significance. There is a lack of consensus about what percentage of reduction in lumen size identifies a clinically important RAS. Previous studies have used different thresholds of between 50% and 70%. In flow models, tube narrowing of greater than 70% cross-sectional area (or approximately 50% of the lumen diameter) will compromise flow and a further reduction in the diameter will lead to a corresponding exponential reduction in perfusion. At present there is no ideal cost-effective noninvasive ‘‘screening’’ investigation for RAS, and this chapter explores the ability and limitations of the various available modalities.
