Pediatr Nephrol (2010) 25:1049–1056 1053 Fig. 3 Two-dimensional (‘volume-rendered’) representation of a three-dimensional computed tomography dataset from a 12-year-old boy. There is severe stenosis of the abdominal aorta (‘mid-aortic syndrome’, blue arrow). Enlarged collateral arteries are present: the marginal artery of Drummond (white arrow) connects the superior and inferior mesenteric arteries, and the epigastric arteries (green arrows) connect the subclavian and femoral arteries on each side. Note that, although the coverage is outstanding, detail of the intra-renal arteries is lost Isotope renography (renal scintigraphy) Renal scintigraphy performed before and after administra- tion of an angiotensin-converting enzyme inhibitor (ACEi; usually captopril) is a potential method of localising RAS in children. The usual radiopharmaceuticals used for this purpose are technetium-99m (99mTc) dimercapto-succinic acid (DMSA) and 99mTc mercapto-acetyl triglycine (MAG3). For 99mTc MAG3 scintigraphy the pre- and post-captopril scans are performed on different days, using an activity of 30–110 MBq (scaled according to the patient’s mass). Each study takes approximately 40 min, and no sedation is required, Early reports in adults suggested that captopril scintig- raphy was a good screening method, with sensitivities of 83–93% for the detection of RVD [32–34]. However, the accuracy of this diagnostic test has been poorer in more recent studies in adult patients, with sensitivities of 52–68% and specificities of 63–92% [14, 34, 35]. There is less published experience in children. Reports from our institution have estimated the sensitivities and specificities at 59–73% and 68–88%, respectively. Some children with potentially treatable RVD were missed on the captopril-primed studies [36, 37]. Studies of 16 children with aorto-arteritis in India showed a sensitivity of 81% [38], while a study from Chile had a sensitivity of 86% [39]. A study of 25 children with hypertension found 44% [11] of children with RVD on DSA, of which nine cases were detected by the isotope study [40]. Although, in principle, it is possible to detect segmental abnormalities with this technique, [41] it is not easy, and we surmise that the high prevalence of bilateral and/or segmental RVD will always limit the utility of ACEi-primed scintigraphy in children. In a recent study from our institution on children, we found a sensitivity of 48% and a specificity of 73% for the post- captopril isotope study to identify correctly children with RVD (submitted for publication). There have also been suggestions that the captopril- primed scintigraphy should be able to define those patients that could benefit from an intervention. One large study of 380 patients correctly identified 93% of those that benefited from an intervention [33]. This finding was later challenged in a Canadian study, where only 58% were correctly predicted a favourable therapeutic outcome [42]. In summary, captopril-primed isotope studies do not have high enough sensitivity to obviate the need for DSA in children with suggested RVD. Digital subtraction angiography DSA images are created by the subtraction of X-ray data acquired before intra-arterial injection of iodinated contrast material from each of a series of images obtained after injection of contrast medium (Figs. 1 and 2). Rotational angiography is a recent technical development, which allows the generation of three- dimensional images. The advantages of DSA are that it currently provides images of the lumens of the renal arteries and their branches with the best spatial and temporal resolution and that it is the platform for endovascular intervention. Various other diagnostic tech- niques, such as renal vein renin sampling and intra- vascular ultrasound, may be performed at the same time, when appropriate. There are several disadvantages of DSA. It requires a significantly higher radiation dose than properly performed CTA, it involves a small risk of arterial damage, either at the puncture site or elsewhere, and it only gives indirect information about the arterial