Kidney Sonography by Duplex and Color Doppler
Author:
Sharlene A. Teefey, M.D.
Objectives: Upon the completion of this CME article, the reader will be able to:
1.
Explain the etiology of, list the risk factors for, and describe the duplex and color
Doppler evaluation of renovascular stenosis.
2.
Explain the use of RI and ureteral jets in the evaluation of patients with renal
parenchymal disease and in differentiating obstruction from non-obstruction in the
presence of a dilated collecting system.
3.
Describe the etiology behind the sonographic findings for renal vein thrombosis.
4.
Describe the duplex and color Doppler findings for renal Arteriovenous (AV)
fistulae.
Renovascular Stenosis
Hypertension is one of the most common medical disorders identified in society
today. In the hypertensive population, there is a 0.5% - 5% prevalence of renovascular
hypertension. Though renal artery stenosis may exist in a normotensive patient, over time
the disorder can lead to renal insufficiency, which is why it is important to identify such
patients. The most common cause for renovascular hypertension is atherosclerosis.
Fibromuscular dysplasia is another cause but is much less common. The natural history of
untreated atherosclerotic renal artery stenosis is one of variable progression, resulting in loss
of renal mass (atrophy) and increasing serum creatinine. The rate of disease progression is
about 20% - 25% over 3 years, which is less than earlier studies would have suggested.
However, it is still important to intervene before irreversible renal damage occurs.
Interventions that have been shown to improve or stabilize renal function include surgical
revascularization, percutaneous transluminal angioplasty, and stent placement. Stent
placement is currently the best option with a higher technical success rate and a lower restenosis rate. Two predictors of poor renal outcome and decreased patient survival after
revascularization are a serum creatinine level > 3 mg/dL or a resistive index (RI) ≥ 0.80,
although the latter parameter is less certain. Thus, the importance of detecting renovascular
hypertension early and properly selecting patients for intervention is obvious. There are
several non-invasive imaging tests that can be utilized to diagnose renovascular hypertension
including duplex/color Doppler, MRA, CTA, and ACEI renography. However, none of
these tests predict improvement in renal function after revascularization or intervention.
Who to Evaluate
It is important to understand which patients should undergo further imaging to
evaluate for renovascular hypertension. Hypertensive patients with well-controlled
hypertension, or those with normal renal function or stable mild renal insufficiency require
no imaging. Factors favoring further evaluation include uncontrolled hypertension, abrupt
onset of moderate or severe hypertension (at less than 30 or more than 50 years of age);
deteriorating renal function, bilateral high grade renal artery stenosis, high grade stenosis in a
single functioning kidney, flash pulmonary edema, or progressive renal failure while using an
ACE inhibitor.
There have been several studies that have attempted to evaluate the renal arteries for
stenosis with duplex and color Doppler over the past several years. In brief review, the
normal renal artery has low resistance flow with continuous forward flow in diastole. The
renal vein has continuous low velocity flow, which is mildly phasic. While some researchers
have recommended evaluation of the main renal arteries (peak systolic velocity and renal
artery to aortic ratio), others have recommended evaluation of the intrarenal vasculature
(early systolic peak, acceleration, and acceleration time). Those studies that evaluated the
main renal artery showed a high sensitivity and specificity for diagnosing renal artery stenosis
using a peak systolic velocity of >180 - 200 cm/second and or a renal artery to aortic ratio of
>3.0 - 3.5 (figures 1&2). Other studies that investigated the downstream hemodynamic
effects from renal artery stenosis showed that waveform morphology, acceleration, and
acceleration time were sensitive and very specific for the diagnosis of renal artery stenosis.
Unfortunately, other researchers were unable to reproduce these latter results and showed
significant overlap between groups of patients with non-stenotic and moderately stenotic
renal arteries. In addition, one study showed that the early systolic peak, reported to have a
high specificity and sensitivity for renal artery stenosis, is often absent in the normal patient.
It is also evident now that many factors can affect waveform pattern such as vessel elasticity
and cardiac output. Atherosclerotic changes may decrease the tardus parvum effect, left
heart failure or left ventricular outflow obstruction may decrease early systolic acceleration,
and aortic insufficiency or hyperkinetic states may increase early systolic acceleration.
Renal Parenchymal Disease
The resistive index (RI) has been used to evaluate renal parenchymal disease. Past
studies have shown that a resistive index of ≥ 0.70 is suggestive of tubulo-interstitial disease
or a vasculitis, whereas patients with a purely glomerular disease often had a resistive index
of < 0.70. These same authors also showed that RI’s are useful for differentiating the more
common causes of acute renal failure, such as acute tubular necrosis and pre-renal failure.
Patients with acute tubular necrosis (excluding hepatorenal syndrome) often had a resistive
index of ≥ 0.75 whereas those with pre-renal failure (excluding patients with severe,
prolonged pre-renal failure which can lead to acute tubular necrosis), had a value of < 0.75.
However, in a study at our institution of 43 patients with biopsy-proven renal parenchymal
disease, we showed that RI does not reliably distinguish glomerular disease from interstitial
disease or vasculopathy and correlates poorly with renal function. Furthermore, our study
showed that greater than 50% of patients had a combination of histological findings rather
than changes isolated to the glomerular, interstitial, or vascular compartment that further
lessened the value of an RI for distinguishing among the different types of parenchymal
disease.
Hydronephrosis
Today, when a patient presents with acute flank pain, it is standard to perform a
renal stone protocol CT scan. Nevertheless, if a dilated collecting system is detected with
sonography, it is important to attempt to differentiate obstructive from non-obstructive
dilatation. Prior studies have suggested that intrarenal Doppler analysis of RI can be used to
make this distinction. It has been shown that in the setting of obstructive dilatation, renal
vascular resistance increases due to the presence of many different chemical mediators
including kallikrien, and a potent renal vasoconstrictor, thromboxane. Studies have reported
that the RI, which measures arterial vascular resistance, is elevated (> 0.70) in the setting of
obstructive dilatation. In a group of patients with acute and chronic obstructive dilatation,
this value was shown to have a specificity of 88% and a sensitivity of 92%. On the other
hand, other researchers have not been able to reproduce these findings and have shown a
sensitivity (using a RI threshold of 0.70) of only 30% - 47%, even in the setting of a highgrade obstruction. They did show, however, that an elevated RI in the proper clinical setting
was highly specific for obstruction. There are several reasons why an RI may have a low
sensitivity including scanning patients with an early ( six hours) partial or intermittent
obstruction, a forniceal rupture, and medications (non-steroidal anti-inflammatory drugs or
NSAIDs, low-dose aspirin, and anti-hypertensive agents). Nevertheless, it is unclear why the
sensitivity of an RI is low in the setting of a high-grade obstruction.
An alternative to RI’s in differentiating obstructive from non-obstructive dilatation is
ureteral jet analysis. Ureteral jets are visualized due to density differences in bladder and
ureteral urine. Hydration increases jet frequency and enhances asymmetry between the
normal and abnormal sides. The absence of a ureteral jet suggests a high-grade obstruction
and has been shown to have a sensitivity of 100% and specificity of 91% (figure 3).
However, a normal ureteral jet does not exclude a partial or low-grade obstruction or a nonobstructing stone.
Renal Vein Thrombosis
Renal vein thrombosis has many different etiologies in adults including nephrotic
syndrome, membranous glomerulonephritis, systemic lupus erythematosis, pyelonephritis,
neoplasm, a hypercoagulable state, or trauma. It may also be caused by extrinsic
compression of the renal vein from acute pancreatitis, retroperitoneal fibrosis, hemorrhage,
or a neoplasm. Patients frequently present with flank pain and hematuria if the renal vein
thrombosis is acute but may be asymptomatic if the thrombosis is chronic. At sonography,
the kidney is enlarged and hypoechoic with poor corticomedullary differentiation. There
may be patchy areas of increased echogenicity due to hemorrhage. At color Doppler, there
will be no detectable flow in the renal vein or partial flow if the thrombus is non-occlusive
(figure 4). However, if the thrombus is chronic, collaterals vessels can be detected. It is
important not to mistake these collaterals for a patent renal vein and to search the entire
renal vein for evidence of thrombus including the inferior vena cava.
When renal vein thrombosis is present in a native kidney, the renal artery waveform
will appear normal due to the rapid development of venous collaterals within 24 hours of the
thrombotic event. However, in a transplanted kidney, the renal artery will show pandiastolic flow reversal.
Renal cell carcinoma is another important cause of renal vein thrombosis. The
thrombus can extend into the renal vein in 10% - 15% of patients, into the inferior vena
cava (IVC) in 4% - 12%, and into the right atrium in 0.5% - 2% (figure 5). It is important to
determine the precise extent of the thrombus because the surgical approach will be decided
based upon this information. Color Doppler has been shown to be very sensitive and
specific in making this determination.
Arteriovenous Fistula
Renal arteriovenous (AV) fistulae usually occur in the setting of a prior renal biopsy
whether in a native or transplanted kidney. Other etiologies include neoplasm, erosion of a
renal artery aneurysm into a vein, or other penetrating trauma, such as a stab wound or
nephrostomy tube placement. Most patients are asymptomatic but occasionally,
hypertension, hemorrhage, hematuria, urinary tract obstruction, or renal insufficiency will
occur. High output right heart failure is rare. Treatment is generally conservative, as most
renal AV fistulae will spontaneously resolve by four weeks. Occasionally, coil embolization
is required. Duplex and color Doppler findings suggestive of a renal AV fistula include an
increased arterial peak systolic and end diastolic velocity, a decreased resistive index, as well
as an arterialization of the venous waveform, and perivascular tissue vibration.
Pseudoaneurysm
Pseudoaneurysms are caused by penetrating trauma, such as from a stab wound,
percutaneous biopsy, nephrostomy tube placement, or surgery. It has also been reported in
tumors (angiomyolipomas), in patients who undergo partial nephrectomy, and in the setting
of inflammation (vasculitis) or infection. Patients may present with flank pain, gross
hematuria, or hypertension. On ultrasound, a “to and fro” arterial waveform is seen in the
pseudoaneurysm neck. The “yin-yang” or swirling appearance is classically seen in the flow
lumen. Pseudoaneurysms can be observed if small and asymptomatic, as most resolve, but if
they are large or symptomatic, a coil embolization may be required.
Figures:
1
Left renal artery stenosis with focal color aliasing at the vessel origin.
2
Elevated peak systolic velocity through a left renal artery stenosis.
3
Absent right ureteral jet in a patient with high-grade ureteral obstruction from a
distal right ureterovesical junction stone.
4
Glomerulonephritis patient with right renal vein thrombosis.
5
Renal cell carcinoma with inferior vena cava thrombus
References or Suggested Reading:
1.
Pepe P, Motta L, Pennisi M, Aragona F. Functional evaluation of the urinary tract by
color-Doppler ultrasonography (CDU) in 100 patients with renal colic. Eur J Radiol
2005; 53: 131-135.
2.
Li JC, Ji ZG, Cai S, et al. Evaluation of severe transplant renal artery stenosis with
Doppler sonography. J Clin Ultrasound. 2005; 33: 261-9.
3.
Kilic S, Altinok MT, Ipek D, et al. Color Doppler sonography examination of
partially obstructed kidneys associated with ureteropelvic junction stone before and
after percutaneous nephrolithotripsy: preliminary report. Int J Urol. 2005; 12: 429-35.
4.
Rademacher J, Chavan A, Bleck J, Vitzthum A, Stoess B, Gebel M, Galanski M,
Koch K, Haller H. Use of Doppler ultrasonography to predict the outcome of
therapy for renal artery stenosis. N Engl J Med 2001;344:410-417
5.
Stavros AT, Parker SH, Yakes WF, Chantelois AE, Burke BJ, Meyers PR, Schenck
JJ. Segmental stenosis of the renal artery: pattern recognition of tardus and parvus
abnormalities with duplex sonography. Radiology 1992; 184: 487-492.
6.
Platt JF, Rubin JM, Ellis JH. Distinction between obstructive and non-obstructive
pyelocaliectasis with duplex Doppler sonography. AJR 1989; 153: 997-1000.
7.
Deyoe LA, Cronan JJ, Breslaw BH, Ridlen MS. New techniques of ultrasound and
color Doppler in the prospective evaluation of acute renal obstruction. Do they
replace the intravenous urogram? Abd Imaging 1995; 20: 58-63.
8.
Tublin ME, Dodd GD, Verdile VP. Acute renal colic: diagnosis with duplex
Doppler US. Radiology 1994; 193: 697-701.
9.
Baker SM, Middleton WD. Color Doppler sonography of ureteral jets of normal
volunteers: importance of the relative specific gravity of urine in the ureter and
bladder. AJR 1992; 159: 773-775.
10.
Burge HJ, Middleton WD, McClennan BL, Hildebolt CF. Ureteral jets in healthy
subjects and in patients with unilateral ureteral calculi: comparison with color
Doppler US. Radiology 1991; 180: 437-442.
11.
Halpern EJ, Deane CR, Needleman L, Merton DA, East SA. Normal renal artery
spectral Doppler waveform: a closer look. Radiology 1995; 196: 667-673.
12.
van der Hulst VPM, van Baalen J, Kool LS, van Bockel JH, van Erkel Ar, Ilgun J,
Pattynama PM. Renal artery stenosis: endovascular flow wire study for validation of
Doppler US. Radiology 1996; 200: 165-168.
13.
Kliewer MA, Tupler RH, Carroll BA, Paine SS, Kreigshauser JS, Hertzberg BS,
Svetkey LP. Renal artery stenosis: analysis of Doppler waveform parameters and
tardus-parvus pattern. Radiology 1993; 189:779-787.
14.
Platt JF, Ellis JH, Rubin JM, DiPietro MA, Sedman AB. Intrarenal arterial Doppler
sonography in patients with non-obstructive renal disease: correlation of resistive
index with biopsy findings. AJR 1990; 154:1223-1227.
15.
Platt JF, Rubin JM, Ellis JH. Acute renal failure: possible role of duplex Doppler US
in distinction between acute pre-renal failure and acute tubular necrosis. Radiology
1991; 179:419-423.
16.
Middleton WD, Kellman GM, Melson GL, Madrazo BL. Postbiopsy renal transplant
arteriovenous fistulas: color Doppler US characteristics. Radiology 1989; 171:253257.
17.
Kliewer MA, Tupler RH, Hertzberg BS, Paine SS, DeLong DM, Svetkey LP, Carroll
BA. Doppler evaluation of renal artery stenosis: interobserver agreement in the
interpretation of waveform morphology. AJR 1994; 162:1371-1376.
18.
Platt JF, Rubin JM, Ellis JH, DiPietro MA. Duplex Doppler US of the kidney:
differentiation of obstructive from non-obstructive dilatation. Radiology 1989;
171:515-517.
About the Author:
Sharlene A. Teefey, M.D. is currently an Associate Professor of Radiology at the
Mallinckrodt Institute of Radiology at Washington University School of Medicine in St.
Louis Missouri. She is a member of numerous societies and organizations including the
American College of Radiology, the Society of Radiologists in Ultrasound, and the American
Institute of Ultrasound in Medicine.
She is a reviewer of manuscripts for Radiology, the American Journal of Roentgenology, and
Radiographics. She has more than 45 publications in peer review medical journals and has
been a speaker at numerous institutions and conferences across the country.
Examination:
1.
In the hypertensive population, there is a _________ prevalence of renovascular
hypertension.
A.
0.05% - 0.1%
B.
0.1% - 0.5%
C.
0.5% - 5%
D.
3% - 9%
E.
8% - 15%
2.
The most common cause for renovascular hypertension is
A.
diabetes
B.
atherosclerosis
C.
fibromuscular dysplasia
D.
smoking
E.
neoplasms
3.
Regarding renovascular stenosis, the rate of disease progression is about 20% - 25%
over
A.
3 months.
B.
9 months.
C.
1 year.
D.
3 years.
E.
5 years.
4.
Regarding renovascular stenosis, an intervention designed to preserve renal function
may include
A.
surgical revascularization
B.
renal transplant
C.
aspirin therapy
D.
anticoagulant therapy
E.
treatment with an ACE inhibitor
5.
A predictor of poor renal outcome and decreased patient survival after
revascularization in renovascular stenosis is a serum creatinine level of
A.
< 3 mg/dL
B.
< 0.3 mg/dL
C.
> 0.03 mg/dL
D.
> 0.3 mg/dL
E.
>3 mg/dL
6.
Non-invasive imaging techniques to diagnose renovascular hypertension include all
of the following EXCEPT
A.
duplex/color Doppler
B.
MRA
C.
CTA
D.
arteriography
E.
ACEI renography
7.
Hypertensive patients with well-controlled hypertension, or those with normal renal
function or stable mild renal insufficiency require
A.
no imaging.
B.
duplex or color Doppler imaging
C.
MRA or CTA
D.
ACEI renography
E.
arteriography
8.
In renovascular stenosis, factors favoring further evaluation include all of the
following EXCEPT
A.
deteriorating renal function
B.
uncontrolled hypertension
C.
flash pulmonary edema
D.
high grade stenosis in a single functioning kidney
E.
well-controlled hypertension with stable mild renal insufficiency
9.
In review of normal renal blood flow,
A.
The normal renal artery has high resistance flow with continuous forward
flow in systole.
B.
The renal vein has intermittent high velocity flow, which is not phasic.
C.
The normal renal artery has low resistance flow with continuous forward
flow in diastole.
D.
The renal vein has high resistance flow with continuous forward flow in
diastole.
E.
The normal renal artery has continuous low velocity flow, which is mildly
phasic.
10.
In studies evaluating the main renal artery, they showed a high sensitivity and
specificity for diagnosing renal artery stenosis using a peak systolic velocity of
A.
> 100 - 120 cm/second
B.
> 140 - 160 cm/second
C.
> 180 - 200 cm/second
D.
> 240 - 260 cm/second
E.
> 280 - 300 cm/second.
11.
Though there are limitations to the clinical application of resistive index (RI) values,
patients with a purely glomerular disease often had a resistive index that is
A.
< 0.70.
B.
< 0.40
C.
> 0.40
D.
> 0.70
E.
> 0.75
12.
It has been shown that in the setting of obstructive dilatation, renal vascular
resistance increases due to the presence of many different chemical mediators
including
A.
NSAIDs
B.
kallikrien
C.
D.
E.
cytokine
low-dose aspirin
atenolol
13.
All of the following statements are true EXCEPT
A.
Ureteral jets are visualized due to density differences in bladder and ureteral
urine.
B.
Hydration increases jet frequency and enhances asymmetry between the
normal and abnormal sides.
C.
A normal ureteral jet excludes a partial or low-grade obstruction or a nonobstructing stone.
D.
An alternative to RI in differentiating obstructive from non-obstructive
dilatation is ureteral jet analysis.
E.
The absence of a ureteral jet is associated with high-grade obstruction at a
sensitivity of 100% and a specificity of 91%.
14.
Renal vein thrombosis has many different etiologies for its development in adults,
which include all of the following EXCEPT
A.
nephrotic syndrome
B.
systemic lupus erythematosis
C.
pyelonephritis
D.
intrinsic compression of the renal vein from a fibroma
E.
a hypercoagulable state
15.
At sonography for renal vein thrombosis,
A.
the kidney is enlarged and hypoechoic with poor corticomedullary
differentiation.
B.
there may be patchy areas of decreased echogenicity due to hemorrhage.
C.
the kidney is small and hypoechoic but with no corticomedullary
differentiation.
D.
at color Doppler sonography, a bright color image will be noted within the
renal vein.
E.
the kidney is small but hyperechoic with distinct corticomedullary
differentiation.
16.
When renal vein thrombosis occurs in a transplanted kidney, the renal artery will
A.
show a “to and fro” waveform
B.
appear normal due to the rapid development of venous collaterals
C.
have an intermittent high velocity flow that is phasic
D.
show pan-diastolic flow reversal
E.
have low resistance flow with continuous forward flow in diastole
17.
Renal cell carcinoma is another important cause of renal vein thrombosis. The
thrombus can extend up into the right atrium in ________ of cases.
A.
20% - 25%
B.
10% - 15%
C.
4 - 12%
D.
3% - 5%
E.
0.5% - 2%
18.
Renal arteriovenous (AV) fistulae usually occur in the setting of a (an)
A.
congenital birth defect
B.
prior renal biopsy
C.
renal stone
D.
obstruction disorder
E.
duplicated collecting system
19.
Regarding renal arteriovenous (AV) fistulae, all of the following statements are true
EXCEPT
A.
On duplex and color Doppler sonography, there is an increased arterial peak
systolic and end diastolic velocity
B.
The fistulae are usually symptomatic leading to hypertension that requires
intervention.
C.
On duplex and color Doppler sonography, there is a decreased resistive
index, as well as perivascular tissue vibration.
D.
Rarely, the fistula can lead to high output right heart failure.
E.
Treatment is generally conservative, as most renal AV fistulae will
spontaneously resolve by four weeks.
20.
Pseudoaneurysms of the kidney are caused by all of the following EXCEPT
A.
penetrating trauma, such as from a percutaneous biopsy
B.
inflammation (vasculitis) or infection
C.
tumors, such as angiomyolipomas
D.
partial nephrectomy procedures
E.
nephrotic syndrome