1050 renovascular disease is potentially amenable to treatment with various endovascular and surgical techniques, any non- invasive imaging test must have a very high sensitivity, or potentially treatable children will be missed [9, 10] In this review we attempted to define the role of these investigations in children with hypertension. However, as there is scanty evidence in the literature to date of using alternative investigations to diagnose RVD in children, we relied on studies of adults and clinical experience in children. Doppler ultrasonography Ultrasound of the abdominal arteries, supplemented with colour and pulsed-wave Doppler examination, is a simple and safe technique [11]. The equipment is widely available, and the procedure is painless and well tolerated by children. Direct visualisation of RAS is usually not possible in children when greyscale imaging is used, but the renal arteries and their branches can be identified with colour Doppler ultrasound and then interrogated with pulsed-wave Doppler, which produces a real-time trace of flow velocity. Various Doppler parameters may then be used as indirect indicators of RAS [12, 13]. The peak systolic velocity (PSV) in intra-renal branches of the renal artery is usually reduced distal to a very severe stenosis or occlusion. The acceleration time (the time from the beginning of the systolic upstroke to the highest systolic peak in the waveform) may be increased (>70 ms). When the acceleration time is increased and the PSV is low, a characteristic flattened waveform (tardus et parvus phenomenon) is observed. This may be seen unilaterally, distal to a severe RAS, or bilaterally in mid-aortic syndrome (MAS) or coarctation [11, 13, 14]. As in adults, a less severe stenosis of the main renal artery may lead to loss of laminar flow and increased PSV [15], and a ratio of renal-to-aortic velocity greater than 3.0 or 3.5 might also be indicative of RAS [13, 15]. In studies of adults, the sensitivity of US has been found to be less favourable than that of magnetic resonance angiography (MRA) or computed tomography angiography (CTA), with values of 73–85% and corresponding specific- ities of 71–92% (Table 1) [14, 16, 17]. A French study of 22 selected children with hypertension found RVD in 13 children, with two false positive findings and two false negative findings on US [12]. The false negative inves- Table 1 Comparison of US, captopril renography, MRA and CTA compiled mainly from studies of adults in the literature Technique US Captopril renography CTA MRA Pediatr Nephrol (2010) 25:1049–1056 tigations were in one child with RAS in an accessory renal artery and in one child with bilateral multiple stenosis of distal branches of the renal arteries. The authors concluded that distal stenosis could be missed with US. A further study of 29 children with renin-mediated hypertension found positive intra-renal US findings in 15 patients and negative findings in 14. A curative procedure was precluded, due to the severity of the vascular lesions in 67% (ten of 15) of the children with positive US findings while this was possible in 79% (11 of 14) of those with negative US findings. This emphasises the importance of our performing DSA for all children with the suggestion of RVD despite negative US results (Fig. 1). Its main roles are to assess the condition of children with hypertension but a low clinical probability of RVD, to look for non-vascular causes of hypertension (for example, tumours or renal abnormality) and to measure renal size. Magnetic resonance angiography Contrast-enhanced MRA of the abdominal aorta and renal arteries is performed using gadolinium-based contrast agents and rapid three-dimensional T1-weighted spoiled gradient-recalled echo imaging sequences [18]. Although MRA involves no exposure to ionising radiation, it has certain disadvantages. Many children will need sedation or general anaesthesia. The use of gadolinium-based contrast agents carries some risk of nephrogenic systemic fibrosis in children with impaired renal function, and, in our institu- tion, an estimated glomerular filtration rate (eGFR) of less than 30 ml/min per 1.73 m2 would be regarded as an absolute contraindication [19]. In most cases children with an eGFR of less than 60 ml/min per 1.73 m2 should not undergo contrast-enhanced MRA. Despite these reserva- tions, MRA is increasingly used in adults and children and a there are several published studies on its usefulness. Adult studies of MRA A meta-analysis of studies in adult patients published in 2001 showed that few studies had been undertaken and suggested that, although MRA could be used with a high sensitivity to detect clinically important RVD, further research was required [20]. A further meta-analysis in Sensitivity 73–85% 52–93% 64–94% 64–93% Specificity 71–92% 63–92% 62–97% 72–97% References [14, 16, 17] [14, 31–36] [14, 16, 25, 28, 29] [14, 16, 20–25]