Diagnosis of renal artery stenosis with magnetic resonance angiography: update 2003

Atherosclerotic renal artery stenosis and revascularization

Atherosclerotic renovascular disease is the most common cause of secondary hypertension. The patients with renovascular disease are at increased risk for adverse cardiac outcomes. Recent trials comparing medical therapy alone to medical therapy with stenting are flawed, but lay to rest any existing debate that unselected revascularization is unwarranted; however, revascularization may be appropriate in high-risk populations. Defining an appropriate population for revascularization is an area of ongoing study. Furthermore, delivery of optimal medical therapy in this population is inadequate. This review describes recent developments in renal artery revascularization.

Diagnosis and management of atherosclerotic renal artery stenosis: improving patient selection and outcomes

Renal artery stenosis (RAS) is common among patients with atherosclerosis, and is found in 20-30% of individuals who undergo diagnostic cardiac catheterization. Renal artery duplex ultrasonography is the diagnostic procedure of choice for screening outpatients for RAS. Percutaneous renal artery stent placement is the preferred method of revascularization for hemodynamically significant RAS, and is favored over balloon angioplasty alone. Stent placement carries a class I recommendation for atherosclerotic RAS according to ACC and AHA guidelines. Discordance exists between the very high (>95%) procedural success rate and the moderate (60-70%) clinical response rate after renal stent placement, which is likely to be a result of poor selection of patients, inadequate angiographic assessment of lesion severity, and the presence of renal parencyhmal disease. Physiologic lesion assessment using translesional pressure gradients, and measurements of biomarkers (e.g. brain natriuretic peptide), or both, could enhance the selection of patients and improve clinical response rates. Long-term patency rates for renal stenting are excellent, with 5-year secondary patency rates greater than 90%. This Review will outline the clinical problem of atherosclerotic RAS and its diagnosis, and will critically assess treatment options and strategies to improve patients' outcomes.

Renal artery stenosis evaluation: diagnostic performance of gadobenate dimeglumine-enhanced MR angiography--comparison with DSA

PURPOSE

To prospectively determine diagnostic performance and safety of contrast material-enhanced (CE) magnetic resonance (MR) angiography with 0.1 mmol per kilogram of body weight gadobenate dimeglumine for depiction of significant steno-occlusive disease (> or =51% stenosis) of renal arteries, with digital subtraction angiography (DSA) as reference standard.

MATERIALS AND METHODS

This multicenter study was approved by local institutional review boards; all patients provided written informed consent. Patient enrollment and examination at centers in the United States complied with HIPAA. Two hundred ninety-three patients (154 men, 139 women; mean age, 61.0 years) with severe hypertension (82.2%), progressive renal failure (11.3%), and suspected renal artery stenosis (6.5%) underwent CE MR angiography with three-dimensional spoiled gradient-echo sequences after administration of 0.1 mmol/kg gadobenate dimeglumine at 2 mL/sec. Anteroposterior and oblique DSA was performed in 268 (91.5%) patients. Three independent blinded reviewers evaluated CE MR angiographic images. Sensitivity, specificity, and accuracy of CE MR angiography for detection of significant steno-occlusive disease (> or =51% vessel lumen narrowing) were determined at segment (main renal artery) and patient levels. Positive and negative predictive values and positive and negative likelihood ratios were determined. Interobserver agreement was analyzed with generalized kappa statistics. A safety evaluation (clinical examination, electrocardiogram, blood and urine analysis, monitoring for adverse events) was performed.

RESULTS

Of 268 patients, 178 who were evaluated with MR angiography and DSA had significant steno-occlusive disease of renal arteries at DSA. Sensitivity, specificity, and accuracy of CE MR angiography for detection of 51% or greater stenosis or occlusion were 60.1%-84.1%, 89.4%-94.7%, and 80.4%-86.9%, respectively, at segment level. Similar values were obtained for predictive values and for patient-level analyses. Few CE MR angiographic examinations (1.9%-2.8%) were technically inadequate. Interobserver agreement for detection of significant steno-occlusive disease was good (79.9% agreement; kappa = 0.69). No safety concerns were noted.

CONCLUSION

CE MR angiography performed with 0.1 mmol/kg gadobenate dimeglumine, compared with DSA, is safe and provides good sensitivity, specificity, and accuracy for detection of significant renal artery steno-occlusive disease.

Renal magnetic resonance angiography at 3.0 T: technical feasibility and clinical perspectives

The increased signal-to-noise ratio at 3.0 T holds promise for high-spatial resolution renal magnetic resonance angiography (MRA). Today, state-of-the-art renal MRA is feasible with submillimeter isotropic spatial resolution in less than 20 seconds acquisition time with sufficient signal-to-noise ratio. This article explains the fundamentals of 3.0-T imaging that are essential for renal MRA, with a focus on the clinical implications. Protocol and imaging recommendations are given based on the physical principles of 3.0-T imaging and underlined by current clinical cases. Apart from pure morphological imaging, the value of functional renal imaging such as renal flow measurements and renal perfusion measurements for a comprehensive 3.0-T renal MRA protocol is discussed.

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.

Renal Arteries: Comparison of Steady-State Free Precession MR Angiography and Contrast-enhanced MR Angiography

All participants provided informed consent to participate in this study, which was approved by the institutional review board. Breath-hold three-dimensional (3D) steady-state free precession (SSFP) magnetic resonance (MR) angiography was compared with 3D contrast material-enhanced MR angiography in patients suspected of having renal artery stenosis. Two radiologists assessed visualization of renal arteries and detection of vascular disease. With SSFP MR angiography, 39 of 41 renal arteries in 19 patients were correctly detected. Relevant stenoses were correctly identified with SSFP MR angiography in two patients. In two patients, SSFP MR angiographic data sets led to false-positive overgrading of vascular disease. Fast breath-hold 3D SSFP MR angiography appears to be feasible for MR angiography of renal arteries.

Severe renovascular hypertension in an infant with congenital solitary pelvic kidney

Renal artery stenosis (RAS) is one of the most common causes of severe arterial hypertension in infants. Its management is very difficult, especially when present in a single kidney. We report a case of severe hypertension caused by RAS of congenital single pelvic kidney in a 4-month-old boy. The patient presented with cardiorespiratory insufficiency that was first treated as acute fulminate myocarditis. Medical treatment of arterial hypertension was disappointing, as it had to be balanced between congestive cardiac failure and acute renal failure. Percutaneous transluminal angioplasty (PTA) done by coronary balloon dilatation catheters through the left axillary access was successful. Following dilatation of the renal artery, blood pressure decreased and its good control was possible by only one drug. With improved medical blood pressure control and normal growth development, the reassessment of clinical therapy options adjusted to a larger vessel size would be possible. Renovascular hypertension due to RAS in infants with a solitary kidney is difficult to control by medical treatment alone. PTA should be considered as a viable option in infants with refractory hypertension due to renal artery stenosis in a solitary kidney, since it has the potential of improving hypertension while preserving renal function.

Screening tests for renal artery stenosis: A case-series from an Australian tertiary referral centre

BACKGROUND

Renal artery stenosis is a common, correctable cause of hypertension and renal impairment, with multiple screening tests available to aid diagnosis. Data assessing the accuracy of screening tests are mostly derived from tight 'experimental' protocols and the application of these tests to large-scale clinical practice is not clear. Our aim was to investigate physician preferences and diagnostic accuracy of screening tests for renal artery stenosis when applied to clinical practice in a large, Australian tertiary referral centre.

METHODS

We investigated all renal angiograms performed at our institution between September 2002 and September 2004, as referred by renal physicians. We accessed hospital and physician records of all patients to document demographics, clinical history, screening investigations, source of screening and angiogram results. The series involved 75 consecutive patients who had 79 screening investigations (four patients had two screening tests).

RESULTS

The case series showed that 19 (24%) patients did not have any screening investigations prior to angiography. Duplex ultrasonography was the most utilised screening test, being used in 20 (33%) of the remaining 60 screening tests. Computed tomographic angiography (CTA) was used in 19 (32%), magnetic resonance imaging in 13 (22%) and renal scintigraphy was used in four (7%) screening procedures. Magnetic resonance angiography was the most accurate screening test with a positive predictive value of 92%, followed by duplex ultrasonography with 88% and CTA was relatively inaccurate, with a positive predictive value (PPV) of 58% (P = 0.036). Clinical suspicion alone was inaccurate with a PPV of 40%, except in previously treated renal artery stenosis (PPV 89%).

CONCLUSION

Duplex ultrasonography was the most utilised screening investigation amongst the physicians of our referral base. Magnetic resonance angiography and duplex ultrasonography had good positive predictive values, while CTA may not be as reliable as previously reported when applied to a large, non-selective clinical practice.

Measurement of single kidney function using dynamic contrast-enhanced MRI: Comparison of two models in human subjects

PURPOSE

To compare two methods for assessing the single kidney glomerular filtration rate (SK-GFR) in humans using dynamic contrast-enhanced (DCE)-MRI.

MATERIALS AND METHODS

Images were acquired from 39 separate MR studies of patients with atherosclerotic renovascular disease (ARVD). Data from the kidneys and descending aorta were analyzed using both a Rutland-Patlak plot and a compartmental model. MR estimates of the SK-GFR were compared with standard radioisotope measures in a total of 75 kidneys.

RESULTS

Estimates of renal function using both techniques correlated well with radioisotope-assessed SK-GFR (Spearman's rho=0.81, Rutland-Patlak; rho=0.71, compartmental model). The Rutland-Patlak approach provided a near one-to-one correspondence, while the compartmental method tended to overestimate SK-GFR. However, the compartmental model fits to the experimental data were significantly better than those obtained using the Rutland-Patlak approach.

CONCLUSION

DCE-MRI of the kidneys provides data that correlate well with reference measures of SK-GFR. However, further work, including image registration, is needed to isolate measurement of glomerular filtration to the level of the renal cortex.

Atherosclerotic renovascular disease in chronic heart failure: should we intervene?

Renal artery stenosis (RAS) is most commonly caused by atherosclerosis, which is also the most common cause of chronic heart failure (CHF). One-third of patients with CHF are reported to have significant renovascular disease. The presence of RAS confers a worse outcome in studies of hypertension and coronary disease, though data are lacking for patients with CHF. As the kidney is intricately involved in the fluid retention that occurs in CHF, an adverse effect of RAS on outcome would be expected. Presentations of RAS in CHF include flash pulmonary oedema, hypertension, worsening of CHF, and worsening renal function. RAS commonly progresses and may cause worsening of renal function in patients with CHF and previously stable renal function. A variety of investigations that can safely and accurately identify RAS in CHF are available, although none is recommended in current guidelines for the management of CHF. Treatment for RAS, whether for hypertension, for renal dysfunction, or for pulmonary oedema, is at the discretion of the physician due to the lack of adequate randomized controlled trials demonstrating the efficacy and safety of intervention. As it is not clear how RAS should be managed in CHF, screening cannot be advocated. Currently, a multicentre randomized outcome trial, which includes a cohort of patients with RAS and CHF, is in progress to provide answers in this area of uncertainty.

Atherosclerotic renal artery stenosis: current status and future directions

PURPOSE OF REVIEW

Atherosclerotic renal artery stenosis is a common, progressive problem that increases in prevalence with age. It can have important clinical consequences such as hypertension, pulmonary edema, and renal failure. In addition, it is associated with increased cardiovascular mortality. The purpose of this review is to describe the current status of knowledge and future directions for this evolving field.

RECENT FINDINGS

In patients who are suspected of having the disease, duplex Doppler ultrasound and magnetic resonance angiography remain the most promising noninvasive screening tests. Percutaneous revascularization continues to advance, and technical success is possible in the vast majority of patients. Revascularization for hypertension is of modest clinical benefit. Limited information is available on the effect of revascularization on preservation of renal function or cardiovascular events and mortality.

SUMMARY

Further studies are still needed focusing on the identification of which patients will derive benefit from percutaneous revascularization and whether intervention provides an advantage over medical therapy, particularly with respect to preservation of renal function and reduction in cardiovascular morbidity and mortality.

Evaluation of Renovascular Hypertension

OBJECTIVE

The main objective of this study was to evaluate a clinically suspected renovascular hypertension (RVH) by means of MRI. It was to find out if functional MRI (fMRI) is able to provide adequate results with regard to MAG3 captopril scintigraphy and if contrast-enhanced MR angiography (MRA) is able to provide adequate results in the stenosis grading compared with the nonselective digital subtraction angiography (DSA).

METHODS

This open, monocentric, prospective, phase 3 study included patients with a clinically suspected RVH. For fMRI a dynamic TurboFLASH sequence and for MRA a single-shot breath-hold flash 3D sequence was performed. Gadodiamide was injected as contrast medium.

RESULTS

Sixty patients were included in the study. The correlation between fMRI and scintigraphy had an accuracy, a sensitivity, and a specificity of 69%, 5%, and 92%, respectively, and correlations between MRA and DSA of 95%, 92%, and 96%.

CONCLUSION

The noninvasive MRA can replace DSA in the diagnosis of renal artery stenosis. However, fMRI can not replace renal scintigraphy.

Magnetic resonance imaging of the peripheral vasculature

BACKGROUND

Atherosclerotic disease of the peripheral vasculature is a prevalent condition for which catheter-based techniques have been considered to be the gold standard for diagnosis. However, because of their invasive nature, these techniques inherently have the potential for complications. Non-invasive diagnostic techniques have historically been limited by low accuracy and high operator dependence. Magnetic resonance angiography (MRA) is a new approach that has diagnostic accuracy comparable with invasive angiography.

METHODS

The literature on MRA for evaluation of carotid, mesenteric, renal, and lower-extremity arterial disease was extensively reviewed. Helpful diagnostic algorithms on the basis of the literature are also provided.

RESULTS

MRA is both sensitive and specific when compared with invasive angiography for the evaluation of peripheral arterial disease and avoids the potential for complications resulting from arterial puncture and use of iodinated contrast.

CONCLUSION

Current MRA techniques are diagnostically robust and have proven to be a highly accurate, safe, and convenient means of diagnosing atherosclerotic disease of the peripheral vascular system.

Current endovascular management of atherosclerotic renal artery stenosis

The recent advances in stent technology and renal endovascular management have provided a technically reproducible method of percutaneously treating atherosclerotic renal artery stenosis (RAS). In many centers, this has resulted in endovascular management being the primary therapy for atherosclerotic RAS. Although still controversial, it appears that endovascular management of RAS by primay stent deployment provides better blood pressure control than that afforded by best medical management. The impact on renal function is less than that found for hypertension, but there is evidence to suggest that the use of protection devices and primary stenting may enhance renal function outcomes. Whether the ultimate benefit of enhanced survival follows remains an important question and should be the subject of future prospective studies.

Current Concepts and Advances in Clinical Parallel Magnetic Resonance Imaging

Parallel imaging (PI) is one of the most promising recent advances in MRI technology and has, similar to the introduction of multidetector helical scanning in CT, revolutionized MR imaging. The speed of all conventional MRI methods has been limited by either gradient strength or their switching times. The basic idea in PI is to use some of the spatial information contained in the individual elements of a radiofrequency (RF) receiver coil array to increase imaging speed. These PI techniques are removing some of the previous limitations in speed of MRI scanners and set the basis for accelerated image formation. Initially, PI was motivated by the wish to accelerate image acquisition without reducing the spatial resolution of the image. However, depending on the application, it turned out that PI harbors several other advantages. Among those is the possibility for higher spatial resolution, shorter breath-holds or multiple averaging to diminish motion artifacts, reduced image blurring and geometric distortions, better temporal resolution, and means for navigator correction. This overview focuses on technical aspects, clinical applications, and ongoing research in different areas of the human body. The critical review demonstrates PI's great versatility as well as the current trends to use this unique technique in the majority of clinical scan protocols.

Spiral laminar flow in the abdominal aorta: a predictor of renal impairment deterioration in patients with renal artery stenosis?

BACKGROUND

Spiral or helical arterial blood flow patterns have been widely observed in both animals and humans. The absence of spiral flow has been associated with carotid arterial disease. The aim of this study was to detect the presence of aortic spiral flow using magnetic resonance imaging (MRI) and to evaluate the relationship of the presence of spiral aortic flow with renal arterial disease and renal function in the follow-up of patients with suspected renal atheromatous disease.

METHODS

Prospective study of 100 patients with suspected renal arterial disease and 44 patient controls. Using a 1.5 T MRI unit (Siemens Symphony), phase contrast flow quantification and three-dimensional contrast enhanced MR angiography of the abdominal aorta were performed. Renal arterial stenoses (RAS) were classified minimal, moderate or severe. Renal function was followed at 3 months before and 6 months after MRI.

RESULTS

Non-spiral flow was more prevalent in patients with more severe RAS. Renal impairment progressed significantly in severe RAS without spiral flow (P = 0.0065), but did not progress significantly in severe RAS with spiral flow (P = 0.12). In minimal or moderate RAS with or without spiral flow there was no significant progression (P = 0.16, 0.13, 0.47, 0.092, respectively).

CONCLUSIONS

Aortic spiral blood flow can be assessed with MRI. Lack of aortic spiral blood flow in patients with severe RAS is associated with significant short-term renal function deterioration. Determination of blood flow patterns may be a useful indicator of renal impairment progression in patients with suspected renal artery stenosis.