Duplex ultrasonography in assessing restenosis of renal artery stents

Recommendations for ultrasonographic assessment of renal arteries

The present clinical practice recommendations are addressed to physicians of all specialties, who perform Doppler ultrasound examinations of the kidneys on a daily basis, and in particular to specialists in radiology and imaging diagnostics. The recommendations were based on the Ultrasonography Standards of the Polish Ultrasound Society and current scientific reports consistent with Evidence Based Medicine. The paper discusses patient preparation protocol, examinat ion technique with particular emphasis on patient’s position allowing to obtain proper Doppler angle of insonation, as well as diagnostic limitations of the technique. Normal blood flow parameters as well as those indicating hemodynamically significant stenosis are also presented. Although the 2013–2014 American guidelines for renal artery duplex sonography (AIUM Practice Parameter for the Performance of Native Renal Artery Duplex Sonography and AIUM Practice Guideline for the Performance of an Ultrasound Examination of Solid-Organ Transplants), which were the basis for many national recommendations, have not been significantly updated to date, a large body of scientific research indicates the need for revision of current Doppler ultrasound standards and parameters, particularly for patients receiving endovascular treatment due to renovascular hypertension. Therefore, the paper refers to the current issue of ultrasound scan interpretation in patients receiving endovascular stenting, after transplantation of kidney, as well as in pediatric patients.

The Society for Vascular Surgery practice guidelines on follow-up after vascular surgery arterial procedures

Although follow-up after open surgical and endovascular procedures is generally regarded as an important part of the care provided by vascular surgeons, there are no detailed or comprehensive guidelines that specify the optimal approaches with regard to testing methods, indications for reintervention, and follow-up intervals. To provide guidance to the vascular surgeon, the Clinical Practice Council of the Society for Vascular Surgery appointed an expert panel and a methodologist to review the current clinical evidence and to develop recommendations for follow-up after vascular surgery procedures. For those procedures for which high-quality evidence was not available, recommendations were based on observational studies, committee consensus, and indirect evidence. Recognizing that there are numerous published reports on the role of duplex ultrasound for surveillance of infrainguinal vein bypass grafts, the Society commissioned a systematic review and meta-analysis on this topic. The panel classified the strength of each recommendation and the corresponding quality of evidence on the basis of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system: recommendations were graded either strong or weak, and the quality of evidence was graded high, moderate, or low. The resulting recommendations represent a wide variety of open surgical and endovascular procedures involving the extracranial carotid artery, thoracic and abdominal aorta, mesenteric and renal arteries, and lower extremity arterial revascularization. The panel also identified many areas in which there was a lack of high-quality evidence to support their recommendations. This suggests that there are opportunities for further clinical research on testing methods, threshold criteria, and the role of surveillance as well as on the modes of failure and indications for reintervention after vascular surgery procedures.

Stent effects on duplex velocity estimates

BACKGROUND

Doppler-derived velocity criteria used to define the presence and severity of in-stent restenosis after percutaneous angioplasty and endoluminal stenting have been called into question. This study uses an in vitro flow model to examine Doppler-derived velocities after placement of balloon-expandable and self-expanding endoluminal stents (BES and SES).

METHODS

An in vitro vascular circuit model consisting of a pulsatile pump, tubing, and a conduit was created. The pump was programmed to replicate the Doppler spectral waveform pattern of the renal and carotid arteries. Peak systolic velocity (PSV) and end diastolic velocity (EDV) were estimated at five distinct conduit locations. Three replicate velocity measurements were made at each location. After initial velocity estimates, a BES or an SES was deployed within the conduit.

RESULTS

Mean ± standard error PSV was 95.8 ± 2.6 cm/s, 97.0 ± 2.7 cm/s, and 101.4 ± 2.7 cm/s for unstented, BES and SES, respectively. PSV estimates were increased between unstented and stented conduits when SESs were present. The increase in mean systolic velocity of 6.4% observed with SES was statistically significant (P < 0.05). EDV values did not differ significantly across conditions. Mean ± standard error EDV was 36.2 ± 1.0 cm/s, 37.3 ± 1.1 cm/s, and 37.2 ± 1.1 cm/s for unstented, BES, and SES, respectively.

CONCLUSION

The presence of an SES was associated with a less than 7% change in estimated PSV. These results suggest that Doppler velocity estimates for renal and carotid arteries are not materially affected by either BES or SES.

Percutaneous revascularization for ischemic nephropathy: the past, present, and future

Occlusion of the renal arteries can threaten the viability of the kidney when severe, in addition to accelerating hypertension and circulatory congestion. Renal artery stenting procedures have evolved from a treatment mainly for renovascular hypertension to a maneuver capable of recovering threatened renal function in patients with “ischemic nephropathy” and improving management of congestive heart failure. Improved catheter design and techniques have reduced, but not eliminated hazards associated with renovascular stenting. Expanded use of endovascular stent grafts to treat abdominal aortic aneurysms has introduced a new indication for renal artery stenting to protect the renal circulation when grafts cross the origins of the renal arteries. Although controversial, prospective randomized trials to evaluate the added benefit of revascularization to current medical therapy for atherosclerotic renal artery stenosis until now have failed to identify major benefits regarding either renal function or blood pressure control. These studies have been limited by selection bias and have been harshly criticized. While studies of tissue oxygenation using blood oxygen level dependent (BOLD) MR establish that kidneys can adapt to reduced blood flow to some degree, more severe occlusive disease leads to cortical hypoxia associated with microvascular rarefication, inflammatory injury and fibrosis. Current research is directed toward identifying pathways of irreversible kidney injury due to vascular occlusion and to increase the potential for renal repair after restoring renal artery patency. The role of nephrologists likely will focus upon recognizing the limits of renal adaptation to vascular disease and identifying kidneys truly at risk for ischemic injury at a time point when renal revascularization can still be of benefit to recovering kidney function.

Renal artery stenosis: prevalence of, risk factors for, and management of in-stent stenosis

Atherosclerotic renal artery stenosis is common and is associated with hypertension and chronic kidney disease. More frequent use of percutaneous renal artery stent placement for the treatment of renal artery stenosis during the past 2 decades has increased the number of patients with implanted stents. In-stent stenosis is a serious problem, occurring more frequently than earlier reports suggest and potentially resulting in late complications. Currently, there are no guidelines covering the approach to restenosis after renal artery stent placement. This article reviews data on the prevalence of and risk factors for the development of in-stent stenosis and the clinical manifestations, evaluation, and treatment of in-stent stenosis and suggests a strategy for the management of patients after percutaneous renal artery stent placement.

Early duplex predicts restenosis after renal artery angioplasty and stenting

OBJECTIVE

To examine the relationship between early renal duplex sonography (RDS) and restenosis after primary renal artery percutaneous angioplasty and stenting (RA-PTAS).

METHODS

Consecutive patients undergoing RA-PTAS for hemodynamically significant atherosclerotic renal artery stenosis with hypertension and/or ischemic nephropathy between September 2003 and July 2010 were identified from a prospective registry. Patients had renal RDS pre-RA-PTAS, within 1 week of RA-PTAS and follow-up RDS examinations after the first postoperative week for surveillance of restenosis. Restenosis was defined as a renal artery peak systolic velocity (PSV) ≥ 180 cm/s on follow-up RDS. Associations between RDS and restenosis were examined using proportional hazards regression.

RESULTS

Eighty-three patients (59% female; 12% nonwhite; mean age, 70 ± 10 years; mean pre-RA-PTAS PSV, 276 ± 107 cm/s) undergoing 91 RA-PTAS procedures comprised the sample for this study. All procedures included a completion arteriogram demonstrating no significant residual stenosis. Mean follow-up time was 14.9 ± 10.8 months. Thirty-four renal arteries (RAs) demonstrated restenosis on follow-up with a median time to restenosis of 8.7 months. There was no significant difference in the mean PSV pre-RA-PTAS in those with and without restenosis (287 ± 96 cm/s vs 269 ± 113 cm/s; P = .455), and PSV pre-RA-PTAS was not predictive of restenosis. Within 1 week of RA-PTAS, mean renal artery PSV differed significantly for renal arteries with and without restenosis (112 ± 27 cm/s vs 91 ± 34 cm/s; P = .003). Proportional hazards regression analysis demonstrated increased PSV on first post-RA-PTAS RDS was significantly and independently associated with subsequent restenosis during follow-up (hazard ratio for 30 cm/s increase, 1.81; 95% confidence interval, 1.32-2.49; P = .0003). There was no difference in pre- minus postprocedural PSV in those with and without restenosis on follow-up (175 ± 104 cm/s vs 179 ± 124 cm/s; P = .88), nor was this associated with time to restenosis. Best subsets model selection identified first postprocedural RDS as the only factor predictive of follow-up restenosis. A receiver-operating characteristic curve was examined to assess the first week PSV post-RA-PTAS most predictive of restenosis during follow-up. The ideal cut point for RA-PSV was 87 cm/s or greater. This value was associated with a sensitivity of 82.4%, specificity of 52.6%, and area under the receiver-operating characteristic curve of 69.3%. Increased first postprocedural RA-PSV was predictive of lower estimated glomerular filtration rate in the first 2 years after the procedure (-1.6 ± 0.7 mL/min/1.73 m(2) lower estimated glomerular filtration rate per 10 cm/s increase in RA-PSV; P = .010).

CONCLUSIONS

Early renal artery PSV within 1 week after RA-PTAS predicted renal artery restenosis and lower postprocedure renal function. Recurrent stenosis demonstrated no association with absolute elevation in PSV prior to RA-PTAS nor with the change in PSV after RA-PTAS. These data suggest that detectable differences exist in renal artery flow parameters following RA-PTAS that are predictive of restenosis during follow-up but are not apparent on completion arteriography or detectable by intra-arterial pressure measurements. Further study is warranted.

Impact of atherosclerosis and age on Doppler sonographic parameters in the diagnosis of renal artery stenosis

OBJECTIVES

The purpose of this study was to investigate the influence of atherosclerosis and age on 4 representative Doppler parameters in the diagnosis of renal artery stenosis.

METHODS

The 4 parameters, renal peak systolic velocity (PSV), renal-aortic ratio, renal-interlobar ratio, and acceleration time, were measured in 208 patients before angiography. The 208 patients were divided into groups according to age and atherosclerosis stratification. The Student t test, 1-way analysis of variance, and the χ(2) test were used to compare all 4 parameters and clinical characteristics. The optimal cutoff values were determined by receiver operating characteristic curves. The diagnostic concordance between atherosclerosis and age strata was evaluated by the Cohen κ coefficient.

RESULTS

Of the 416 renal arteries shown on Doppler sonography, 204 had a diagnosis of renal artery stenosis and 19 as occlusion on angiography. The optimal cutoff values for the renal-aortic ratio and renal-interlobar ratio in the groups aged 46 years or older and younger than 46 years were much different (2.3 versus 1.4 and 5.1 versus 6.5, respectively), whereas those for the renal PSV and acceleration time were close to each other or the same (170 versus 180 cm/s and 51 versus 51 milliseconds). The κ coefficients for the renal PSV, renal-interlobar ratio, acceleration time, and renal-aortic ratio between the atherosclerosis and age strata were 0.93, 0.99, 1.00, and 0.71.

CONCLUSIONS

Atherosclerosis and age show comparable influences on Doppler parameters in the diagnosis of renal artery stenosis. For clinical convenience, cutoff values may be separately established on the basis of a 46-year-old borderline for the renal-aortic ratio and renal-interlobar ratio, although this process is not necessary for the renal PSV and acceleration time.

Magnetic resonance angiography and Doppler scanning for detecting atherosclerotic renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is a progressive but potentially reversible chronic kidney disease. Although the high sensitivity and specificity of renal Doppler scanning (RDS) for ARAS has been reported in western countries, ARAS has not been detected by RDS. This study used magnetic resonance angiography (MRA) to evaluate the sensitivity and specificity of RDS for detecting ARAS among outpatients at a nephrology clinic, and to calculate the degree of underestimation of ARAS by RDS.

METHODS

A total of 257 outpatients, aged > 50 years were examined for ARAS by RDS and MRA.

RESULTS

Thirty-seven (14.4%) and 139 (54.1%) of 257 patients had stenosis detected by RDS and MRA, respectively. Among the 220 patients whose RDS results were negative, MRA detected stenosis in 111 (50.45%). Multivariate logistic regression analysis showed that age > 65 years, duration of smoking, coronary artery disease, and serum creatinine levels > 354 mmol/L (4 mg/dL) were significant and independent factors that influenced ARAS in patients with negative results by RDS.

CONCLUSION

RDS might still be the diagnostic procedure of choice for screening outpatients for ARAS because it is inexpensive, convenient, able to detect severity, and avoids the use of contrast media. When RDS is negative in aged people who have smoked longer than 20 years, with coronary artery disease or serum creatinine > 4 mg/dL, MRA is recommended for further evaluation of ARAS.

Doppler ultrasound and renal artery stenosis: An overview

Renovascular disease is a complex disorder, most commonly caused by fibromuscular dysplasia and atherosclerotic diseases. It can be found in one of three forms: asymptomatic renal artery stenosis (RAS), renovascular hypertension, and ischemic nephropathy. Particularly, the atherosclerotic form is a progressive disease that may lead to gradual and silent loss of renal function. Thus, early diagnosis of RAS is an important clinical objective since interventional therapy may improve or cure hypertension and preserve renal function. Screening for RAS is indicated in suspected renovascular hypertension or ischemic nephropathy, in order to identify patients in whom an endoluminal or surgical revascularization is advisable. Screening tests for RAS have improved considerably over the last decade. While captopril renography was widely used in the past, Doppler ultrasound (US) of the renal arteries (RAs), angio-CT, or magnetic resonance angiography (MRA) have replaced other modalities and they are now considered the screening tests of choice. An arteriogram is rarely needed for diagnostic purposes only. Color-Doppler US (CDUS) is a noninvasive, repeatable, relatively inexpensive diagnostic procedure which can accurately screen for renovascular diseases if performed by an expert. Moreover, the evaluation of the resistive index (RI) at Doppler US may be very useful in RAS affected patients for predicting the response to revascularization. However, when a discrepancy exists between clinical data and the results of Doppler US, additional tests are mandatory.

Restenosis after renal artery angioplasty and stenting: incidence and risk factors

BACKGROUND

Management of renal artery stenosis (RAS) with primary renal artery percutaneous angioplasty and stenting (RA-PTAS) is associated with a low risk of periprocedural death and major complications; however, restenosis develops in a subset of patients and repeat intervention may be required. We examined the incidence of restenosis after RA-PTAS and associations with clinical factors.

METHODS

Consecutive patients undergoing RA-PTAS for hemodynamically significant atherosclerotic RAS associated with hypertension or ischemic nephropathy, or both, between October 2003 and September 2007 were identified from a registry. Restenosis was defined using duplex ultrasound (DUS) imaging as a renal artery postintervention peak systolic velocity (PSV) >or=180 cm/s. The incidence and temporal distribution of restenosis was analyzed using survival analysis based on treated kidneys. Associations between clinical factors and recurrent stenosis were examined using proportional hazards regression.

RESULTS

RA-PTAS was performed on 112 kidneys for atherosclerotic RAS during the study period. Initial postintervention renal artery DUS imaging confirming PSV <180 cm/s in 101 kidneys, which formed the basis of this analysis. Estimated restenosis-free survival was 50% at 12 months and 40% at 18 months. Decreased risk of restenosis was associated with preoperative statin use (hazard ratio [HR], 0.35; 95% confidence interval [CI], 0.16-0.74; P = .006) and increased preoperative diastolic blood pressure (DBP; HR, 0.70 per 10-mm Hg increase in preoperative DBP; 95% CI, 0.49-0.99; P = .049). No other factors assessed were associated with restenosis.

CONCLUSION

Restenosis occurs in a substantial number of patients treated with RA-PTAS. Preoperative statin medication use and increased preoperative DBP are associated with reduced risk of restenosis. In the absence of contraindications, statins should be considered standard therapy for patients with atherosclerotic renal artery stenosis.

Renal artery stenting with noninvasive duplex ultrasound follow-up: 3-year results from the RENAISSANCE renal stent trial

OBJECTIVE

The multicenter, single-arm RENAISSANCE trial evaluated outcomes in patients with progressive atherosclerotic renal artery stenosis (ARAS) treated with the Express Renal Premounted Stent System (Boston Scientific, Natick, MA).

BACKGROUND

Renal artery stenting may prevent the morbidity and mortality of surgical revascularization and high restenosis rates of percutaneous renal angioplasty (PTRA). Renal artery duplex ultrasonography (DUS) offers an alternative to traditional invasive poststenting angiographic surveillance, though concordance with angiography for in-stent restenosis has yet to be validated independently.

METHODS

RENAISSANCE enrolled 100 patients (117 lesions) with de novo or restenotic ostial atherosclerotic lesions <or=15 mm long in vessels >or=4.0 and <or=7.0 mm diameter with diameter stenosis >or=70%. The primary endpoint, 9-month binary restenosis, was compared to an objective performance criterion (OPC) of 40% for published PTRA results. Follow-up was conducted through 3 years.

RESULTS

Technical and procedural success was both 99%. Follow-up angiography, triggered clinically or by ultrasonography, revealed 21.3% binary restenosis at 9 months, which was superior to the OPC (P < 0.0001). Concordance between ultrasonography and angiography for detection of binary restenosis at 9 months was 87%. Peak systolic velocity and renal-to-aortic ratio were both significantly improved compared to baseline at 9 months and 2 years. The major adverse event (defined as device- or procedure-related death, target lesion revascularization or significant embolic event) rate was 10.5% at 9 months and 20.9% at 3 years.

CONCLUSIONS

RENAISSANCE demonstrates that renal artery stenting is superior to the prespecified OPC at 9 months, and also shows that DUS can accurately identify in-stent restenosis.

Multidetector CT Angiography in the Follow-Up of Patients Treated with Renal Artery Stents: Value of Different Reformation Techniques Compared with Axial Source Images

PURPOSE

To evaluate the role of 4 different reformation techniques in comparison with axial images from multidetector computed tomographic angiography (MDCTA) in the follow-up of renal artery stents.

METHODS

Data on 40 patients (20 men; mean age 65 years) who underwent MDCTA as part of their routine follow-up after successful primary stenting of a main renal artery were retrospectively analyzed. Multiplanar reformation (MPR), curved planar reformation (CPR), volume rendering threshold (VRT), and virtual angioscopy (VA) were reviewed by 2 independent observers who were blinded to the results of the axial source images, which served as the gold standard. The stenosis degree was scored as I = 0%, II <50%, III = 51%-75%, IV = 76%-99%, or V = occlusion; a stenosis >50% was considered hemodynamically significant.

RESULTS

Five hemodynamically significant stenoses were identified on axial images. The correlation with axial images was perfect for both observers using MPR and CPR (kappa = 1 for each observer); corresponding results were kappa = 0.69 and kappa = 0.64 for VRT and kappa = 0.88 and kappa = 0.83 for VA, respectively. The interobserver correlations were excellent for all reformation techniques (kappa = 0.95 to 1).

CONCLUSION

Compared to axial images, MPR and CPR correlated perfectly with axial images; VA performed surprisingly well, while VRT was affected by artifacts and consequently showed inferior results.

Observations from multidetector CT imaging of different types of renal artery stents

PURPOSE

To present an optimized protocol for acquisition and reconstruction of multidetector computed tomographic angiographic (CTA) images of the stents most commonly used in renal arteries.

TECHNIQUE

CTA was performed on a 16-detector row CT scanner using 0.75-mm collimation. Multiplanar reformatted images perpendicular to the stents and 2-dimensional curved reformatted images were displayed. Two different view windows ("vascular" and "stent") were used, each adapted to the stent density, the vascular wall density, and the aortic enhancement. Five different types of stainless steel balloon-expandable stents were examined; all caused discernable artifacts. These artifacts became more prominent as the stent density increased, becoming most significant when 2 stents were positioned one inside the other. The "stent" window allowed better appreciation of the stent shape and its position compared to the aortic wall and ostial calcifications. The "vascular" window afforded a better view of the vascular lumen, in addition to visualizing the stent in several planes.

CONCLUSIONS

Multidetector CTA using dedicated acquisition and reconstruction protocols is capable of visualizing the vascular lumen of different types of renal stents while avoiding metallic artifacts.

Sonographic follow-up after visceral artery stenting

OBJECTIVE

The aim of this study was to evaluate the sonographic features of stents and the flow parameters of the visceral arteries after stent implantation.

METHODS

Since 1996, 34 stenoses of the visceral arteries (2 mesenteric, 4 celiac trunk, and 28 renal arteries) in 28 patients have been treated with metallic stent implantation in the Department of Radiology of Szeged Medical University. All these patients were regularly followed sonographically. For the diagnosis of restenosis, previously published criteria were used.

RESULTS

All the mesenteric and celiac stents could be visualized, but none of the renal stents were clearly seen sonographically. The flow parameters could be established in all cases. Sonographic examination revealed 1 occlusion, 2 restenoses, and 1 stent displacement. All these abnormalities were confirmed by other imaging modalities.

CONCLUSIONS

Sonography is a useful tool in the follow-up of patients after visceral artery stenting. Despite the fact that none of the renal artery stents were visualized directly, the flow parameters could be evaluated, and the pathologic changes were found.

Value, limitations, and techniques of renal artery stenting

Percutaneous therapy for renovascular occlusive disease has become the preferred alternative to open renal artery revascularization. Angioplasty and stenting of renal artery stenoses has been shown to be a safe and effective option for severe hypertension and ischemic nephropathy. Catheter-based treatment, especially when performed with lower-profile systems can be performed with minimal morbidity and a reliably high degree of initial technical success. The long-term beneficial effects on blood pressure control and renal function, while debated, appear to be valid. In this article, data supporting the value and limitations of renal artery stenting are reviewed, and our technique for renal artery stenting using a lower-profile platform of balloons and stents is described.

Renal function and outcome of PTRA and stenting for atherosclerotic renal artery stenosis

BACKGROUND

Prior studies of percutaneous transluminal renal artery angioplasty and stenting (PTRAS) for atherosclerotic renal artery stenosis (RAS) have shown that renal function is improved in about 25%, stabilizes in about 40%, but worsens in about 25% of patients. The factors predicting benefit remain controversial. We tested the hypothesis that the baseline glomerular filtration rate (GFR) predicts the changes in GFR and blood pressure (BP) after PTRAS.

METHODS

Treated hypertensive patients with positive renal color-coded duplex Doppler velocimetry and clinical criteria were screened by arteriography. Patients (N = 105) were included if they had an RAS >or=70%, a transluminal pressure gradient >or=30 mm Hg and, they had more than 100 days of follow-up. GFR was calculated from the serum creatinine concentration (SCr). Patients were divided by baseline GFR into subgroups with normal to mildly impaired (N = 52) or moderately to severely impaired (N = 53) initial GFR, according to a GFR >or=50 or <50 mL. min-1 respectively. All received PTRAS.

RESULTS

For the entire group, after a mean follow-up period of 371 days, there were significant reductions in systolic and diastolic BP (before, 160 +/- 26/91 +/- 12 vs. after, 145 +/- 20/83 +/- 10 mm Hg, respectively; mean +/- SD; P < 0.0001), and a modest increase in the calculated GFR (before, 54 +/- 26 vs. after, 62 +/- 28 mL. min-1; mean +/- SD; P < 0.007). However, in the subgroup of patients with an initially lower GFR there was a significant increase in the calculated GFR (from 33.3 +/- 10 to 54 +/- 24 mL. min-1; mean +/- SD; P < 0.0001) despite no significant change in BP (161 +/- 27/90 +/- 12 vs. 151 +/- 21/86 +/- 12; P = NS). In contrast, in the subgroup with an initially higher GFR, there were significant (P < 0.0001) reductions in systolic BP (from 159 +/- 25 to 138 +/- 16 mm Hg) and diastolic BP (from 91 +/- 11 to 81 +/- 9 mm Hg), but no significant change in the calculated GFR (from 75 +/- 21 to 70.2 +/- 30 mL. min-1; P = NS). The significance of GFR variation in subgroups remained after correction of baseline data to exclude the influence of the expected regression to the mean.

CONCLUSIONS

Patients with atherosclerotic RAS fulfilling strict criteria of severity may have significant improvements in BP one year after PTRAS but only modest in GFR. The initial GFR may anticipate whether the benefits in the outcome will be in renal function enhancement (those with an initially depressed GFR) or in hypertension control (those with an initially normal or mildly impaired GFR).

Volume-rendered multidetector CT angiography: noninvasive follow-up of patients treated with renal artery stents

OBJECTIVE

The purpose of our study was to evaluate the role of multidetector CT (MDCT) angiography with volume rendering for estimating the patency of renal artery stents.

SUBJECTS AND METHODS

In 16 patients, 16 renal artery stents were evaluated with MDCT renal angiography and digital subtraction angiography (DSA). CT data were evaluated using multiplanar volume reformations and the volume-rendering algorithm with three different volume-rendered parameter settings (low-to-high, high-to-low, and high-low-high opacity transfer functions: VR(LH), VR(HL), and VR(VE), respectively). Targeted images of each stent were rendered in paraaxial and paracoronal planes and were interactively interpreted. The overall restenosis severity was measured on postprocessed paraaxial and paracoronal images and compared with that obtained on DSA using linear regression analysis. Image quality and lumen delineation on rendered images were also compared using Wilcoxon's signed rank test.

RESULTS

Eight restenoses were identified on DSA. Correlations between restenosis severity measured with DSA and those measured with MDCT were significant (p < 0.001). Volume rendering with VR(HL) allowed the best correlation with DSA (reviewer 1, r(2) = 0.86; reviewer 2, r(2) = 0.94) and was significantly better than multiplanar volume reformations (p = 0.028). Overall image quality was high with all rendering techniques and with no significant differences (p > 0.59, for all comparisons). Stent lumen was well delineated with volume-rendering modalities; however, VR(HL) was significantly better than VR(LH) (p = 0.033).

CONCLUSION

Volume-rendered MDCT angiography enabled high-quality three-dimensional reproducible evaluation of the patency of implanted renal artery stents. Volume rendering with VR(HL) achieved the best performance.

Repeated intervention for in-stent restenosis of the renal arteries

PURPOSE

To assess the long-term technical success of repeated endovascular intervention in stenosed renal artery stents.

MATERIALS AND METHODS

Fifteen patients with stenoses >or=50% in a renal stent placed because of an ostial atherosclerotic renal artery stenosis were included in this study. In the presence of increased blood pressure or decreased renal function, the in-stent restenosis was treated with percutaneous transluminal angioplasty (PTA) in the stent or placement of a second stent if the stenosis was located too distally in the stent. The results of these repeat interventions were evaluated by angiography.

RESULTS

The 15 patients had a total of 20 stenosed stents. Eighteen of these in-stent stenoses were treated with PTA and two were treated with placement of a second stent. Angiographic follow-up was available in 16 arteries, showing in-stent restenosis in four (25%; mean follow-up, 11 mo). The cumulative patency rates after repeat endoluminal intervention were 93% (95% CI: 80%-106%) and 76% (95% CI: 52%-101%) after 6 and 12 months, respectively. Renal function remained stable or improved in most patients (80%) after repeated intervention in the stent, and hypertension was classified as improved or cured in 47% of patients after 1 year.

CONCLUSION

Patients with stenosed renal artery stents can be treated successfully with PTA in a majority of cases, with a long-term success rate of 75% and stable renal function 1 year after repeated intervention.

Sonography in renovascular hypertension

OBJECTIVE

To familiarize practitioners with different sonographic manifestations of renal artery compromise and the sonographic techniques for renal artery imaging.

METHODS

Approximately 1500 examinations evaluating for renal artery disease are performed in our vascular laboratory every year. Most of the patients have the symptoms of hypertension (possibly related to renovascular etiology) and renal insufficiency. From our cumulative experience, the optimal scanning techniques are defined for each renal artery, for extrarenal versus intrarenal vascular evaluation, and for patients with different body habitus. We have also tabulated our technical success rate. Cases with sonographic evidence of renal artery compromise are identified. The validity, sensitivity, and specificity of different parameters are examined.

RESULTS

We achieve an approximately 75% to 80% success rate in obtaining technically adequate studies. We have not found the tardus-parvus waveform evaluation to be as valuable as direct interrogation of the renal artery.

CONCLUSIONS

Duplex/color Doppler sonography serves a vital role in the diagnosis of renal artery stenosis and occlusion; it has an excellent correlation with contrast-enhanced angiography. It is also used for intraoperative or postrevascularization surveillance to show evidence of recurring stenosis, thrombosis, and other complications.

Noninvasive imaging of the renal arteries

Currently, four screening/diagnostic studies are available that provide imaging of the renal arteries: duplex ultrasonography, CT angiography, MR angiography, and intravenous DSA. Intravenous DSA is no longer used because of better imaging with MR and CT angiography. MR angiography, CT angiography, and duplex ultrasonography provide excellent sensitivity and specificity when performed by experienced personnel. The screening test of choice depends on the availability, expertise, and cost at individual centers.

Long-term effects of arterial stenting on kidney function for patients with ostial atherosclerotic renal artery stenosis and renal insufficiency

It is uncertain whether renal artery stent placement in patients with atherosclerotic renovascular renal failure can prevent further deterioration of renal function. Therefore, the effects of renal artery stent placement, followed by patency surveillance, were prospectively studied in 63 patients with ostial atherosclerotic renal artery stenosis and renal dysfunction (i.e., serum creatinine concentrations of >120 micromol/L (median serum creatinine concentration, 171 micromol/L; serum creatinine concentration range, 121 to 650 micromol/L). Pre-stent renal (dys) function was stable for 28 patients and declining for 35 patients (defined as a serum creatinine concentration increase of > or =20% in 12 mo). The median follow-up period was 23 mo (interquartile range, 13 to 29 mo). Angioplasty to treat restenosis was performed in 12 cases. Five patients reached end-stage renal failure within 6 mo, and this was related to stent placement in two cases. Two other patients died or were lost to follow-up monitoring within 6 mo, with stable renal function. For the remaining 56 patients, the treatment had no effect on serum creatinine levels if function had previously been stable; if function had been declining, median serum creatinine concentrations improved in the first 1 yr [from 182 micromol/L (135 to 270 micromol/L ) to 154 micromol/L (127 to 225 micromol/L ); P < 0.05] and remained stable during further follow-up monitoring. In conclusion, stent placement, followed by patency surveillance, to treat ostial atherosclerotic renal artery stenosis can stabilize declining renal function. For patients with stable renal dysfunction, the usefulness is less clear. The possible advantages must be weighed against the risk of renal failure advancement with stent placement.