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Potential Role of Duplex Doppler
Sonography in Acute Renal Colic
Catherine Roy, MD,1 Christine Tuchmann, MD,1 Dominique Pfleger, MD,1 Stéphane Guth, MD,1
Christian Saussine, MD,2 Didier Jacqmin, MD2
1
Department of Radiology B, Les Hôpitaux Universitaires de Strasbourg, Hôpital Civil, BP 426,
F-67091 Strasbourg, France
2
Department of Urology, Les Hôpitaux Universitaires de Strasbourg, Hôpital Civil, BP 426,
F-67091 Strasbourg, France
Received 21 January 1998; accepted 18 June 1998
ABSTRACT: Purpose. We assessed the value of renal
duplex Doppler sonography in diagnosing obstruction
in patients with acute renal colic.
Methods. We compared the results of renal duplex
Doppler sonography with those of intravenous urography (IVU) in 65 patients presenting with symptoms
of renal colic. The Doppler spectral waveforms were
used to calculate the resistance index (RI). The difference between the mean RIs (⌬RI) in the 2 kidneys was
calculated for each patient. The sensitivity, specificity,
and accuracy of ⌬RI for the diagnosis of obstruction
were calculated with several discriminatory thresholds.
Results. All patients had an obstruction on IVU.
When a high ⌬RI threshold for obstruction (⌬RI ⱖ 0.1)
was applied, the sensitivity and specificity of duplex
Doppler sonography were 10% and 80%, respectively.
When the ⌬RI threshold was decreased, the sensitivity
increased but the specificity decreased, and both remained quite low. Twelve patients had a lower mean
RI in the obstructed kidney than in the normal contralateral kidney. Among 14 patients without pyelocaliceal dilatation, the sensitivity of duplex Doppler sonography was 70% with a ⌬RI threshold of 0.03.
Conclusions. Duplex Doppler sonography is not
sensitive enough to diagnose obstruction in patients
with acute renal colic. © 1998 John Wiley & Sons, Inc.
J Clin Ultrasound 26:427–432, 1998.
Keywords: kidney; blood supply, kidney; Doppler ultrasonography; kidney, stenosis; kidney, obstruction;
hydronephrosis
Correspondence to: C. Roy
© 1998 John Wiley & Sons, Inc.
CCC 0091-2751/98/090427-06
VOL. 26, NO. 9, NOVEMBER/DECEMBER 1998
S
onography is commonly used as the initial imaging procedure in the evaluation of patients
with suspected renal obstruction. Gray-scale sonography is quite sensitive for the detection of
dilatation of the collecting system. However, pyelocaliectasis identified by sonography is certainly not synonymous with true obstruction. Duplex Doppler sonography has recently been
reported to be an excellent noninvasive technique
for the diagnosis of acute and chronic urinary
tract obstruction. Previous clinical studies have
shown that duplex Doppler sonography has the
potential to provide physiologic information about
renal arterial resistance.1–4 The resistance index
(RI) has been used to quantify the changes in renal arterial Doppler spectra that occur with obstruction. Obstruction produces an elevation of RI
that is not found in nonobstructive dilatation.
Therefore, duplex Doppler imaging appears to be
an attractive adjunct in evaluating the dilated,
possibly obstructed kidney. It has been reported
that a unilaterally elevated mean RI of more than
0.7 and a difference of more than 0.1 between the
mean RIs in a patient’s symptomatic and contralateral asymptomatic kidneys (⌬RI) are highly
sensitive and specific signs for the diagnosis of
obstruction.1–5 However, our own routine experience has shown these signs to be less useful.
We undertook a retrospective study of a series
of 65 patients presenting with acute renal colic to
determine the diagnostic sensitivity and specificity of duplex Doppler sonography. We focused on
the difference between the mean RI in each patient’s 2 kidneys (⌬RI) and compared results of
duplex Doppler sonography and intravenous
427
ROY ET AL
urography (IVU), which remains the gold standard for diagnosing urinary tract obstruction.
PATIENTS AND METHODS
Between December 1995 and January 1997, 65
patients presenting with acute renal colic and
strongly suspected of having ureteral calculus obstruction after initial clinical examination in the
general emergency room were immediately investigated with color and duplex Doppler sonography
and IVU upon admission to the department of
urology. For this retrospective study, we reviewed
the medical records, sonograms, and videotapes of
the sonography and IVU examinations.
There were 19 women and 46 men with an age
range of 18–61 years (mean, 32.5 years). Their
symptoms had lasted less than 24 hours. Fifteen
patients had received antispasmodic [phloroglucinol (Spasfon)] or nonsteroidal anti-inflammatory (ketoprofen) drugs before imaging examinations. All patients had normal hydration status.
None of them had previous kidney disease.
All patients underwent sonography first followed immediately by IVU. Ultrasound examinations were performed using a commercially available scanner (P 700; Philips, Paris, France) with a
3.5-MHz transducer. All patients were examined
first by gray-scale sonography of both kidneys for
detection of hydronephrosis, manifested as separation of the renal sinus echoes with a tubular
configuration of the dilated calices. Color and
pulsed Doppler evaluations of intrarenal arteries
were performed on each kidney. Doppler waveforms were obtained from interlobar arteries
along the border of the medullary pyramids.
Doppler traces were optimized by using the lowest pulse repetition frequency possible without
aliasing, the highest gain without background
noise, a low wall filter (100 Hz), and a 2–4-mm
Doppler gate. Three samplings were recorded
from the upper, middle, and lower parts of each
kidney. Only waveforms that were identical for at
least 3 consecutive heartbeats were analyzed. The
RI [(peak systolic velocity − minimum enddiastolic velocity)/peak systolic velocity] was determined from the Doppler waveforms using the
built-in calipers and software of the ultrasound
scanner. The mean RI was calculated as the average from at least 9 waveforms for each kidney.
The difference between the mean RIs of the 2 kidneys (⌬RI) was calculated for each patient.
IVU was then done to detect signs of urinary
tract obstruction. The diagnosis of obstruction
was made on the basis of a delayed visualization
of the nephrogram and opacification of the collect428
ing system and/or the presence of a persistent column of contrast material in a dilated collecting
system. Obstruction was classified as either highgrade or low-grade. The diagnosis of high-grade
obstruction was made when visualization of the
nephrogram and opacification of the collecting
system were substantially delayed (up to 4 minutes). Conversely, a low-grade obstruction was diagnosed when only a persistent column of contrast was seen in a dilated urinary segment,
without a substantial delay in visualization of the
nephrogram and opacification of the collecting
system. No case was difficult to grade. The IVU
examinations were evaluated in a blinded fashion, without knowledge of sonographic findings.
Doppler examination results were compared
with findings of IVU. The sensitivity and specificity of the ⌬RI for the diagnosis of high-grade obstruction were calculated. The data were then
analyzed to determine whether a change in the
discriminatory threshold for the mean ⌬RI would
improve the sensitivity and specificity for this diagnosis. The ⌬RI value in healthy patients has
been established to be 0.01 with a standard deviation of 0.01.5 Multiple discriminatory thresholds of ⌬RI between 0.03 and 0.1 were examined.
In addition, the ⌬RI data were correlated with the
degree of obstruction, that is, the length of the
delay in opacification of the collecting system on
IVU.
RESULTS
All 65 patients had a unilateral urinary tract obstruction secondary to a calculus confirmed by
IVU. Fifty-nine patients had a high-grade obstruction, and 6 patients had a low-grade obstruction. None of our patients had pyelocaliceal
extravasation. There were no cases of nonobstructive hydronephrosis.
Gray-scale sonography demonstrated dilatation of the pyelocaliceal system in 51 patients. In
14 cases, there was no dilatation. Only 14 patients had a mean RI equal or superior to 0.7 in
the obstructed kidney. None of our patients had
bilateral mean RIs of more than 0.7. The mean RI
value for obstructed kidneys as a group was 0.63
± 0.07. The mean RI value for the normal contralateral kidneys was 0.59 ± 0.04.
The ⌬RI was considered normal (0 or 0.01) in
15 patients with obstruction. The mean ⌬RI for
all patients was 0.044 (± 0.009). The mean ⌬RI
value for patients with high-grade obstruction
was 0.043 ± 0.009. The mean ⌬RI value for patients with low-grade obstruction was 0.055 ±
0.032. Only 7 patients had a ⌬RI equal to or more
JOURNAL OF CLINICAL ULTRASOUND
DUPLEX SONOGRAPHY IN ACUTE RENAL COLIC
than 0.1, and 22 patients had a ⌬RI equal to or
more than 0.05. When a ⌬RI equal to or more
than 0.03 was used as the discriminatory threshold, the sensitivity and specificity of duplex Doppler sonography for the diagnosis of high-grade obstruction were 62% and 33%, respectively (Table
1). When a ⌬RI equal to or more than 0.1 was
used as the discriminatory threshold, the sensitivity and specificity were 10% and 80%, respectively. Further modifications of the discriminatory threshold did not produce better results
(Table 1); reducing the discriminatory threshold
below 0.1 increased sensitivity but markedly reduced specificity.
Twelve patients had a negative ⌬RI, that is,
the mean RI of the obstructed kidney was lower
than that of the normal, nonobstructed contralateral kidney (Figure 1).
There was no correlation between the degree of
obstruction on IVU and the frequency of truepositive Doppler results. Among 59 high-grade
obstructions, true-positive results were obtained
in 37 cases with a ⌬RI threshold of 0.03, in 22
cases with a ⌬RI threshold of 0.05, and in 6 cases
with a ⌬RI threshold of 0.1. Among 6 cases of
low-grade obstruction, true-positive results were
obtained in 4 cases with a ⌬RI threshold of 0.03,
in 3 cases with a ⌬RI threshold of 0.05, and in 1
case with a ⌬RI threshold of 0.1. Analysis of the
data for high-grade obstructed kidneys suggested
no correlation between the severity of obstruction
based on the delay in opacification on IVU and the
value of ⌬RI (Figure 1).
The sensitivity of gray-scale imaging, without
Doppler, based on pelvocaliceal dilatation alone
was 78%. Among 14 patients without pyelocaliceal dilatation, 10 had a high-grade obstruction
on IVU. In this group, 3 ⌬RIs were lower than
0.03 and 7 ⌬RIs were greater than or equal to
0.03, with 3 ⌬RIs greater than or equal to 0.05.
Three patients with low-grade obstruction had
⌬RIs lower than 0.03; the fourth had a ⌬RI of
0.09. The sensitivity of Doppler imaging for de-
TABLE 1
Effect of Modifications in Discriminatory Thresholds on
Diagnosis of High-Grade Obstruction (59 Cases)
⌬RI
Threshold
SE
SP
PPV
NPV
ACC
No. True
Positives
⌬RI ⱖ 0.03
⌬RI ⱖ 0.05
⌬RI ⱖ 0.07
⌬RI ⱖ 0.1
62%
37%
20%
10%
33%
50%
50%
80%
90%
88%
80%
85%
8%
7%
6%
6%
60%
38%
23%
15%
37
22
12
6
Abbreviations: SE, sensitivity; SP, specificity; PPV, positive predictive value; NPV, negative predictive value; ACC, accuracy.
VOL. 26, NO. 9, NOVEMBER/DECEMBER 1998
tecting high-grade obstruction without pyelocaliceal dilatation was 30% with a ⌬RI threshold of
0.05 and 70% with a ⌬RI threshold of 0.03.
DISCUSSION
In the presence of typical acute clinical signs and
symptoms, the demonstration of pyelocaliceal dilatation on sonography is highly suggestive of obstruction. However, gray-scale sonography gives
no functional information on the degree or severity of obstruction.6,7 Many authors have theorized
that acute or chronic urinary tract obstruction
would change the Doppler RI in the affected kidney1,3,6 by increasing renal vascular resistance.8–11
In previous studies, this change consisted of an
increase in the mean RI in the obstructed kidney.
The variability of RI measurements in the same
kidney suggests that a number of RI values
should be averaged before a single representative
value is given.5,12 Mean RI values of 0.58–0.60 for
normal kidneys and of 0.75–0.77 for obstructed
kidneys have been reported.1,12
In an attempt to define a reasonably discriminatory RI value to differentiate obstructive from
nonobstructive pyelocaliectasis, Platt et al1 studied a series of 229 kidneys. The obstructed kidneys had an elevated RI (0.77 ± 0.05) compared
with nonobstructed kidneys with dilatation (0.63
± 0.06). These authors found that a renal arterial
mean RI greater than 0.70 was 92% sensitive,
88% specific, and 90% accurate for the diagnosis
of obstruction.1 On the basis of these data, 0.70 is
a reasonable upper limit for normal intrarenal RI.
In a kidney with a dilated collecting system, an RI
of 0.70 or more is suggestive of obstruction, while
an RI less than 0.70 is suggestive of nonobstructive dilatation.1,12
An unavoidable limitation of Doppler analysis
is that the RI is a nonspecific parameter. Obstruction is not the only cause of an elevated RI. In a
setting of known renal medical disease and pyelocaliectasis, an elevated RI could be due either to
true obstruction or to the renal medical disease
and coexisting nonobstructive dilatation. Therefore, it is important to compare the mean RI values for each kidney in the same patient, looking
for a significant difference in RI between the obstructed kidney and the contralateral normal kidney.13 In 2 studies of patients with acute urinary
tract obstruction, the combination of a mean RI
greater than 0.70 and a difference of more than
0.06–0.10 between the mean RIs of the obstructed
and contralateral nonobstructed kidneys was
found to be highly sensitive and specific for the
diagnosis of urinary tract obstruction.2,4
429
ROY ET AL
FIGURE 1. Relationship between delay in collecting system opacification on intravenous urography and difference in resistance index between symptomatic and asymptomatic kidney (⌬RI).
In our investigation, we retrospectively evaluated the ability of duplex Doppler sonography to
diagnose the cause of acute renal colic. Our results are not comparable to recent studies13–15
with regard to ⌬RI values, although the mean RI
for nonobstructed kidneys was equivalent to that
reported in other studies.2–4 The difference between the mean RI of obstructed and nonobstructed kidneys was statistically significant.
However, when we applied a ⌬RI threshold equal
to or greater than 0.03, our sensitivity and specificity for the diagnosis of high-grade obstruction
were far below those previously published.2–5 We
achieved a sensitivity and specificity of only 62%
and 33%, respectively. Moreover, the threshold of
0.03 may be too low, as the standard deviation of
the RI in normal kidneys in our series was 0.04.
Manipulations of the discriminatory thresholds
for ⌬RI did not improve the results. When the ⌬RI
threshold was increased to 0.1, as previously suggested,2–4 the specificity increased to 80%, but the
sensitivity decreased to 10% and the accuracy
was only 15%.
Our results add to the growing body of literature suggesting that Doppler assessment of RI
has a very limited value in the diagnosis of acute
urinary tract obstruction.12–14 The cause of the
marked discrepancy between our results and
those previously published in the past 5 years is
not clear.2–4,13–15 The rules for performing a reliable Doppler examination are now well established, although operator-dependent variations in
evaluating the RI might account for the discrepancy. Decompression of an obstructed collecting
system by spontaneous pelvocaliceal rupture and
430
extravasation has been reported as a cause of
false-negative RI results.2 However, none of our
patients had pyelocaliceal extravasation.
In our series, 12 patients had a negative value
for ⌬RI, that is, the mean RI value in the obstructed kidney was lower than that in the nonobstructed kidney. To our knowledge, such a finding has not previously been reported. The reason
for the negative ⌬RIs is not clear. The application
of duplex Doppler sonography in the diagnosis of
urinary tract obstruction is based on previous animal research that evaluated the effect of urinary
tract obstruction on renal perfusion.2,16–18 The RI
can be elevated owing to a rise in renal arterial
vascular resistance produced by preglomerular
vasoconstriction with subsequent reduction in diastolic blood flow and glomerular filtration. Many
researchers believe that the renal vascular resistance changes observed with obstruction may be
due to locally acting circulating vasoactive factors
and hormones.1,6,19,20 Those studies showed that
renal arterial blood flow exhibits a biphasic hemodynamic response to complete urinary tract
obstruction. In the first phase (immediately after
the onset of obstruction), an increase in renal pelvic pressure causes a release of local prostaglandins that in turn causes diffuse vasodilatation of
the renal vascular bed. Prolonged complete obstruction induces hormonal alterations and
thereby produces diffuse vasoconstriction of the
renal vascular bed that lasts for the duration of
the obstruction. The precise time of transition between the 2 phases is not clearly defined, but the
transition appears to occur a few hours after the
onset of obstruction. This first phase may be the
JOURNAL OF CLINICAL ULTRASOUND
DUPLEX SONOGRAPHY IN ACUTE RENAL COLIC
explanation for our cases of negative ⌬RI. In fact,
the 12 patients with a negative ⌬RI all underwent
Doppler evaluation less than 10 hours after their
symptoms began.
It has been postulated that the degree of obstruction may affect the renal arterial resistance.1–4 We attempted to evaluate this potential
effect by grading the degree of obstruction with
IVU by taking into account the delay between injection of contrast medium and opacification of
cavities. As shown in Figure 1, we found no correlation between the intensity of obstruction and
the value of ⌬RI. Thus, the information provided
by duplex Doppler sonography cannot help to differentiate varying degrees of obstruction. Some
patients with a long delay had a low ⌬RI, and
some with a shorter delay had a higher ⌬RI.
Other potential limitations of Doppler sonography have been proposed.14,15,17 The administration of narcotics and nonsteroidal anti-inflammatory drugs may mask the expected increase in
the renal arterial RI.21 Fifteen patients in our
study received antispasmodic or anti-inflammatory drugs, although we did not attempt to correlate drug use and RI. Pyelocaliceal dilatation on
gray-scale sonography is highly suggestive of obstruction caused by a stone, even if the stone remains unfound. However, some patients in our
study had no dilatation. An important point
shown in prior studies of acute obstruction is that
Doppler findings may be abnormal before the development of pyelocaliectasis.1,4 Among 14 of our
patients without dilatation, 10 of them had a
high-grade obstruction. In such cases, an abnormal ⌬RI may be a useful indicator of obstruction;
the highest sensitivity is obtained with a threshold of 0.03.
In conclusion, we found duplex Doppler sonography to be a highly insensitive technique for the
detection of obstruction in patients with acute renal colic. Although a positive Doppler examination is fairly specific for the diagnosis of obstruction, it is not useful in the further evaluation of
cases of pyelocaliceal dilatation seen on grayscale sonography. Multiple factors, still partially
unknown, may directly or indirectly affect renal
arterial resistance, so there are limits to Doppler
sonography’s usefulness as a routine screening
examination. Gray-scale imaging, with a sensitivity of 78%, was more accurate than Doppler
study. However, a nondilated collecting system in
acute renal colic remains a diagnostic pitfall for
gray-scale sonography. In that particular circumstance, Doppler examination may help suggest
the diagnosis.
VOL. 26, NO. 9, NOVEMBER/DECEMBER 1998
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