Original research

Gravity-assisted drainage imaging in the assessment of pediatric

hydronephrosis

Matthew R. Acker, MD, FRCSC; Roderick Clark, MD; Peter Anderson, MD, FRCSC

Department of Urology, University of Miami, Miami, FL, U.S.; Division of Urology, University of Western Ontario, London, ON, Canada; Department of Urology, Dalhousie University, Halifax, NS, Canada

Cite as: Can Urol Assoc J 2016;10(3-4):96-100. http://dx.doi.org/10.5489/cuaj.3237

can improve kidney drainage and preserve renal function.

Those patients with mechanical obstruction suggestive of

UPJO on diuretic renography, significant flank pain, or

recurrent urinary tract infections are often considered for

pyeloplasty, particularly if there is evidence of decline in

differential renal function (DRF) on serial diuretic renal

See related article on page 101.

Abstract

scans. Selecting which patients will beneﬁt from pyeloplasty

Introduction: As early detection of hydronephrosis increases,

we require better methods of distinguishing between pediatric

patients who require pyeloplasty vs. those with transient obstruc-

tion. Gravity-assisted drainage (GAD) as part of a standardized

diuretic renography protocol has been suggested as a simple and

safe method to differentiate patients.

Methods: Renal scans of 89 subjects with 121 hydronephrotic

renal units between January 2004 and March 2007 were identi-

ﬁed and analyzed.

remains a challenge. There is a lack of standardized proto-

cols for both performing and interpreting diuretic renogra-

phy. Additionally, many centres image patients in the supine

position, which may underestimate drainage compared to

the upright position, where the effects of gravity can help

facilitate drainage (Fig. 1).

Methodsꢀ

Results: Of all renal units, 65% showed obstruction. GAD maneu-

ver resulted in signiﬁcant residual tracer drainage in eight renal

units, moderate drainage in 12 renal units, and some improvement

in 40 units after the GAD maneuver. Of the eight renal units with

signiﬁcant residual tracer drainage, only two proceeded to pyelo-

plasty. After pyeloplasty, nine children had improved time to half

The present study was approved by the Research Ethics Board

at the IWK Health Centre. Ultrasonography was used to iden-

tify the presence of hydronephrosis, after which patients were

referred for diuretic renal scans. Diuretic renography involves

serial imaging of an injected radioactive tracer as it is ﬁltered

or secreted within the kidney through to its excretion in urine.

Each child received simultaneous intravenous injection of 5

maximum (T Max) and 13 were unchanged.

Conclusions: Our study was limited due to its retrospective design

and descriptive analyses, but includes a sufﬁcient number of sub-

jects to conclude that GAD as part of a diuretic renography pro-

tocol is an effective and simple technique that can help prevent

unnecessary surgical procedures in pediatric patients.

99m

MBq/kg Tc mercapto-acetyl-triglycine (MAG-3) and 1 mg/

kg (to a maximum of 40 mg) of furosemide. After radiotracer

injection, the patient is placed supine over a gamma camera

that takes serial images of the radiotracer transit through the

kidney, typically over a period of 20‒30 minutes. Computer

analysis of the uptake and excretion phases is performed to

quantitate differential renal function (right vs. left), time to

Introduction

half maximum tracer activity (T max), as well as the degree

With the adoption of antenatal sonography as a routine

screening tool, early detection of hydronephrosis has

and signiﬁcance of any obstruction. T max of less than 10

minutes indicates the absence of obstruction, while a T

max of greater than 20 minutes is compatible with obstruc-

1,2

increased. When pelvicaliceal system distention is detect-

ed, it often leads to further investigation, including diuretic

renography. This imaging modality can help identify patients

with ureteropelvic junction obstruction (UPJO) and com-

tion. A T max between 10 and 20 minutes is considered

equivocal. A gravity-assisted drainage (GAD) image was then

performed at the end of the renal scan. The GAD image is a

single, static image obtained after positioning the child in the

upright position for ﬁve minutes to promote additional drain-

promised renal function. Early identiﬁcation of signiﬁcant

UPJO allows for interventions such as pyeloplasty, which

CUAJ • March-April 2016 • Volume 10, Issues 3-4

2016 Canadian Urological Association

gꢀꢁvꢂty-ꢁꢃꢃꢂꢃtꢄd dꢀꢁꢂꢅꢁꢆꢄ ꢂꢅ dꢂuꢀꢄtꢂꢇ ꢀꢄꢅoꢆꢀꢁpꢈy

Fig. 1. Balloon analogy for describing gravity-assisted drainage. UPJ: ureteropelvic junction.

age of tracer from the collecting system. Percent drainage was

calculated after the GAD maneuver. Residual tracer drainage

were excluded from analysis if they showed duplicated

collecting systems, ectopic ureter or ureterocele (n= 25),

megaureter or ureterovesical junction obstruction (n=21),

vesicoureteral reﬂux (n= 19), incomplete studies (n=7), pres-

ence of horseshoe kidney (n=4), non-functioning renal unit

(n=6), or posterior urethral valves (n=3). Descriptive statistics

were used in this observational study.

50% was considered signiﬁcant, while 30‒49% was con-

sidered moderate, 10‒29% showing some improvement, and

10% was classiﬁed as no change. Followup was limited to

the ﬁrst postoperative renal scan, typically performed 3‒6

months post-pyeloplasty.

Dismembered pyeloplasty was offered to patients who

had an obstructed renal unit and a low GAD score on serial

imaging, an obstructed renal unit with deterioration in renal

function on serial imaging, or were experiencing symptoms

or complications (e.g., ﬂank pain or pyelonephritis) related

to their UPJO. For patients who underwent pyeloplasty, per-

cent change in dynamic renal function was assessed through

comparison of preoperative and most recent postoperative

Results

Renal scans of 174 consecutive children with sonographi-

cally detected hydronephrosis who were referred for GAD

renography between January 2004 and March 2007 were

reviewed; 85 scans were excluded from analysis, as per

exclusion criteria. Data from 18 of the remaining renal scans

1/2

diuretic renography, including T max calculations and

were missing complete T max data and were excluded

quantiﬁcation of GAD.

Our study included children who were referred for GAD

renography between January 2004 and March 2007. Scans

from analyses. After exclusion, 89 subjects with 121 hydro-

nephrotic renal units remained for analysis (Fig. 2). Among

the scans remaining, 76 were left-sided, 21 were right-sided,

Table 1. Descriptive statistics by renal unit

BaselineT¹^/²normal

Baseline T¹^/²equivocal

(10–20 min)

BaselineT¹^/²abnormal

(>20 min)

Total

(<10 min)

Mean time

Female

Male

8.47 min

16.39 min

Not reached

14.10

Sex

Yes

Pyelopasty

Left

Laterality

Right

Bilateral

CUAJ • March-April 2016 • Volume 10, Issues 3-4

aꢇkꢄꢀ ꢄt ꢁꢉ.

74 children with hydronephrosis referred

for gravity-assisted diuretic renography

5 renal scans removed

according to exclusion criteria

9 children with 121 hydronephrotic renal

8 renal scans excluded

1/2

units remained for analysis

due to missing T max data

7 renal units with baseline T¹^/²

25 renal units with baseline T¹^/²

max equivocal (10-20 min)

79 renal units with baseline T¹^/²

max abnormal (>20 min)

max normal (<10 min)

5 renal units <0–9% GAD

renal units 10–29% GAD

renal units 30–49% GAD

19 renal units <0–9% GAD

40 renal units 10–29% GAD

12 renal unit 30–49% GAD

8 renal units >50% GAD

renal units >50% GAD

9 renal units <0–9% GAD

renal units 10–29% GAD

renal unit 30–49% GAD

renal units >50% GAD

renal units proceeded

to pyeloplasty

4 (16%) renal units proceeded

to pyeolplasty

22 (27%) renal units proceeded

to pyeloplasty

Fig. 2. Summary of patient management. GAD: gravity-assisted diuretic renography.

and 12 showed bilateral hydronephrosis (for 24 renal units),

corresponding to a 2.7:1 ratio of left- to right-sided obstruc-

tion. Twenty-two pyeloplasty procedures were performed in

our analyses (Table 1).

in signiﬁcant (>50%) residual tracer drainage in no renal

units (0%), moderate (30‒49%) drainage in three renal units

(14%), some improvement (10‒29% change) in six units

(27%), and no improvement in 13 units (59%) (Fig. 3).

Of all renal units, 79 (65%) showed renographic evidence

of obstruction (T >20 minutes). The average T max in

normal unobstructed renal units (T <10 minutes) was 8.56

1/2

minutes. For equivocal renal units (T max 10‒20 minutes),

the average time to drainage was 15.60 minutes. For the

1/2

9 obstructed renal units (T max >20 minutes) the GAD

maneuver resulted in signiﬁcant (>50%) residual tracer drain-

age in eight renal units (10%), moderate (30‒49%) drain-

age in 12 renal units (15%), some improvement (10‒29%

change) in 40 units (51%), and no improvement (<10%)

in 19 units (24%) (Fig. 2). Of the eight renal units with a

signiﬁcant residual tracer drainage, only two proceeded to

pyeloplasty, as they had multiple episodes of hydronephrosis

that necessitated eventual operative management.

Pre- and post-pyeloplasty data on GAD percent change

for obstructed renal units (T max >20) was analyzed for

all 22 individuals (Fig. 2). Post-pyeloplasty T max was

normal in two individuals, equivocal in eight individuals

and unchanged (T max >20) in 12 individuals. Following

the pyeloplasty procedure, the GAD maneuver resulted

Fig. 3. Pre- vs post-pyeloplasty gravity-assisted drainage change in obstructed

(

1/2

T max >20 min) renal units.

CUAJ • March-April 2016 • Volume 10, Issues 3-4

gꢀꢁvꢂty-ꢁꢃꢃꢂꢃtꢄd dꢀꢁꢂꢅꢁꢆꢄ ꢂꢅ dꢂuꢀꢄtꢂꢇ ꢀꢄꢅoꢆꢀꢁpꢈy

Discussion

and those with moderate rather than severely compromised

preoperative function seem to have the greatest chance of

functional improvement after surgery.

GAD as part of a diuretic renography protocol is an effective,

simple procedure that may provide additional diagnostic

information in pediatric patients with hydronephrosis being

considered for surgical management. In our retrospective

study, eight renal units (10%) showed a signiﬁcant (>50%)

improvement in drainage with the GAD maneuver, while 12

There are several limitations to our study. Our data were

obtained retrospectively, which limited the type of informa-

tion we could collect and the types of statistical analyses

we could perform. Our followup period was also limited

to the ﬁrst postoperative renal scan in patients who under-

went a pyeloplasty. Future studies should follow patients

longitudinally to determine long-term renal function. It is

possible that the small number of participants has biased

our observations, although our results are similar to trends

(15%) showed moderate improvement (30–49%) in residual

tracer activity following this simple preoperative maneu-

ver. This suggests that 25% of these “obstructed” renal units

were not truly obstructed, but simply required gravity to

assist drainage of residual urine from an unobstructed, capa-

cious collecting system. We demonstrated that this simple

maneuver during diuretic renography obviated the need for

pyeloplasty in six of eight “obstructed” renal units.

noted in previous studies. Since this is an observational

study, we did not perform calculations to determine appro-

priate sample size, but felt that our analysis of these 174

scans before exclusion criteria represented an appropriate

and practical sample for our analyses.

The GAD procedure has been previously reported and

has been recommended by at least one clinical practice

guideline, although it has not become standard of prac-

Conclusion

tice at all institutions. This procedure is easy to implement,

carries no risk to the patient, and is demonstrated to have

acceptable sensitivity and speciﬁcity to differentiate chil-

dren who truly have obstructed renal units from those who

GAD imaging during diuretic renography is safe and effec-

tive, and provides valuable, additional diagnostic informa-

tion in pediatric patients with hydronephrosis and possible

UPJO. It has become the standard practice at our institution.

do not. Our results are also consistent with other reports

on the advantage of the GAD maneuver for improving the

diagnostic accuracy of diuretic renography. Amarante et

al (2003) performed a retrospective review of 24 patients

that showed 43% of kidneys were classiﬁed as adequately

drained on a post-void GAD image, as compared to 13%

Competing interests: The authors declare no competing ꢀnancial or personal interests.

Acknowledgements: Dr. Clark was supported by the Dalhousie University Faculty of Medicine 2013

Department of Urology Ralph Pickard Bell Endowment.

in the pre-void image.

Other studies have also demonstrated the need for diag-

nostic accuracy using diuretic renography before undertak-

ing pyeloplasty. Koff et al (2005) demonstrated that obstruc-

tive appearance on diuretic renography was ultimately

determined to be non-obstructed in 40% of renal units, and

that this ﬁnding was particularly evident in children under

This paper has been peer-reviewed.

References

the age of two years. They highlight the need for caution

in the use of diuretic renography to determine if surgical

Tripp BM, Homsy YL. Neonatal hydronephrosis—the controversy and the management. Pediatr Nephrol

Berl Ger 1995;9:503-9. http://dx.doi.org/10.1007/BF00866741

Nguyen HT, Herndon CDA, Cooper C, et al. The Society for Fetal Urology consensus statement on the

evaluation and management of antenatal hydronephrosis. J Pediatr Urol 2010;6:212-31. http://dx.doi.

org/10.1016/j.jpurol.2010.02.205

management is required. Yang et al (2010) showed that

an early observation period is beneﬁcial before undertak-

ing pyeloplasty, especially given that many subjects with

asymptomatic Grade 1 and 2 hydronephrosis have benign

conditions that do not often improve with intervention. They

demonstrated some beneﬁt from pyeloplasty in individuals

3. Belarmino JM, Kogan BA. Management of neonatal hydronephrosis. Early Hum Dev 2006;82:9-14.

http://dx.doi.org/10.1016/j.earlhumdev.2005.11.004

Wong DC, Rossleigh MA, Farnsworth RH. Diuretic renography with the addition of quantitative gravity-

assisted drainage in infants and children. J Nucl Med Off Publ Soc Nucl Med 2000;41:1030-6.

Houben CH, Wischermann A, Börner G, et al. Outcome analysis of pyeloplasty in infants. Pediatr Surg Int

with more severe (≥ Grade 3 hydronephrosis) obstruction,

although the literature has been mixed in this area.

2,13

Our

000;16:189-93. http://dx.doi.org/10.1007/s003830050720

series showed overall little beneﬁt of pyeloplasty, with return

to normal function in only two renal units. Helmy et al

6. Shulkin BL, Mandell GA, Cooper JA, et al. Procedure guideline for diuretic renography in children 3.0. J

Nucl Med Technol 2008;36:162-8. http://dx.doi.org/10.2967/jnmt.108.056622

Rossleigh MA, Leighton DM, Farnsworth RH. Diuresis renography. The need for an additional view after

(

2012) showed improvement in hydronephrosis on all sub-

gravity-assisted drainage. Clin Nucl Med 1993;18:210-3. http://dx.doi.org/10.1097/00003072-

jects who underwent pyeloplasty, although 65% continued

99303000-00005

to show persistent obstruction on diuretic renography. A

systematic review in this area by Castagnetti et al (2008)

concluded that symptomatic patients diagnosed postnatally,

Gordon I, Piepsz A, Sixt R, Auspices of Pediatric Committee of European Association of Nuclear Medicine.

Guidelines for standard and diuretic renogram in children. Eur J Nucl Med Mol Imaging 2011;38:1175-88.

http://dx.doi.org/10.1007/s00259-011-1811-3

CUAJ • March-April 2016 • Volume 10, Issues 3-4

aꢇkꢄꢀ ꢄt ꢁꢉ.

Amarante J, Anderson PJ, Gordon I. Impaired drainage on diuretic renography using half-time or pelvic

excretion efꢀciency is not a sign of obstruction in children with a prenatal diagnosis of unilateral renal pelvic

dilatation. J Urol 2003;169:1828-31. http://dx.doi.org/10.1097/01.ju.0000062640.46274.21

13. Duong HP, Piepsz A, Collier F, et al. Predicting the clinical outcome of antenatally detected unilateral pelvi-

ureteric junction stenosis. Urology 2013;82:691-6. http://dx.doi.org/10.1016/j.urology.2013.03.041

14. Helmy TE, Sarhan OM, Sharaf DE. Critical analysis of outcome after open dismembered pyeloplasty in

ectopic pelvic kidneys in a pediatric cohort. Urology 2012;1357-60. http://dx.doi.org/10.1016/j.

urology.2012.07.057

15. Castagnetti M, Novara G, Beniamin F, et al. Scintigraphic renal function after unilateral pyeloplasty

in children: A systematic review. BJU Int 2008;102:862-8. http://dx.doi.org/10.1111/j.1464-

410X.2008.07597.x

0. Koff SA, Binkovitz L, Coley B, et al. Renal pelvis volume during diuresis in children with hydronephrosis:

Implications for diagnosing obstruction with diuretic renography. J Urol 2005;174:303-7. http://dx.doi.

org/10.1097/01.ju.0000161217.47446.0b

1. Yang Y, Hou Y, Niu ZB, et al. Long-term followup and management of prenatally detected, isolated

hydronephrosis. J Pediatr Surg 2010;45:1701-6. http://dx.doi.org/10.1016/j.jpedsurg.2010.03.030

2. Gordon I. Diuretic renography in infants with prenatal unilateral hydronephrosis: An explanation for

the controversy about poor drainage. BJU Int 2001;87:551-5. http://dx.doi.org/10.1046/j.1464-

Correspondence: Dr. Roderick Clark, Division of Urology, University of Western Ontario, London,

ON, Canada; Roderick.Clark@lhsc.on.ca

10X.2001.00081.x

CUAJ • March-April 2016 • Volume 10, Issues 3-4