Keywords
diagnostic imaging - furosemide - megaureter - radioisotope renography - sitting position
Introduction
Primary megaureter is the second most common cause of hydronephrosis in newborns,
the incidence of obstructed megaureter is 1 per 10,000 population.[1] A primary megaureter is a ureter dilation with a diameter greater than 7 mm.[2] This complication is due to a congenital developmental defect in the muscular layer
of the ureter, which can be complete or segmental. Ultrasound may easily reveal ureteral
dilation, but ultrasonography is only descriptive and supplies no details on renal
function or drainage. We recommend long-term follow-up of conservatively managed primary
megaureters due to evidence of late recurrence in teenage and adult patients.[3] The need for a correct assessment of ureteric function in patients with a dilated
ureter has increased, given that approximately 20% of patients may present with urinary
tract infection and abdominal pain.[4] Many patients with megaureter often present without any symptoms and have a normal
serum creatinine level.[5] Voiding cystography may easily detect the presence/absence of vesicoureteral reflux
in the megaureter.[6]
[7] If there is no obstruction, the recommended treatment is conservative management;
if not, it is surgical treatment. For patients with primary megaureter, we recommend
renography. Nuclear medicine labels any obstructed ureter with a delay in radiotracer
drainage. However, when performing imaging in the supine position, urine stasis in
the dilated ureter could potentially mislead the test, even in the absence of obstruction.
Currently, a decrease in split renal function (SRF) less than 40% is considered the
criterion for surgical treatment.[5] We calculate SRF by dividing the radioactive tracer accumulation from each side
in the first 2 minutes of the renographic curve by the total accumulation in both
kidneys in the same period. The relative function is expressed as a percentage of
the overall function. A decrease in SRF% may indicate a loss of kidney function.[8]
[9]
[10] Regrettably, other authors have confirmed that even in the presence of partial or
no drainage, the SRF may not be significantly impaired.[11]
[12] To find out how well primary megaureters are working, we performed diuretic renography
(DR) with the F + 10(sitting position [sp]) method, while sitting to measure the direct
urine outflow indices after giving a diuretic in a gravity-favorable environment.[13]
Materials and Methods
We obtained the results by retrospectively observing patients who visited our nuclear
medicine center between 2016 and 2023. We studied 28 adult patients, 15 males and
13 females, with a median age of 42 years (range: 18–73) and diagnosed them with primary
megaureters based on radiological findings such as dilatation of the ureter with a
diameter greater than 7 mm and stasis of contrast in the ureter. Twenty-six patients
had a unilateral megaureter, and two patients bilaterally (16 left megaureters, 14
right megaureters). Seventeen patients received conservative treatment, while 11 patients
underwent surgical treatment. A significant obstruction or progressive loss of kidney
function was indications for intervention. All patients who had routine micturating
cystography or cystoscopy with visualization of the ureteral orifices did not have
significant reflux. We performed 28 DR with 99mTc-mercaptoacetyltriglycine (MAG3)
using the F + 10(sp) method, examining the patient in a sitting position. Due to clinical
needs, a subgroup of five patients (4 males and 1 female) underwent DR several times
for follow-up with adjunctive 15 exams. This study followed the national guidelines
set by the Italian Association of Nuclear Medicine, AIMN (v. 03/2017) for the F + 10(sp)
method. Written informed consent was waived. We stopped angiotensin-converting enzyme
inhibitors and diuretics 48 hours before the test. We asked all patients to empty
their bladders before the scan. We studied patients under normal hydration conditions.
Before the test, we measured blood pressure and weight to calculate the right dose
of furosemide (0.25 mg/kg) for intravenous delivery. We used a dual-detector, large-field-of-view
gamma camera (General Electric, Infinia Xeleris III system) with a free geometry gantry
design, enabling 0-, 90-, and 180-degree orientations of the detectors, allowing scanning
at all positions. We positioned a detector vertically, tilting it 90 degrees toward
the posterior view. The camera reached a peak at 140 keV with a 20% window. We used
a low-energy general-purpose collimator, as the purpose of the study was to increase
the sensitivity to better quantify radioactivity in the kidneys, ureters, and bladder.
We seated the patient in a suitable imaging chair providing sufficient support to
prevent movement during the study. During dynamic acquisition, we aligned the shoulders
and pelvis with the patient's back facing the detector. To improve resolution and
reduce scatter, we minimized the distance between the detector and the patient's back.
The field of view included the kidneys, heart, and bladder. After putting in an intravenous
catheter with an injection valve, we gave a bolus dose of 150 to 200 MBq of 99mTc-MAG3
diluted in 0.2 to 0.3 mL at time 0'. This was followed right away by flushing with
1 to 2 mL of normal saline solution. We acquired images from the posterior view starting
when the radioactive bolus was in the mediastinum. According to the protocol, we obtained
a 20-minute dynamic scan with a frame rate of 2 sec/frame for the first 60 frames
and 10 sec/frame for 108 frames, using a 128 × 128 matrix and zoom ×1. At the fifth
minute, the patient drank 400 to 500 mL of water. During dynamic acquisition, we administered
diuretics intravenously 10 minutes after tracer injection. We injected a furosemide
dose of 0.25 mg/kg (range 10–20 mg). However, we systematically adjusted the furosemide
dose to 10 mg in patients whose systolic blood pressure was lower than 105 mm Hg.
We checked the blood pressure in patients with persistent hypotension throughout the
test. We applied an ice pack to the hand only if it was strictly necessary, as cold
conditions tend to release catecholamines into the body, thereby preventing orthostatic
hypotension. We acquired postvoiding images in the seated and supine positions at
20 and 60 minutes after the tracer injection, respectively, to complete the test.
Two independent observers separately processed the data. A cine of raw data dynamic
images with two locators was displayed for assessing patient motion. Following the
automatic dynamic motion correction processing, the user drew the master kidney regions
of interest (ROIs), as well as the ROIs for the aorta, bladder, and collecting system.
We semiautomatically generated the kidney, background, and cortex ROIs using a commercial
software (Xeleris 3.1 release, GE). We measured several indices: SRF%, also known
as differential renal function, determines the relative contribution of each kidney
to total renal function by comparing the first to second minute tracer accumulation.
The normal range for renal activity is 45 to 55.[11]
Tmax is the time it takes for the renogram to reach its highest level of activity (normal
value: < 6 minutes). Diuretic half-time (T1/2) is the time between giving furosemide and the half-time of renal time-activity
curve measured in sitting position (normal value: < 8 minutes); and the 20-minute/peak
ratio is the ratio between the average activity of the curves from minutes 19 to 20
and the peak activity (normal value: < 0.25). The 20-minute/peak ratio value, measured
in conditions of favorable gravity, may allow a clear and objective distinction between
obstructed and normal kidneys, as verified in our previously published works.[13]
[14]
[15] Accordingly, we considered the 20-minute/peak ratio value to be the gold standard
for obstruction diagnosis.
Results
We evaluated 28 DRs. Thirty megaureters (16 left, 14 right) were considered suspected
obstructive megaureters, based on radiological findings. [Table 1] displays demographic, clinical data, and main functional indices for surgically
treated patients, while [Table 2] displays the same information for conservatively treated patients. We diagnosed
17 out of 30 megaureters as obstructed (56.6%) based on the values of the 20-minute/peak
ratio. We found a discrepancy between the SRF% and the 20-minute/peak ratio findings
([Table 3]). [Table 4] expresses the sensitivity, specificity, disease incidence, positive and negative
predictive values, and accuracy of the main renal functional indices (SRF%, Tmax, and diuretic T1/2) in percentage terms. Adjunctive 15 DRs were performed as follow-up
in a subgroup of 5 patients ([Table 5]). Two independent observers processed all the data. The agreement was 97.6%, and
Cohen's k was 0.94. During the test, we measured an average blood pressure drop of 10 mm Hg.
We observed no side effects such as orthostatic diuretic-related hypotension, bladder
fullness, or disruption of the test due to voiding.
Table 1
Demographic, clinical data, and comparison between SRF and 20-minute/peak ratio in
patients surgically treated
|
Patient #
|
Sex
|
Years
|
Creatinine (mg/dL)
|
L SRF (%)
|
L 20-minute/peak ratio
|
R SRF (%)
|
R 20-minute/peak ratio
|
Diagnosis
|
|
1
|
F
|
62
|
1.20
|
66
|
0.26
|
34
|
0.37
|
Right megaureter
|
|
2
|
M
|
20
|
1.13
|
40
|
0.80
|
60
|
0.20
|
Left megaureter
|
|
3
|
F
|
65
|
0.76
|
61
|
0.20
|
39
|
0.53
|
Right megaureter
|
|
4
|
F
|
41
|
0.80
|
48
|
0.19
|
52
|
0.22
|
Left megaureter
|
|
5
|
M
|
41
|
1.20
|
64
|
0.12
|
36
|
0.89
|
Right megaureter
|
|
7
|
F
|
18
|
0.82
|
52
|
0.17
|
48
|
0.24
|
Right megaureter
|
|
15
|
M
|
43
|
1.10
|
48
|
0.21
|
52
|
0.18
|
Right megaureter
|
|
17
|
F
|
54
|
0.93
|
36
|
0.27
|
64
|
0.15
|
Left megaureter
|
|
20
|
M
|
50
|
1.00
|
45
|
0.18
|
55
|
0.15
|
Left megaureter
|
|
21
|
M
|
51
|
1.84
|
46
|
0.09
|
54
|
0.26
|
Right megaureter
|
|
24
|
M
|
23
|
1.19
|
28
|
0.06
|
72
|
0.09
|
Left megaureter
|
Abbreviations: F, female; L, left; M, male; R, right; SRF, split renal function.
Table 2
Demographic, clinical data, and comparison between SRF and 20-minute/peak ratio in
patients conservatively treated
|
Patient #
|
Sex
|
Years
|
Creatinine (mg/dL)
|
L SRF (%)
|
L 20-minute/peak ratio
|
R SRF (%)
|
R 20-minute/peak ratio
|
Diagnosis
|
|
6
|
M
|
53
|
0.85
|
45
|
0.18
|
55
|
0.21
|
Left megaureter
|
|
8
|
F
|
39
|
1.20
|
54
|
0.21
|
46
|
0,19
|
Right megaureter
|
|
9
|
M
|
42
|
0.81
|
66
|
0.10
|
34
|
0.24
|
Right megaureter
|
|
10
|
M
|
29
|
1.69
|
40
|
0.62
|
60
|
0.30
|
Bilateral megaureter
|
|
11
|
M
|
52
|
0.69
|
76
|
0.21
|
24
|
0.74
|
Right megaureter
|
|
12
|
F
|
51
|
0.75
|
52
|
0.45
|
48
|
0.22
|
Left megaureter
|
|
13
|
F
|
47
|
0.90
|
53
|
0.21
|
47
|
0.20
|
Left megaureter
|
|
14
|
M
|
21
|
0.96
|
44
|
0.15
|
56
|
0.21
|
Bilateral megaureter
|
|
16
|
F
|
65
|
1.20
|
20
|
0.38
|
80
|
0.21
|
Left megaureter
|
|
18
|
M
|
42
|
1.20
|
26
|
0.47
|
74
|
0.26
|
Left megaureter
|
|
19
|
F
|
43
|
0.59
|
56
|
0.26
|
44
|
0.20
|
Left megaureter
|
|
22
|
F
|
57
|
0.84
|
38
|
0.53
|
62
|
0.23
|
Left megaureter
|
|
23
|
M
|
23
|
1.06
|
44
|
0.19
|
56
|
0.14
|
Left megaureter
|
|
25
|
M
|
31
|
1.19
|
66
|
0.17
|
34
|
0.45
|
Right megaureter
|
|
26
|
M
|
45
|
1.00
|
49
|
0.50
|
51
|
0.23
|
Left megaureter
|
|
27
|
F
|
45
|
0.89
|
49
|
0.17
|
51
|
0.27
|
Right megaureter
|
|
28
|
F
|
38
|
0.90
|
50
|
0.17
|
50
|
0.14
|
Left megaureter
|
Abbreviations: F, female; L, left; M, male; R, right; SRF, split renal function.
Table 3
Univariate analysis of variables (sex, side, SRF%, 20-minute/peak ratio) that predict
obstruction in 30 renal unit (RU) with radiologically diagnosed obstructive megaureter
|
Variable
|
RU
No obstruction
(n = 13)
|
RU
obstruction
(n = 17)
|
p-Value
|
|
Sex (male/female)
|
8/8
|
8/6
|
NS
|
|
Side (left/right)
|
8/5
|
9/8
|
NS
|
|
SRF%
(Nv = 45–55)
|
45.62
(SD 7.56)
|
40.53
(SD 11.60)
|
NS
|
|
20-minute/peak ratio
(Nv < 0.25)
|
0.18
(SD 0.04)
|
0.48
(SD 19.43)
|
< 0.0001
|
Abbreviations: NS, not significant; SD, standard deviation; SRF, split renal function.
Table 4
A comparison of statistic values of main renal functional indices SRF%, Tmax, and diuretic T1/2, considering 20-minute/peak ratio > 0.25 as suggestive for
diagnosis of obstruction
|
Statistic
|
SRF%
|
Tmax
|
Diuretic T1/2
|
|
Sensitivity
|
64.71%
|
88.24%
|
75.00%
|
|
Specificity
|
76.92%
|
30.77%
|
85.71%
|
|
Positive likelihood ratio
|
2.80
|
1.27
|
5.25
|
|
Negative likelihood ratio
|
0.46
|
0.38
|
0.29
|
|
Disease prevalence
|
56.60%
|
|
Positive predictive value
|
78.53%
|
62.44%
|
87.26%
|
|
Negative predictive value
|
62.56%
|
66.73%
|
72.44%
|
|
Accuracy
|
70.01%
|
63.30%
|
79.65%
|
Abbreviation: SRF, split renal function.
Table 5
In the subgroup of patients who had multiple diuretic renography procedures as part
of a follow-up, demographic, clinical, and primary functional indices data were collected
|
Patient #
|
Sex
|
Years
|
Conservative/Surgical
(C/S)
|
Creatinine (mg/dL)
|
L SRF (%)
|
L 20-minute/peak ratio
|
R SRF (%)
|
R 20-minute/peak ratio
|
Diagnosis
|
|
2
|
M
|
20
|
S
|
1.13
|
40
|
0.80
|
60
|
0.20
|
Left megaureter
[*]
stent jj
|
|
2a
|
21
|
1.40
|
29
|
0.85
|
71
|
0.08
|
|
2b
|
22
|
1.10
|
25
|
0.87
|
75
|
0.26
|
|
2c[*]
|
23
|
1.10
|
16
|
0.58
|
84
|
0.15
|
|
2d[*]
|
23
|
1.11
|
25
|
0.79
|
75
|
0.23
|
|
3
|
F
|
65
|
S
|
0.76
|
61
|
0.20
|
39
|
0.53
|
Right megaureter
|
|
3a
|
66
|
0.85
|
67
|
0.22
|
33
|
0.60
|
|
3b
|
67
|
1.39
|
62
|
0.30
|
38
|
0.70
|
|
3c
|
73
|
1.09
|
58
|
0.31
|
42
|
0.89
|
|
9
|
M
|
42
|
C
|
0.81
|
66
|
0.10
|
34
|
0.24
|
Right megaureter
|
|
9a
|
42
|
0.81
|
69
|
0.09
|
31
|
0.16
|
|
9b
|
44
|
0.82
|
69
|
0.08
|
31
|
0.11
|
|
21
|
M
|
51
|
S
|
1.84
|
46
|
0.09
|
54
|
0.26
|
Right megaureter
|
|
21a
|
55
|
1.30
|
44
|
0.28
|
56
|
0.51
|
|
24
|
M
|
23
|
S
|
1.19
|
28
|
0.06
|
72
|
0.09
|
Left megaureter
|
|
24a
|
25
|
30
|
0.09
|
70
|
0.09
|
|
24b
|
26
|
27
|
0.08
|
73
|
0.09
|
|
24c
|
28
|
28
|
0.12
|
72
|
0.13
|
|
24d
|
32
|
27
|
0.10
|
73
|
0.13
|
|
24e
|
34
|
28
|
0.10
|
72
|
0.09
|
Abbreviations: F, female; L, left; M, male; R, right; SRF, split renal function.
Note: Data from the first examination and data from later exams were compared.
* indicates the presence of a jj ureteral stent.
Discussion
Today, a more conservative approach to treating primary megaureters is becoming more
common. The purpose of urological imaging is to quickly separate the kidneys that
do not need surgery from those that do. Approximately 30% of patients with primary
megaureters will require intervention due to either functional imaging-based diagnosis
of obstructive uropathy progression or clinical indications, including breakthrough
urinary tract infection.[16] Computed tomography urography (CTU) and magnetic resonance imaging are equivalent
to renography for measuring SRF%, but urine drainage and transit time are difficult
to evaluate with radiological methods.
Some authors associated CTU protocols with a split-bolus dual-phase protocol, which
includes furosemide (10–15 mg). This approach obtained the best dilation of the collecting
system and distal ureter, reducing examination time and radiation exposure. However,
the large volume of contrast medium administered at a flow rate of 2.5 mL/s, combined
with the supine position, resulted in a continuous presence of contrast in the megaureter,
making the CTU unable to distinguish between obstruction and dilation. This could
potentially result in incorrect diagnoses even when there is no obstruction present.[17]
[18]
Instead of CTU, renography has the advantage of injecting a minimum volume of radiotracer
(0.2–0.3 mL) as a bolus. Normally, the radioactive bolus passes from the bloodstream
through the kidneys and ureters to the bladder in around 20 minutes; this is the reason
for which, in many centers, data are collected for 20 minutes after a tracer injection.[19]
To date, renography is considered the best choice for the management of primary megaureters
due to the lack of a suitable alternative for urine drainage assessment. The kidneys
rapidly clear the tracer from the blood and excrete it via active tubular secretion
and glomerular filtration following the intravenous injection of 99mTc-MAG3. We generated
the 20-minute kidney and aortic time-activity curves from their respective ROIs. In
clinical practice, the diagnosis is based on the SRF% level as well as a visual assessment
of a late postvoiding scan. Some authors suggested injecting furosemide, but due to
the supine position and various methods used, the diagnosis of obstructive megaureter
remained subjective.[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27] The British Association of Paediatric Urologists consensus meeting decided that
since there is not a clear line between partial and good drainage, surgery should
only be considered if the SRF percentage is less than 40% and there is massive or
progressive hydronephrosis or a decrease in differential function on serial renograms.[5] A reduction of SRF%, calculated during the parenchymal phase of renography, may
indicate a loss in kidney function. Other writers, however, have attested to the possibility
that SRF can be normal even when there is aberrant drainage, and vice versa, that
because comparing the radioactive tracer accumulation from each side in the first
2 minutes SRF is a measure of tracer input rather than output.[11]
[12] To date, despite significant advancements in imaging, there is still no reliable
assessment of drainage, as the megaureter is a large capacity conduit that retains
urine. In a recent systematic review on conservative management of primary megaureters
based on changes in SRF%, Buder et al[28] suggested that future studies should overcome imaging methods' limitations by using
standardized, comparable criteria and precise reporting of quantitative outcome data.
In our study, we suggest overcoming this diagnostic limitation by evaluating patients
by DR in sitting position with the F + 10(sp) method.
The patient typically undergoes DR in a supine position, and the Society of Nuclear
Medicine and Molecular Imaging-European Association of Nuclear Medicine recommends
an adult dose of intravenous furosemide of 0.5 mg/kg, while the American College of
Radiology–Society of Pediatric Radiology recommends 0.5 to 1.0 mg/kg, with variable
timing and agreement on a maximum dose of 40 mg in healthy adults ([Table 6]).[29]
[30]
Table 6
A comparison of the many diuretic renography techniques
|
Method
|
Hydration
|
Position
|
Furosemide dose
|
Timing
|
|
F + 20
|
500 mL oral water at 20 min
|
Sitting or supine[a]
|
0.50 mg/kg
(max 40 mg)
|
+20 min
|
|
F-15
|
500 mL oral water
|
Sitting or
supine[a]
|
0.50 mg/kg
(max 40 mg)
|
–15 min
|
|
Well-tempered
|
15 mL/kg/min saline solution IV in 30' + bladder catheter
|
Prone or supine[a]
|
1 mg/kg
(up to 80 mg)
|
+20 min
|
|
F0
|
Oral water
|
Supine[a]
|
1 mg/kg
(max 40 mg)
|
0 min
|
|
F + 10(sp)
|
500 mL oral water at 5 min
|
Sitting
|
0.25 mg/kg
(10–20 mg)
|
+10 min
|
Abbreviations: IV, intravenous; sp, sitting position.
Note: The timing is the number of minutes that pass between injecting the tracer and
administering the diuretic. The diuretic is administered a few minutes after the tracer
injection, as indicated by F + , or a few minutes prior to the tracer administration,
as indicated by F-.
a A later scan following voiding is recommended for a qualitative assessment of urine
drainage because the urine output indices cannot be accurately quantified when the
test is conducted in the supine or prone position.
It would be better to do DR while sitting down because this would stop the body from
holding on to the radioactive urine. This could make it possible to get a good reading
of the direct urine outflow indices, like the 20-minute/peak ratio or the diuretic
T1/2.
However, it is crucial to emphasize that, when examining a patient in a sitting position,
one should adjust the furosemide dose to prevent diuretic-related hypotension, considering
the patient's body weight and systolic blood pressure. We administered a 0.25 mg/kg
dose of furosemide (range: 10–20 mg). In patients with persistent hypotension and
a systolic blood pressure lower than 105 mm Hg, we suggest injecting systematically
a low dose of furosemide (10 mg). In our study, an adapted dose of furosemide with
a suitable oral hydration volume of 400 to 500 mL demonstrated a high diagnostic value,
avoiding the risk of diuretic-induced hypotension and bladder fullness-related problems
without the need for a bladder catheter. We assessed 28 patients, of whom 11 underwent
surgical treatment and 17 underwent conservative management.
Two tertiary referral hospitals performed the ureteroneocystostomy surgical treatment,
either with or without ureteral tapering. Four patients underwent surgery with the
full-thickness technique, and seven underwent surgery with the Lich–Gregoir technique.
We performed all the procedures laparoscopically with robot assistance (Da Vinci Xi,
Intuitive Surgical, Sunnyvale, California, United States). We did not observe any
statistically significant differences in estimated blood loss, operative time, complications,
or length of hospital stay between the two techniques.
When examining patients in a sitting position, the 20-minute/peak ratio (normal value < 0.25)
may allow us to clearly distinguish between nonobstructed and obstructed megaureters.
By comparing the SRF% and the 20-minute/peak ratio, we found that the SRF% had a lower
sensitivity for evaluating patients in the conservative management setting. A decrease
in SRF% might be an index of decreased kidney function, and it may occur late after
obstruction ([Fig. 1]). In addition, the SRS% may remain unchanged in patients treated surgically despite
a normalized outflow ([Fig. 2]) or restenosis ([Fig. 3]), as confirmed by follow-up data. Our experience suggests that the 20-minute/peak
ratio may be more accurate than the SRF% for diagnosing obstructive megaureter in
the early clinical stage, before renal function is impaired.
Fig. 1 Female, 38 years, serum creatinine 0.90 mg/dL, left megaureter in conservative management
with normal split renal function (SRF) % and outflow, (A) renogram, (B) summed image, (C) late scans, and (D) functional indices for side.
Fig. 2 Male, 34 years, serum creatinine 1.1 mg/dL ureteroneocystostomy (UNC) left megaureter
in follow-up with reduced split renal function (SRF) % and normal outflow, (A) renogram, (B) late scan, (C) dynamic images, and (D) functional indices for side.
Fig. 3 Male, 24 years, serum creatinine 1.2 mg/dL, ureteroneocystostomy (UNC) left megaureter
with restenosis, (A) renogram, (B) late scans, (C) dynamic images, and (D) functional indices for side.
So, now that there are new minimally invasive techniques like robotic-assisted ureteroneocystostomy
or other endoscopic ways to treat obstructive megaureter with low operative morbidity,
we need a new tool to better measure transit time in the urinary tract. This creates
the need for more accurate urological diagnostic imaging.[31]
[32] DR using the F + 10(sp) method while sitting down might give a more accurate evaluation
of radioactive urine outflow by measuring the direct indicators of urine outflow when
gravity is favorable. This is especially specific for diagnosing renal obstruction
as soon as it develops.
The main limitation of the study is related to its single-center, retrospective design.
Conclusion
To find out if someone has obstructive primary megaureters, the F + 10(sp) method
with an adapted dose of furosemide is a noninvasive, safe, and well-tolerated test
that can be used. We study patients without catheters in a more comfortable and natural
setting.
A drop in SRF% is an indirect and late sign of obstruction; it does not seem to be
very useful for diagnosing obstructive megaureter early on or checking on obstructive
megaureters after surgery.
The 20-minute/peak ratio measured with the F + 10(sp) method may offer urologists
an earlier, direct, and reliable index of urine outflow in monitoring ureteral flow,
allowing prompt surgical intervention to avoid no restorable deterioration of SRF%.
That may improve the accuracy of diagnostic management of primary megaureter in adult
patients, preventing renal impairment.
