James A. O’Neill, Jr.

Etiology

Renovascular hypertension may be congenital or acquired. Congenital causes include arterial hypoplasia or aplasia; neurofibromatosis and tuberous sclerosis tumors involving the renal artery; and Williams syndrome, which includes manifestations of supravalvular aortic stenosis, peripheral vascular stenosis particularly in the subclavian and renal arteries, mid-aortic narrowing, hypercalcemia, and elfin facies.⁶ The most common acquired forms of renovascular hypertension are fibromuscular dysplasia (FMD), which involves one or both renal arteries, or a more generalized type of disease, such as Takayasu arteritis and subisthmic abdominal coarctation, now referred to as the mid-aortic syndrome.^7,8 Stenoses of visceral arteries such as the superior mesenteric and celiac arteries are also common in mid-aortic syndrome.⁷ Other less common forms of acquired renovascular hypertension are renal artery trauma or thrombosis, thrombosis secondary to antithrombin deficiency, Kawasaki disease, and an anastomotic stenosis in renal transplants.⁹

Overall, the vast majority of children with renovascular hypertension have FMD. Presentation of newborns with aortic and arterial aplasia and hypoplasia suggest a congenital origin. In young adults, FMD appears to have an acquired pattern and may have a genetic basis in the syndromes mentioned above.⁶ The majority of patients initially present at several years of age, usually with an active inflammatory phase followed by a quiescent phase of arteritis.^4,7 Although it was initially thought that FMD might be an autoimmune disease, relatively recent evidence suggests that T-cell-based immune mechanisms, macrophages, and antigen-presenting cells are mainly responsible for renovascular arteritis, and a variety of other arteritides as well.¹⁰ The histology of the vascular lesion seen in the renal artery and aorta reveals medial and perimedial fibroplasia, which has inherent implications about approaches to treatment, particularly angioplasty. Although FMD is a systemic, occlusive arteriopathy that may involve the entire abdominal aorta and its branches, the renal arteries are the predominant vessels involved.¹¹

Clinical Presentation

Children with renovascular hypertension generally come to attention in one of two ways. Approximately 70% of patients are asymptomatic and are identified when they have their blood pressure taken during a routine evaluation. It is usually not known how long the hypertension has been present. Repeated measurements verify the chronic nature of this problem, which leads to diagnostic evaluation. Approximately one-half of these asymptomatic patients will be found to have correctable hypertension. The remaining 30% of children are symptomatic with headaches, vision problems, encephalopathy, congestive heart failure, oliguric renal failure, and, occasionally, leg claudication. Physical findings may indicate the presence of heart failure with enlargement of the liver and heart, as well as retinopathy and retinal hemorrhage. In cases of mid-aortic syndrome, peripheral pulses and blood pressure may be diminished in the lower extremities. Although an abdominal bruit could probably be heard in the majority of instances of renal artery stenosis, it is not commonly found until a diagnosis is suspected.

In contrast to a young female predominance in adults with FMD, gender incidence is equal in children. Both renal arteries are involved in approximately 70% of patients. In occasional patients with unilateral lesions, FMD may develop in the opposite renal artery years later. Renovascular causes of hypertension are more common in children younger than 10 years, as evidenced by an average age of 7 years in one of our studies.⁵ In infants and toddlers, malignant forms of hypertension with encephalopathy and retinopathy are more likely to develop than in older children.

Diagnosis

Before any invasive diagnostic studies are undertaken, clinical manifestations of severe hypertension such as headache, irritability, abdominal pain, heart failure, and seizures should be controlled with medications.