Journal of Human Hypertension (1999) 13, 595–603 1999 Stockton Press. All rights reserved 0950-9240/99 $15.00 http://www.stockton-press.co.uk/jhh REVIEW ARTICLE Diagnostic imaging of renal artery stenosis F Aitchison and A Page City Hospital NHS Trust, Birmingham, UK Many different imaging modalities and techniques have enzyme inhibitors, intra-venous and intra-arterial cath- been used in the past for the diagnosis of renal artery eter angiography, computed tomographic angiography stenosis. The ideal accurate, non-invasive and inexpen- and magnetic resonance angiography. At present intra- sive diagnostic test has yet to be found but there have arterial catheter angiography remains the ‘gold stan- been promising developments during the last few years. dard’ test. Magnetic resonance angiography is currently In this review we consider in detail the use of the follow- of limited availability in the United Kingdom but is the ing tests for the diagnosis of renal artery stenosis; intra- most promising new development because it is a non- venous urography, B Mode ultrasound, Doppler ultra- invasive test which can be used to obtain both anatom- sound, renal scintigraphy with angiotensin-converting ical and functional information. Keywords: diagnostic imaging; renal artery stenosis Introduction the non-invasive tests have previously had only a moderate level of sensitivity and specificity for RAS. Renal artery stenosis (RAS) remains the commonest Therefore these non-invasive imaging methods were curable cause of hypertension and is a significant used as screening tests to select those patients con- cause of end-stage renal failure. In the young hyper- sidered at sufficiently high risk of the disease to jus- tensive patient a diagnosis of RAS caused by fibro- tify proceeding to catheter angiography for definite muscular dysplasia is unusual but must be con- diagnosis. It is hoped that newer non-invasive tech- sidered in the appropriate clinical circumstances. In niques such as magnetic resonance angiography will the United Kingdom there is a much larger group of combine both screening and definitive diagnostic patients with RAS caused by atherosclerotic disease. 1 roles. In this review we will discuss in detail the A recent paper in this journal considered whether diagnostic tests which have previously been used it is worthwhile to diagnose atherosclerotic renal for RAS and those which are currently being artery stenosis (ARAS). The authors concluded that developed. patients with renovascular hypertension caused by ARAS should only be treated when there is true drug resistant hypertension and that the results of Imaging methods treatment for ARAS to halt progression of ischaemic Intravenous urography renal failure are promising. The intravenous urogram (IVU) was first modified Much attention during the past 30 years has for use as a screening test for RAS nearly 40 years focused on the need to find an accurate, inexpensive ago.2,3 It was thought that by taking X-ray films at 1, and non-invasive diagnostic test for RAS. Radiology 2, 3, 4 and 30 min post contrast injection in addition has evolved rapidly during this time. New, non- to the conventional films at 5 and 15 min that cer- invasive diagnostic methods which can be used for tain features could be identified which would indi- RAS imaging such as ultrasound, computed tom- cate renovascular hypertension. These features were ography and magnetic resonance imaging have been believed to be related to reduced arterial blood flow developed. Interventional radiological techniques and hyperconcentration of urine in the affected kid- have been refined to use a lower radiation dose and ney. The specific appearance which were sought smaller calibre catheters. In addition, non-surgical were disparity in renal length, delayed calyceal treatments such as renal angioplasty and renal artery appearance and hyperconcentration of contrast on stenting have become possible. delayed films. At present conventional arterial catheter angiogra- The largest series to favourably assess the use of phy is the ‘gold standard’ diagnostic test for RAS. the IVU in the diagnosis of RAS was the prospective, However, it is an expensive and invasive procedure multi-institutional Cooperative study published in associated with a measurable morbidity. In general, 1972.4 However, the authors also concluded that the IVU was not able to distinguish between those Correspondence: Dr F Aitchison, Department of Radiology, City patients who would respond favourably to surgical Hospital NHS Trust, Dudley Road, Birmingham B18 7QH, UK intervention and those who would not. Received 24 February 1999; revised and accepted 30 April 1999 During the next decade several papers were pub- Diagnostic imaging of RAS F Aitchison and A Page 596 lished which questioned the use of the IVU in the renal length and volume in normal subjects over 70 diagnosis of renovascular hypertension. The most years of age12 which is believed to be due to a influential of these was published by Thornbury et decrease in the number of glomeruli and a reduction al.5 This was a large retrospective study from a sin- in the mass of the juxtamedullary nephrons.13 The gle institution and the authors found a true positive other problem is that a reduction in renal length can rate for the diagnosis of RAS (greater than 50% be caused by many other chronic renal parenchymal stenosis) of only 58.4%. In addition they performed diseases. Therefore measurement of renal length is a re-analysis of the Cooperative study data using a both a relatively insensitive and non-specific test more widely accepted, lower estimate of the inci- for RAS. dence of reno-vascular disease in the general popu- Although it is not a good diagnostic test for RAS lation than the 10% used in the original paper. The it is possible to justify the use of B Mode US in the conclusion was that when used as a screening test general investigation of hypertensive patients to for the detection of RAS (greater than 50%), the exclude other renal disease, such as polycystic dis- Cooperative study data showed a true positive rate ease, chronic pyelonephritis and hydronephrosis. for IVU of 78%. Doppler US is a more complex technique, which In a later review it was calculated that the prob- has been developed during the past two decades to ability of renovascular hypertension in the general demonstrate patterns of blood flow. Recently, hypertensive population only increased from 1% to Doppler US has become much more widely avail- 5% when the patient had a positive IVU examin- able, easier to use and more accurate due to techno- ation. This was concluded to be insufficient evi- logical advances. It now has a well-established place dence for most clinicians to consider referral for in other areas of vascular imaging. There has been catheter angiography.6 very considerable interest in Doppler US as a diag- The IVU involves the use of intravenous iodinated nostic technique for RAS because of its non-invasive contrast material with the small associated risk of nature and relatively low cost. However, despite contrast reaction. The rare adverse effects are extensive study the role of Doppler US in the screen- diverse including urticaria, nausea and vomiting ing, diagnosis and follow-up of RAS still remains and anaphylactoid reactions such as hypotension unclear. and cardiac arrest.7 Iodinated contrast material is The basic principle of US is the use of the reflec- potentially nephrotoxic in diabetics and those with tion of an inaudible sound beam by surfaces at dif- pre-existing renal impairment8 and the IVU is asso- ferent depths within the body to create a map of ciated with a significant effective radiation dose structure. Doppler US depends on detecting a (equivalent to more than 200 chest X-rays). The IVU change in the frequency of the ultrasound beam is not an invasive test but when used for detection when the surface is a moving particle such as a of RAS results have been disappointing. The IVU is blood cell (Doppler effect). A complex mathematical no longer considered an appropriate test in the process is then used to convert this information into investigation of suspected RAS.9 a map of flow in the area under assessment. Both the direction and velocity of flow are indicated by a colour code on the US screen. In addition, a detailed Ultrasound quantitative analysis of the waveform pattern of the Conventional B Mode ultrasound (US) allows blood flow in a smaller area such as a single vessel detailed assessment of the anatomy of the kidney can be obtained as a graph. and accurate measurement of renal size. It is an eas- The earliest studies of Doppler US for RAS diag- ily performed, inexpensive procedure which is well nosis were a direct development of the technique tolerated by patients. Although it was long accepted which had already been successfully used to detect that a reduction in renal size was associated with stenosis in carotid arteries. This depended on find- RAS there was a paucity of formal reports on this ing an increase in blood velocity at the stenosis site subject in the literature for many years. This was and turbulent flow just beyond the abnormal seg- due to the difficulty in performing natural history ment of the main renal artery. Various criteria that studies based on follow-up using invasive func- related to the peak systolic arterial velocity and ratio tional tests or arteriography. With the development of renal artery to aortic peak systolic velocity were of B Mode and Doppler US, non-invasive assess- proposed for the detection of a haemodynamically ment of the natural history of RAS became possible. significant stenosis.14–16 These studies demonstrated that over 20% of Initial reports were encouraging, however during patients with greater than 60% stenosis of the main the next few years a wide range of accuracies for renal artery will sustain a reduction in renal length diagnosing or excluding RAS were reported17 and it of at least 1 cm during a 2-year follow-up period.10,11 soon became clear that there were significant diffi- There are three main problems with the use of a culties in the study of the main renal artery.