Supranormal Differential Renal Function Research Articles

Supranormal differential renal function on MAG3 scan in children with ureteropelvic junction obstruction – Prevalence and pyeloplasty during follow-up

Children with suspected ureteropelvic junction obstruction (UPJO) may present with a paradoxical ipsilateral supranormal differential renal function (snDRF) on 99mTechnetium mercaptoacetyltriglycine scintigraphy (MAG3 scan). The aim was to investigate the prevalence of snDRF, the risk of pyeloplasty among children with UPJO and snDRF, and to explore the experience of snDRF among international pediatric urologists. A retrospective cohort study of children with suspected unilateral UPJO who underwent MAG3 scan at four hospitals in Sweden between 2005 and 2020. SnDRF was defined as DRF ≥55%. Normal DRF was defined as DRF 45-54%. Primary outcome was risk of pyeloplasty. Indications for pyeloplasty were loss of >10%-points of differential renal function (DRF), ipsilateral DRF <40%, or symptomatic UPJO. Logistic and cox regressions were performed in univariate and multivariable analyses, adjusting for age, gender, year, laterality, antenatal hydronephrosis, anterior-posterior diameter (APD), and kidney size. An international questionnaire regarding the management of snDRF was developed and distributed to pediatric urologists. The prevalence of snDRF was 19%. SnDRF was more common in boys, children with antenatal hydronephrosis, children undergoing their first MAG3 scan at a younger age, and in the left kidney. After further exclusion of 70 children with DRF <45%, a total of 264 were included for longitudinal follow-up of median 6.6 (IQR 2.5-11.5) years. SnDRF was not associated with increased risk of pyeloplasty (adjusted OR 0.98 (95% CI 0.41-2.33), p=0.96, and adjusted HR 1.00 (95% CI 0.53-1.91), p=0.99) or time to pyeloplasty (1.1 years vs. 1.6 years, p=0.40). Among the 79 surveyed pediatric urologists, a majority would not change clinical UPJO-management based on the presence or absence of ipsilateral snDRF. There are only a few studies considering the need of pyeloplasty based on the presence of snDRF and this is the first survey among pediatric urologists on its management. With more included patients than previous studies, this study showed a snDRF prevalence of 19%, congruent with the findings of others. The underlying cause of snDRF is debated, but it cannot solely be explained as an artifact of hydronephrotic kidneys. Further studies on the clinical implications of snDRF are warranted, since DRF influences the decision to operate. A fifth of all children with suspected UPJO presented with ipsilateral snDRF on initial MAG3 scan, and snDRF was not associated with a greater risk of pyeloplasty. Supported by a large group of international pediatric urology colleagues, this study concludes that the same clinical follow-up and management apply, regardless of presence of snDRF.

Commentary to “Urinary Biomarkers Can Identify the Need for Pyeloplasty in Presence of Supranormal Differential Renal Function in Antenatally Diagnosed Unilateral Hydronephrosis”

Commentary to “Urinary Biomarkers Can Identify the Need for Pyeloplasty in Presence of Supranormal Differential Renal Function in Antenatally Diagnosed Unilateral Hydronephrosis”

Urinary biomarkers can identify the need for pyeloplasty in presence of supranormal differential renal function in antenatally diagnosed unilateral hydronephrosis

Decision for surgery can be challenging in children with AH (Antenatal Hydronephrosis) especially in the setting of supranormal differential renal function (SnDRF). Aim of this study is to investigate whether IP-10 (interferon gamma-induced protein 10), MCP-1 (monocyte chemotactic protein-1), NGAL (neutrophil gelatinase-associated lipocalin), CA 19-9 (carbohydrate antigen 19-9), and KIM-1 (kidney injury molecule-1) can identify the need for pyeloplasty in presence of SnDRF in antenatally diagnosed unilateral hydronephrosis. A prospectively collected urinary biomarker database was used for the study. There was a total of 53 patients in the AH group. Nineteen children with no history of AH and a normal urinary ultrasonography were taken as controls. Patients with initial ipsilateral DRF (Differential Renal Function) over 50% were included in the SnDRF group while the remaining were named as non-SnDRF. Patients that didn't undergo surgery were classified as non-obstructive dilation (NOD) in both groups. Pyeloplasty was performed in 6/20 patients in SnDRF group, and in 19/33 patients in non-SnDRF group. Biomarker levels in the pyeloplasty and NOD groups were not affected by the presence or absence of SnDRF (p=1.00, for both). Urinary NGAL, and CA 19-9 could determine the need for surgery in SnDRF group with 83% and 100% sensitivity, 86% and 79% specificity, respectively whereas urinary IP-10 and KIM-1 could with 84% and 83% sensitivity, 57% and 71% specificity, respectively. Urinary MCP-1 could differentiate patients who underwent surgery with 83% sensitivity and 50% specificity in SnDRF groups. Our results showed that biomarker levels were not affected whether the kidney has SnDRF. Furthermore, in patients with SnDRF, NGAL and CA 19-9 appear to better estimate requirement for surgical correction before deterioration of renal function.

Supranormal differential renal function in adults with ureteropelvic junction obstruction: Does it really exist?

Introduction:Some patients with ureteropelvic junction obstruction (UPJO) have supranormal differential renal function (snDRF). We aimed to study the outcomes of pyeloplasty in adult patients with UPJO and either snDRF or normal differential renal function (nDRF) and to identify preoperative factors responsible for the snDRF phenomenon.Materials and Methods:We retrospectively retrieved data for all patients who underwent pyeloplasty and had snDRF (differential renal function [DRF] ≥55%) and nDRF (DRF between 45 and 55%) preoperatively. Preoperative radiological data using computed tomography or magnetic resonance imaging were correlated with the presence of snDRF phenomenon. In addition, scintigraphic findings pre- and post-operatively were also assessed to evaluate the functional outcomes.Results:Of a total of 856 patients, 31 had snDRF (group 1) and 42 had nDRF (group 2). After a mean of 37 months’ follow-up in Group 1, 22 patients developed DRF reduction with non-obstructive pattern. Mean DRF % decreased from 59 ± 2.8 to 48 ± 13 (P < 0.0001). However, in Group 2, five patients had DRF decrease. Four patients developed snDRF phenomenon postoperatively. Increased renal pelvis volume ≥50 mm3 and increased anteroposterior pelvic diameter (APD) ≥37 mm were found to predict snDRF phenomenon. The same findings, in addition to preoperative snDRF, correlated with postoperative DRF decrease.Conclusion:SnDRF function could be expected in patients with increased renal pelvis volume and APD. The absolute value or changes in DRF are not reliable to judge treatment failure.

Comparative Outcome Analysis of Children Who Underwent Pyeloplasty for Ureteropelvic Junction Obstruction Associated With or Without Supranormal Differential Renal Function

To compare pyeloplasty outcomes in children with and without "supra-normal" differential renal function (SNDRF) defined as >55% differential renal function (DRF) in children with ureteropelvic junction obstruction. Our prospectively collected pyeloplasty database (2008-2015) was reviewed (n = 151). A total of 140/151 (93%) patients had preoperative renograms and 26/140 (19%) were found to have SNDRF (DRF ≥ 55%). Of 151 patients, 51 (34%) had pre- and postoperative renograms allowing determination of change ≥5% in function. After excluding 2 patients with solitary kidneys, a total of 49 patients defined the study group. Of 49 patients, 12 had SNDRF and 37 did not. Baseline characteristics were similar including mean age at surgery (47.3 months vs 45.4 months) and time to surgery (8.7 months vs 9.8 months). Mean preoperative anteroposterior diameter was significantly different between groups (23.2 mm vs 31.0 mm; P = .04), but postoperative was similar (9.0 mm vs 12.1 mm; P = .14). Mean preoperative DRF was 60.2% in the SNDRF group vs 44.3% in the non-SNDRF. Mean postoperative DRF was 52.4% and 45.3%, respectively (P = .04). There were 9/12 (75%) SNDRF patients who experienced ≥5% loss in function compared to 2/37 (5%) in the non-SNDRF group (P < .01). Three-quarters of SNDRF patients demonstrated a decline of ≥5%DRF postoperatively when compared to non-SNDRF. This finding may not reflect true elevated renal function, but rather hyperfiltration in the setting of obstruction, which-if unrecognized as such-could result in postponing an otherwise beneficial surgical intervention.

Supranormal differential renal function in unilateral hydronephrotic kidney: Insights from functional MR urography

To retrospectively assess supranormal differential renal function (DRF) in unilateral hydronephrotic kidney by functional MR urography (fMRU). The ethics committees granted exempt status for this study and also waived the need for informed consent. A retrospective analysis was performed of all patients undergoing fMRU from January 2008 to November 2011. DRF was measured by both the area under the curve method and Rutland-Patlak plot. Glomerular DRF per unit of volume and kidney volumes were analyzed. Kidney volumes were compared with nomograms. Of 170 children, 3 patients (2, 12, and 14 years) with a left ureteropelvic junction obstruction were included. Glomerular DRF per unit of volume was slightly higher on the dilated side but remained within normal range (<55%). Dilated kidney volumes were higher on the dilated side (≥55%). The volumes of nondilated kidneys were within normal range. The data support the fact that the dilated kidney was not hyperfunctioning and that the nondilated kidney was not hypofunctioning. Based on these three patients, it could be assumed that supranormal DRF on the dilated side might be explained by a slight kidney volume asymmetry, in association with higher DRF per unit of volume, remaining within normal physiological range. J. Magn. Reson. Imaging 2014;40:577-582. © 2013 Wiley Periodicals, Inc.

Nature and Fate of Supranormal Differential Renal Function: Lessons From Long-term Follow-up After Pyeloplasty

To understand the nature and long-term fate of supranormal differential renal function (snDRF), analysis of a post-pyeloplasty database was performed. Preoperative diethylenetriaminepentaacetic acid (DTPA) diuretic renal scans (DRS) identified 33 children with snDRF (>55%). Postoperatively, all showed improved hydronephrosis in ultrasound imaging or normalized drainage pattern in DRS during more than 5 years of follow-up. The fate of snDRF was described, and the nature of snDRF was speculated by associating it with clinical and ultrasound-related variables. Median age at operation was 22 months. Preoperative hydronephrosis was grade III in 27 patients (82%) and grade IV in 6 (18%). Hydronephrosis was normalized or improved, showing relief of obstruction. Overall fate of snDRF revealed significant reduction of DRF in 23 patients (70%), of whom 18 (81%) showed normalization during 5 years of follow-up. Stationary change of snDRF was seen in one-third of patients. Comparison of clinical and ultrasound-related variables revealed lower age, lower renal parenchyma thickness (RPT) increase, and higher preoperative DRF in the normalized group compared with the other group. The normalized group also showed a higher number in Society of Fetal Urology grade 4 hydronephrosis and lower RPT, although they reached borderline statistical significance. Long-term follow-up revealed that 70% of snDRF significantly decreased and normalized in most patients. The normalized group was younger and showed more hydronephrotic changes. Hydronephrotic change is suggested as a possible cause of snDRF.

569 CAN PYELOPLASTY BE DELAYED IN URETEROPELVIC JUNCTION OBSTRUCTION WITH SUPRANORMAL DIFFERENTIAL RENAL FUNCTION?

You have accessJournal of UrologyPediatrics: Imaging/Infections & Vesicoureteral Reflux1 Apr 2011569 CAN PYELOPLASTY BE DELAYED IN URETEROPELVIC JUNCTION OBSTRUCTION WITH SUPRANORMAL DIFFERENTIAL RENAL FUNCTION? Myung Up Kim, Young Jae Im, Hyun Jin Jung, Yong Seung Lee, Chang Hee Hong, and Sang Won Han Myung Up KimMyung Up Kim Seoul, Korea, Republic of More articles by this author , Young Jae ImYoung Jae Im Seoul, Korea, Republic of More articles by this author , Hyun Jin JungHyun Jin Jung Seoul, Korea, Republic of More articles by this author , Yong Seung LeeYong Seung Lee Seoul, Korea, Republic of More articles by this author , Chang Hee HongChang Hee Hong Seoul, Korea, Republic of More articles by this author , and Sang Won HanSang Won Han Seoul, Korea, Republic of More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.1379AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The management of ureteropelvic junction obstruction (UPJO) in patients with supranormal ipsilateral differential renal function (DRF) is obscure. We analyzed the change of ipsilateral DRF before and after pyeloplasty to understand the significance of supranormal ipsilateral DRF. METHODS We retrospectively reviewed the medical records of 206 patients who underwent pyeloplasty between January 2005 and June 2009. In 56 patients, ipsilateral DRF at initial diagnosis was more than 55%. We divided them into two groups-patients with more than 5% decreased in ipsilateral DRF before pyeloplasty as group A (23 patients) and all other patients as group B (33 patients). We analyzed ultrasonography and MAG3 scan before and after surgery along with other clinical parameters. RESULTS There was no difference in age, sex, laterality, grade of hydronephrosis between the two groups. Mean ipsilateral DRF was not significantly different (57.8% vs. 58.3%). Duration from diagnosis to surgery was 9.1 months and 3.5 months for group A and B, respectively (p=0.002). In group A, the mean duration from initial diagnosis to a more than 5% decrease in ipsilateral DRF was 7.5 months. Postoperatively mean 15.7 months , mean ipsilateral DRF was 42.4% in group A and 50.8 in group B (p=0.004). 10 patients (43.5%) in group A and 3 patients (9.1%) in group B eventually had ipsilateral DRF below 45%. CONCLUSIONS Supranormal ipsilateral DRF may be temporary. If it is decreased more than 5%, it could be the reason for irreversible renal damage even after pyeloplasty. We should carefully follow up patients with supranormal DRF in UPJO. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e229 Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information Myung Up Kim Seoul, Korea, Republic of More articles by this author Young Jae Im Seoul, Korea, Republic of More articles by this author Hyun Jin Jung Seoul, Korea, Republic of More articles by this author Yong Seung Lee Seoul, Korea, Republic of More articles by this author Chang Hee Hong Seoul, Korea, Republic of More articles by this author Sang Won Han Seoul, Korea, Republic of More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

The Importance of Obtaining Conjugate Views on Renographic Evaluation of Large Hydronephrotic Kidneys: An In Vitro and Ex Vivo Analysis

It is postulated that significant obstruction leads to decreased ipsilateral renal function. However, maintained or even increased differential renal function is often seen in patients with large hydronephrotic kidneys. The reason for such a phenomenon is unclear. We designed an in vitro and ex vivo experimental model that permits the controlled orientation of thinned renal parenchyma and background activity during gamma camera detection. A 5-step experimental study was designed with balloons or reservoirs containing known amounts of radioisotope. A balloon was incrementally compressed between 2 Plexiglas sheets (step 1). Simultaneous measurement of radio emission was done of 5 glass beakers of varying diameters filled with the same amount of water and (99m)Tc (step 2). A single beaker containing diluted (99m)Tc was interfaced with air (step 3) or water (step 4) at different distances from the gamma camera. Pig kidneys previously injected with dimercapto-succinic acid were removed and scanned (step 5). One of the kidneys was then progressively sliced, thinning its parenchyma, and sliced and nonsliced kidneys were simultaneously scanned again. Progressively increased counts were detected as the projected surface area of the radioactive balloons (step 1) and beakers (step 2) increased. Counts detected were inversely proportional to the amount of water interfaced between the container and the gamma camera. Significantly more radiation was detectable in sliced kidneys containing dimercapto-succinic acid than in intact control kidneys. These findings suggest that the artifactual supranormal differential renal function that is observed during renographic evaluation of large hydronephrotic kidneys actually exists. Parenchymal proximity and distribution in relation to the pelvis are critical determinants. These findings suggest that the conjugate view technique may be more suitable for renographic evaluation of large hydronephrotic kidneys.

The change in renal function in the supranormal hydronephrotic kidney after pyeloplasty

To investigate changes in the differential renal function (DRF) before and after pyeloplasty in renal units with unilateral pelvi-ureteric junction obstruction (PUJO) with supranormal function, and to evaluate the clinical significance. We reviewed the medical and radiographic records of 29 children (26 boys and three girls) with unilateral PUJO with a DRF (estimated by (99m)Tc-mercaptoacetyltriglycine renal scintigraphy) of >/= 50% in the affected renal unit, who had pyeloplasty and were followed for >1 year after surgery. Patients were divided into two groups according to the degree of change in their DRF to compare the clinical variables, anteroposterior pelvic diameter and parenchymal thickness measured by renal ultrasonography. The mean (range) follow-up after pyeloplasty was 35 (12-89) months. After pyeloplasty, although the mean DRF reduced from 53.8% to 51.4%, in seven (24%) patients the DRF decreased significantly (>5%) while most (76%) showed a change of </= 5% of the preoperative function, or further improvement. In the seven patients with a DRF of >/= 55% before surgery, the DRF afterward was >55% in four and 50-55% in one. Between those with and with no significant reduction in DRF, only the preoperative renal parenchymal thickness differed significantly (2.78 vs 5.00 mm, P = 0.006). Supranormal DRF exists and represents the true split function of the affected renal unit in patients with adequate renal parenchyma; these units maintained the supranormal function after pyeloplasty. Parenchymal thickness might be useful to differentiate between the true and false estimates and predict surgical outcome before surgery.

Supranormal renal function in unilateral hydronephrosis: does it represent true hyperfunction?

The existence of supranormal differential renal function in unilateral hydronephrosis remains controversial. While some authors consider it as fact, others believe that it is just a technical artifact. Within our department, chromium-51 ethylene diamine tetra-acetic acid (Cr-EDTA) renal clearance is systematically performed in conjunction with technetium-99m mercaptoacetyltriglycine (MAG3) renograms to derive an absolute single kidney glomerular filtration rate (SKGFR). Our data allows us to ascertain whether supranormal differential renal function in unilateral hydronephrosis might be due to hypofunction of the contralateral kidney. Children with marked unilateral hydronephrosis were selected from a large database of MAG3 diuretic(s) renograms. We excluded patients with posterior urethral valves, duplex anomalies, neurogenic bladder, solitary kidney, and those who underwent any previous urological surgery. We also excluded children who had an early furosemide injection (F0 procedure), selecting only those having received furosemide at the end of the renogram (F+20 test). Seventy-three patients (92 renograms) fulfilled these criteria. Differential renal function was calculated using the integral method. Hydronephrotic kidney with a relative uptake > or =55% was defined as supranormal. Six renograms (four patients) demonstrated supranormal relative function on the hydronephrotic side. However, the SKGFR of these kidneys was in all cases within the range of normal values, while the contralateral side demonstrated borderline low SKGFR. Increased relative function on the side of the hydronephrotic kidney is relatively infrequent. When it occurs, it may be related to a borderline hypofunction of the contralateral kidney.

INCREASED NEPHRON VOLUME IS NOT A CAUSE OF SUPRANORMAL RENOGRAPHIC DIFFERENTIAL RENAL FUNCTION IN PATIENTS WITH URETEROPELVIC JUNCTION OBSTRUCTION

Increasing clinical importance is being placed on the role of differential renal function (DRF) in the management of congenital ureteropelvic junction obstruction. Supranormal DRF of the hydronephrotic kidney on renal scan is a puzzling phenomenon and is hypothesized to be due to an increase in single nephron filtration or nephron volume without sound evidence. We studied the histopathological changes of hydronephrotic kidneys to determine whether glomerular hypertrophy underlies supranormal DRF. We retrospectively evaluated the records of 3 females and 32 males with unilateral congenital hydronephrosis who underwent pyeloplasty. Mean patient age at operation was 12.6 months (range 0.1 to 144). Needle biopsies from 3 different sites at the lower pole of the kidney were performed during surgery. To evaluate the presence of glomerular hypertrophy, the maximal planar area of glomeruli was measured under light microscopy using an image analyzer. Tissue samples obtained from kidneys without a history of urinary tract disease at autopsy were used as controls. The mean glomerular areas of the patient and control groups were evaluated according to DRF and age. The mean glomerular area values of the patient group were smaller than those of the control group, except for 4 patients. The glomerular areas of the hydronephrotic kidneys with supranormal DRF were not significantly different from those of the control group. Instead, the probability of larger renal glomeruli increased with decreasing DRF (p = 0.1155). Increased nephron volume can be discounted as a cause of supranormal DRF.

Supranormal renal function in unilateral hydronephrotic kidney can be avoided.

There are reports and controversy in the literature of supranormal (defined as >55%) differential renal function (DRF) in the hydronephrotic kidney in children with unilateral hydronephrosis. It is not confirmed whether supranormal DRF is an artifact or a true finding. In patients in whom the relative renal function deteriorates, relief of obstruction becomes surgically necessary and if this artifact can be removed. Supranormal function in an obstructed kidney is confusing and there is no consensus on how to manage these patients. There is no agreement if this is a true entity or an artifact. We wanted to address this issue by reporting our experience. We reviewed all the consecutive cases from August 2000 to October 2001 who were studied in our center with the diagnosis of unilateral renal obstruction for confirmation or evaluation of DRF. All patients had MAG-3 studies that were interpreted by experienced nuclear medicine physicians. The DRF were measured within the first to second minute of the MAG-3 injection. Regions of interest were drawn by the imaging software and the images were corrected for background counts by drawing regions of interest 2 pixels away from the edge of the renal cortex. Fifty-seven patients were confirmed to be obstructed unilaterally; 41 (72%) patients had obstructive lesions in the left kidney and 16 (28%) in the right kidney. There was no case of supranormal DRF in the obstructed kidneys in our study. The supranormal renal function, as noted in some reports in the literature, was not seen in any patients at our institution. We believe that this entity is an artifact and can be avoided by using MAG-3 and projecting regions of interest by computer software; we plan to start analyzing multiple algorithms in phantoms with different ROI selection for background analysis.

SUPRANORMAL DIFFERENTIAL RENAL FUNCTION IS REAL BUT MAY BE PATHOLOGICAL: ASSESSMENT BY 99mTECHNETIUM MERCAPTOACETYLTRIGLYCINE RENAL SCAN OF CONGENITAL UNILATERAL HYDRONEPHROSIS

It is unclear whether supranormal differential renal function of the hydronephrotic kidney is real or artifactual. We investigated the effect of clinical and renographic parameters on differential renal function. The study included 34 males and 10 females from 1 to 9 months old (median age 2.6 months) with unilateral congenital hydronephrosis. A 99mtechnetium (Tc) mercaptoacetyltriglycine (MAG3) scan was performed, and regions of interest were drawn on the kidneys, and perirenal and lateral backgrounds. Differential renal function was calculated with and without background subtraction at 30-second intervals from 0.5 to 3 minutes after injection of 99mTc-MAG3. The effects of age, sex, obstruction, site and size of the hydronephrotic kidney were analyzed using the generalized estimating equations method. There were 11 right and 33 left hydronephrotic kidneys. An obstructive renographic pattern was present in 33 cases. The trends of differential renal function according to intervals were different between kidneys with and without background subtraction, and differential renal function increased significantly as size increased (p <0.05). Differential renal function of the hydronephrotic kidney with an obstructive renographic pattern increased with time when perirenal or no background subtraction was applied (p <0.05). The effects of age, sex or laterality on differential renal function were not significant. Supranormal function (differential renal function 55% or greater) was present regardless of background subtraction methods and measurement time. Differential renal function is higher in larger hydronephrotic kidney but function of the kidney with an obstructive pattern is overestimated on later phases of 99mTc-MAG3 renal scan. Supranormal differential renal function is real and may be pathologic since it is prone to occur in larger obstructive hydronephrotic kidneys.

SUPRANORMAL DIFFERENTIAL RENAL FUNCTION IS REAL BUT MAY BE PATHOLOGICAL: ASSESSMENT BY 99mTECHNETIUM MERCAPTOACETYLTRIGLYCINE RENAL SCAN OF CONGENITAL UNILATERAL HYDRONEPHROSIS

It is unclear whether supranormal differential renal function of the hydronephrotic kidney is real or artifactual. We investigated the effect of clinical and renographic parameters on differential renal function. The study included 34 males and 10 females from 1 to 9 months old (median age 2.6 months) with unilateral congenital hydronephrosis. A 99mtechnetium (Tc) mercaptoacetyltriglycine (MAG3) scan was performed, and regions of interest were drawn on the kidneys, and perirenal and lateral backgrounds. Differential renal function was calculated with and without background subtraction at 30-second intervals from 0.5 to 3 minutes after injection of 99mTc-MAG3. The effects of age, sex, obstruction, site and size of the hydronephrotic kidney were analyzed using the generalized estimating equations method. There were 11 right and 33 left hydronephrotic kidneys. An obstructive renographic pattern was present in 33 cases. The trends of differential renal function according to intervals were different between kidneys with and without background subtraction, and differential renal function increased significantly as size increased (p <0.05). Differential renal function of the hydronephrotic kidney with an obstructive renographic pattern increased with time when perirenal or no background subtraction was applied (p <0.05). The effects of age, sex or laterality on differential renal function were not significant. Supranormal function (differential renal function 55% or greater) was present regardless of background subtraction methods and measurement time. Differential renal function is higher in larger hydronephrotic kidney but function of the kidney with an obstructive pattern is overestimated on later phases of 99mTc-MAG3 renal scan. Supranormal differential renal function is real and may be pathologic since it is prone to occur in larger obstructive hydronephrotic kidneys.

Contradictory Supranormal Differential Renal Function During Nuclear Renographic Investigation of Hydroureteronephrosis

We selected a group of children with unilateral hydroureteronephrosis to assess the significance of the differential renal function as determined by nuclear renography as a factor in defining obstructive dilatation. All children who presented to our institution during a 21-month period with unilateral hydroureteronephrosis and a normal contralateral kidney were reviewed. Patients with reflux or bladder pathology were excluded, resulting in 13 evaluable patients younger than age 2 years. Diuretic renography was performed using 99mtechnetium-diethylene- triaminepentaacetic acid in accordance with the well tempered renogram. Ancillary studies included voiding cystourethrography, ultrasonography and/or excretory urography.Of the 13 patients 5 had a differential function greater than 55% in the hydronephrotic kidney. Ten of the 13 patients, including the 5 with supranormal function, underwent surgical correction in the form of ureteral reimplantation for recurrent infections, increasing hydronephrosis, decreasing or decreased function and loss of parenchyma. Stenotic distal adynamic ureteral segments with proximal dilatation were confirmed in all cases.The implication by nuclear renography that a dilated kidney has better function than its morphologically normal counterpart is at variance with any available clinical or experimental data. The etiology of this apparently elevated function is unclear and its presence on a renographic study should not be interpreted as suggestive that the kidney is free of risk of nephron loss. Management decisions should not be based solely on the differential function as determined by nuclear renography.