Although much less represented than its adult counterpart, pediatric endocrinologi­cal disturbances can be further investigated with certain procedures that interven­tional radiology can provide. Given that primary endocrine pathology has far less prevalence, there has not been a great push to develop tests or protocols in the eld of pediatric interventional radiology for this population; however, a mainstay that has not entirely fallen out of favor is renal vein sampling performed for very specic indications. Specically, pediatric renal vein sampling has been demonstrated to be helpful when troubleshooting cases of pediatric hypertension in cases of renovascu­lar hypertension, of which poorly demarcated bromuscular dysplasia (FMD) is a common cause among certain age groups. Note, FMD is not a primary endocrine pathology, but it leads to renovascular hypertension by releasing a cascade of mea­surable hormones causing secondary hypertension.

It should be noted that pediatric FMD is poorly understood and beyond the scope of this chapter, but it is suspected to be vastly different from the adult process. Although able to occur anywhere within the body, the most common subset of pediatric FMD is the focal broplasia variety which causes a long, narrow, and smooth focal stenosis anywhere within the arterial bed [6]. In the setting of pedi­atric FMD or any disease process affecting the vasculature, there is decreased perfusion to the juxtaglomerular apparatus via upstream stenosis. The result is that the apparatuses are hypoperfused, and renin secretion is upregulated by the affected kidney. This allows the operator to detect the unilateral differences in the amount of renin when venous sampling. The best candidates for pediatric renal vein sampling are ones that could benet from treatment should there be a positive result, but also where there is a strong clinical suspicion that there the cause of the child’s hypertension is stemming from a renal etiology without imaging ndings.

The process of renal vein sampling in the setting of refractory pediatric hyperten­sion can be a powerful diagnostic tool for interventional radiologists to have in their armamentarium and can help drive clinical care for these patients. This technique has been falling out of favor due to the advances of medical imaging to visualize the stenotic arterial segments, but still remains a troubleshooting tool for hinting at questionable tertiary or more distal, segmental arterial stenosis leading to elevated renin levels, in turn leading to renovascular hypertension. The power of the exami­nation is its positive predictive value as a large unilateral discrepancy points to the diagnosis of FMD or other focal renal abnormality within these patients. On the other hand, the ratio of less than 1.5:1 between the two renal veins cannot entirely exclude renovascular hypertension as operator error may be present; however, other causes for hypertension should be considered more likely.