Renal artery stenosis: value of contrast-enhanced ultrasonography

Value of contrast-enhanced ultrasound for diagnosis and follow-up of renal artery stenosis in patients with chronic kidney disease

OBJECTIVE

To evaluate whether contrast-enhanced ultrasound (CEUS) is an accurate, non-nephrotoxic diagnostic method and follow-up tool for use in patients with chronic kidney disease (CKD) and renal artery stenosis (RAS).

METHODS

In this prospective and monocentric study, we compared the sensitivity and specificity of CEUS for the diagnosis of RAS in CKD patients, using digital subtraction angiography (DSA) or computed tomographic angiography (CTA) as the gold standard methods. Further, the value of CEUS for distinguishing restenosis from other diseases was assessed. The ultrasound physicians conducted the examinations and served as the CEUS report readers who were blinded to the DSA or CTA results.

RESULTS

Patients with RAS (n = 60) were enrolled. Average patient age was 64.4 ± 18.0 years and median estimated glomerular filtration rate was 66.1 mL/min/1.73 m². CEUS was used to image 94 stenotic renal arteries and DSA- or CTA-verified stenosis was present in 96 renal arteries. The kappa value for CEUS was 0.776 (P < 0.001), with an accuracy of 92.5%, a sensitivity of 94.7%, and a specificity of 84.0%. The accuracy of CEUS was the same for the diagnosis of the CKD3b-5 group as for the CKD1-3a group (100% vs. 87.5%, P = 0.148). There was no difference in CEUS accuracy for the diagnosis of Takayasu RAS compared with atherosclerotic RAS (95.8% vs. 91.7%, P = 0.795). Twenty-nine CEUS examinations were performed to follow in-stent restenosis or progression of RAS, with a median follow-up time of 5.0 months (range 1.0-20.0). Two cases of in-stent restenosis in patients suffering from deteriorating kidney function and recurrent hypertension were examined by CEUS.

CONCLUSION

CEUS examination is a credible alternative for diagnosing moderate and severe RAS in patients with CKD, and is a reliable tool for follow-up surveillance after renal artery revascularization treatment. It shouldn't be thought as a color-coded duplex ultrasonography rescue in these patients.

The Value of Contrast-Enhanced Ultrasound versus Doppler Ultrasound in Grading Renal Artery Stenosis

Objective

This study is aimed at exploring the accuracy of contrast-enhanced ultrasound (CEUS) in grading renal artery stenosis.

Methods

122 renal arteries with suspected renal artery stenosis were selected. DSA, DUS, and CEUS were performed for all patients with suspected renal artery stenosis in the research. DSA was selected as the gold standard. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of CEUS or Doppler ultrasound (DUS) in the diagnosis of renal artery stenosis were analyzed. The consistency between CEUS and digital subtraction angiography (DSA) was compared. The accuracy of DUS or CEUS in grading renal artery stenosis was assessed by the area under the receiver operating characteristic (ROC) curves and compared between groups.

Results

The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CEUS in the diagnosis of renal artery stenosis were 88.9%, 87.8%, 88.5%, 93.5%, and 80.0%, respectively. There was no significant difference in grading renal artery stenosis between CEUS and DSA (X² = 0.643, P = 0.424). 77 of the 122 renal arteries were diagnosed with the stenosis rate more than 30% by CEUS. Compared with the results of DSA, the kappa value of CEUS was 0.749 (P < 0.05).

Conclusion

CEUS is accurate in grading renal artery stenosis, and it may represent the method of choice in diagnosing renal artery stenosis.

An investigation of the detection capability of pulsed wave duplex Doppler of low grade stenosis using ultrasound contrast agent microbubbles - An in-vitro study

OBJECTIVE

The objective of the study was to investigate whether clinically used ultrasonic contrast agents improved the accuracy of spectral Doppler ultrasound in the detection of low grade (<50%) renal artery stenosis. Low grade stenoses in the renal artery are notoriously difficult to reliably detect using Doppler ultrasound due to difficulties such as overlying fat and bowel gas.

METHODS

A range of anatomically-realistic renal artery phantoms with varying low degrees of stenosis (0, 30 and 50%) were constructed and peak velocity data was measured from within the pre-stenotic and mid-stenotic regions in each phantom, for both unenhanced and contrast-enhanced spectral Doppler data acquisitions. The effect of a 20 mm overlying fat layer on the ultrasound beam distortion and phase aberration, and hence on the measured peak velocity data, was also investigated.

RESULTS

The overlying fat layer produced a statistically significant underestimation (p < 0.01) in both the peak velocity and peak velocity ratio [Stenotic Region(Vmax)/Pre-stenotic Region(Vmax)] for the 0% and 30% stenosis models, but not the 50% model. A statistically significant increase (p < 0.01) in the peak velocity was found in the contrast-enhanced Doppler spectra; however, no significant difference was found between the unenhanced and contrast enhanced peak velocity ratio data, which suggests that the ratio metric has better diagnostic accuracy. The peak velocity ratios determined for each of the contrast-enhanced phantoms correctly predicted if the phantom had a stenosis and furthermore correctly classified the degree of stenosis.

CONCLUSION

Contrast-enhanced Doppler ultrasound could significantly assist in the early detection of renal artery disease.

Renal Doppler evaluation in the child with hypertension: a reasonable screening discriminator?

BACKGROUND

Hypertension is diagnosed in 1-5% of children, and 5-10% of those hypertensive children have renovascular disease. The gold standard for a diagnosis of renal artery stenosis is arteriography, and Doppler ultrasound (Doppler US) continues to be advocated as a useful screening test.

OBJECTIVE

The purpose of this study was to determine the utility of Doppler US in children as a screening tool and to better define clinical features of children in whom arteriography should be performed.

MATERIALS AND METHODS

This retrospective study evaluated the imaging and clinical parameters for all children who had a renal US with Doppler followed by a diagnostic arteriogram for the evaluation of hypertension during a 12-year period at a tertiary children's hospital. Sixty-two children were included. We evaluated each child's clinical parameters and placed each child into one of three categories of hypertension: mild, moderate or severe.

RESULTS

Eleven of 17 kidneys with proven renal artery stenosis were detected with Doppler US (sensitivity 64%). Six children with renal artery stenosis were missed by Doppler US, four of whom had segmental artery lesions. Of the children with positive renal artery stenosis on arteriography, all but three (79%) were classified as having moderate to severe hypertension.

CONCLUSION

Doppler US is a useful screening examination when evaluating children with hypertension, detecting renal artery stenosis in most affected children. The clinical risk classifications are helpful in guiding which children should proceed with arteriography regardless of the Doppler US results.

Predictors of diagnostic success with renal artery duplex ultrasonography

BACKGROUND

Renal artery duplex ultrasonography (RA-DUS) is commonly used for the evaluation and follow-up of renal artery atherosclerotic disease. In a complete study, renal artery flow is evaluated from the vessel origin to the intraparenchymal branches. The quality of RA-DUS is in part technologist-dependent, but many factors may affect the ability to complete a diagnostic examination. This study evaluated the clinical and technical factors that predict the ability to obtain a complete RA-DUS examination.

METHODS

A prospective evaluation of all patients undergoing RA-DUS between July 2008 and February 2009 was performed. Factors such as patient age, gender, body mass index, technologists' years of experience, patient care setting (inpatient vs. outpatient), bedside examination, smoking before the examination, fasting status, and recent abdominal surgery were all recorded. Multivariate logistic regression analysis was performed. A p value of ≤ 0.05 was considered significant.

RESULTS

During the study period, 250 patients underwent RA-DUS (mean age: 59.9 ± 17.8 years, 57% [143] female). A total of 87 (35%) examinations were incomplete. This included nondiagnostic examinations which did not exhibit any segment of the renal artery. Factors that were associated with an incomplete examination included technologists' years of experience (OR = 0.92, p = 0.042), bedside examination (OR = 4.17, p = 0.016), and recent abdominal surgery (OR = 3.45, p = 0.047). Body mass index, fasting status, and smoking before the examination did not affect the ability to obtain a complete study.

CONCLUSIONS

One-third of the RA-DUS studies were classified as incomplete by the strict criteria used in this prospective study. An experienced ultrasound technologist is more likely to obtain a complete RA-DUS examination. Recent abdominal surgery and bedside examinations were predictive of a limited examination as well. Vascular laboratories should consider these factors when scheduling examinations so as to obtain complete RA-DUS studies, as well as improve the cost-effectiveness of resource utilization.

Integrated evaluation of hypertensive patients with cardiovascular magnetic resonance

BACKGROUND

Hypertension causes cardiac morbidity and premature mortality. Accurate evaluation to exclude potentially curable causes is important. Cardiovascular Magnetic Resonance and Magnetic Resonance Angiography (CMR/CE-MRA) provide an integrated approach to the assessment of hypertensive patients - a single study can identify certain secondary causes and assess left ventricular (LV) mass and function. The aim of this study was to prospectively evaluate the feasibility of CMR/CE-MRA to define LV dimensions and exclude some secondary causes in a selected group of hypertensives.

METHODS AND RESULTS

Fifty-three hypertensives (46+/-17 years, 18 females) were prospectively studied (early onset hypertension, n=17; drug resistant hypertension, n=23; hypertension with increased creatinine at baseline/after ACEi, n=12; hypertension with peripheral vessel disease, n=1). Study protocol included assessment of LV and aorta, imaging of adrenals and 3D CE-MRA of aorta and renal arteries. Significant abnormalities were found in 13 patients (25%) - renal artery stenosis (n=8), aortic coarctation (n=4), adrenal mass (n=1). Mean LV mass index was increased compared with matched controls. LV systolic dysfunction was found in 9 patients.

CONCLUSIONS

CMR/CE-MRA provides comprehensive evaluation of hypertensive patients and could allow for a unique integrated approach with assessment of LV dimensions as well as detection of some secondary causes.

Ultrasound Contrast Agents in the Study of Kidney Function in Health and Disease

Ultrasound contrast agents are gas filled microbubbles that enhance the ultrasound image. They behave similarly to red blood cells and cross all capillary beds; making contrast enhanced ultrasonography (CEU) a suitable technique to study vasculature and tissue blood flow. Ultrasound contrast agents have been found to be safe after intravenous injection. CEU has been used extensively in the field of cardiology. Currently, study of renal vasculature and renal blood flow requires complicated, time consuming and expensive techniques, which are not commonly used in clinical settings. CEU potentially may serve as a relatively noninvasive and safe technique for studying renal hemodynamics in health and disease. In this article we have reviewed the literature on the use of CEU in the study of kidney disease.