eMedicine Specialties > Pediatrics: Surgery > Vascular Surgery

Renovascular Hypertension: Surgical Perspective

Author: Andre Hebra, MD, Chief, Division of Pediatric Surgery, Medical University of South Carolina; Professor of Surgery and Pediatrics, Medical University of South Carolina
Coauthor(s): Patrick B Thomas, MD, Fellow, Department of Pediatric Surgery, Texas Children's Hospital
Contributor Information and Disclosures

Updated: Aug 8, 2008

Introduction

Background

Systemic hypertension is less common in children than in adults, but the incidence of hypertension in children is approximately 1-5%. The presence of hypertension in younger children is usually indicative of an underlying disease process (secondary hypertension). In children, approximately 5-25% of secondary hypertension is attributed to renovascular disease.

In 1934, Goldblatt et al demonstrated a relationship between hypertension and renal ischemia. They were able to consistently produce elevations in systolic blood pressure by producing renal ischemia with a constricting clamp. Removal of the clamp restored blood pressure to the reference range. Four years later, Leadbetter and Burkland applied this information by performing a nephrectomy of a unilateral ischemic kidney. This remained the method of surgical treatment until 1960 when Lambeth et al reported resolving hypertension by correction of renal artery stenosis. Nephrectomy is now reserved as a last resort in the treatment of renovascular hypertension. In the 1960s, the delineation of the renin-angiotensin system and its relation to hypertension also had a large impact on the medical therapy and diagnostic studies used in renovascular hypertension.

Pathophysiology

Often, the cause of renovascular disease is unknown. Most severe forms of renovascular hypertension seem to involve ischemic-related stimulation of the renin-angiotensin system. Blood flow in renal vessels is hindered by constriction or even complete reduction of the vessel diameter. With the decreased perfusion, renin release is stimulated. This results in vascular constriction and increased release of aldosterone. The additional aldosterone leads to the retention of sodium and water. This increases blood volume. Together, the increased constriction and blood volume increase blood pressure.

Some congenital lesions are related to renal hypoplasia. Tumors and other masses may impinge on the renal vasculature. Trauma, irradiation, vessel anastomosis in transplantation, and thrombosis all may lead to constriction of vessels and the resulting hypertension. The most common cause of renal hypertension in newborns is a thrombosis or embolization related to umbilical artery catheterization.

Fibromuscular dysplasia

Fibromuscular dysplasia (FMD) involves fibrous or muscular hypertrophy of the vessel tunica media with fibrous intimal hyperplasia. Some authors even refer to this disease as fibromuscular hyperplasia. Often, poststenotic dilatation is also present. The process may range from mild occlusion to complete occlusion of the vessel. On radiographs, FMD produces the classic string-of-beads appearance less often in children than in adults. Rather, FMD tends to show short discrete or longer tubular segments of stenosis.

The site of stenosis usually occurs at the orifice of the renal artery at its origin in the aortic wall. The next most common location is within the main renal artery, and the segmental arteries are the least common site of stenosis. Total occlusion most often occurs at the orifice of the renal artery. The disease may be unilateral or bilateral, but the inciting event for FMD is unknown. Some have suggested an autoimmune origin. In 1995, Stanley proposed that the lesion forms as a developmental disease in the muscular layer, which is followed by intimal hyperplasia from the abnormal flow through the constricted lumen.¹

Midaortic syndrome

Midaortic syndrome consists of more widespread vascular involvement than just the renal artery. Aortic narrowing exists that often extends from the aortic hiatus to just above the inferior mesenteric artery. One or both of the renal arteries are usually involved, and narrowing of the celiac and superior mesenteric arteries may exist. Midaortic syndrome is considered a variant of FMD and may result in total occlusion of the renal artery, with perfusion dependent on collateral circulation. Extensive collateralization from the inferior mesenteric artery and a Riolan arcade may exist. Renal artery stenosis is usually bilateral.

Neurofibromatosis

Hypertension in patients with neurofibromatosis is often essential, but some patients also present with renovascular hypertension. These children have a pattern of renal artery stenosis that is similar to that observed in FMD. However, involvement of the intrarenal arteries and arterioles may also exist. Neurofibromatosis usually involves the renal arteries of both kidneys.

Frequency

United States

As mentioned above, the incidence of hypertension in children is reported to be 1-5%. In adolescents, it may be as high as 10%. Unlike in adults, 70-80% of hypertension in children may be due to secondary hypertension, which is often correctable. Of those children with secondary hypertension, 5-25% have elevated blood pressure with a renovascular etiology. Renovascular hypertension is common in children and is second only to coarctation of the aorta as a surgically correctable cause of hypertension. With improved screening for coarctation in younger children, renovascular hypertension may be the most common cause of surgically correctable hypertension.

International

Geographic differences in the overall prevalence of renovascular hypertension have not been reported, although the etiology of renovascular hypertension does appear to vary geographically. In the western hemisphere, FMD is the most common cause of pediatric renovascular hypertension. Reports from Asia identify arteritis, either aortoarteritis or Takayasu arteritis, as the most common cause of renovascular hypertension in children. One study in south Asia found that 87% of the patients presenting with renovascular hypertension had arteritis.² A report from South Africa also indicated that Takayasu arteritis was the most important cause of renovascular hypertension in nonwhite children.

Mortality/Morbidity

Renovascular hypertension can develop into chronic hypertension, and patients usually present with malignant hypertension. If left untreated, this can produce serious consequences, including coma and death.

• The actual mortality rate of untreated renovascular hypertension has not been reported, in part because effective treatments are available.
• Chronic hypertension can damage blood vessels, leading to such pathology as plaques, aneurysms, claudication, and dissection.
• The main comorbidity of renovascular hypertension is directly related to its effects in end-organ damage.
• Neurologic manifestations are often the presenting symptoms because severe hypertension can lead to retinopathy, headaches, dizziness, confusion, seizures, and stroke.
• The heart is frequently affected because increased afterload leads to congestive heart failure and ventricular hypertrophy.
• Renovascular hypertension may also damage the kidneys, especially when significant stenosis of the perfusing vessels is present.
• Although they are rare, oliguric renal failure and ischemic kidneys have been reported with renovascular disease.
• Finally, renovascular hypertension is often associated with failure to thrive in young children.

Race

Blood pressure has been shown to be higher in black children than in white children, but the difference has not been deemed clinically significant. When adjusted for height, much of this difference is eliminated. Renovascular hypertension is less common among older black children than among adolescent whites, but the prevalence is actually higher in young black children.

Sex

Multiple studies have demonstrated that no clear sex difference occurs in childhood renovascular hypertension.

Age

In children, the prevalence of renovascular disease as the cause of hypertension is inversely related to age. In other words, younger children are more likely to have hypertension that is due to renovascular disease. In children younger than 5 years, the incidence of potentially surgically correctable hypertension is close to 80%. This incidence drops to 40-45% in children aged 6-10 years. In children aged 11-20 years, a 20% incidence of surgically correctable hypertension is observed.

Clinical

History

• Patients may be asymptomatic, and hypertension may be discovered during routine examination or preparation for surgical treatment of another problem.
• In most studies, more than one half of children who were hypertensive were also asymptomatic or their hypertension was discovered during a routine examination.
• When present, symptoms are nonspecific and are often related to the organ systems most affected by hypertension.
  • The most common symptom of renovascular hypertension seems to be headache.
  • Other neurologic symptoms of renovascular hypertension include changes in mental status, vision changes, vomiting, seizures, coma, encephalopathy, hyperexcitability, and hyperirritability.
  • Symptoms of resulting congestive heart failure may also be present, such as decreased energy, edema, and shortness of breath.
  • In patients with abdominal aortic narrowing, claudication may be present.
  • Some children have anorexia, and infants or young children often present with failure to thrive.
  • Occasionally, patients have oliguric renal failure.

Physical

• Upon physical examination, patients have a blood pressure elevation above the 95th percentile for their age, sex, and height. Generally, children with blood pressures greater than 140/100 mm Hg are thought to be more likely to have secondary hypertension, and renovascular hypertension is more likely in children with higher blood pressure.
• Eye examination may reveal retinopathy and retinal hemorrhages.
• Patients with heart failure may present with tachypnea, cardiomegaly, and vasomotor instability leading to mottling and acrocyanosis.
• Lower extremity pulses may be diminished with aortic coarctation, whether thoracic or abdominal.
• An enlarged liver may be palpated, and an abdominal bruit may be auscultated.
• Patients with tumors impinging on renal vasculature may present with an abdominal mass in the area of the kidney.
• Rarely, signs or symptoms of visceral artery involvement are present because of the extensive collateralization that occurs.
• Café au lait macules are classic in the presentation of neurofibromatosis. Patients with neurofibromatosis may also have macrocephaly, neurofibromas, dermal neurofibromas, and axillary freckling.

Causes

Renovascular hypertension implies the cause of the elevated blood pressure is decreased arterial inflow to the kidneys. This results in activation of the renin-angiotensin system, with the development of systemic hypertension. Some congenital disorders may lead to renovascular hypertension, including arterial hypoplasia (as observed in multicystic renal dysplasia), neurofibromatosis, and Williams syndrome. The focus of this article is on the disease processes that most commonly cause renovascular hypertension in children.

• More commonly, renovascular disease in children is considered an acquired disease. FMD is the most common form of acquired renovascular hypertension. Its incidence varies geographically, but in the United States, it is the most common cause of secondary hypertension in children.
• Other forms of acquired renovascular hypertension include subisthmic coarctation, Moyamoya disease, Takayasu arteritis, Kawasaki disease, vasculitis, vascular trauma, renal artery thrombosis, tumors, midaortic syndrome, or anastomotic stenosis (such as posttransplantation).
  • Trauma or kidney transplantation can lead to scarring or anastomotic lesions that produce renovascular constriction.
  • Although Takayasu arteritis and Kawasaki disease occasionally lead to FMD, the cause of FMD is not always known.
• Often, the cause of renovascular disease is unknown. Umbilical catheters in newborns, especially those born prematurely, may result in embolization of the renal vasculature. Radiation therapy of tumors in the renal area may lead to renovascular hypertension.
• Multicystic renal dysplasia is commonly encountered in newborns. Prenatal detection by screening ultrasonography is common. These lesions are rarely bilateral and are usually associated with ipsilateral ureteral atresia. Hypertension and recurrent infections can result from this condition. As previously mentioned, multicystic dysplastic kidneys are not discussed in this article.

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