Renovascular Hypertension


Renovascular Hypertension



In 1934, Goldblatt and coworkers described the association between coarctation of the aorta and renal artery stenosis with hypertension.1 However, it was not until the 1960s that activation of the renin–angiotensin system, which leads to the release of renin and the production of angiotensin II, was found to be the mechanism for the hypertension (Fig. 63-1). Subsequently, it has been shown that diminished renal perfusion pressure has direct effects on sodium excretion, sympathetic nerve activity, nitric oxide production, and intrarenal prostaglandin concentrations, resulting in renovascular hypertension.2 Other studies have demonstrated different fractional angiotensin elevation patterns in children with renovascular hypertension as compared with essential hypertension.3



The incidence of hypertension in children in all age groups is 2–10%, with the higher figure representative of adolescence. However, because blood pressure is not routinely measured in infants and younger children, the diagnosis of hypertension is often delayed. Table 63-1 lists the common causes of hypertension in children according to the organ system involved. This chapter will focus on renovascular causes of hypertension, most of which are correctable.



The natural history of progressive, untreated renovascular hypertension often results in the development of renovascular lesions in sites other than those originally identified. The progressive nature of this disorder is the best justification for an aggressive approach for correction. Also, sustained and malignant forms of hypertension may result in left-sided heart failure, chronic renal failure based on chronic ischemic nephropathy, and stroke.


Essential hypertension is the most common cause (60%) of hypertension between birth and 20 years of age. However, the incidence of correctable hypertension is very high in patients younger than 15 years. In previous studies by our group, the incidence of correctable hypertension in the birth to 5-year age group was around 80%; in the 6- to 10-year age group, 45%; and in the 11- to 15-year and 16- to 20-year age groups, 20%.4 Although a variety of causes were identified, the vast majority were renovascular. Renovascular disease comprises 8–10% of all forms of hypertension in children, while it is 1% of all forms in adults. Additionally, long-term follow-up of patients with renovascular hypertension clearly indicates that patients who have had successful repair of their lesions have sustained results and longer survival than those who do not. Moreover, the younger the patient, the better the result.5 Such studies support an aggressive approach to correction of identified renovascular lesions in young patients.



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.



Laboratory Studies


Renovascular hypertension cannot be diagnosed by any specific laboratory study. Most laboratory studies are performed to document the patient’s clinical status and renal function. Erythrocyte sedimentation rate (ESR) is important to assess whether the patient is in the inflammatory or the quiescent phase of arteritis. Urinary catecholamines are evaluated to exclude pheochromocytoma and other common endocrine causes, particularly in patients with manifestations of neurofibromatosis. (The author has not found plasma renin or provocative studies like captopril-stimulated renin studies to be helpful in young children.) Technetium-labeled pentetic acid (DTPA) radionuclide fractional-flow studies may indicate unilateral renovascular disease, but they are not useful when bilateral disease is present. Captopril renography has the same limitation.



Imaging


Although a number of imaging studies exist, currently it seems best to perform aortography and selective arteriography in all children with significant hypertension. Minimal complications have been encountered with these studies, even in very small patients. With appropriate hydration, even patients with some degree of oliguric renal failure can undergo aortography and selective arteriography by using CO2 or low-osmolar or noniodinated contrast agents in limited amounts. For patients with a distal or intrarenal vascular stenosis, nitroglycerin-enhanced selective studies promote the identification of segmental areas of ischemia in the involved kidney. Angiography may also facilitate endoluminal procedures when feasible.


Duplex color-coded Doppler ultrasonography (US) is capable of demonstrating the renal arteries, as well as measuring flow velocity as an index of the degree of stenosis. However, Doppler ultrasound studies, whether performed preoperatively or postoperatively for follow-up, have limitations in terms of demonstrating precise anatomic detail, particularly in small vessels. The same is true of captopril scintigraphy and contrast-enhanced ultrasound. Magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) are capable of demonstrating the renal arteries and the aorta and its branches better than Doppler ultrasound, but there are resolution issues in small subjects.12,13

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Jun 18, 2016 | Posted by in PEDIATRICS | Comments Off on Renovascular Hypertension

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