Andersons pediatric cardiology 1615

of the nonexperimental kidney This can, in some way that is not yet clear, cause the retention of sodium The mechanism may be similar to that involved in the later stages of essential hypertension, and to the increased peripheral vascular resistance caused by medial and intimal hypertrophy of peripheral arterioles.280 The complexities of experimental renal hypertension are such that it can come as no surprise that the amelioration of renal ischemia in the human does not always lead to a reduction in hypertension.281 Fortunately, in children, perhaps because the period of hypertension is shorter, the results of surgery for renovascular hypertension are more predictable Renovascular Hypertension Renovascular hypertension can be defined as hypertension resulting from obstruction to the flow of blood in the renal artery or its branches The obstruction may be caused by intrinsic disease of the artery, or by compression on the artery from outside Renovascular lesions account for up to 10% of cases of children referred with hypertension,282–285 and are the third most common cause of significant hypertension in children after renal scarring and glomerular disease Fibromuscular dysplasia, or fibromuscular nonatherosclerotic stenosis of the renal vessels, is the main vascular abnormality, and is classified according to the arterial layer in which the lesions predominate.286,287 Intimal fibroplasia is a rare cause in adults, but occurs primarily in children Fibromuscular dysplasia, or hyperplasia of the media, is more common, and predominates in adolescents and adults Overall, the condition is most common in middle-aged females.286,287 The lesion in adults is commonly situated in the middle or distal part of the renal artery, whereas stenosis occurs more frequently at the origin of the vessel in children The etiology of the condition is unknown, but a cellular reaction to altered dynamics of pressure and flow in the artery has been proposed.286 Genetic factors may play a role, with the condition being commoner in first-degree relatives of those with involvement of the renal arteries,288 and in those carrying the ACE-1 allele for the angiotensin-converting enzyme.289 It is important to recognize that the condition may be progressive,286,287,290 and may also involve arteries other than the renal vessels.286–288 A careful search for the involvement of other arteries is mandatory, with particular note taken of absent peripheral pulses or the presence of bruits, especially over the carotids A number of cases are associated with neurofibromatosis type 1.281–285,291 A careful family history, and clinical examination for other features of the condition, is important The renal arterial stenosis in neurofibromatosis type 1 is usually caused by intimal proliferation or neurofibromatotic proliferation in the arterial wall.194 Associated coarctation of the abdominal aorta is common Occasionally, compression on the artery from outside by a neurofibroma or ganglion neuroma is responsible for hypertension Other space-occupying lesions that may involve compression of the renal artery include tumors, fibrous bands, hematomas, and pheochromocytomas Acquired narrowing of the abdominal aorta has been observed following radiotherapy for intra-abdominal malignant disease.292 Coarctation of the abdominal aorta without neurofibromatosis is often accompanied by renal arterial stenosis.283,293 Other vessels originating from the abdominal aorta are usually involved Takayasu's arteritis is an important cause of renovascular hypertension in nonwhite children.294 The arteritis affects the aorta, the proximal portions of its major branches, and the pulmonary arteries The onset of the vasculitis is associated with an acute systemic illness, which usually subsides after a few weeks but may recur The etiology is unknown, though a link with tuberculosis has been suggested.295,296 A raised erythrocytic sedimentation rate, and elevated levels of immunoglobulin, indicate active disease Diagnostic imaging includes Doppler ultrasound and arteriography Three-dimensional magnetic resonance angiography and positron emission tomography have been shown to reveal early changes in the process of the disease, avoiding the need for intravenous contrast or ionizing radiation.297,298 Therapy of the arteritis is based on the use of corticosteroids,299 and in some patients the addition of other immunosuppressive drugs such as methotrexate or azathioprine.300 Following this, management is mainly concerned with the control of the hypertension The prognosis is, to some extent, dependent on the severity of the vasculitis and the resultant damage Other miscellaneous causes may be found Renal arterial stenosis can be present in some cases of infantile hypercalcemia syndrome.301 As already discussed, thrombosis or embolism of the renal artery is an important cause of hypertension in infants Stenosis of arterial branches within the kidney may lead to severe hypertension, and is difficult to diagnose.302 Diffuse renal arteriolar stenotic lesions can occur in polyarteritis nodosa, hemolytic uremic syndrome, and following renal irradiation.303 Renal venous thrombosis in infancy can lead to the development of hypertension.250,304 Hypertension is common after renal transplantation, but only rarely is caused by renal arterial stenosis Renal hypertension can occur after traumatic injury to the kidney, causing renal arterial thrombosis or intrarenal vascular damage, or from perinephric inflammation causing constriction on the kidney.194 Arteriovenous fistulas, either congenital or acquired, following trauma, surgery, or renal biopsy, can all cause hypertension A bruit over the renal artery is a useful diagnostic sign, albeit often absent in children with renovascular hypertension Hypokalemic alkalosis suggests underlying secondary hyperaldosteronism, which is a consistent feature of renovascular hypertension Doppler ultrasound has limited sensitivity for detecting renal arterial stenosis.305,306 Computed duplex sonography is able to measure blood flow velocity as a guide to the presence of stenosis.307 Overall sensitivity is moderate, but specificity for Doppler assessment is excellent.308,309 Renal scintigraphy may show asymmetry of function and size, with reduced uptake on the side of the stenosed renal artery, but pediatric renovascular disease may be bilateral,283 and these investigations may not be helpful Direct evidence of renal ischemia with stimulation of the renin-angiotensin system is derived from the differential determination of renal venous renin A ratio of 1.5 or more between the affected and the nonaffected kidney may predict unilateral renal ischemia and an anticipated positive response to surgery.310–312 Using this ratio to predict unilateral disease, however, does not always correlate with the arteriographic findings,209 and in no way removes the need for arteriography The level of renin in the renal vein of the nonaffected kidney is usually suppressed to the level of the systemic concentrations A ratio of less than 1.5 suggests either bilateral disease or nonrenovascular hypertension, though renovascular hypertension and successful surgery have been reported in some patients.313 A normal renal arteriogram, with similar activities of renin in both renal veins, will certainly exclude a renal cause for hypertension in most, if not all, cases The gold standard investigation for renal arterial stenosis is selective renal arteriography and estimation of renal venous renin The procedure is usually performed under sedation or general anesthesia, with access to the renal artery and vein from puncture of the femoral vessels If the hypertension is mild and easily controlled, and if the other investigations do not suggest renovascular hypertension, it is reasonable not to recommend arteriography, though careful follow-up is essential The blood pressure should be carefully controlled before attempting arteriography Adequate hydration should be maintained, and the ... Renal scintigraphy may show asymmetry of function and size, with reduced uptake on the side of the stenosed renal artery, but pediatric renovascular disease may be bilateral,283 and these investigations may not be helpful