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Continue to enjoy the benefits of your RSNA membership. Other renal vascular pathologies include AVF, dissection, vasculitis, and pseudoaneurysm formation. Renal artery stenosis may result from a diverse group of conditions, including atherosclerosis, FMD, vasculitis, neurofibromatosis, congenital bands, extrinsic compression, and radiation.
FMD is usually found in patients younger than 40 years of age and affects the mid and distal segments of the renal arteries. Both atherosclerotic and FMD-related lesions gradually progress over time. These progressive stenotic lesions eventually lead to renal hypoperfusion, which in turn leads to impairment of renal function, renal atrophy, and ischemic nephropathy.
In addition to development of end-stage renal disease, patients with renovascular disease also develop hypertension, which is triggered by a complex set of pressor signals, including activation of the renin-angiotensin system, recruitment of oxidative stress pathways, and sympathoadrenergic activation.
The threshold level of renal artery stenosis that produces hypertension or ischemic damage is uncertain, and likely varies among patients. In the last decade, clinical interest has focused on the role of renal ischemia in the etiology of chronic renal insufficiency and renovascular hypertension, and the search for a potential cure or a way to prevent the development of chronic renal dysfunction.
Although renal artery disease represents the most common correctable cause of hypertension, the topic of renovascularization restoration of renal perfusion via either vascular stenting or angioplasty for treatment of atherosclerotic renovascular disease has become increasingly controversial. The CORAL Cardiovascular Outcomes in Renal Atherosclerotic Lesions study found that renal artery stenting did not confer a significant benefit for patients with renal artery stenosis and hypertension, or chronic kidney disease.
Despite this controversy, renovascularization is still performed by many institutions, and the number of requests to perform renal duplex examination is increasing. Does this mean, however, that we should seek to diagnose renal artery disease in every patient with hypertension or renal insufficiency?
To do so could be expensive and not cost-effective. Furthermore, intervention for renal artery disease may be risky e. Considering these points, we believe that evaluation for renal artery stenosis and possible revascularization should be performed in the following groups of patients: 1 young patients with severe hypertension; 2 patients with abrupt onset of hypertension, rapidly accelerating hypertension, or malignant hypertension; 3 patients with refractory hypertension that is difficult to control despite a suitable treatment program; 4 patients with concomitant hypertension and deteriorating renal function; 5 patients with renal insufficiency and discrepant kidney size implying renal artery stenosis ; 6 patients with recurrent flash pulmonary edema; or 7 patients with diagnosed FMD.
As noted previously, color flow imaging is used to identify blood flow abnormalities that may be stenosis-related, but spectral Doppler measurements provide quantitative data that are essential for determining the severity of stenosis. The following general comments about the Doppler-based diagnosis of renal artery stenosis are noteworthy:.
The principal Doppler ultrasound criterion for renal artery stenosis is elevated blood flow velocity within a stenotic segment of the vessel. Proper assignment of the Doppler angle is essential for reliable measurement of stenosis-related velocity elevation. A Doppler-to-vessel angle of 60 degrees or less is mandatory to ensure that velocity information is accurate.
A significant stenosis is accompanied by poststenotic flow disturbance turbulence Fig. Although disturbed flow is a useful beacon for the presence of stenosis, it is neither quantitative nor specific.
Disturbed flow may occur without significant stenosis and may be related to lesser degrees of narrowing or vessel tortuosity. The presence of color bruit artifacts, on the other hand, usually indicates a significant flow abnormality.
Arterial waveforms within the segmental or interlobar arteries of the kidney may be scrutinized for evidence of damping, which is a downstream manifestation of significant renal artery stenosis. The most important downstream findings are the absence of an early systolic peak ESP , a prolonged systolic acceleration time, and a reduced acceleration index tardus-parvus waveform.
Color flow and pulsed Doppler are both required to optimize detection of significant renal artery stenosis. Spectral analysis of the PSV in the stenosis allows determination of the severity of the stenosis. As mentioned earlier, normal blood flow in the renal artery and its branches demonstrates a low-resistance pattern with a rapid peak to systole and forward flow throughout diastole.
Numerous Doppler velocity criteria have been proposed to diagnose hemodynamically significant renal artery stenosis. In theory, the RAR compensates for hemodynamic variability between patients. Older adult patients, particularly patients with severe cardiac disease and poor cardiac output, may demonstrate low PSVs even in regions of stenosis.
Damping of the intrarenal arterial waveform tardus-parvus waveform is another valuable criterion for the diagnosis of renal artery stenosis see Fig. Damping is defined numerically with the acceleration index or the acceleration time.
Both of these measures reflect the rate of systolic acceleration, which is slower than normal downstream from a hemodynamically significant stenosis. Some authors use an acceleration time of 0. An ideal survey method for renal artery stenosis would be one that is accurate, quick, and easy to perform.
This is the appeal of the indirect diagnosis of renal artery stenosis through the detection of damped Doppler waveforms in segmental or interlobar arteries within the kidney. For an experienced sonographer, the acquisition of intrarenal arterial Doppler signals is relatively easy, and therefore the examination is brief and successful in most individuals.
It has long been recognized that renal artery stenosis can cause pulsus tardus and parvus tardus-parvus changes in intrarenal arterial flow signals see Fig. It would be very convenient to simply look for these flow changes in the kidneys and thereby diagnose renal artery stenosis without the arduous task of finding and directly evaluating the renal arteries. Unfortunately, the accuracy of this diagnostic method is questionable. But other literature, on the basis of the same Doppler parameters, indicated poor results ranging from moderate accuracy to complete absence of correlation between Doppler and angiographic findings.
So, what is the role of intrarenal Doppler assessment? This is because the shape of intrarenal arterial waveforms is affected by multiple factors, including the stiffness compliance of the arteries, the resistance of the microcirculation, and inflow phenomena such as renal artery stenosis. To make matters worse, damped intrarenal waveforms can occasionally be seen in the absence of significant renal artery stenosis in patients with aortic stenosis or aortic occlusion.
Accurate waveform analysis requires adequate placement of the sample volume in the segmental artery branch. Waveforms obtained with sample volumes that are too large or not adequately located may appear abnormal and suggest proximal disease. We recommend that multiple tracings be obtained from a vessel with suspected tardus-parvus waveforms to confirm the abnormality.
A normal waveform can appear abnormal because of poor technique, but an abnormal waveform cannot be normalized. Because intrarenal Doppler waveform analysis has not been consistently accurate, we do not recommend the exclusive use of hilar waveform analysis for the diagnosis of renal artery stenosis. However, this is not meant to suggest that intra-arterial waveform findings should be ignored.
We always evaluate acceleration and waveform shape in the intrarenal arteries in conjunction with direct renal artery interrogation. The detection of abnormal waveforms confirms the hemodynamic significance of a main renal artery stenosis. Furthermore, damped intrarenal arterial signals may indicate occult stenosis of the main renal artery, a duplicated renal artery, or a segmental artery. This is a particularly important finding when the direct examination of the main renal arteries is technically limited.
It has been suggested that the downstream effects of renal artery stenosis can be diagnosed merely by visual inspection of the shape of the segmental or interlobar Doppler waveforms. The initial systolic peak is either absent or grossly rounded in patients with severe ipsilateral stenosis, as illustrated in Fig. We recommend comparing intrarenal waveforms from both kidneys to assess the difference in systolic upstroke.
Subtle changes may be noted, indicating underlying stenosis. Loss of the early systolic peak ESP is associated with significant renal artery stenosis. The ESP is recognized as the initial acceleration phase in systole that is followed by a short acceleration phase and a second systolic peak.
Unfortunately, the ESP is not seen consistently in all patients. In our practice, some of the interpreting physicians choose visual inspection rather than measurement of the acceleration index or acceleration time for intrarenal waveform analysis. Doppler assessment of the renal arteries is also valuable following revascularization with angioplasty, bypass, or stent placement.
Measurement of renal artery PSV is used to assess residual or recurrent stenosis after therapy. There is a reduction in PSV in the stenotic region following successful angioplasty and stent placement. A Renal Doppler ultrasound gives information about the presence and direction of blood flow in the blood vessels of kidneys renal blood vessels.
There are different types of Doppler ultrasound tests, namely, colour Doppler , power Doppler, spectral Doppler, duplex Doppler and continuous wave Doppler. There are no contraindications for this test. This test is also ordered during pregnancy. Nicotine may narrow blood vessels and give false results. Therefore, you may need to stop using nicotine-containing products, like cigarettes and chewing tobacco, two hours before the test. Usually, no discomfort is felt during the test. The gel may feel cold unless it is first warmed to body temperature.
You will occasionally feel the pressure of the transducer, which can be a little uncomfortable but should not hurt.
The procedure is painless and non-invasive, with no radiation involved. No risk is associated with this test. In some cases, your medical practitioner may order additional tests, such as arteriography, to further evaluate abnormal findings and determine the course of treatment. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.
En - English. Search Doctors. Yoga And Fitness. Other Topics. There may be a slight delay in the audio. What is a Renal Doppler Ultrasound? Who cannot have a Renal Doppler Ultrasound? Why is a Renal Doppler Ultrasound done? Healthcare practitioners may order this test for the following purposes: To look for renal hypertension, especially when the results of an angiogram test are ambiguous. An angiogram is an x-ray test that determines blockages in blood vessels.
Lukas M. Trunz ; Rashmi Balasubramanya. Authors Lukas M. Trunz 1 ; Rashmi Balasubramanya. Renal Doppler ultrasound is routinely performed because it is a useful technique for evaluating a wide range of various renal pathologic conditions. An understanding of normal anatomy, as well as important anatomic variants, as well as basic physical concepts, are necessary for correct interpretation.
This activity outlines the vascular anatomy, imaging indications, and technique and briefly reviews some of the common pathologies where it may be used by an interprofessional team.
Objectives: Outline the common renal vascular anatomy. Summarize the common indications for a renal Doppler ultrasound examination for native as well as transplant kidneys. Explain the typical equipment required for a renal Doppler ultrasound used by an interprofessional team.
Access free multiple choice questions on this topic. Doppler ultrasound US is a well-established and useful technique for evaluating the renovascular system and associated pathologic conditions. As with other US examinations, advantages include its noninvasive nature, relatively low-costs, and generally well-tolerated. However, the technique is highly operator-dependent and can be time-consuming.
Furthermore, the interpretation of renal Doppler US examinations might be challenging for those with limited experience or those unfamiliar with fundamental concepts and nomenclature. Nevertheless, due to its benefits, the American College of Radiology ACR Appropriateness Criteria guidelines rate renal Doppler US as appropriate or even first-line imaging technique in various clinical scenarios, especially in patients with decreased renal function or renal transplants when contrast administration for computed tomography or magnetic resonance imaging examinations might be problematic.
The main renal arteries are approximately 4 to 6 cm long with a 5 to 6 mm diameter. The right renal artery, which is longer than the left, arises from the anterolateral aorta and runs in an inferior course posterior to the inferior vena cava IVC to reach the right kidney.
The left renal artery arises more lateral of the aorta and courses almost horizontally to the left kidney posterior to the left renal vein.
Before entering the renal hilum and parenchyma, the main renal artery divides into five segmental branches, including apical, superior, middle, inferior, and posterior segmental arteries. The segmental arteries supply end arteries to the renal parenchyma and divide further into lobar, interlobar, arcuate, and interlobular arteries.
The interlobular arteries supply the afferent glomerular arterioles, which, in turn, feed into the glomeruli. The renal veins generally lie anterior to the renal arteries at the renal hilum. The left renal vein measures 6 to 10 cm in length and is significantly longer than the right renal vein, which measures 2 to 4 cm. The left renal vein passes between the aorta and the superior mesenteric artery before entering the IVC medially. During its course, the left renal vein receives almost always blood from the left adrenal and gonadal veins and, in the majority of patients, from the lumbar veins.
Doppler US examination of the renal vasculature plays a critical role in the evaluation of native as well as transplanted kidneys. There are no absolute contraindications to perform a renal Doppler US examination.
Ultrasound machines used for Doppler US examinations need to be able to perform Duplex scanning, which refers to the combination of 2D B-mode imaging and pulsed Doppler data acquisition. This usually includes three types of Doppler: color Doppler to obtain flow information such as direction and magnitude of flow , power Doppler to visualize subtle and slow blood flow at the expense of directional and quantitative flow information , and spectral Doppler to show blood flow velocity over time as a waveform.
Probe selection should be based on body habitus. In general, a lower frequency, the curvilinear transducer, is preferred typically 3.
However, a 6 to 12 MHz linear transducer might be used to improve flow detection in thin or pediatric patients. Interpreting physicians should have a comprehensive understanding of renal Doppler US. That includes knowledge about study indications and limitations, anatomy and pathophysiology of the examined organ system, and the ability to correlate additional medical information with the sonographic findings.
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