Assessment of drainage in PUJ dilatation: pelvic excretion efficiency as an index of renal function

Guidelines for standard and diuretic renogram in children

Special consideration needs to be given to children who undergo dynamic renography. The Paediatric Committee of the European Association of Nuclear Medicine has updated the previous guidelines. Details are provided on how to manage the child, the equipment, and the acquisition and processing protocols. The pitfalls, difficulties and controversies that are encountered are also discussed, as well as the interpretation of the results.

[Functional MR urography in children]

MR Urography (MRU) provides both morphologic and functional information without radiation exposure. It enables the assessment of split renal function, excretion, and quantification of obstruction. MRU is thus complementary to ultrasonography in the assessment of pre- and post-natal obstructive uropathies in children. If available, MRU should be definitely preferred to intravenous urography.

Robustness of estimation of differential renal function in infants and children with unilateral prenatal diagnosis of a hydronephrotic kidney on dynamic renography: How real is the supranormal kidney?

PURPOSE

The two methods recommended for estimation of differential renal function (DRF) in the renography guidelines published by the European Association of Nuclear Medicine are the area under the background-subtracted time-activity curves (AUCs) (often called the integral method) and the regression slope of the background-subtracted Rutland/Patlak plot analysis. The current study investigated the agreement/disagreement of DRF estimations obtained using these two techniques. This report also focusses on the occurrence of supranormal function of the affected kidney (defined as DRF >55%) and reviews the related technical and physiological factors.

METHODS

A total of 394 renographic studies in 101 children with a prenatal diagnosis of unilateral renal pelvic dilatation confirmed on postnatal studies were retrieved from optical disc and reprocessed by one author. DRF was calculated using the Rutland/Patlak plot and the AUC over the time period 40-120 s following an injection of( 99m)Tc-mercaptoacetyltriglycine. The difference in DRF between the methods (Rutland/Patlak minus AUC) and 95% limits of agreement were calculated. The age distribution of the difference between the methods was also analysed.

RESULTS

For all 394 measurements the mean difference was -0.8% (range -21.0% to 16.9%, SD 3.9%). The 95% limits of agreement were -7.0% to 8.6%. Analysis of the data revealed that greater spread of DRF between the techniques was seen in studies performed at a younger age: a discrepancy of >5% DRF was significantly more common in those <1 year of age than in those >1 year old (25.3% vs 9.9%; chi-square, p<0.0005). Supranormal function was found less frequently using the Rutland/Patlak method than with the AUC method (8.4% vs 11.2%; chi-square, p<0.0005). The frequency of this diagnosis was reduced to 4.6% when both methods were required to be in agreement.

CONCLUSION

The current study supports the existence of age-related variation in the disparity of DRF estimations using the AUC and Rutland/Patlak methods in children with unilateral pelvic dilatation. The close agreement between the AUC and Rutland/Patlak techniques in estimation of DRF in older children supports their use. However, careful quality control of the renogram analysis is essential in young babies. Supranormal renal function (>55% DRF) may in fact be much less common in this group of children than is currently reported.

Renal pelvis volume during diuresis in children with hydronephrosis: implications for diagnosing obstruction with diuretic renography

PURPOSE

We measured the volume of the renal pelvis during diuretic renography (DR) in children with normal and hydronephrotic kidneys to determine if changes in pelvic volume could affect the accuracy of DR in diagnosing obstruction.

MATERIALS AND METHODS

We studied 18 patients 1 month to 10 years old with unilateral hydronephrosis ultimately proved to be either obstructive or nonobstructive. Simultaneous DR and ultrasound were performed with patients supine using the gamma camera. Ultrasound measurements of the renal pelvis in 3 dimensions, obtained before and at intervals after diuretic injection, were used to calculate renal pelvic volume. The contralateral normal kidneys were used as controls.

RESULTS

Between 15 and 60 minutes after diuretic injection the renal pelvis enlarged to a maximum volume in all hydronephrotic and normal kidneys and then gradually decreased in size. Mean average increase in volume for hydronephrotic kidneys ranged from 46% in obstructed kidneys to 88% in nonobstructed kidneys. Volume expansion caused dilution of isotope within the renal pelvis, which resulted in prolongation of elimination half-time (T1/2) in 42% of nonobstructed hydronephrotic kidneys sufficient to register an obstructed washout pattern. However, there were no differences in the initial pelvic volume or the rate or extent of increases or decreases in pelvic volume that would permit nonobstructed hydronephrotic kidneys to be distinguished from obstructed ones.

CONCLUSIONS

The renal pelvis enlarges during diuresis in children with hydronephrosis. This enlargement causes dilution of isotope within the renal pelvis during DR, which prolonged the isotope washout rate or T1/2 sufficiently to produce an obstructed washout pattern in more than 40% of hydronephrotic kidneys that were ultimately proved to be nonobstructed. This misdiagnosis of obstruction is particularly likely to occur in children younger than 2 years because pelvic volume expansion is so exaggerated. Consequently, T1/2 appears to be particularly vulnerable to inaccuracy in diagnosing obstruction in this age group, and, therefore, it should not be relied on as an operative determinant.

The estimation of renal transit using renography--our opinion

Renal transit estimation using renography has been employed for decades. A variety of methods have been developed, ranging from simple quantitative to more sophisticated techniques. In this review, the methods are discussed in perspective of their advantages and drawbacks. Finally, the most robust methods for estimation of renal transit are proposed.

Interpretation of the renogram: problems and pitfalls in hydronephrosis in children

OBJECTIVE

To discuss the main steps of renographic technique and underline some pitfalls related to the acquisition, processing and interpretation of diuretic renography, an important method for guiding the management of asymptomatic congenital hydronephrosis.

METHODS

Despite guidelines and consensus protocols, renographic procedures differ among centres, causing difficulties in comparison and controversy in the interpretation of results. Thus we comprehensively assessed published papers on the subject of diuretic renography.

RESULTS

Differential renal function (DRF) is a robust measure provided there is adequate background subtraction. Pitfalls are related to the drawing of regions of interest, particularly in infants, to estimating the interval during which DRF is calculated, and to an adequate signal-to-noise ratio. There is no definition of a 'significant' reduction in DRF. The classical variables of the diuretic renogram may not allow an estimate of the best drainage. Poor pelvic emptying may be apparent because the bladder is full and because the effect of gravity on drainage is incomplete. Estimating the drainage as residual activity rather than any parameter on the slope might be more adequate, especially if the time of frusemide administration is changed. Renal function and pelvic volume can influence the quality of drainage. Drainage may be better estimated using new tools.

CONCLUSION

Provided the investigation is standardized and potential pitfalls accounted for, the diuretic renogram provides valuable and reproducible quantitative information on DRF and drainage.

PRENATALLY DIAGNOSED UNILATERAL RENAL PELVIC DILATATION: A DYNAMIC CONDITION ON ULTRASOUND AND DIURETIC RENOGRAPHY

PURPOSE

Imaging characteristics obtained from serial scintigraphic and ultrasonographic studies in children with the prenatal diagnosis of unilateral pelvic dilatation are presented.

MATERIALS AND METHODS

Serial ultrasonographic and scintigraphic findings in 101 children with unilateral pelvic dilatation collected during followup were reviewed. Changes in hydronephrotic kidney in terms of renal pelvis diameter, kidney size, differential renal function and drainage were noted. A total of 42 children underwent surgery at a mean age of 15.6 months (range 3.1 to 69.2, median 8.2), while 59 were treated nonsurgically.

RESULTS

Mean age at presentation was 5.6 months (range 0.8 to 36.4, median 3.5). Mean followup was 35.5 months (range 6.4 to 78.4, median 29.6). Differential renal function remained stable (46.4% vs 47.3%) but improved drainage (68.4% vs 81.2%) and decreased renal pelvis size (22.2 vs 18.3 mm) was noted in the 2 groups. With age drainage function improved, especially between the younger than 12-month and 12-month or older groups. The mean affected-to-unaffected kidney length ratio at presentation was significantly greater than the ratio at the final followup (paired t test p <0.05).

CONCLUSIONS

In this retrospective review drainage function was prolonged in infants. During followup drainage, dilatation and relative renal size improved in the surgery and nonsurgery groups. There was no change in renal function in either groups during followup. These data support the benign nature of prenatal unilateral hydronephrosis.

Impaired drainage on diuretic renography using half-time or pelvic excretion efficiency is not a sign of obstruction in children with a prenatal diagnosis of unilateral renal pelvic dilatation

PURPOSE

Delayed drainage on diuretic renography is an accepted sign of obstruction in adults and symptomatic children. We investigated how to analyze the diuretic challenge as well as assess the significance of impaired drainage.

MATERIALS AND METHODS

We followed 24 children with a unilateral prenatal diagnosis of pelvic dilatation up to a minimum of 2 years. A total of 91 diuretic renograms were performed. All children had stable differential renal function and renal pelvic diameter did not change by greater than 9 mm. on sequential ultrasound. Kidneys with stable differential function and no increase in dilatation were considered not obstructed. Analysis of the diuretic challenge included half-time, a post-void image with a change in posture, that is the child erect for 5 to 7 minutes, and drainage considering renal function using the pelvic excretion efficiency. Prolonged drainage was defined as a half-time of greater than 20 minutes or a post-void pelvic excretion efficiency of less than 71%.

RESULTS

Median patient age at presentation was 0.32 years and median followup was 3.07 years. The affected nonobstructed hydronephrotic kidney showed impaired drainage in 68% of the children using the half-time parameter, and in 80% and 44% using pelvic excretion efficiency before and after voiding, respectively. Variability in drainage was documented on sequential diuretic renography.

CONCLUSIONS

Using the guidelines for data acquisition and processing of diuretic renograms we nevertheless noted impaired drainage in 44% of this young group with nonobstructed kidneys. The half-time parameter was an inappropriate parameter. The diagnosis of obstruction cannot be simply based on delayed drainage in this group of asymptomatic children with a prenatal diagnosis of unilateral renal pelvic dilatation.

Diuretic renography in infants with prenatal unilateral hydronephrosis: an explanation for the controversy about poor drainage

OBJECTIVE

To present an explanation for impaired drainage on diuretic renography in infants with a prenatal diagnosis of unilateral renal pelvic dilatation (RPD) who are stable both in terms of renal function and dilatation on follow-up investigations, despite undergoing no surgical intervention, and who undergo diuretic renography postnatally; this should provide some insight into whether impaired drainage is a sign of obstruction in these asymptomatic infants.

MATERIALS AND METHODS

Using a combination of published studies on the technique of diuretic renography and an analysis of such studies, a theoretical model of the infant kidney was developed to assess the possibility of prolonged drainage.

RESULTS

The results from the model showed prolonged drainage in many different situations, thus offering an explanation of expected impaired drainage even if there was no obstruction.

CONCLUSION

Understanding the pathophysiology of prenatally diagnosed RPD allows different interpretations of the diuretic renogram and may affect the treatment of these children.

Factors influencing the accuracy of renal output efficiency

Output efficiency (OE) has been proposed as an objective tool for the estimation of renal emptying. The aim of this paper was to evaluate some factors that may affect the value of this parameter obtained by a 99Tcm MAG3 renogram. In 22 patients, the effect of different types of renal background correction was calculated. In 10 patients, simultaneous gamma camera renography and multiple blood sampling allowed the error of using a heart curve instead of a plasma curve to be evaluated. Finally, an evaluation was carried out on the effect of neglecting the change of plasma activity between the end of the furosemide acquisition and the post-micturition view obtained after repositioning of the patient on the gamma camera: 142 patients who had had multiple blood sampling were retrospectively selected for that purpose. It has been shown that all these factors may significantly affect the value of OE, particularly in cases with poor renal drainage. Unless standardization of the procedure is introduced for some of these factors, the cut-off levels for good, fair and poor drainage may vary between centres.

Consensus report on quality control of quantitative measurements of renal function obtained from the renogram: International Consensus Committee from the Scientific Committee of Radionuclides in Nephrourology

Among all the physiological indices that can be quantified using renography, measurement of renal function is the most basic. These measurements are used to make critical clinical management decisions and, as such, their reliability needs to be quality assured. This article seeks to address each aspect of the renography procedure, with particular emphasis on the effect on measurement of relative renal function. Estimation of individual kidney function is mentioned, but only briefly. A consensus approach was adopted, overseen, and directed by a chairman appointed by the Scientific Committee of the International Radionuclides in Nephro-Urology Group. The chairman selected the panel of experts from eight different countries based on their practical experience in the field. Where evidence exists to support the various recommendations it is given. Otherwise, the stated guidance represents the considered opinion of a body of experts, based on long experience and unpublished data. Some necessary compromises were made to account for the fact that renography is seldom performed solely with the purpose of measuring relative renal function. The technicalities of renography have always been a source of debate in nuclear medicine, which is reflected by the fact that a consensus could simply not be reached on a small number of issues. The structure of the report ensures that these are clearly indicated. This should serve to highlight gaps in our current knowledge, thus helping to direct future research. It is envisaged that the recommendations will be revised on a 2-year cycle to ensure that they remain up to date. An "open" process will be used to encourage participation and ownership. It is hoped that promotion of these guidelines, suitably complemented by audit processes, will raise standards in the practice of gamma camera renography.