eMedicine - Fibromuscular Dysplasia (Visceral Arteries) : Article by Ali Nawaz Khan

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Fibromuscular Dysplasia (Visceral Arteries)

Article Last Updated: May 28, 2008

Background

Fibromuscular dysplasia (FMD) is an uncommon angiopathy of uncertain etiology associated with heterogeneous histologic changes that may affect the carotid and vertebral circulation, visceral arteries, and peripheral arteries.^{1, 2, 3, 4, 5, 6, 7}

The frequency with which FMD affects the renal artery varies. Hartnell reports an incidence 2.2% (personal communication). Andreoni et al reported a 4.4% incidence of FMD in renal donors.⁸ The disease predominantly occurs in young to middle-aged women. The disease ultimately results in arterial stenosis, causing organ ischemia or infarction (see Image 1).

Pathophysiology

Leadbetter and Burkland first reported FMD of a renal artery in 1938 when they removed an ectopic kidney from a 5-year-old boy who presented with sustained hypertension.⁹

FMD may involve any layer of a visceral artery, and it may be classified on the basis of the primary involvement of the arterial wall. The classification system includes intimal, medial, or adventitial fibrosis. The medial variety can be subdivided. In 1967, McCormack et al histologically classified FMD on the basis of the primary site of involvement of the arterial wall.¹² Their classification of fibrosing lesions of renal arteries included the categories of intimal fibroplasia, medial fibrosis with microaneurysms, subadventitial fibroplasia, and fibromuscular hyperplasia. They coined the term chain of beads to describe radiographic changes in medial fibroplasia of the renal artery. The term has subsequently been modified to string of beads.¹¹ Medial fibroplasia is the most common type of FMD and represents 80-95% of cases. The string-of-beads sign is classically seen in medial fibroplasia.

Subadventitial fibroplasia can have a similar radiographic appearance. However, in this variant, the size of the aneurysms does not exceed the diameter of the renal artery. Medial fibroplasias may appear as a single stenosis of a visceral artery, but it is most often seen as multiple stenoses with intervening outpouchings that form a chain. This is radiographically depicted as the string-of-beads sign.

On histologic evaluation, medial fibroplasias can be subdivided into 2 types: a peripheral form and a diffuse form. The peripheral form generally affects the outer media, replacing the smooth muscle with fibrous-appearing tissue. The diffuse form affects the media more extensively than the other form, with replacement of the media with fibrous tissue and medial thinning. The media can be completely absent in some areas, giving rise to aneurysmal dilatation. Although FMD was initially described in the renal arteries, many other visceral arteries are now known to be involved, and multiple visceral artery aneurysms have been reported.^{7, 13}

Although the pathogenesis is not completely understood, humoral, mechanical, and genetic factors, as well as mural ischemia, may play a role. Hormonal factors have been implicated because medial fibroplasias and subadventitial fibroplasias are found predominantly in women. The common association with ptotic kidneys has supported the mechanical theory in which stretching of the renal artery may be responsible for the development of FMD. Ischemia from inadequate nutrition of the renal artery by the vasa vasorum has also been proposed. A deficiency of alpha-1-antitrypsin (AAT) has also been implicated in the development of various disorders affecting medium-sized arteries; these include intracranial aneurysms, cervicocephalic arterial dissections, and FMD. Some have suggested that heterozygous AAT deficiency may be a genetic risk factor for FMD.^{6, 14, 15, 16, 17}

Schievink et al retrospectively studied the frequency of FMD in patients with AAT deficiency on postmortem examination in 1983-1992 at the Mayo Clinic.¹⁵ Arterial FMD was found in 2 of 6 patients with AAT deficiency (33.3%; 95% confidence interval [CI] = 4.3%, 77.7%), compared with 23 of 6690 patients without the deficiency (0.3%; 95% CI = 0.2%, 0.5%). In patients with both AAT deficiency and FMD, the arterial media was thickened and was composed of irregular arrays of muscular and connective tissue fibers in a background of mucoid ground substance. The authors concluded that these findings provided further evidence of an underlying arteriopathy in patients with AAT deficiency and suggested that FMD may be a nonspecific disorder.

Sang examined the role of several suggested etiologic factors in renovascular FMD in a case-control study of 33 patients with angiographically demonstrated FMD and in 61 control subjects (renal transplant donors) with normal renal arteries.¹⁴ Factors included use of oral contraceptives or markers of sex hormone dysfunction, mechanical stress to the renal artery wall, human lymphocyte antigen (HLA) type, cigarette smoking, hypertension for more than 5 years, and a family history of cardiovascular disease.

The risk of FMD was significantly (P = 0.003) increased (odds ratio [OR] = 4.1, 95% CI = 1.5, 10.9) among cigarette smokers. A significant (P <0.001) dose-response relation was noted between cigarette use and FMD (OR = 8.6 for those who had smoked >10 pack-years). Personal history of hypertension for more than 5 years was also an associated factor (OR = 5.0, 95% CI = 1.1%, 22.8%) with a significantly (P = 0.036) increased risk of FMD. HLA-DRw6 antigen was more common in the patients with FMD than in the donor control subjects (OR = 3.00, P = 0.067) or a second group of 934 ambulatory control subjects (OR = 2.51, P = 0.031). Adjustment for cigarette smoking increased the OR to 5.0 (95% CI = 1.3%, 19.6%). A family history of cardiovascular disease was positively but not significantly (OR = 1.7, P = 0.175) associated with FMD.

Boutouyrie et al defined a new carotid phenotype in FMD by using a noninvasive echo-tracking system and found increased wall thickness and distensibility of the radial artery.¹⁸ Their data indicated the presence of subclinical lesions at arterial sites distant from the renal arteries, suggesting that renal FD is not a focal but a systemic arterial disease.

Meacham and Brantley reported a family with FMD of the superior mesenteric arteries (SMAs).¹⁹ They described a critically ill 17-year-old girl who had an evolving GI infarction; the patient died 11 months after she presented. After surgical revascularization, biopsy of the SMA showed FMD. The patient's close consanguineous relatives were interviewed and examined; the patient's mother and younger sister were found to have abdominal bruits. Arteriograms showed total occlusion of the celiac artery and SMA in the sister and subtotal celiac occlusion in the mother. Postprandial abdominal pain and constipation in the sister prompted elective mesenteric revascularization, and biopsy confirmed FMD identical to that of her older sister. The mother, who was asymptomatic, had single-vessel disease and did not require surgery. This report supports a genetic basis for FMD.

Frequency

United States

Renovascular hypertension, observed mainly in women aged 30-50 years, is the most common manifestation of FMD. Its prevalence in hypertensive patients is estimated to be less than 1%. The true prevalence of the disease is probably higher because in normotensive or asymptomatic hypertensive patients, many cases go undetected.^{10, 20, 21}

Renovascular disease is an important cause of hypertension in children and is associated with considerable increase in the risk of morbidity and mortality. Secondary hypertension is more common in children than in adults, with 75-80% of cases affecting children. In 70% of all cases of secondary hypertension in children, the cause is fibromuscular hyperplasia. Other associated conditions are aorto-aortitis, midaortic syndrome, Williams-Beuren syndrome, neurofibromatosis, Takayasu arteritis, William syndrome, pheochromocytoma, Kawasaki disease, Fabry disease, Marfan syndrome, and Degos-Köhlmeier disease.²²

Tyagi et al described their initial and long-term results of percutaneous transluminal angioplasty (PTA) in the management of renovascular hypertension in children; 11.5% of the patients were found to have FMD.²³ A Russian group from the Bakulev Institute of Cardiovascular Surgery described the results of surgery to manage renovascular hypertension; 71 of their 185 pediatric patients had FMD.²⁴

International

No data suggest that the frequency of FMD in other countries is different from that in the United States.

Mortality/Morbidity

The natural history of FMD is variable and not necessarily benign. In 1 study of 42 patients (50% male) with FMD, angiography showed a progression of disease in all patients during follow-up (1 mo to 11 y 4 mo). All forms of FMD are progressive at variable rates.²⁵

By contrast, Pohl and Novick reported disease progression in 33% of 66 patients with FMD.²⁶ No stenosis progressed to complete occlusion, and no clear association with renal atrophy was observed. In general, FMD affects the mid or distal renal artery, and it may be associated with branch RAS. However, the renal microcirculation is normal, in sharp contrast to atheromatous renal vascular disease. Therefore, progression to renal atrophy is the result of hemodynamically significant proximal arterial stenosis that exceeds 75-80%.^{27, 28}

Schreiber et al showed that loss of renal function, as demonstrated by an increased serum creatinine level or reduced kidney size, seldom occurs despite progressive disease on angiography.²⁴ Anatomic progression of medial fibroplasias in the renal artery has been reported in 12-66% of patients with disease of the main renal artery. However, as mentioned, deterioration of renal function, as determined on the basis of the creatinine level or a reduction in renal size, seldom occurs despite progression of RAS, as demonstrated angiographically.²⁹

Abbas et al reviewed the experience at the Mayo Clinic with outcomes of hepatic-artery aneurysms (HAAs).³⁰ They retrospectively reviewed 306 patients with true visceral aneurysms diagnosed from 1980-1998, identifying 36 patients (12%) with HAA (23 men, 13 women; mean age, 62.2 y; range, 20-85 y). Most aneurysms were extrahepatic (78%) and single (92%). Mean aneurysmal diameter at presentation was 3.6 cm (range, 1.5-14 cm). Five aneurysms had ruptured (14%), and 4 were symptomatic (11%). Mortality from rupture was 40%. Of 9 patients with ruptured or symptomatic aneurysms, 2 had multiple HAAs, 3 had FMD, and 2 had polyarteritis nodosa. All 5 HAAs that ruptured were of nonatherosclerotic origin (P = 0.001). The authors concluded that HAA is associated with a definite risk of rupture (14%). Risk factors include multiple HAAs and a nonatherosclerotic origin.

Complete obstruction of the renal artery (20%) leading to total renal infarction has been reported.²⁵ Studying potential arterial donors with angiographic evidence of FMD, Cragg et al found that 26% developed hypertension, compared with 6% of age- and sex-matched control subjects.³¹

Hepatic and superior mesenteric involvement occurs infrequently, and sporadic cases of severe intestinal ischemia and HAA rupture have been reported. FMD is a rare cause of abdominal aortic aneurysm.³²

Race

Sex

Age

Anatomy

FMD can affect the renal, hepatic, left gastric, and splenic arteries, the SMA, and the inferior mesenteric artery (IMA). Although classified as dorsal branches, the renal arteries usually arise as lateral aortic branches slightly below the disk between L1 and L2. In rare cases, the renal arteries may arise below the inferior aspect of T12 or below the lower border of L2. The position of the kidney is variable, and though most renal arteries arise between L1 and L2, the length of the renal arteries and the angle between the aorta and the renal arteries varies. The lower the kidneys, the longer and more acutely angulated the renal arteries. The right renal artery may originate slightly anterior to the coronal plane.

Supplemental renal arteries may be problematic for the angiographer because they may be difficult to find, and the catheter tip may obstruct the orifice. The origin of the renal arteries may again be variable; it may arise from D11 down to the iliac vessels. To make things worse for the interventionist, supplemental branches may arise from visceral arteries. Cadaveric studies have shown that single renal arteries are bilaterally present in 72% of cases.

The kidney may be divided into dorsal and ventral segments, and the arteries to these segments can be identified with angiography. The intrarenal branches of renal arteries taper uniformly. The intralobar branches branch repeatedly to give rise to arcuate arteries. The interlobular arteries arise from the arcuate arteries, where they extend into the renal cortex in a parallel fashion. FMD may affect the main renal and intralobar arteries.

RAS caused by FMD affects the middle and distal renal artery in 79% of the patients; a branch renal artery in 4%; or a combination of the 2 in 17%. FMD is bilateral in approximately 65%; the left-to-right ratio is 4:1.

Clinical Details

Clinical manifestations

The clinical manifestations reflect the arterial bed involved. Patients most commonly present with renovascular hypertension (renal) and stroke (carotid), but rare presentations include subarachnoid hemorrhage, abdominal angina, or claudication of the legs or arms. An acute presentation has been described with renal infarction, rupture of a visceral abdominal aneurysm, and mesenteric and/or intestinal infarction.

FMD often causes hypertension as a result of RAS with no other signs of its presence. It is usually discovered in the workup of difficult-to-control hypertension. The disorder may also be discovered when a bruit is noted over the kidney on a routine examination or on abdominal examination for other disorders.

Patients with FMD of the mesenteric arteries may present with manifestations of bowel ischemia, such as abdominal pain and melena.³³ FMD is a pathologic diagnosis, but the characteristic changes may be confirmed by means of angiography, and the diagnosis may be made in the appropriate clinical setting.

Antihypertensive therapy may increase or decrease plasma renin levels. Nonsteroidal anti-inflammatory drugs can also decrease plasma renin levels. The baseline plasma renin activity is elevated in 50-80% of patients with renovascular hypertension. Measuring the increase in the baseline plasma renin activity 1 hour after the administration of 25-50 mg of the ACE inhibitor captopril can increase the predictive value of baseline plasma renin activity.^{34, 35} In patients with RAS, the increase in baseline plasma renin activity is exaggerated; this is perhaps the result of the elimination of the normal suppressive effect of high angiotensin II levels on renin secretion in the ischemic kidney.

Other problems to consider

Atheroma is the most common cause of RAS. The stenosis from atheroma is usually orificial or located in the proximal third of the renal artery. Atheromatous RAS is frequently associated with aortic disease.

The vasculitides are a heterogeneous group of diseases characterized by vascular inflammation and necrosis. They have a wide spectrum of manifestations resulting from the involvement of arteries and other vessels of various sizes and locations.

Data from patients with large and small vasculitides suggest a genetic influence in disease susceptibility.

A variety of vasculitides have been described. Common forms include polyarteritis nodosa, giant-cell arteritis, systemic lupus, systemic sclerosis, Wegener granulomatosis, and Henoch-Schönlein purpura.

Angiographic findings in systemic necrotizing vasculitis include 4 basic arterial anomalies: saccular microaneurysms (62%), arterial thrombosis (81%), arterial stenosis (81%), and luminal irregularities (90%). Alterations in the renal vascular flow are also observed in accordance with changes in the cortical medullary differentiation, heterogeneous nephrogram, and prolonged washout. Microaneurysms may regress after immunosuppressive therapy.

Neurofibromatosis is a rare cause of RAS; it usually occurs as a direct effect of fibrous proliferation of the intima or media. In some cases, neurofibromatous tissue may affect the adventitia, producing periarterial fibrosis indistinguishable from RAS of other causes. These lesions are usually at the origin of the artery, and they may be bilateral.

Congenital stenosis (coarctation of the renal artery) is extremely rare and is assumed to be congenital because of its discovery in early life. This type of stenosis is generally confined to the main renal artery and may be associated with aortic coarctation. Some patients may eventually have changes of arteritis, FMD, or neurofibromatosis.

Standing waves in the renal arteries appear as multiple serrated indentations symmetrically distributed at evenly spaced intervals. These are of pathologic importance and may represent arterial spasm. They may also affect intrarenal branches.

A fibrous musculotendinous band may cause extrinsic compression of the renal artery.

Klippel-Trenaunay syndrome is a congenital angiodysplasia consisting of a triad of angiomas, osteohypertrophy, and venous varicosities. Visceral involvement is not uncommon and may cause life-threatening complications.

Binswanger disease is a complex disorder characterized by a progressive multi-infarct dementia. Patients often present with recurrent transient ischemic attacks (TIAs), ischemic and hemorrhagic strokes, and other blood-supply disturbances that lead to numerous types of vasogenic brain tissue damage of various intensities. Diffuse arteriosclerosis associated with hypertension is often present.^{36, 37}

Grange and associates reported 4 of 9 siblings with a syndrome of stenosis of the renal arteries and chronic hypertension; variable stenosis or occlusion of cerebral, abdominal, and probably coronary arteries suspected to be caused by FMD; congenital cardiac abnormalities; brachydactyly and syndactyly of the hands and feet; and increased bone fragility consistent with a mild form of osteogenesis imperfecta.¹⁶

Three of the affected siblings had mild to moderate learning disabilities. The parents and remaining 5 siblings had normal hands and feet and no history of excessive fractures. Individual components of this syndrome may appear as isolated conditions, including FMD, brachydactyly, syndactyly, and osteogenesis imperfecta, and they are autosomal dominant traits in many cases. Explanations for this familial occurrence included autosomal recessive inheritance, autosomal dominant inheritance with decreased penetrance, or parental gonadal mosaicism for a mutation involving a single gene or several contiguous genes.

Weymann and associates reported a 15-year-old boy with stenosis and occlusion of multiple cranial, renal, and celiac arteries; aneurysm of the basilar artery; bilateral cutaneous syndactyly between fingers 4 and 5; partial cutaneous syndactyly between fingers 3 and 4 on the right hand; brachydactyly; and borderline mental retardation.³⁸ The patient's clinical course was characterized by recurrent abdominal pain, gastritis, and high blood pressure.

Preferred Examination

CT angiography (CTA) with maximum intensity projection (MIP) and quantitative measurement of stenosis is an accurate noninvasive technique for diagnosing stenosis of the visceral arteries, whatever the etiology. ³⁹

Magnetic resonance angiography (MRA) produces excellent contrast-enhanced angiograms without the risk of iodinated compounds and radiation exposure. Unlike contrast-enhanced angiography, MRA has no attendant risk of nephropathy caused by contrast agent or cholesterol-emboli syndrome. MRA provides accurate information about the number of renal arteries, the size of the kidneys, and the presence of anatomic variants. Future developments may shorten MRA imaging times to reduce the problem of claustrophobia while still allowing the test to provide both anatomic and functional information.^{40, 41, 42, 43}

Local and regional preferences differ regarding the use of CTA vs MRA for cross-sectional imaging. However, as a group, radiologists are using MRA in place of contrast-enhanced angiography as the diagnostic modality of choice. With both CTA and MRA, mild FMD or FMD in the accessory arteries may be missed; therefore, it is still likely that contrast-enhanced angiography is the criterion standard.

Data support the superiority of MRA over duplex Doppler ultrasonography (US) in patients with uremia associated with RAS, though the data do not specifically apply to FMD.⁴⁰ As availability increases, MRA will likely become the screening test of choice in the diagnosis of RAS, including FMD.

Beregi et al examined 20 patients with hypertension (mean age, 56 y) and CTA-proven FMD of the renal artery.⁴⁴ The acquisition protocol was as follows: collimation, 3 mm; table speed, 3 mm/s; and incremental algorithm, 1. A consensus panel reviewed MIP and shaded-surface–display (SSD) reconstructions and transverse sections to determine the sensitivity and specificity of each technique in revealing renal-artery FMD.

Helical CTA enabled successful diagnosis of FMD in all 20 patients. Helical CTA showed 31 of 34 pathologic arteries and 33 of 38 lesions. Aneurysms (>6 mm) on arteriography (n = 12) were revealed in 83% of transverse sections, 75% of MIP reconstructions, and 58% of SSD reconstructions. Lesions that had a string-of-pearls appearance on arteriography (n = 19) were shown on 53% of transverse sections, 84% of MIP reconstructions (P <0.05 vs transverse sections), and 74% of SSD reconstructions. Stenoses (n = 7 on arteriography) were revealed on 57% of transverse sections, 71% of MIP reconstructions, and 57% of SSD reconstructions. MIP alone revealed 30 (79%) of the 38 angiographic lesions; however, use of both MIP and transverse sections increased the sensitivity to 87%.

The authors concluded that helical CTA, especially the combination of transverse sections and MIP reconstructions, can reliably depict renal-artery FMD. They further reiterated that, because some lesions may not be shown, arteriography with pressure measurements is the only technique that can be used to assess the physiologic importance of the dysplasia.

Doppler US can be used to measure the velocity of blood flow. It is a noninvasive technique and has a high sensitivity in expert hands. Color flow Doppler US may demonstrate disorganized flow patterns and a high-velocity flow stream associated with hemodynamically significant stenosis.^{45, 46, 47, 48}

Leung et al compared contrast-enhanced MRA with duplex US for the detection of RAS, with catheter angiography as the standard. Eighty-nine patients with clinically suspected renovascular disease underwent duplex renal scanning and MRA. Sixty also underwent catheter angiography.⁴⁰ Readers blinded to other imaging results interpreted all studies for RAS. In detecting hemodynamically significant (diameter reduction of at least 60%) main RAS, sensitivity and specificity were, respectively, 90% and 86% for MRA and 81% and 87% for duplex US. Most false readings involved differential grading of stenoses detected with all 3 techniques. When patients with FMD were excluded, the sensitivity of MRA increased to 97%, with a negative predictive value of 98%. MRA depicted 96% of the accessory renal arteries seen with catheter angiography; duplex US showed 5%.

The authors concluded that contrast-enhanced MRA is a useful technique for diagnosing atherosclerotic renovascular disease. It overcomes the major limitations of duplex renal scanning. However, duplex imaging has the advantage of providing hemodynamic information, and it appears to be best suited for the assessment of suspected FMD.

Radionuclide renography with technetium-mercaptoacetyltriglycine (MAG3)–captopril has a high sensitivity and specificity and adds a physiologic element to the diagnosis of RAS. In FMD, a positive captopril renographic finding supports intervention, though hypertension is unlikely to be cured.^{34, 35}

Hypertensive urography is of historical interest and is no longer used as a screening technique for RAS. Likewise, plain-film radiography has a limited role in patients presenting acutely as a result of mesenteric ischemia, which is a rare complication of FMD.

Renal arteriography can be performed by using conventional or digital subtraction technique. Angiography is particularly indicated when vascular intervention is contemplated. Carbon dioxide has recently emerged as an alternative angiographic contrast agent for use in combination with digital subtraction angiography (DSA) to avoid the risk of conventional nephrotoxic contrast agents in patients with severe renal insufficiency.

At present, angiography remains the criterion standard for detecting arterial stenoses and aneurysms, though its role is being redefined. The diagnostic and prognostic information available from captopril renography and the increasing availability of MRA have reduced the use of renal arteriography as a diagnostic tool, except in evaluating kidneys with intrarenal branch-artery stenoses and those with complex vascular anatomy, including multiple accessory arteries.

Limitations of Techniques

With CTA or MRA, the physician may overlook mild cases of FMD. Most false-negative and false-positive results for RAS arise from accessory renal arteries. MRI is expensive, and its availability is limited.

Measurements of the size of RAS on angiography (an important clinical consideration) may be imprecise and do not permit an assessment of the cross-sectional area or, most importantly, the flow through the stenotic segment. Some of these limitations may be overcome by using pressure measurements across the stenosis and by using intravenous US (IVUS). However IVUS has limited availability.

The various histologic types of FMD are difficult to distinguish on angiograms; this difficulty has an important clinical bearing from a prognostic point of view.

Doppler US is operator dependent, time consuming, and cumbersome. Several factors, including anatomic, technical, patient-related, and pathologic factors, can affect Doppler US.

The false-positive and false-negative rates of hypertensive urography are too high for it to be used as a screening test for RAS. Acceptance of radionuclide renography as a primary screening tool for RAS has been hindered by the lack of standardized protocols.

Other Problems to Be Considered

Atherosclerosis
Systemic necrotizing vasculitis
Neurofibromatosis
Congenital stenosis
Standing waves
Fibrous musculotendinous band
Klippel-Trenaunay syndrome
Binswanger disease
Grange syndrome

Findings

Plain radiographs have a role only when patients present acutely with bowel ischemia as a result of severe stenosis of the mesenteric arteries in association with thrombosis (see Images 3-6). The radiographic findings include bowel distention, mucosal edema (shown as thumb printing), small-bowel pseudo-obstruction, gasless abdomen, pneumatosis, mesenteric and portal venous gas, and ascites.

For the evaluation of RAS, hypertensive urography is performed by rapidly administering an intravenous bolus into a peripheral vein and taking sequential 1-minute radiographs for 5 minutes. Additional delayed radiographs may be obtained to assess the rest of the urinary tract.

Findings that suggest renovascular hypertension caused by RAS include the following: small kidneys, delayed excretion caused by decreased glomerular filtration, increased density of contrast medium on the involved side caused by increased water reabsorption, delayed washout of contrast material, lack of distention of the renal collecting system, and extrinsic impression on the renal pelvis and or upper ureter from collateral vessels.

Degree of Confidence

Hypertensive urography is of historical interest only; it is no longer used as a screening technique for RAS because of its inconsistent results. The urogram may be normal in the presence of established RAS.

False Positives/Negatives

The false-negative rate for hypertensive urography is 22%; the false-positive rate is 13%.

Findings

CTA, MIP, multiplanar reconstruction (MPR), and quantitative measurement of stenosis are accurate, noninvasive techniques in the diagnosis of visceral-artery stenosis. The advent of spiral and multisection CT scanning has made CTA feasible. Continuous scanning through an area of interest during a single breath hold provides sufficient data to reconstruct 3-dimensional (3D) images (see Images 7-8).^{39, 44}

Many scanning protocols are available. The general consensus is that both a timed bolus and a rapid injection rate improve image quality. No positive oral contrast material should be used because it severely degrades image quality. Immediately before the procedure, the authors' patients ingest water, and glucagon is then given intravenously to diminish bowel movement and maximize bowel distention. Some centers do not find this protocol essential.

The 3 most common techniques used for 3D reconstruction are MIP, SSD, and volume rendering (VR). MIP is often the single most useful technique for 3D reconstructions. Axial CT with sagittal and coronal reconstruction may elegantly depict visceral-artery aneurysms associated with arterial-wall thickening, as seen in FMD.

Mesenteric occlusion is a rare complication of FMD. In an acutely ill patient, CTA may show either an arterial mesenteric occlusion or high-grade stenosis. Scrutinizing the axial CT images may show thickening of the bowel wall, pneumatosis, portal venous gas, or mesenteric hemorrhage.

Degree of Confidence

The diagnostic accuracy of CT and gadolinium-enhanced 3D MRA have generally both been good, with sensitivities and specificities of 90-100%. The sensitivity and specificity of CTA in the diagnosis of RAS of 50% or more are approximately 90% and 97%, respectively. With RAS stenosis of 75% or more, the sensitivity of CTA is even higher. Because most of the false-negative and false-positive results arise from accessory renal arteries, the accuracy in detecting RAS of the main renal artery with CTA may be as good as that of angiography. Most published data apply to atherosclerotic RAS. The accuracy of detection of FMD remains unknown.^{41, 44, 49}

Accessory renal arteries are reliably identified by using CTA. RAS of either the mainstem artery or its intrarenal branches is detected with a high degree of accuracy.

An advantage of CTA is that the lumen of the vessel and the pathologic vessel wall are both visualized. This can be an advantage in determining the choice of interventional therapy, such as stenting, angioplasty or surgery, though it applies more to atheromatous disease than to FMD.⁵⁰

Visualization of small intrarenal vessels is difficult, and accurate assessment of peripheral stenoses beyond the renal hilum may be problematic. However, once again, this feature applies more to atheromatous disease than to FMD.⁴¹

One distinct drawback of CTA is the 120-150 mL of iodinated contrast used per scan. This amount of contrast agent increases the risk of nephropathy. In the setting of a kidney that is already compromised by arterial stenosis, nephropathy may cause further function compromise. Olbricht et al have shown that, in patients with preexisting impaired renal function, CTA may be unreliable in the assessment of RAS, though their study was not specific for FMD.³⁹

In patients with chronic symptoms that are possibly related to mesenteric angina, a normal celiac axis and SMA virtually exclude mesenteric ischemia. However, in patients with moderate arterial stenosis, MRA may be more precise than CTA.

False Positives/Negatives

Andreoni et al expressed concern that CTA or MRA may cause mild cases of DSA-detectable FMD to be overlooked. Most of the false-negative and false-positive results for RAS arise from accessory renal arteries.⁸

Verswijvel et al have reported magnetic susceptibility artifacts due to titanium surgical clips that mimicked FMD of the renal artery in a kidney transplant.⁵¹

Findings

MRA produces excellent contrast-enhanced angiograms without the risk of iodinated compounds and without radiation exposure. MRA provides accurate information about the number of renal arteries, the size of the kidneys, and the presence of anatomic variants (see Images 2, 10-12).

Comprehensive examination includes both 3D dynamic gadolinium-enhanced and 3D phase-contrast MRA techniques, which allow for evaluation of the renal arteries and other visceral arteries. The 3D phase-contrast technique is flow based and is subject to dephasing in the presence of clinically significant arterial stenosis. 3D gadolinium-enhanced MRA produces excellent contrast-enhanced angiograms without the risk of iodinated compounds and without radiation exposure. Local and regional preferences differ regarding the use of CTA or MRA for cross-sectional imaging. However, as a group, MRA is replacing contrast-enhanced angiography as the diagnostic modality of choice.^{40, 41}

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

As of late December 2006, the FDA had received reports of 90 such cases of NSF/NFD. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Degree of Confidence

Gadolinium-enhanced MRA has high sensitivity for detecting stenosis in the main and accessory renal arteries. At present, MRA provides anatomic information regarding a vascular stenosis, but it provides little information about the functional significance of a stenosis.

False Positives/Negatives

Andreoni et al expressed concern that CTA or MRA may cause mild cases of DSA-detectable FMD to be overlooked.⁸ Although false-negative studies in RAS are rare, stenoses tend to be overestimated, and a false-positive diagnosis may result. Phase-contrast MRA, a type of MRA based on accumulated phase differences, can be performed to somewhat compensate for this tendency. Both CTA and MRA may cause mild FMD or FMD in the accessory arteries to be missed. Therefore, contrast-enhanced angiography likely remains the criterion standard.

Findings

Data about the use of US, specifically in FMD, are limited. Most studies have been dedicated to the more common atheromatous stenoses of the visceral arteries (see Image 9).

Gowda et al compared color-flow duplex imaging, IVUS, and renal arteriography in diagnosing renal artery FMD and correlated their results with the hemodynamic response to balloon angioplasty in patients with drug-resistant hypertension. They included 20 women (aged 31-86 y; mean, 62 y) with hypertension and duplex results suggestive of renal-artery FMD (mid-to-distal flow derangement and velocity augmentation). Patients underwent renal arteriography, IVUS, and balloon angioplasty, with both immediate and long-term assessment of blood pressure.⁵²

On IVUS, various endoluminal defects (eccentric ridges, fluttering membranes, spiraling folds) were depicted at locations predicted on duplex imaging, and they were uniformly identified at sites where arteriography depicted classic evidence of FMD (8 patients). However, similar defects were detected on IVUS when angiographic findings were borderline (7 patients) or normal (5 patients). Balloon angioplasty eliminated (16 patients) or reduced (4 patients) IVUS findings and lowered systolic blood pressure in all (mean reduction, 53 mm Hg; P <0.0001). This reduction was maintained during follow-up of 4-22 months (mean, 13 mo), with a mean reduction of 44 mm Hg (P <0.0001); this finding was independent of the baseline angiographic appearance.

The authors concluded that both color flow duplex imaging and IVUS depicted blood-flow and endoluminal abnormalities of renal-artery FMD. Balloon angioplasty eliminated or improved IVUS findings and produced substantial, sustained reductions in blood pressure, an effect that was independent of baseline arteriographic appearance. This finding calls into question the legitimacy of arteriography as the diagnostic criterion standard.

The diagnosis of RAS is based on systolic and diastolic velocity changes throughout the length of the renal artery. Renal-artery flow patterns can be classified into 4 categories: normal, diameter-reducing stenosis less than 60%, diameter-reducing stenosis more than 60%, and occlusion.^{45, 46, 47, 53}

The peak systolic velocity in normal renal arteries is 120 cm/s ± 12. With an average peak systolic aortic velocity of 60 m/s ± 15, both velocities decrease with age. The kidneys offer a low-resistance vascular bed; therefore, the Doppler spectral waveform from the normal kidney is that of a constant, forward, diastolic flow. In renal parenchymal disease, vascular resistance is increased; this results in a decrease in the diastolic flow component and an increase in the pulsatility of the Doppler spectral waveform. Parenchymal diastolic flow velocities of less than 20% of the peak systolic velocities are consistent with renal parenchymal disease.

In RAS of whatever cause, the peak systolic velocity increases more than 150 cm/s for angles less than 60° or 180 cm/s for angles greater than 70°. Poststenotic spectral broadening may be present with or without flow reversal. Flow may be absent during diastole in stenosis of more than 50%. A ratio of the peak systolic renal artery velocity to the aortic peak systolic velocity of 3.5 or more is said to be predictive of >60% stenosis.

Certain indirect Doppler US signs have been described for RAS. One such sign is a tardus-pavus pulse,⁵³ which is demonstrated as a gradual slope of Doppler waveform during systole (pulse time increase > 0.07-0.12 s) and as an attenuated Doppler waveform amplitude (peak systolic velocity < 20-30 cm/s). The acceleration index is determined by dividing the slope of the systolic upstroke (in kilohertz per second) by the carrier Doppler frequency, and the acceleration time is the interval between the onset of systole and the initial peak. The acceleration index in RAS is greater than 3 m/s². The resistive index in RAS is usually less than 0.56. The early systolic peak may be absent in RAS.⁵³

Color flow Doppler images may demonstrate disorganized flow patterns and a high-velocity flow stream associated with hemodynamically significant stenosis. A false-negative diagnosis may occur with an accessory renal artery, whereas a false-positive diagnosis may be made when coarctation of the aorta is present.

Color flow Doppler imaging is effective in demonstrating flow disturbance associated with tortuosity and stenosis at the origin of the celiac axis. Doppler spectral waveforms in a normal fasting celiac axis demonstrate a forward flow with an average peak systolic velocity of 123 cm/s ± 9 (age range, 48-79 y) associated with a significant increase in the systolic or diastolic flow velocity after a meal. This increase is also reflected in the hepatic and splenic arteries. The average postprandial systolic velocity 30 minutes after a meal of 355 kcal is 132 cm/s ± 7. In the presence of 60% celiac-axis stenosis, the peak velocity is increased to 167-208 cm/s ± 9. With this degree of stenosis, color Doppler imaging demonstrates a high-velocity jet at the stenotic site associated with poststenotic turbulent flow.

The potential for collateralization between the celiac axis, the SMA, and the IMA is remarkable. As a result, the reading of peak systolic pressure in the celiac axis may be lower or higher than that expected when concomitant SMA occlusion is present. This feature may result in the overestimation or underestimation of ischemic disease.

The fasting SMA demonstrates a low diastolic flow; however, after a meal, both the peak systolic and end-diastolic velocities show a tremendous increase in the absence of arterial stenosis. The normal fasting SMA velocities are 128 cm/s ± 16 (age range, 23-42 y). After a meal, the peak systolic velocity increases to 162 cm/s ± 11 with an end-diastolic velocity in the range of 48 cm/s ± 7 within 15 minutes after a meal. The peak systolic velocity almost doubles within 45 minutes after a meal. With significant SMA stenosis, the peak systolic velocity exceeds 270 cm/s, with a concomitant increase in diastolic flow. Color flow Doppler imaging shows a jet through the stenotic segment with turbulent flow downstream for some distance.

By using color and pulsed Doppler evaluation of visceral artery aneurysms, turbulent arterial flow can be shown within the anechoic masses related to major visceral arteries. Diagnosing these aneurysms is essential because the mortality rate is as high as 82% with spontaneous rupture.

Degree of Confidence

Duplex US of the abdominal visceral arteries is perhaps the most technically demanding US procedure. This study has operator- and patient-related limitations, such as the operator's expertise and optimization of the equipment and the patient's habitus and preparation.

Doppler US has several limitations in the diagnosis of RAS. These include patient-related factors (eg, bowel gas, obesity, respiratory renal movements, poor compliance), anatomic factors (eg, multiple renal arteries [16-28%], variation of renal veins used as imaging landmarks, horseshoe kidneys, crossed ectopia), technical factors (eg, false-positive results due to suboptimal angles, variation in operator experience, incomplete examination [because complete renal evaluation is cumbersome], need to visualize the entire length of artery, transmitted cardiac and/or aortic pulsation that may obscure renal waveforms, different emphasis on variable parameters), and pathologic factors (eg, false tracings recorded from large collateral vessels and reconstituted main renal artery, variable effects of RAS of different causes, including atheroma, fibromuscular hyperplasia, vasculitis, arteriovenous fistula, retroperitoneal fibrosis, and neurofibromatosis).

Color flow Doppler imaging in RAS of whatever cause may demonstrate disorganized flow patterns and a high-velocity flow stream associated with hemodynamically significant stenosis.^{45, 46, 47, 54}

US is a sensitive yet noninvasive technique that may provide useful information in mesenteric ischemia by demonstrating absent or barely visible color-flow arterial signals and thickened bowel wall loops. Doppler techniques are particularly useful for investigating chronic mesenteric ischemia.

False Positives/Negatives

With RAS, a false-negative diagnosis may occur with accessory renal artery, whereas a false-positive diagnosis may be due to coarctation of aorta.

There are several limitations of Doppler analysis of celiac-axis and SMA ischemia. First, the extensive potential for collateralization in splanchnic vessels may make assessment of a single vessel stenosis difficult. Second, the risk of error is increased when the angle of insonation used is greater than 60°. Third, careful placement of the sample volume is crucial. Unless the SMA is examined throughout, visualization of the vessel may result in a false-negative finding.

Findings

Radionuclide renography can be performed in the diagnosis of RAS regardless of the cause. Several radiopharmaceuticals are available, including diethylenetriamine pentaacetic acid (DTPA) and 131-iodine–labeled orthoiodohippurate (OIH), to serve this purpose. Technetium-labeled mertiatide (MAG3) has also been used. Since the introduction of captopril renography, various modifications have been made. Some centers use only 1 agent—either DTPA or MAG3.^{34, 35, 55}

A positive ACE-inhibitor radionuclide scan indicates that renovascular hypertension is present; it also implies the existence of hemodynamically significant RAS (>60-75% of the lumen).

Preliminary data suggest that aspirin renography may be as sensitive as captopril renography for RAS. Data about the use of aspirin renography in FMD are not available. Given that aspirin, compared with captopril, reduces renal blood flow and thus tubular tracer delivery in poststenotic kidneys, aspirin renography is expected to be more useful than other techniques, particularly if tubular tracers are used.^{56, 57, 58}

Degree of Confidence

Standard renography with OIH has low specificity and sensitivity in the diagnosis of RAS, including stenosis from FMD.

For RAS greater than 50%, Tc-MAG3-captopril renography has a sensitivity of 90%, a specificity of 91%, a positive predictive value of 70%, and a negative predictive value of 97%.

Data from Imanishi et al suggest that the sensitivity of iodine-123 OIH or MAG3 renography for the diagnosis of unilateral renovascular hypertension increases when aspirin is given.⁵⁶ Although Maini et al found that aspirin renography is superior to captopril renography,⁵⁷ van de Ven et al concluded that, for the identification of RAS, the usefulness of aspirin renography equals but does not surpass that of captopril renography.^{34, 35, 58}

In FMD, a result on positive captopril renography supports intervention, though hypertension is unlikely to be cured. However, the value of captopril renography for patients with significantly impaired renal function is not clear, and little evidence suggests that a positive test can be used to predict a favorable outcome from intervention in terms of preservation of renal function.

The sensitivity and specificity of studies of the captopril renin test are 75-100% and 60-95%, respectively. A major limitation is the need to discontinue antihypertensive therapy, including ACE inhibitors, beta blockers, and diuretics, because they can affect the baseline plasma renin activity. The sensitivity of the test is also low, and its predictive value is less than that of a captopril renogram.

Estepa et al examined 20 children (aged 5 d to 15 y) with hypertension whose diagnoses were confirmed on aortography.²² Captopril renograms and Doppler sonograms were initially obtained in only 8 children and suggested the diagnosis of RAS (7 with FMD).

False Positives/Negatives

With standard radionuclide (OIH) renography, false-positive results can occur from conditions that cause unilateral reduction in blood flow. These include chronic pyelonephritis, renal-outlet obstruction, renal-vein thrombosis, compression of the renal hilum, perirenal abscess, perirenal hematoma, and ptosis of the kidney.

Patients with renovascular hypertension may have false-negative captopril renograms after the long-term administration of captopril despite adequately maintained blood pressure. Therefore, when possible, ACE inhibitors should be discontinued before captopril renography is performed. Overhydration may result in false-negative findings, and underhydration may result in a false-positive finding. Bilateral RAS may be difficult to diagnose. Poor renal function most often results in a nondiagnostic examination. An asymmetric, small kidney with poor function is often unresponsive to captopril renography.

Findings

Conventional angiography remains the criterion standard for the detection of RAS, though it is being challenged by CTA and MRA. The hemodynamic significance of RAS may be assessed by evaluating the severity of the stenosis and the presence of collateral circulation to the kidney.

Indications for renal-artery interventions are determined on the basis of clinical, anatomic and physiologic criteria. Anatomic criteria are stenosis greater than 60% of the diameter, poststenotic dilatation, collateral circulation, and diminished renal size. Physiologic criteria are abnormal radionuclide scan, lateralizing renal vein renin, duplex US findings, and transstenotic pressure gradient (during angiography, >10% peak systolic). When the stenosis is 70%, it is most likely hemodynamically significant, and no pressure measurement is needed. For 50-70% stenosis, the pressure gradient should be determined before intervention.

Flush aortography is usually performed in the anteroposterior and slight left anterior oblique projections to best visualize the origins of the renal arteries. If the main renal arteries are normal, selective renal arteriography should be performed in the anteroposterior and contralateral oblique projections by using the magnification technique to best define renal-branch stenoses.

Intimal fibroplasia affects the main renal artery and major segmental arterial branches. It is often bilateral and characterized by narrow annular radiolucent bands associated with poststenotic fusiform dilatation.

Medial fibroplasias also involve the main renal artery and larger branches, often bilaterally; it is characterized by the classic string-of-beads sign with alternating areas of stenoses and intervening aneurysmal dilatation. A single focal stenosis may occur.

Subadventitial fibroplasia usually affects the distal main renal artery and is characterized by long irregular stenosis. There may be associated beading, but usually there is no aneurysm formation. The diameter of beads is not wider than the normal diameter of artery.

Celiac, hepatic, splenic, left gastric, SMA, and IMA stenoses caused by FMD are rare, but all of these have been reported. The angiographic appearances are similar to those seen in RAS. When stenosis occurs at these sites, the collateral circulation is more obvious on angiograms, as a result of rich potential pathways between the celiac axis and the SMA and IMA.

Ischemic kidneys release high levels of renin in their veins. Renal venous sampling for measuring renin levels to compare the venous drainage from each kidney can be used to predict the degree of renal ischemia and the potential success of revascularization. A 1.5-fold increase in renin level in the ischemic kidney constitutes a positive result; in such cases, use of revascularization to treat elevated blood pressure will likely be successful.

Renin secretion in the contralateral kidney is suppressed, as evidenced by the similar levels of renin measured in the renal artery, infrarenal inferior vena cava and renal vein. In approximately 10% of healthy patients, the ratio is above 1.5; in fewer than 20% is the ratio below 1.1. The accuracy of the measurements may be improved with the prior administration of an ACE inhibitor, which increases renin secretion on the affected side.

False-negative and false-positive results are frequent. Although more than 90% of patients with unilateral RAS and increased renin levels in the affected renal vein have a positive response to angioplasty or surgery, approximately 50% of patients with nondiagnostic findings also benefit from revascularization. As a result, most clinicians rely on the clinical index of suspicion rather than renal vein renin measurements to estimate the physiologic significance of RAS. However, renal renin vein measurements may still be useful in patients with bilateral RAS, in whom measurements may determine the side that contributes most to the hypertension.

Degree of Confidence

Renal angiography remains the criterion standard for the diagnosis of RAS. Angiography is an essential step when renovascular intervention is contemplated. Angiography only provides anatomic information; it does not allow assessment of blood flow through the stenosis. Angiography may lead to an underestimation of the severity of renal artery obstruction, which is better assessed by means of pressure measurements. On occasion, carbon dioxide angiography cannot be used to image a particular segment of a renal artery because of superimposed bowel gas.

False Positives/Negatives

Artifact caused by moving structures such as peristalsis on DSA may be mistaken for RAS.

Tremendous controversy surrounds the optimal treatment of patients with renal vascular disease. This debate is compounded by the fact that patients are not a homogeneous group; each has a different prognosis and potential response to therapy.

Therapeutic options include medical management, surgery, and percutaneous approaches (angioplasty or stenting). For patients with fibromuscular disease, the results of percutaneous management are generally superior to those of medical therapy. Although data from observational studies are difficult to compare, results with interventional procedures appear to be roughly similar to those of medical therapy in patients with atheromatous disease.^{23, 27, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71}

Three randomized, prospective trials have been conducted to compare routine angioplasty with medical management. These trials showed little advantage with interventional therapies in patients whose blood pressure was well controlled with medication and who did not have progression of renal insufficiency during medical care. Given these data, the potential management strategy should be based on an individualized risk-benefit assessment.

Clinically significant cortical and/or medullary atrophy has been demonstrated in poststenotic kidneys compared with contralateral normal kidneys. Despite intraparenchymal disease, clinical outcomes are favorable after revascularization. Cortical and/or medullary thinning appears to be an early marker of renal ischemia that could support revascularization in FMD disease with renal artery angioplasty. Isolated dissection of the renal artery is a rare condition that has been reported in association with FMD.

Medical treatment of FMD-associated hypertension carries the risk of further reduction of renal blood flow, which may result in ischemic atrophy or even total infarction of the involved kidney. If treatment with antihypertensive drugs is instituted, optimal blood-pressure control is essential. ACE inhibitors should be avoided. Other risk factors, such as cessation of smoking and hyperlipidemia, should be addressed. Definitive therapy should always be considered to prevent ischemic nephropathy.^{62, 65, 70}

Surgical bypass, such as by an autogenous vein grafting to replace the artery, with excision and repair by means of patch angioplasty or end-to-end anastomoses of the stenotic segment, was once the preferred option. With surgery, the vascular anatomy is restored permanently. However, surgery requires general anesthesia. Moreover, the cost of surgery is high owing to long hospital stay with possible procedure-related complications; the mortality rate is 2.2-7.8%.^{59, 60, 61, 63, 64, 66, 67, 68, 69}

Reiher et al examined the long-term results of surgical reconstruction of FMD of the renal artery.⁶⁴ They retrospectively reviewed preprocedural and postprocedural clinical records of 101 patients (80 women, 21 men; mean age at surgery, 43 y). All surviving patients were invited for clinical reexamination and color duplex US of the renal arteries.

Initial technical success was achieved in 83 (89%) of 93 patients, in whom postoperative angiography (90 patients) or renal scintigraphy (2 patients) was performed to assess renal artery reconstruction (RAR). Early occlusion (4 patients) or stenosis (1 patient) resulted in repeat surgery in 5 patients (5%). The 30-day mortality and morbidity rates were 2% and 12% for the entire group. The primary patency rate was 74% at 5 years. Fifteen patients had to undergo repeat surgery for restenosis after a mean time of 33 months, resulting in a secondary patency rate of 85% after 5 years. In 61 patients with a patent RAR at the time of reexamination, arterial hypertension was cured only in 22 (36%); improvement was observed in 19 (31%).

The authors concluded that vascular surgery for renal FMD yields good long-term results with regard to kidney perfusion and function. They suggested that surveillance of RAR-patency by means of US is mandatory in cases of recurrence or deterioration of arterial hypertension. Rates of cure of hypertension were disappointing.

PTA has become the procedure of choice for the treatment of symptomatic stenoses of visceral arteries, particularly those caused by FMD. Patency rates after PTA strongly depend on the size of the vessel treated and the quality of inflow and outflow through the vessel. RAS is an established cause of renovascular hypertension and chronic renal insufficiency. Because of the excellent results obtained with renal angioplasty, it is the most commonly performed procedure in symptomatic RAS. PTA may completely relieve the stenosis and cure hypertension in FMD; however, most patients still require some antihypertensive medication, and as many as 25% of patients have restenosis after 1 year.⁶⁵

Angioplasty was previously considered a contraindication in patients with a solitary or transplanted kidney. This is no longer the case, and in fact, angioplasty is now considered the procedure of choice for treatment of RAS in these patients. Technical success is achieved in more than 90% of patients. Patency rates of 90-95% at 2 years for FMD and 80-85% for atherosclerosis are commonly reported. Angioplasty of other visceral arteries has been reported infrequently, but it appears to be similar to renal artery angioplasty in terms of success and patency rates.

Mounier-Vehier et al demonstrated significant cortical and/or medullary atrophy in poststenotic kidneys compared to contralateral normal kidneys.²⁷ They assessed 20 patients (18 women, 2 men; age 48.7 ± 15.4 y) with hypertension and unilateral de novo FMD stenosis before and 6 months after revascularization (balloon angioplasty in 19 patients, bypass surgery in 1). Despite intraparenchymal disease, clinical outcomes were favorable after revascularization. Cortical and/or medullary thinning appeared to be an early marker of renal ischemia that could support revascularization in FMD disease.

Birrer assessed restenosis rates and blood pressure response in 27 patients 12 months after PTRA in patients treated for FMD RAS.⁶⁶ Although the restenosis rate after PTRA in FMD was as high as that in nonostial atherosclerotic lesions, a considerably increased therapeutic effect remained. Profound pressure response and recurrent arterial hypertension with restenosis supported the high probability of a renovascular origin of arterial hypertension in this young and otherwise healthy population compared with patients with atherosclerotic lesions of the renal artery.

Vascular stenting is considered complementary to PTA. The general consensus at the moment is that stenting should be reserved for patients in whom angioplasty fails. Many vascular stents are now available. Stents used in the recanalization of renal arteries are metallic devices, which are either self-expanding or balloon expandable. The United States Food and Drug Administration (FDA) has approved a few stents for peripheral use, coronary work, and transjugular intrahepatic portosystemic shunt (TIPS) procedures.

PTA is the treatment of choice for FMD, with excellent outcomes. Stenting is performed for orificial RAS, usually atherosclerotic, and for cases in which PTA fails or causes complications, such as flow-limiting dissection. Most renal-artery stenting is performed with balloon-expandable stents; some procedures are performed with self-expanding or covered stents. Strecker tantalum stents are not used in the United States.⁶⁷ Because renal failure is a major complication of PTA and stenting (as a result of cholesterol embolism), renal angioplasty with distal protection will be used increasingly in the future.

The ultimate role of stents in the treatment of vascular disease has yet to be established, but these devices have already had a dramatic effect on the practice of interventional radiology. In studies from both the United States and Europe, stenting of small vessels has resulted in an unacceptably high incidence of thrombosis.

Strecker et al described the extended role of knitted flexible tantalum stents as a valuable adjunct to PTA in cases in which PTA results were insufficient.⁶⁷ The use of this technique is now established in the distal aorta, the iliac. Long arterial occlusions were recently defined as new indications for primary stenting; indications were further extended to the subclavian, the carotid, and the splanchnic arteries, including the renal arteries. The authors suggested that because of the high incidence of acute and late complications after stent treatment of small-diameter arteries, patients must be thoroughly screened and carefully selected.

Newly designed drug-releasing stents tested in animal experiments may diminish the incidence of late restenosis caused by intimal hyperplasia, thereby improving long-term patency.

A single case report describes the successful diagnosis of hypertension secondary to FMD with intravascular US and curative intravascular US-guided renal atherectomy.

Fibromuscular Dysplasia (Visceral Arteries)

AUTHOR AND EDITOR INFORMATION

INTRODUCTION

Background

Pathophysiology

Frequency

United States

International

Mortality/Morbidity

Race

Sex

Age

Anatomy

Clinical Details

Clinical manifestations

Other problems to consider

Preferred Examination

Limitations of Techniques

DIFFERENTIALS

Other Problems to Be Considered

RADIOGRAPH

Findings

Degree of Confidence

False Positives/Negatives

CT SCAN

Findings

Degree of Confidence

False Positives/Negatives

MRI

Findings

Degree of Confidence

False Positives/Negatives

ULTRASOUND

Findings

Degree of Confidence

False Positives/Negatives

NUCLEAR MEDICINE

Findings

Degree of Confidence

False Positives/Negatives

ANGIOGRAPHY

Findings

Degree of Confidence

False Positives/Negatives

INTERVENTION

MULTIMEDIA