Diagnostic imaging of renal artery stenosis.

Many different imaging modalities and techniques have been used in the past for the diagnosis of renal artery stenosis. The ideal accurate, non-invasive and inexpensive diagnostic test has yet to be found but there have been promising developments during the last few years. In this review we consider in detail the use of the following tests for the diagnosis of renal artery stenosis; intravenous urography, B Mode ultrasound, Doppler ultrasound, renal scintigraphy with angiotensin-converting enzyme inhibitors, intra-venous and intra-arterial catheter angiography, computed tomographic angiography and magnetic resonance angiography. At present intra-arterial catheter angiography remains the 'gold standard' test. Magnetic resonance angiography is currently of limited availability in the United Kingdom but is the most promising new development because it is a non-invasive test which can be used to obtain both anatomical and functional information.     

Technology insight: Clinical role of magnetic resonance angiography in the diagnosis and management of renal artery stenosis

Noninvasive modalities, including duplex ultrasonography, renal scintigraphy, CT angiography and magnetic resonance angiography (MRA), may usefully contribute to diagnosis and treatment planning in patients with suspected renal artery stenosis. Important technical developments have increased the accuracy and feasibility of MRA for the detection of renal artery stenosis. A number of different MRA techniques can be applied to the study of renal arteries, but contrast-enhanced MRA represents the most valuable approach; several studies corroborate the high diagnostic accuracy of this technique, especially for the detection of atherosclerotic renal artery stenosis. A combined MRA protocol, which might include angiographic information provided by contrast-enhanced technique in addition to renal flow information derived from phase-contrast imaging, could help in classifying patients appropriately. Limitations of renal MRA include low accuracy in the evaluation of renal fibromuscular dysplasia and in the assessment of patients who undergo stenting of the renal arteries. This review describes the MRA techniques applied to the study of renal artery stenosis, including the technical features of current approaches and forthcoming developments. An overview of the clinical role of MRA, in conjunction with the other diagnostic modalities, in the identification and management of patients with renal artery stenosis, is also presented.     

Renovascular disease imaging: today more than ever the invasive cardiologist may make the difference

Doppler ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) are gaining wide acceptance as gold standard for diagnosing peripheral artery disease at thoracic and abdominal aorta level and infrainguinal arteries. A different case is that of renal artery stenosis (RAS): noninvasive techniques, CT and MRI in particular, failed to become the new gold standard. Image interpretation and artifacts seems to invalidate MRI and CT sensitivity and specificity that remain quite low. The debacle of noninvasive imaging of renal arteries may have important reflexes on the invasive cardiology practice. In the light of the results of noninvasive tests for renal artery stenosis, the angiography of renal vessels performed at the time of coronary artery angiography may became a new tool for invasive professional to optimize the diagnosis of renal artery stenosis at least in patients scheduled for coronary angiography. The invasive cardiologist, today more than ever, has the chance to really impact the diagnosis and therapy of patients with renovascular disease and the prognosis of patients with both coronary artery and renal artery disease.     

Magnetic resonance angiography versus duplex sonography for diagnosing renovascular disease

Noninvasive testing for renovascular disease is required to identify patients who may benefit from revascularization procedures without exposing an unnecessary amount of patients to the risks of catheter angiography. All available methods of diagnosing renal artery stenosis have significant limitations. We compared a new technique, contrast-enhanced magnetic resonance angiography, with an established technique, duplex ultrasonography, for the detection of renal artery stenosis using catheter angiography as the standard of reference. Eighty-nine patients with clinically suspected renovascular disease underwent duplex renal scanning and contrast-enhanced magnetic resonance angiography. Sixty of these also underwent catheter angiography. All studies were interpreted for the presence of renal artery stenosis blinded to the results of the other imaging modalities. For detection of hemodynamically significant (>/=60% diameter reduction) main renal artery stenosis, sensitivity and specificity were 90% and 86%, respectively, for magnetic resonance angiography and 81% and 87% for duplex sonography. Most false readings involved differential grading of stenoses detected with all 3 techniques. When patients with fibromuscular dysplasia were excluded from the analysis, the sensitivity of magnetic resonance angiography increased to 97%, with a negative predictive value of 98%. Magnetic resonance angiography detected 96% and duplex 5% of accessory renal arteries seen at catheter angiography. Contrast-enhanced magnetic resonance angiography is a useful technique for diagnosing atherosclerotic renovascular disease. It overcomes the major limitations of duplex renal scanning. However, duplex has the advantage of providing hemodynamic information and appears better suited for the assessment of patients with suspected fibromuscular dysplasia.     

Magnetic Resonance Angiography Has a High Reliability in the Detection of Renal Artery Stenosis

In this prospective study we examined the value of magnetic resonance angiography (MRA) in the imaging of the proximal renal arteries, with the main aim of detecting renal arterial stenosis, as compared with intraarterial digital subtraction angiography.The study was done among a group of 38 hypertensive patients seen in the outpatient department of the department of medicine of our university hospital. In all patients a magnetic resonance angiography and an intraarterial subtraction angiography of the renal arteries was made, and the outcomes of the investigations were compared. Clinical and biochemical data of the patients also were analyzed in relation to the presence or absence of a stenosis.In one patient, MRA resulted in technical failure because of unsuspected claustrophobia. Of the remaining 37 patients, 14 had renal artery stenosis. Of 12 patients in whom the stenoses were >50% of luminal surface on intraarterial digital subtraction angiography, eight were unilateral and four bilateral. All these stenoses were recognized by magnetic resonance angiography. There was also one false positive result by magnetic resonance. Thus, for the identification of stenoses >50%, magnetic resonance has a sensitivity of 100% and a specificity of 96%. Of the 12 accessory renal arteries seen on digital subtraction angiography, only three were identified by magnetic resonance angiography.We conclude that magnetic resonance angiography has great accuracy in depicting the main renal arteries and detecting clinically significant renal artery stenosis; however, the identification of accessory renal arteries is suboptimal and should be improved.     

Current issues in the diagnosis and management of patients with renal artery stenosis: a cardiologic perspective

Renal artery stenosis most often is caused by atherosclerosis. Although patients with renal artery stenosis can be managed conservatively, renal revascularization may be indicated, particularly in patients with refractory hypertension on a multidrug regimen and patients with declining renal function. Duplex ultrasonography of the renal arteries and magnetic resonance angiography are currently the most efficient noninvasive methods for the evaluation of renal artery stenosis. Selective digital subtraction renal arteriography remains the gold standard for the definitive diagnosis. In selected patients undergoing coronary studies and angiography immediately after the coronary procedure can be efficient. Atherosclerotic renal artery lesions, which commonly affect the renal artery ostium, can be treated safely and effectively with balloon-expandable stents. Successful angioplasty commonly results in improved control of hypertension, but an overall benefit on renal function and/or patient survival has not been shown. Generally the risk/benefit ratio of renal artery stenting seems favorable, but further randomized studies are needed for evidence-based decision making. All patients with atherosclerotic renal artery stenosis should receive rigorous secondary prevention measures including platelet inhibitors, statins, and beta-blockers.     

Assessment of non-ST-segment elevation acute coronary syndromes with cardiac magnetic resonance imaging

OBJECTIVES: The goal of this study was to determine: 1) if the presence of significant coronary stenosis in patients presenting with non-ST-segment elevation acute coronary syndromes (NSTE-ACS) can be predicted by cardiac magnetic resonance (CMR) imaging; and 2) if the analysis of several CMR methods improves its diagnostic yield compared with analysis of individual methods. BACKGROUND: With modern acquisition techniques, several CMR methods for the assessment of coronary artery disease (CAD) can be combined in a single noninvasive scanning session. Such a multicomponent CMR examination has not previously been applied to a large patient population, in particular those with a high prevalence of CAD in an acute situation. METHODS: Sixty-eight patients presenting with NSTE-ACS underwent CMR imaging of myocardial function, perfusion (rest and adenosine-stress), viability (by late contrast enhancement), and coronary artery anatomy. Visual analysis of CMR was carried out. First, all CMR data were reviewed in combination ("comprehensive analysis"). In further separate analyses, each CMR method was analyzed individually. The ability of CMR to detect coronary stenosis >/=70% on X-ray angiography was determined. RESULTS: Comprehensive CMR analysis yielded a sensitivity of 96% and a specificity of 83% to predict the presence of significant coronary stenosis and was more accurate than analysis of any individual CMR method; CMR was significantly more sensitive and accurate than the Thrombolysis In Myocardial Infarction risk score (p < 0.001). CONCLUSIONS: Cardiac magnetic resonance imaging accurately predicts the presence of significant CAD in patients with NSTE-ACS. In this study, a comprehensive analysis of several CMR methods improved the accuracy of the test.     

Non invasive assessment of renal artery using dual MRA techniques compared with invasive renal angiography in cases of renovascular hypertension

IntroductionRenal artery stenosis (RAS) is one of the leading causes of secondary hypertension, and can result in refractory hypertension or ischemic renal failure. RAS is present in 0.5–5% of all hypertensive patients. It became even more important to diagnose it in the time of intervention. Direct Angiography is the Gold Standard for evaluation of renal artery stenosis and severity. It cannot be used as a screening test because of its invasiveness, high cost and use of nephrotoxic gents. Different non invasive techniques have evolved for the evaluation of renal artery including; captopril renography, computed tomography (CT) angiography, magnetic resonance (MR) angiography and ultrasound (US) Doppler. Recently, the advent of CE 3D MRA appears to be a new promising approach.PurposeTo evaluate the diagnostic value of both contrast enhanced magnetic resonance angiography (CE MRA) and phase contrast MRA (PC MRA) techniques in cases of renal artery stenosis as compared to conventional angiography.Methods and materialsThirty patients (22 males and 8 females), with mean age 37 years (range 23–72 years). All with suspected renal artery stenosis were evaluated using both CE MRA and PC MRA techniques. All were subsequently subjected to conventional renal angiography.ResultsCE MRA alone compared to direct Angiography (Gold standard) had a 91% sensitivity and 87% specificity. PC MRA had overall 50% sensitivity and 25% specificity. PC MRA alone was unable to differentiate mild stenosis from normal and could not distinguish severe stenosis from total occlusion. Combining both MRA techniques yielded 100% specificity 94% positive and 100% negative predictive values.ConclusionThe combined approach of non-invasive CE MRA and PC MRA techniques achieves a very high specificity, PPV and NPV for the detection of renal arterial pathomorphologic features as compared to standard renal angiography. Adding PC MRA to CE MRA helps to differentiate between mild and moderate stenoses as well as moderate and sever arterial stenotic lesions. So, CE MRA is a morphological test while PC MRA helps in grading the arterial stenoses.     

Assessment of coronary artery stenosis by magnetic resonance imaging.

OBJECTIVE: The findings of magnetic resonance and x-ray angiography were compared for assessment of coronary artery stenosis in this validation study. BACKGROUND: Magnetic resonance angiography of the coronary arteries has recently been described, but there has been no comparison with x-ray angiography of localisation or assessment of important characteristics of coronary stenosis. METHODS: A breath hold, segmented k-space, 2D gradient echo imaging technique incorporating fat suppression was used in 39 patients (55 coronary stenoses) with known coronary artery disease. RESULTS: Overall, 47 stenoses (85%) were assessed by magnetic resonance (29 of 33 stenoses in the left anterior descending artery, one of one in the left main stem, 14 of 17 in the right coronary artery, and three of four in the left circumflex artery were detected). There was close agreement between magnetic resonance and x-ray angiography for the distance of the stenosis from the arterial origin (magnetic resonance mean (SD) 27 (16) mm versus x-ray angiography 27 (16) mm, P = NS, mean difference -0.2 mm). The distance to 39 stenoses (83%) agreed to within 5 mm, with increased scatter for more distal stenoses. The severity of magnetic resonance signal loss, assessed visually at the site of stenosis, varied significantly according to the percentage diameter stenosis (F = 30, P < 0.0001); stenosis severity with severe signal loss was 89 (7)%, with partial signal was 70 (16)%, and with irregular wall only 37 (11)%, with significant differences among the three groups (P < 0.001). A significant correlation was found between the proportional magnetic resonance signal loss at the stenosis and the percentage diameter stenosis severity (r = -0.67, P < 0.0001). The length of stenosis measured by magnetic resonance (6 (3) mm) was greater than by x-ray angiography (5 (2) mm, P < 0.006, mean difference +1.1 mm). Spearman's rank test showed that there was significant overestimation of stenosis length by magnetic resonance as stenosis severity increased (rs = 0.34, P < 0.02). CONCLUSIONS: Accurate localisation of coronary stenosis and a qualitative assessment of stenosis severity are possible by magnetic resonance, but stenosis length is overestimated as severity increases, probably because of disturbed patterns of flow with turbulence distal to severe stenoses. Reasonable results for the detection of coronary artery stenosis by magnetic resonance were achieved in this highly selected population, but further progress in imaging techniques is necessary before moving towards appreciable clinical application.     

Magnetic resonance angiography of renal arterial stenosis.

Recent developments in renal magnetic resonance angiography (MRA) have led to a significant improvement in the technical success rate and diagnostic accuracy of the methods. Specifically, three-dimensional contrast-enhanced MRA methods have been shown to provide a more reliable depiction of renal artery morphology than do older MRA techniques. In addition, preliminary work using adjunctive MRA techniques suggests that it is possible to determine the hemodynamic significance of renal artery disease using MRA and magnetic resonance imaging. MRA methods will therefore likely play an important role in the evaluation of patients with renovascular disease.     

Moderne Bildgebung von Raumforderungen der Niere

Noninvasive imaging of renal masses has improved in recent years. Five different techniques are now available for a stepwise diagnostic procedure. While renal ultrasound and color Doppler sonography are used for tumor screening, computed tomographic angiography remains the imaging technique of choice for grading and classifying cystic and solid renal masses. In patients with allergies to iodinated contrast media or with renal insufficiency, magnetic resonance tomography (MRT) can play a major role, especially for cystic renal masses. However, nephrogenic systemic fibrosis has been recently described in more than 200 cases after MRT-associated application of gadolinium-based contrast media, thus currently limiting the use of MRT. Positron emission tomography should be limited to patients under surveillance or with suspected metastatic lesions. Recent developments in imaging techniques with new classifications to improve diagnostic accuracy are discussed in this article.     

Evaluation of the spatial resolution with 1.5-4 tesla in a stenosis model

Since it was first described in the early 1990s, magnetic resonance coronary angiography has evolved into a promising noninvasive modality for imaging the coronary arteries. The aim of this study was to evaluate the detection accuracy and spatial resolution of vascular stenosis in contrast-enhanced 3-dimensional magnetic resonance angiography on a flow phantom. The examinations were performed with 1.5, 3, and 4 T whole-body imaging systems. For imaging at 4 T, we used a gradient-echo-multi-slice sequence. The system was flushed with gadopentetate dimeglumine contrast medium at flow rates of 40 and 60 mL.min(-1). The accurate detection of in vitro stenoses was possible in segments of 0.4 mm in diameter at 4 T. The best results were obtained at a flow velocity of 40 mL.min(-1) and a contrast medium concentration of 0.2 mmol.L(-1). Contrast-enhanced high-field 3-dimensional magnetic resonance imaging provided a highly accurate evaluation of the degree of stenosis in this model. Exact evaluation of vessel diameters < 0.4 mm was not possible, even with 4 T. In vivo studies are necessary to overcome the current limitations in the visualization of small distal vessel segments.     

Atherosclerotic renal artery disease

Atherosclerotic renal artery stenosis may present with hypertension, renal failure (ischemic nephropathy), or congestive heart failure. The prevalence of renal artery stenosis is increasing in patients with other manifestations of atherosclerosis. The diagnosis is being made more frequently due to better screening tests such as duplex ultrasound and magnetic resonance angiography. Renal artery stenosis is discovered incidentally during imaging studies performed for other reasons. Revascularization should be performed using angioplasty and stenting in patients who have hypertension that cannot be adequately controlled with medications, in patients with severe bilateral renal artery stenosis or stenosis to a solitary functioning kidney and in patients with congestive heart failure when no other clear cut cause can be found.     

Multiple organ infarctions following disseminated intravascular coagulation precipitated by sepsis in a healthy infant: a case report

Multiple organ infarctions are a very rare clinical event in children. We report a 3-month-old infant with sepsis and disseminated intravascular coagulation, who was diagnosed with cerebral ischemic stroke associated with middle cerebral artery stenosis and subsequent retinal infarction by magnetic resonance imaging, fundoscopy and magnetic resonance angiography. In addition, he suffered from renal infarction with hypertension and was treated until 1 year of age. We emphasize the importance of early recognition of organ infarctions, prophylaxis of risk factors and of optimized therapy of the underlying etiology.     

Fibromuscular dysplasia of renal arteries: percutaneous revascularization based on hemodynamic assessment with a pressure measurement guidewire.

Fibromuscular dysplasia (FMD) leading to renal artery stenosis and hypertension is one of the most common treatable causes of secondary hypertension. However, frequently it can be difficult to judge the anatomical severity of a stenotic lesion with various noninvasive and invasive imaging modalities. We present two patients with poorly controlled hypertension and FMD affecting the renal arteries, in whom there were no anatomically significant stenoses by renal magnetic resonance angiography or selective renal artery angiography. Utilizing a 0.014' high fidelity micromanometer tipped PressureWire XT (Radi, Reading, MA), to measure intravascular pressure gradients throughout the diseased renal arteries, we identified physiologically significant stenoses, and successfully treated both patients with percutaneous transluminal angioplasty.     

Imaging and endovascular treatment of renal artery stenosis in the diabetic patient

Although diabetes is a classical risk factor for macroangiopathy, the prevalence of renal artery stenosis (RAS) in this type of pathology has not been clearly determined. More than 50% of RAS occur in diabetic patients (almost exclusively Type 2), whereas autopsy findings and the few clinical surveys reported indicate that the percentage of RAS within the diabetic population is close to 30%. RAS occur especially in elderly subjects with Type 2 diabetes and multiple vascular involvement, and bilateral stenoses are frequent. Diagnostic imaging of RAS can cause adverse effects in the diabetic patient if iodinated contrast media are used, especially in cases of renal insufficiency. The presence of this risk factor requires that iodinated radiological explorations be performed with due caution, or that another product be substituted as a contrast agent (CO(2) or gadolinium), or that an imaging technique without iodine be used (colour Doppler ultrasound, magnetic resonance angiography). The therapeutic management of RAS in the diabetic patient differs little from that employed for other atheromatous stenoses of the renal artery. Endovascular treatment of RAS is the technique of choice for most patients, whether diabetic or not. The existence of diabetes has little effect on therapeutic strategy, except in cases of renal insufficiency when the risk of iodine overload should limit the doses of contrast medium or require the partial or even total substitution of another agent (CO(2), gadolinium). As in the case of other RAS, the indications depend on the lesion and the clinical presentation. Similarly, the results are both clinical and anatomical, and the existence of diabetes has a limited impact on these different parameters.     

Atherosclerotic plaque imaging: contemporary role in preventive cardiology

Coronary artery disease imaging has traditionally been based on luminal angiography, but it has become evident that this tool, although extremely useful in diagnosing obstructive disease, is insufficient to define the presence and extent of atherosclerotic disease in the vessel wall. Progression of coronary artery disease was also initially evaluated using quantitative coronary angiography, and evidence soon accumulated that minor regression or nonprogression of luminal disease was associated with a favorable cardiovascular outcome. In recent years, however, several other techniques have been developed to image atherosclerosis and are emerging as useful tools in preventive cardiovascular medicine. These techniques provide new methods to assess the burden of atherosclerosis, gauge the risk of cardiovascular events, and offer a means to test the efficacy of therapeutic approaches to atherosclerosis. Furthermore, noninvasive coronary angiography can be performed with some of the new imaging modalities, potentially reducing the number of unnecessary invasive tests. This review focuses on techniques such as cardiac computed tomography, carotid artery intima-media thickness, cardiovascular magnetic resonance imaging, and intravascular ultrasonography as emerging tools in cardiovascular disease prevention.     

高血压合并动脉粥样硬化性肾动脉狭窄的诊治进展

高血压伴动脉粥样硬化性肾动脉狭窄是引起老年患者终末期肾脏病的主要原因,尤其是65岁以上糖尿病合并外周血管病的患者。当临床出现急进性高血压、顽固性高血压、恶性高血压及无法解释的肾脏萎缩、难治性肺水肿时高度提示肾动脉狭窄的可能。彩色多普勒超声、磁共振血管成像、螺旋CT血管造影和肾动脉造影是主要的检查方法。除药物治疗外,也可采取介入和外科手术治疗,但要严格掌握适应证,预防并发症。     

Is coronary magnetic resonance angiography already a clinically useful diagnostic tool?

Magnetic resonance imaging (MRI) allows the evaluation of coronary arteries non-invasively and without the use of ionizing radiation. Coronary magnetic resonance angiography (MRA) is technically demanding due to the small size, tortuous course, and bulk motion of the coronary arteries as well as signal from surrounding epicardial fat and myocardium. In comparison to invasive x-ray coronary angiography not all coronary artery segments can be assessed by coronary MRA. At present the diagnostic accuracy of coronary MRA for detection of significant stenosis in coronary arteries is suboptimal. The presence of coronary anomalies and the patency of aortocoronary bypass grafts can be assessed by MRA with high diagnostic accuracy. The combination of coronary MRA with other MRI techniques for detection of ischemia has the potential to be of clinical value in the diagnostic work-up of patients with coronary artery disease.     

Non-invasive coronary bypass graft imaging after multivessel revascularisation

Non-invasive imaging techniques for the detection of graft patency after multivessel coronary revascularisation may be useful for follow-up after surgery. Forty consecutive asymptomatic patients (38 men, age 59.9+/-1.3 years) who had undergone coronary bypass surgery with at least three grafts were examined by spiral computed tomography or magnetic resonance angiography 24.9+/-0.3 months after surgery, using conventional angiography as reference. In total, 133 grafts (37 internal mammary artery, 96 venous grafts) were analysed. Spiral computed tomography studies were performed with a subsecond scanner; for magnetic resonance angiography, a three-dimensional contrast-enhanced gradient echo technique with ultrashort echo time during breath holding was used. For spiral computed tomography, sensitivities were 76% (internal mammary artery) and 100% (venous graft). This was compared with 100% (internal mammary artery) and 92% (venous graft) assessed by magnetic resonance angiography (P=ns). The positive predictive values were 100% for internal mammary artery and venous graft (spiral computed tomography) and 100% (internal mammary artery), 92% for venous grafts studied by magnetic resonance angiography (P=ns). Both subsecond spiral computed tomography and contrast-enhanced magnetic resonance angiography are highly accurate and relatively non-invasive approaches of assessing coronary graft patency after multivessel revascularisation and have potential for follow-up assessment in the long term.