Intravenous digital subtraction renal angiography: use in screening for renovascular hypertension

[Current methods for diagnosing renal artery stenosis]

PURPOSE

Today, the methods for detecting renal artery stenosis are numerous. They lead to the identification either of anatomic stenosis or functional stenosis (onset of renin-angiotensin system). The purpose of this review is to emphasize the performances, limitations and diagnostic criteria for each technique.

CURRENT KNOWLEDGE AND KEY POINTS

For detection of anatomic stenosis, the feasibility of Doppler examination has been increased by the improvement of US systems and the development of contrast agents. However, the criteria used nowadays still need wider evaluation. Helical CT angiography allows a better detection of accessory arteries and calcifications but MR angiography has a better spatial resolution and uses a non-nephrotoxic contrast agent. The performances of these two techniques have never been compared. The choice between these techniques depends on the operators' experience and the availability of the systems. For functional stenosis, detection is now based on captopril-sensitized scintigraphy.

FUTURE PROSPECTS AND PROJECTS

It would be necessary to better compare performances and cost-effectiveness ratios of these methods and of the two imaging strategies (detection of anatomic stenosis versus functional stenoses). Probably in the future, MR will gain a major place, providing, in the same imaging session, morphologic and functional data.

Evaluating patients with renal failure for renal artery stenosis with gadolinium-enhanced magnetic resonance angiography

The incidence and prevalence of end-stage renal disease (ESRD) continues to increase, especially in the elderly population. The role of renovascular disease in contributing to ESRD is still not well defined. The objective of this study was to determine the utility of gadolinium (Gd)-enhanced magnetic resonance angiography (MRA) in evaluating elderly patients with renal insufficiency for renal artery stenosis (RAS). A 7-month prospective study conducted in a tertiary referral center evaluated 40 consecutive patients with progressive renal insufficiency (18 men and 22 women; mean age, 70 +/- 5.6 [standard deviation] years) and high clinical suspicion for renovascular disease with Gd-enhanced MRA. Digital subtraction angiography (DSA) was obtained in only those patients with significant RAS detected by MRA. Twelve patients had significant RAS. Six of these patients had percutaneous transluminal renal angioplasty (PTRA), five patients had renal artery bypass surgery, and one patient had a stent placed after PTRA. Seventy-eight renal arteries were satisfactorily evaluated by MRA. Twenty-two renal arteries were evaluated by both MRA and DSA. Of the 12 significant stenoses detected by the MRA, 11 were confirmed by DSA and 1 was confirmed at the time of surgical revascularization. It is concluded that Gd-enhanced MRA is a useful test for the evaluation of RAS in patients with compromised renal function.

Progression of renal artery stenosis in patients undergoing cardiac catheterization

BACKGROUND

Renal artery stenosis is potentially correctable by either revascularization surgery or percutaneous methods. However, appropriate use of these techniques has been hampered by a lack of data on the natural history of this disease. This study assesses the prevalence, risk factors for progression, and effect on renal function of angiographically demonstrated renal artery disease in patients undergoing cardiac catheterization.

METHODS

The severity of renal artery stenosis was quantified in all patients who underwent abdominal aortography as part of a diagnostic cardiac catheterization study at Duke University Medical Center between January 1989 and February 1996.

RESULTS

There were 14,152 patients in the study (mean age 61+/-12 years, 62% male). Normal renal arteries were identified in 12,543 (88.7%) patients, insignificant disease (<50% stenosis) in 1 or more vessels in 726 patients (5.1 %), and significant stenosis in 883 patients (6.3%). Significant bilateral renal artery stenosis was present in 178 patients (1.3%). By multivariate logistic regression, elevated serum creatinine level, coronary artery disease, peripheral vascular disease, hypertension, cerebrovascular disease, older age, female sex, and family history of coronary artery disease were identified as independent predictors of significant renal arterial disease. Disease progression was assessed in 1189 patients. Mean time between cardiac catheterizations was 2.6+/-1.6 years. Significant disease progression occurred in 133 patients (11.1 %). Independent predictors of disease progression were female sex, age, coronary artery disease at baseline, and time between baseline and follow-up. At follow-up, serum creatinine level was significantly higher in patients who demonstrated > or =75% stenosis in 1 or more vessels (mean creatinine level 141+114 micromol/L compared with those with insignificant disease (mean creatinine level 97+/-44 micromol/L (P= .01).

CONCLUSIONS

Renal artery disease is frequently progressive in patients who undergo cardiac catheterization for investigation of coronary artery disease. Significant stenotic disease may develop over a short period despite evidence of normal renal arteries at prior catheterization.

Can the IVIM model be used for renal perfusion imaging?

OBJECTIVE

Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion.

METHODS AND MATERIAL

Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated.

RESULTS AND CONCLUSION

Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.

Atherosclerotic ischemic renal disease

Over the past decade, ischemic nephropathy has gained recognition as a distinct and treatable clinical entity. Atherosclerotic renal artery stenosis is the leading cause of ischemic renal disease. Among the aging population entering renal replacement programs, both renal artery and systemic atherosclerosis are common. Over recent years, patients with ischemic renal disease are presenting later and have diffuse atherosclerosis and other comorbid conditions. Improved screening techniques, patient selection, and interventional approaches have resulted in better outcomes in most centers. Percutaneous transluminal renal angioplasty has emerged as the treatment of choice in some centers for nonostial renal artery stenosis. Both percutaneous transluminal renal angioplasty and surgical repair have proven beneficial for renal function salvage. Many studies have elegantly demonstrated the pathophysiologic consequences of acute ischemia to the kidney. The concepts derived from acute studies have served as a springboard for considering the adaptive and maladaptive renal responses to chronic ischemia.

Spiral computed tomographic angiography of the renal arteries: a prospective comparison with intravenous and intraarterial digital subtraction angiography

PURPOSE

To assess the accuracy of computed tomographic angiography (CTA) in the evaluation of the renal arteries in comparison with intravenous (IVDSA) and intraarterial digital subtraction angiography (IADSA).

METHODS

In 18 patients, 35 CTAs and DSAs (27 IADSA, 8 IVDSA) of the renal arteries were performed. CTA was done with 2-3 mm collimation,2-4 mm/sec table speed, after intravenous injection of 80 ml of contrast medium at 4 ml/sec with a scanning delay time of 14-21 sec. No previous circulation time curve was performed. CTA data were reconstructed with maximum intensity projection (MIP) and shaded surface display (SSD). The presence of stenosis was assessed on a three-point rating scale (grade 1-3). The quality of the examinations; visualization of the ostium, the main artery, and its branches; vessel sharpness, linearity, and intraluminal contrast filling were evaluated. We compared CTA with DSA.

RESULTS

CTA had 96% sensitivity, 77% specificity, and 89% accuracy in the detection of stenoses > 50%. Due to technical errors two stenoses were erroneously diagnosed as positive but there were no false negative diagnoses. The quality of CTA was good in 56% and moderate in 34% of cases. Visualization of the ostium and main artery was graded as 1.74 (out of 2) points and of the renal branches as 1.02 (out of 2) points and of the renal branches as 1.02 (out of 2) points. The quality of CTA images was worse than that of IADSA in 52%, equal in 41%, and better in 7% of cases. CTA was equal to IVDSA in 25% and better in 75% of the cases.

CONCLUSION

CTA is an accurate noninvasive method for the evaluation of renal arteries. Examination quality is essential for the diagnosis. CTA is limited in its ability to visualize the branches of the renal artery and accessory arteries. CTA seems to be superior to IVDSA.

Minimally invasive diagnosis of renal artery stenosis by spiral computed tomography angiography

We prospectively compared in a blinded fashion spiral computed tomography angiography (CTA) with arteriography in 62 consecutive patients with suspected renal artery stenosis (RAS). For CTA 150 ml of contrast material were injected intravenously. Arteriography was performed by DSA technique with selective catheterization of renal arteries. Of the 157 visualized renal arteries 155 could be evaluated with DSA and a total of 157 with CTA. Sensitivity of CTA for RAS > or = 50% was 98% and the specificity was 94%. Comparison of the grade of stenosis as evaluated by DSA versus CTA showed: identical gradation in 59 arteries (DSA > or = 50%/CTA > or = 50%), underestimation by CTA in one artery (DSA 50 to 75%/CTA < 50%), and overestimation by CTA in six arteries (DSA < 50%/CTA 50 to 75%). Factors that may contribute to these differences include impaired renal function and possibly "underestimation" of ostial RAS by arteriography. One artery not evaluable by arteriography showed a 70% stenosis by CTA. CTA showed no major side effects. We conclude that CTA has the same accuracy for the diagnosis of RAS > or = 50% as arteriography. However, CTA is only minimally invasive, safe, and causes less discomfort to patients.

Diagnostic imaging evaluation of renovascular hypertension

Over 50 million people in the United States are hypertensive. Renovascular disease accounts for 3-5% of these hypertensive patients. Because renovascular hypertension is potentially curable, much effort has been devoted to detecting and treating renal artery stenosis. Conventional angiography has been traditionally used to diagnose renal artery stenosis. However, because of its invasiveness and cost, conventional angiography cannot be utilized as a screening test in all patients who may have renal artery stenosis. Several noninvasive studies have been advocated for screening in hypertensive patients who may have renovascular disease. However, the accuracy of these noninvasive studies is widely variable, and appropriate use of these noninvasive studies needs to be better defined. Appropriate use of diagnostic imaging examinations for hypertensive patients depends on the index of suspicion for renovascular disease and on the patient's renal function. If certain clinical findings suggest the possibility of renovascular disease, then conventional angiography/intraarterial digital subtraction angiography should be performed. Captopril renography or duplex Doppler sonography could also be utilized if angiography is not desired or is contraindicated because of impaired renal function or a contrast allergy. Magnetic resonance angiography appears to be most helpful in a small, select group of patients who are likely to have proximal renal artery stenosis.

Defining the role of renal angiography in the diagnosis of renal artery disease

The current goal of angiography in the diagnosis of renal artery disease is poorly defined, probably because of the diversity of patients presenting for management. The current application of angiography is better understood when put into perspective with the patient population that we are trying to screen. There are two distinct patient populations with renovascular disease: those with uncontrolled hypertension and those with azotemia or risk of progression to end-stage renal disease. The role of angiography in these two patient populations is quite different. In patients with hypertensive renovascular disease, angiography should be applied rather late and should be preceded by other noninvasive testing to screen patients from those with essential hypertension, since the prevalence of this disease is low and the cost implications of applying angiography primarily are immense. The two promising tests in this setting are captropril renography and duplex ultrasound scanning. In contradistinction, patients with azotemic renovascular disease, suffering from bilateral renal artery stenoses, or suffering from stenosis of the renal artery in a solitary kidney may be better studied by early application of renal angiography, especially those at risk of progression and for whom intervention is indicated.

Correlative imaging of the kidney

The proliferation of imaging methods for the kidney and urinary tract, combined with advances in technology and the introduction of new techniques, has created uncertainty in selecting the most efficient method for evaluating many problems encountered in clinical medicine. The main advantage of nuclear medicine lies in demonstrating the pathophysiology involved. Recent developments in Doppler ultrasound and magnetic resonance imaging with different pulse sequences and paramagnetic contrast agents also have shown promise for imaging physiological processes. However, there is little literature to support their advantage over nuclear medicine procedures in many common clinical situations. The complementary nature of nuclear medicine studies in the imaging evaluation of hydronephrosis, renal artery stenosis, flank pain, renal mass, pyelonephritis, and the transplant kidney is reviewed.

Renal imaging in children with persistent hypertension

The role that imaging plays in the evaluation of the child with hypertension depends in large part on the results of thorough historical, physical, and laboratory examinations. How aggressively one searches for an underlying renal parenchymal or renovascular disorder must be individualized in each child. An individualized approach to renal imaging in children with hypertension is presented.

Renal revascularization: indications and results

Although the prevalence of renovascular hypertension is low, clinical criteria can select a population in which renovascular hypertension is significantly more common (prevalence of 15%). In these selected patients, it is appropriate to proceed to a screening modality to look for a significant renal artery stenosis. Choices of the noninvasive methods include captopril-enhanced renal scintigraphy, magnetic resonance (MR) angiography, and intravenous digital subtraction renal angiography (DSRA). Intraarterial DSRA or conventional arteriography may also be used to reliably detect renal artery stenosis, with the advantage that both the diagnostic and the interventional procedure can be performed at the same setting. A high percentage of a group of patients who are selected by means of clinical and arteriographic studies will benefit from revascularization. Thus, the renal artery angioplasty may be performed during the arteriogram in which the stenosis is confirmed.

[Renovascular hypertension: diagnostic and therapeutic strategy]

Investigations for renal artery stenosis have been greatly facilitated by advances in imaging techniques. Intravenous digital subtraction angiography is now performed in all patients with progressive, drug-resistant hypertension associated with aorto-iliac lesions or with renal impairment induced by angiotensin-converting enzyme inhibitors. Yet the finding of hypertension with renal artery stenosis is not enough to make the diagnosis of renovascular hypertension, this term being reserved to hypertension reversible by revascularization. The selection of patients who may benefit from revascularization rests on urography to explore the excretory and endocrine functions of the ischaemic kidney, as well as on scintigraphy and measurement of renin levels in renal veins before and after administration of captopril. The functional data are completed by vascular exploration which helps in evaluating the usefulness and safety of revascularization: repercussions of hypertension on target organs and extension of the vascular disease to other territories. Revascularization as first-line treatment consists of percutaneous transluminal dilatation; surgery must be reserved to difficult cases, such as arterial obliteration or failed dilatation.

Renal artery imaging: a prospective comparison of intra-arterial digital subtraction angiography with conventional angiography

This study describes a systematic comparison of intra-arterial digital subtraction angiography (DSA) of the main renal arteries with conventional angiography (CA), the currently accepted "gold standard" for the diagnosis of renal artery stenosis. Twenty-five patients scheduled for abdominal aortography for various indications underwent first DSA then CA. The DSA and CA images were evaluated for number of renal arteries, presence and grade of renal artery stenosis, presence of post-stenotic dilation or fibromuscular changes, and diagnostic and pictorial adequacy of the images. DSA was found to be diagnostically adequate in 92% of cases, compared with 96% for CA. In evaluating significant main renal artery stenosis, which the authors assumed to be any stenosis greater than 50%, there were 10 such stenoses seen by CA. DSA also detected 10 cases, but there was 1 false positive and 1 false negative, yielding a sensitivity of 90% and a specificity of 98%. There was also close correlation of DSA and CA for the few cases of post-stenotic dilatation and fibromuscular dysplasia encountered. The authors conclude that DSA is an acceptable substitute for CA in the evaluation of patients for main renal artery stenosis.