Atherosclerotic stenosis of the renal arteries. Indications for intervention

Advances in the ability to diagnose atherosclerotic stenosis of the renal arteries have increased awareness of this disorder over the past decade, and several medical specialties have become interested in its pathophysiology, diagnosis, and therapy. Improved surgical and anesthetic techniques and the development of endovascular technology have paved the way for more aggressive management of atherosclerotic renal artery stenosis. However, there is a lack of prospective data supporting this aggressive approach, and there is little agreement among physician groups concerning the appropriateness of revascularization in many patient scenarios. We will examine the available data and make recommendations about which patient groups might benefit most from renal artery revascularization (surgical or endovascular).

Renal artery stenosis: evaluation with breath-hold, three-dimensional, dynamic, gadolinium-enhanced versus three-dimensional, phase-contrast MR angiography

PURPOSE

To compare breath-hold, three-dimensional, gadolinium-enhanced magnetic resonance (MR) angiography with three-dimensional, phase-contrast MR angiography in the evaluation of renal artery stenosis.

MATERIALS AND METHODS

Fifty-five consecutive adult patients with clinical suspicion of renovascular disease were prospectively examined with three-dimensional, phase-contrast MR angiography and breath-hold, three-dimensional MR angiography with injection of a standard dose of gadopentetate dimeglumine to evaluate the number of renal arteries and the presence and degree of stenosis. The standard of reference was intraarterial digital subtraction angiography.

RESULTS

Gadolinium-enhanced MR angiography depicted all 105 main renal arteries, whereas phase-contrast MR angiography depicted 104. The number of accessory renal arteries depicted was significantly higher with gadolinium-enhanced (17 of 18) than with phase-contrast (11 of 18) studies (P = .04). Both techniques depicted 27 of the 29 stenoses (sensitivity, 93%; P > .05). Sensitivities, specificities, and accuracies in the diagnosis of hemodynamically significant stenosis (> 50% narrowing) were, respectively, 94%, 96%, and 96% for phase-contrast and 100%, 97%, and 98% for gadolinium-enhanced MR angiography (P > .05).

CONCLUSION

Gadolinium-enhanced MR angiography is superior to phase-contrast MR angiography in accessory renal artery depiction. No statistically significant difference in the assessment of stenosis has been found between the two techniques.

Colour-coded duplex sonography in the diagnostic assessment of vascular complications after kidney transplantation in children

BACKGROUND

Vascular complications are a major cause of dysfunction or transplant loss in children. Arterial or venous occlusion, transplant renal artery stenosis (TRAS) and some arteriovenous (AV) fistula require rapid detection and prompt intervention. The present study was performed to determine the accuracy of colour Doppler sonography (CDS) in the early and late phase after renal transplantation and to correlate the results with angiographic and intraoperative findings.

OBJECTIVE

CDS is the preferred imaging modality with a high diagnostic accuracy for follow-up of renal transplantation in children. The indication for angiography should be established on the basis of the CDS diagnosis.

MATERIALS AND METHODS

In 87 children (mean age 10.9 years, range 2-17), 423 CDS examinations were performed after renal transplantation. Angiography was performed in 17 cases; surgery was necessary in 16 patients.

RESULTS

CDS correctly identified 8/8 arterial or venous occlusions and 7/7 TRAS. The only false positive diagnosis of TRAS was due to misinterpretation of an iliac artery stenosis. Six AV fistulae were diagnosed by CDS. The overall positive predictive value of CDS was 94 % in this study.

CONCLUSION

CDS is a noninvasive, non-radiation producing imaging modality with a high diagnostic accuracy. It is the method of choice in the assessment of vascular complications after renal transplantation in children.

Relation between arteriosclerosis in the coronary and renal arteries

This study analyzes the severity of coronary artery disease in terms of the severity of renal artery disease in 609 patients undergoing coronary and renal angiography. The presence of renal artery disease of any severity is strongly suggestive of advanced coronary artery disease.

Pulsus alternans in diastolic left ventricular dysfunction--a case report

Pulsus alternans is usually found in patients with reduced systolic ventricular function. We describe a patient with recurrent pulmonary edema, hypertension, bilateral renal artery stenosis, but with normal systolic function. Pulsus alternans was demonstrated in both pulmonary artery, right ventricle, and left ventricle pressures. After successful renal artery revascularization, the pulsus alternans disappeared. This case illustrates that pulsus alternans can be present with diastolic dysfunction of the left ventricle in the absence of systolic dysfunction.

Noninvasive comprehensive characterization of renal artery stenosis by combination of STAR angiography and EPISTAR perfusion imaging

In a small fraction of patients with hypertension, the cause is stenosis of the renal artery. To date, there is no established noninvasive screening technique available to identify this population, for whom treatment with a surgical procedure or percutaneous transluminal angioplasty is often possible. In this study, the sensitivity and specificity of STAR angiography and EPISTAR perfusion imaging in characterizing renal artery stenosis were evaluated in an animal model. Qualitatively, STAR provided projection angiograms that were comparably sensitive to x-ray angiograms but obtained noninvasively. The sensitivity for detecting the stenosis was 100%. The specificity varied according to the definition of the threshold for significance, which varied 78-94%, depending on whether > 70% or > 50% diameter reduction was considered. Improvements in specificity will depend upon use of shorter echo times and higher spatial resolution. Our preliminary data indicate that EPISTAR provides sensitivity and specificity of 100% for characterizing stenosis with diameter reductions of > 70%.

Noninvasive comprehensive characterization of renal artery stenosis by combination of STAR angiography and EPISTAR perfusion imaging

In a small fraction of patients with hypertension, the cause is stenosis of the renal artery. To date, there is no established noninvasive screening technique available to identify this population, for whom treatment with a surgical procedure or percutaneous transluminal angioplasty is often possible. In this study, the sensitivity and specificity of STAR angiography and EPISTAR perfusion imaging in characterizing renal artery stenosis were evaluated in an animal model. Qualitatively, STAR provided projection angiograms that were comparably sensitive to x-ray angiograms but obtained noninvasively. The sensitivity for detecting the stenosis was 100%. The specificity varied according to the definition of the threshold for significance, which varied 78-94%, depending on whether > 70% or > 50% diameter reduction was considered. Improvements in specificity will depend upon use of shorter echo times and higher spatial resolution. Our preliminary data indicate that EPISTAR provides sensitivity and specificity of 100% for characterizing stenosis with diameter reductions of > 70%.

Hemodynamically significant atherosclerotic renal artery stenosis: MR angiographic features

PURPOSE

To identify magnetic resonance (MR) angiographic features of hemodynamically significant renal artery stenosis.

MATERIALS AND METHODS

Forty-seven patients underwent MR angiography of the renal arteries, including T1-weighted spin-echo and three-dimensional gadolinium-enhanced spoiled gradient-echo and three-dimensional phase-contrast pulse sequences, followed by renal revascularization. Thirty-five patients (52 arteries) were identified who benefited from renal revascularization, which indicated that they had hemodynamically significant renal artery stenoses. Kidney length, cortical thickness, parenchymal enhancement, and poststenotic dilatation were measured. Arteries were also examined for signal drop-out (dephasing) on phase-contrast angiograms; dephasing was considered severe if the stenotic artery appeared occluded on phase-contrast angiograms.

RESULTS

Poststenotic dilatation of greater than 20% was present in 36 (59%) of 52 hemodynamically significant renal artery stenoses, and severe dephasing was present in 45 (87%) of 52. In patients with unilateral hemodynamically significant stenosis or occlusion, mean ischemic kidney length was reduced to 9.3 cm compared with 10.7 cm for the contralateral normal kidney (P = .009), mean parenchymal thickness was reduced (1.2 vs 1.7 cm; P < .001), and mean parenchymal enhancement was 15% less on the ischemic side (P = .05). Severe dephasing on phase-contrast angiograms was present in nine (75%) of 12 unilateral hemodynamically significant stenoses but in only one contralateral normal renal artery (P < .001).

CONCLUSION

MR angiography depicts features of renal artery stenosis that are markers of hemodynamic significance.

Ability of a phase shift US contrast agent to improve imaging of the main renal arteries

PURPOSE

To evaluate the ability of a phase shift contrast agent to improve Doppler sonographic imaging of the main renal arteries in cases of suspected renal artery stenosis.

MATERIALS AND METHODS

In 25 patients in whom renal artery stenosis was suspected, baseline Doppler sonography was performed followed by two studies performed after blinded administration of contrast material or placebo (saline). Each kidney (n = 45) was evaluated for (a) visualization of the main renal artery on a scale of 0-4, (b) presence of accessory renal arteries, and (c) direct Doppler sonographic findings suggestive of renal artery stenosis. Correlative magnetic resonance angiography was performed in 24 patients, and angiograms were obtained in eight kidneys with stenosis at one or both imaging studies.

RESULTS

Contrast enhancement was observed in 23 patients. Enhancement was 8-20 minutes. Renal artery visualization scores improved from a mean of 2.56 and 2.71 on baseline and noncontrast scans, respectively, to 3.69 after administration of contrast material. Contrast-enhanced images depicted seven kidneys with accessory renal arteries not seen at other studies. Two of eight cases of stenosis were seen only with contrast-enhanced sonography.

CONCLUSION

Use of the phase shift contrast agent appears to enable a reduction in the number of equivocal findings of renal artery stenosis.

Fluoroscopically triggered contrast-enhanced three-dimensional MR angiography with elliptical centric view order: application to the renal arteries

PURPOSE

To determine the reliability of obtaining arterial-phase, contrast-material-enhanced three-dimensional (3D) magnetic resonance (MR) angiograms of the renal arteries by using a technique that combines two-dimensional real-time MR fluoroscopy and a 3D MR angiographic acquisition with elliptical centric view order.

MATERIALS AND METHODS

Twenty-five consecutive patients suspected of having renal artery disease were evaluated with the fluoroscopically triggered technique by using a mean dose of 0.18 mmol/kg gadoteridol. Left renal vein suppression, inferior vena cava suppression, motion artifact, and image quality for depiction of the renal arteries were each evaluated on a five-point scale (1 = best). The findings were compared with those of another 25 consecutive patients who underwent conventional gadolinium-enhanced 3D MR angiography.

RESULTS

The fluoroscopically triggered technique produced 4.6 times less left renal vein enhancement than did the conventional method (P < .01). With the fluoroscopically triggered technique, visualization of the renal arteries was adequate for diagnosis in 24 patients (96%) and the overall result (score of 1-3 for all criteria) was of good quality in 22 patients (88%).

CONCLUSION

With this fluoroscopically triggered MR angiographic technique, high-quality, arterial phase, relatively motion immune angiograms can be routinely obtained.

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.

Partial renal embolization for pediatric renovascular hypertension secondary to fibromuscular dysplasia

We report a 7-year-old boy with renovascular hypertension showing multiple stenoses and microaneurysms of the dorsal branch of the left renal artery caused by fibromuscular dysplasia. Hypertension was successfully treated with transcatheter alcohol and gelatin sponge embolization of the dorsal branch and its distribution. The vertebral branch remained intact. No severe complication was encountered. Loss of renal function by renal scintigraphy was minimal. The patient remains asymptomatic at 1 year.

[Detection of renal artery stenoses by MRI with surface reconstruction. Value in patients with chronic renal failure]

Forty-three patients with renal artery stenoses were examined with time of flight MR angiography using maximum intensity projection and surface shaded rendering, and with digital substraction angiography. Sensitivity and specificity were 0.83 and 0.78 for main and secondary arteries, 0.87 and 0.84 for main arteries. In azotemic patients, the positive predictive value was estimated at 40%-70% and the negative predictive value at 95%-98%, while the prevalence of renal artery stenoses varied from 10% to 30%. These results validate MRI for the detection of renal artery stenoses in this population. Surface shaded display was more accurate than maximum intensity projection to reconstruct time of flight sequences and to grade renal artery stenoses.

Renal artery repair in African-Americans

PURPOSE

This retrospective review examines the results of atherosclerotic renal artery (RA) repair in consecutive hypertensive African-Americans treated at our center and compares these results with Caucasians treated during the same period.

METHODS

From Jan. 1987 through Sep. 1996, a total of 485 patients underwent operative RA repair. Of these, 28 African-Americans and 370 Caucasians were managed for atherosclerotic renovascular disease. These cohorts were compared on the basis of preoperative blood pressure and renal function, extent of renal disease, extrarenal atherosclerosis, response to operation, and estimated survival.

RESULTS

The African-American cohort included nine men and 19 women (mean age, 62 years) with hypertension (mean blood pressure, 204 +/- 31/109 +/- 20 mm Hg) for an average of 10.2 +/- 7.5 years. Ischemic nephropathy (serum creatinine level, > 1.3 mg/dl) was present in 82% (n = 23) of the African-American group. RA reconstructions were unilateral in nine patients and bilateral in 19 patients (including repair to two solitary kidneys), for a total of 45 RA reconstructions (30 RA bypass procedures; eight transrenal/transaortic RA endarterectomy procedures; two RA reimplantations; five nephrectomies). Nine patients underwent combined aortic procedures (four abdominal aortic aneurysm; five occlusive disease). There was one perioperative death in the African-American group as a result of sepsis and multiple organ failure. Among surgical survivors, 20 African-American patients (74%) had a beneficial hypertension response (7% cured, 67% improved). Mean estimated glomerular filtration rate improved significantly from 34 to 42 ml/min/1.73 m2 (p < 0.001). In the 23 patients with ischemic nephropathy, 13 (57%) demonstrated greater than 20% decrease in serum creatinine level. In comparison with the 370 Caucasians (191 men, 179 women), the African-American cohort had significantly more preoperative heart disease (congestive heart failure or left ventricular hypertrophy; 68% vs 46%; p = 0.03) and tended toward more severe renal dysfunction (mean serum creatinine level, 2.5 vs 2.1 mg/dl; p = 0.25). However, African-Americans demonstrated a beneficial blood pressure and renal function response after operation, similar to Caucasians.

CONCLUSIONS

Our results indicate that the majority of selected African-Americans have a favorable blood pressure and renal function response to operative renal artery repair. This beneficial clinical response appears equivalent to the response observed in Caucasian patients and supports the search for RA disease in hypertensive African-Americans.

[Bilateral renal artery stenosis diagnosed during pregnancy]

Bilateral renal artery stenosis was diagnosed noninvasively in the 17th gestational week, in a chronically hypertensive pregnant woman, by renal artery duplex ultrasound examination, MRI and MR angiography. Continuous monitoring of the mother and the fetus was performed. Blood pressure was stabilized by complex antihypertensive therapy, but from the beginning of the third trimester superimposed preeclampsia developed gradually. In the 34th gestational week a 1600-g newborn was delivered by elective cesarean section. The case report draws attention to the significance of the thorough examination of hypertensive women before pregnancy.

[Classification of hemodynamic changes in renal artery stenosis using cine magnetic resonance phase contrast flow measurements]

PURPOSE

To evaluate the use of high-temporal resolution cine MR phase-contrast flow measurements for assessment of flow dynamics in renal artery stenosis (RAS).

MATERIAL AND METHODS

In a dog model, cine MR flow measurements were validated by comparing the MR flow data to an invasive transit-time ultrasound reference technique for different degrees of RAS. Cardiac-gated MR flow curves were recorded in 56 renal arteries of 28 patients with a temporal resolution of at least 32 ms. In all cases RAS was confirmed by digital subtraction angiography (DSA). Abnormalities of flow dynamics were assessed in the calculated flow curves using the MR parameters mean flow, maximum velocity, and time to systolic maximum.

RESULTS

By means of the MR blood flow parameters high-grade stenoses (> 50%, n = 23) were detected with sensitivity of 100% and specificity of 94% with reference to DSA. The overall differentiation between stenoses (n = 37) and non-stenosed vessels (n = 19) revealed a sensitivity of 87% and a specificity of 100%.

CONCLUSION

Analysis of cardiac-gated MR flow curves provides a non-invasive method to assess the hemodynamic significance of RAS and thus allows a functional evaluation in relation to the morphologic characteristics of the stenosis.

Evaluation of the aortoiliac and renal arteries: comparison of breath-hold, contrast-enhanced, three-dimensional MR angiography with conventional catheter angiography

PURPOSE

To determine the diagnostic accuracy of breath-hold, contrast material-enhanced, three-dimensional (3D) magnetic resonance (MR) angiography in the assessment of the aortoiliac inflow tract and renal arteries with conventional catheter angiography as the standard of reference.

MATERIALS AND METHODS

In 39 patients with symptomatic peripheral vascular disease, both catheter and contrast-enhanced, 3D MR angiography were performed. In a prospective blinded analysis, each vascular segment (23 segments per arterial tree) was evaluated for the presence of obstructive stenosis, graded as mild (<50%), severe (50%-99%), or occlusion (100%), as well as for aneurysmal disease.

RESULTS

Obstructive (n = 2) and aneurysmatic aortic (n = 6) lesions and 10 of 11 accessory renal arteries were identified and graded correctly with MR angiography. For detection of hemodynamically significant stenotic lesions (>50%) or occlusions with MR angiography, sensitivity and specificity, respectively, were 93% and 98% for the renal arteries, 96% and 100% for the common iliac arteries, 93% and 93% for the external iliac arteries, and 96% and 94% for the internal iliac arteries.

CONCLUSION

The diagnostic performance of contrast-enhanced 3D MR angiography is comparable with that of catheter angiography and thus may contribute to assessment of the aorta, the renal arteries, and the pelvic arterial system in patients with peripheral vascular disease before they undergo therapy.

[Value of contrast-enhanced 3D magnetic resonance angiography of the renal arteries]

PURPOSE

To determine the value of gadolinium-enhanced, three-dimensional breath-hold Magnetic Resonance Angiography (MRA) in the assessment of the aorta and renal arteries in comparison to conventional arteriography (CA).

PATIENTS AND METHODS

49 patients were evaluated with both CA and 3D MRA. 0.3 mmol/kg BW gadolinium-DTPA was administered intravenously in a bolus, using an automated injector. A test bolus method was used for timing of the bolus and beginning of the data acquisition. The intraarterial CA was used as the gold standard.

RESULTS

MRA-based assessment of renal artery stenosis was identical with CA in 31 of 45 stenoses (68.8%). Sensitivity and specificity for assessment of renal arterial disease by MRA were 84% and 96%; for clinically relevant lesions they amounted to 90% and 98%.

CONCLUSION

The presented contrast-enhanced 3D MRA technique allows for the reliable assessment of renal arterial morphology and pathology.

[Primary retroperitoneal fibrosis with renal involvement]

We report on a patient suffering from primary retroperitoneal fibrosis with histologically proven involvement of the right kidney. The problems in making the correct diagnosis, for which in this case a laparotomy and histological examination were also necessary, are discussed.

Evaluation of renal artery stenosis with dynamic gadolinium-enhanced MR angiography

OBJECTIVE

The purpose of this study was to compare dynamic gadolinium-enhanced three-dimensional spoiled gradient-recalled MR angiography with conventional arteriography in the evaluation of proximal renal artery stenosis (RAS).

MATERIALS AND METHODS

MR angiography and conventional arteriographic examinations of 30 patients evaluated for RAS were analyzed retrospectively. Three-dimensional MR angiography was performed with an RF spoiled gradient-recalled imaging sequence acquired during the dynamic i.v. injection of gadolinium (0.2-0.3 mmol/kg), MR data and conventional arteriograms were independently evaluated for the number and location of renal arteries and the degree and location of stenoses. The patients had a mean age of 70 years old and a mean serum creatinine level of 2.9 mg/dl, reflecting a population in whom atherosclerotic RAS was the primary concern.

RESULTS

Gadolinium-enhanced MR angiography revealed 100% of main renal arteries. For RAS of 50% or greater occlusion, the technique was 100% sensitive and 71% specific; the negative predictive value was 100%. The technique was 100% sensitive and 71% specific for RAS of 75% or greater occlusion.

CONCLUSION

Dynamic gadolinium-enhanced three-dimensional spoiled gradient-recalled MR angiography has a high sensitivity for revealing proximal RAS and is a quick and reliable technique for obtaining helpful anatomic information.

Contrast-enhanced, K-space-centered, breath-hold MR angiography of the renal arteries and the abdominal aorta

The purpose of this study was to evaluate the capability of contrast-enhanced breath-hold fast imaging with steady-state precession (FISP) three-dimensional MR angiography (MRA) to detect stenotic lesions of the abdominal aorta, the renal arteries, and the iliac arteries by using a K-space-centered 20-ml gadolinium-diethylene pentaacetic acid (Gd-DTPA) bolus. Fifty patients were studied before conventional x-ray angiography. Contrast-enhanced breath-hold FISP three-dimensional MRA was applied in the coronal view, centered at the renal arteries. Twenty ml of Gd-DTPA was used in all subjects. A test bolus was applied to determine the injection time for the K-space-centered bolus injection. Of 300 segments, 284 segments were classified correctly, 11 were overestimated, and five were underestimated. Sensitivity was 98%, specificity was 96%, positive predictive value was 96%, negative predictive value was 98%, and accuracy was 97%. Of the 50 patients studied, 43 were staged correctly. No venous overlay was seen in 31 patients; partial overlay was seen in 16 patients, and venous structure overlay obscuring arterial anatomy was found in two patients. Six of nine accessory renal arteries could be identified by MRA. Intraobserver variability was .94. This study has shown the ability of contrast-enhanced breath-hold FISP three-dimensional MRA to detect and grade vascular lesions in the abdominal aorta and the renal arteries. The method may serve as a screening tool in the future.

[Screening and diagnosis for eliminating renovascular hypertension. Value of 24-hour blood pressure monitoring and color-coded duplex ultrasound diagnosis]

BACKGROUND

Direct renal angiography is still the method of choice for identification of renal artery stenosis. Newer non-invasive diagnostic methods include color coded duplex sonography and also ambulatory 24-h blood pressure monitoring, since in a large proportion of patients with secondary forms of hypertension the usual blood pressure fall during nighttime disappears.

PATIENTS AND METHODS

In a prospective in-hospital study we investigated 86 patients with suspected renovascular hypertension. Circadian blood pressure was measured oscillometrically and color coded duplex sonography was performed immediately before direct renal angiography.

RESULTS

Angiography revealed renal artery stenosis (> or = 50%) in 42 patients. This compared to a sensitivity of 92.9% and specificity of 91.7% for the use of sonography in those patients (70.4%) who could be adequately examined. Mean 24-h pressure values as well as standard deviations of blood pressure means as an indicator for blood pressure variability were not different in the 2 groups of patients, when all the data were analysed together and also when the data for nighttime and daytime were examined separately. The percent of blood pressure fall during nighttime was also not different in the 2 groups. In both groups 4 hypertensive patients had a blood pressure increase during nighttime. In 11 patients without renal artery stenosis a blood pressure fall of < 10% was observed, compared to 12 patients with renal artery stenosis. The circadian pattern of pulse rate was similar in both groups.

CONCLUSION

We conclude that ambulatory blood pressure monitoring has a considerably lower diagnostic value for renal artery stenosis compared to angiography and also to color duplex sonography. This method therefore does not appear to be an appropriate screening approach for this kind of secondary hypertension. The color coded duplex sonography, however, seems to be the best non-invasive diagnostic method in those patients, who can be adequately examined.