Pediatr Nephrol (2010) 25:1049–1056 1051 Fig. 1 A 6-year-old boy with hypertension. a Doppler ultrasound of the right renal artery or one of its major branches shows a normal waveform. b Digital subtraction angiography shows a critical stenosis of a large branch of the right renal artery (white arrow), associated with tiny aneurysms. Collateral vessels are seen, both locally and arising from a capsular artery (black arrows) 2002 compiled data from 25 studies of 998 patients, of whom 499 had had non-enhanced MRA and 499 gadolinium-enhanced MRA compared to catheter angiog- raphy [21]. The authors found sensitivities of 94% and 97% for non-enhanced and gadolinium-enhanced MRA, respec- tively, with 85% and 93% specificity for these methods. In a further retrospective study of 30 adults evaluated for atherosclerotic RAS with MRA and DSA used as gold standard (where a trans-stenotic gradient of 15 mmHg was regarded as haemodynamically significant), MRAs were independently evaluated by three different radiologists [22]. There were 26 arteries with a significant stenosis of ≥60%, and 85–96% (22, 25 and 22, respectively) were correctly identified on MRA by the three radiologists. Accessory arteries are more difficult to be visualised, with MRA identifying only four out of nine, which is potentially relevant to paediatric RVD. The same authors then prospectively compared US, captopril-primed renography, MRA and CT angiography (CTA) in 58 hypertensive patients [14]. MRA showed 93% sensitivity and 91% specificity, although further studies of 35 to 60 patients each have shown quite variable sensitivities, ranging from 64% to 92% and specificities ranging from 72% to 96% [16, 23, 24]. A large multi-centre study from the Netherlands performed MRA, CTA and DSA in 402 adult hypertensive patients with the suggestion of RAS [25]. Patients were included from six hospitals, and two panels of three observers judged the data. Of the patients, 20% were found to have clinically relevant RAS, defined as ≥50% stenosis or FMD. The interobserver agreement was found to be only moderate (κ-values 0.40 to 0.51), with 62% sensitivity [confidence interval (CI) 54% to 71%] and 84% specificity (CI 81% to 87%). Therefore, in this study, MRA was not judged to be sensitive enough to rule out RAS. MRA in childhood There are no published studies comparing MRA with DSA in a useful number of children. Although MRA can, in principle, identify RAS, in our clinical experience we have seen several cases where MRA has over-diagnosed RVD as well as missed severe intra-renal arterial disease (Fig. 2). In summary, MRA data are still conflicting, with very high sensitivities found in some single-centre studies but with less good performance in larger studies involving several centres. This may be due to centres gaining experience of MRA over time, as well as the limitations of MRA, including poor inter-observer agreements. The main problems of MRA are inadequate spatial resolution, movement artefacts and difficulties when the cause is FMD [26, 27]. Despite these limitations, which are all particularly relevant in the diagnosis of childhood RVD, new techni- ques, including quantification of renal blood flow and perfusion imaging, may increase the role of MRA in the future. Computed tomography angiography CTA has recently become more widely used in the diagnosis of RVD, due to improvements in image quality related to multidetector technology (Fig. 3). CTA can be defined as any contrast-enhanced CT technique intended