Diuretic renography in hydronephrosis: delayed tissue tracer transit accompanies both functional decline and tissue reorganization

Nuclear medicine and pediatric nephro-urology: a long-lasting successful partnership

Congenital anomalies of the kidney and urinary tract, as well as urinary infections, are very frequent in children. After the clinical and laboratory evaluation, the first imaging procedure to be done is a renal and bladder ultrasound, but afterwards, a main contribution comes from nuclear medicine. Through minimally invasive and sedation-free procedures, nuclear medicine allows the evaluation of the functional anatomy of the urinary tract, and the quantification of renal function and drainage. If pediatric dosage cards provided by scientific societies are used, radiation exposure can also be low. In the pediatric conditions previously mentioned, nuclear medicine is used both for initial diagnosis and follow-up, mostly in cases of suspicion of ureteropelvic or ureterovesical junction syndromes, as well as vesicoureteral reflux or renal scars of febrile infectious episodes. Pediatric nephro-urology constitutes a significant workload of pediatric nuclear medicine departments. The following paragraphs are a revision of the renal radiopharmaceuticals, as well as the nuclear nephro-urology procedures - dynamic and static renal scintigraphy, and direct and indirect radionuclide cystography. A summary of the techniques, main indications, interpretation criteria and pitfalls will be provided. Some future directions for the field are also pointed out, among which the most relevant is the need for nuclear medicine professionals to use standardized protocols and integrate multidisciplinary teams with other pediatric and adult health professionals that manage these life-long pediatric pathologies, which are recognized as an important cause of adult chronic kidney disease.

The Delayed Nephrogram: Point-of-care Quantitative Measurement, Validation as an Indicator of Obstruction, and Novel Use as a Predictor of Renal Functional Impairment

BACKGROUND

The diagnostic value of delayed nephrograms on contrast-enhanced computed tomography has not been studied rigorously.

OBJECTIVE

To develop a method for quantitatively assessing delayed and diminished nephrograms (DDNs) easily at the point of care and to assess the association of DDNs with renal obstruction and renal function.

DESIGN, SETTING, AND PARTICIPANTS

Data were reviewed from 76 patients who underwent a contrast-enhanced computed tomography scan within 30 days of a technetium-99m mercaptoacetyltriglycine diuretic renal scintigraphy (MAG3-DRS) which showed at least one kidney to have normal drainage (T1/2 <10 min) between 2010 and 2021 at a tertiary academic center.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Attenuations of the renal cortex and medulla were measured using circular regions of interest. These attenuations were compared between kidneys to compute several measures of DDN in the kidney with a greater concern for obstruction. Renal parenchymal volume and anterior-posterior renal pelvis diameter (APD) were estimated using simple linear measurements. Inter-rater reliability was computed using the intraclass correlation coefficient (ICC), correlations were computed using Spearman's R, and the relationships between DDN, APD, and renal function of the subject kidney were estimated using linear regression.

RESULTS AND LIMITATIONS

Measures of DDN were highly reliable between raters (ICC 0.71-0.87). DDN was almost always associated with prolonged drainage on MAG3-DRS (90-100%); however, 33-52% of patients with prolonged drainage on MAG3-DRS had no appreciable DDN, depending on the measure of the DDN chosen. All measures of DDN were associated with decreased renal function (<0.001). APD did not significantly predict renal function when controlling for a DDN.

CONCLUSIONS

DDNs on contrast-enhanced computed tomography are associated with renal obstruction and can easily and accurately be quantified at the point of care. A DDN is more closely associated with renal dysfunction than renal pelvic dilation and therefore may be useful in assessing the severity of upper tract obstruction.

PATIENT SUMMARY

In this report, we confirm that a "delayed nephrogram", a classic x-ray finding thought to be associated with kidney blockage, is associated with blockage of the affected kidney. Furthermore, we show that a delayed nephrogram indicates that the affected kidney is not functioning as well as we would expect for a normal kidney of the same size. Since the severity of a delayed nephrogram predicts this decreased function better than the degree of dilation of the kidney, which is a different measurement often used to measure the severity of kidney blockage, the delayed nephrogram may be a better way of measuring the severity of kidney blockage in clinical practice.

Noninvasive assessment of renal dynamics and pH in a unilateral ureter obstruction model using DCE MR‐CEST urography

PURPOSE

To assess the potential of DCE MR CEST urography for assessing renal function in mice with unilateral ureter obstruction (UUO) by simultaneous pH and renal uptake/clearance measurements following injection of iopamidol.

METHODS

The right ureter of nine mice was obstructed via suture ligation. The animals were imaged at day 1, 2, and 3 post-obstruction on an 11.7T MRI scanner. Ninety-six sets of saturated CEST images at 4.3 and 5.5 ppm were collected. Renal pH values were obtained by calculating the signal ratio for these two frequencies and using a pH calibration curve. Renal time activity curves were measured as a percentage change in the post-injection CEST signal at 4.3 ppm relative to the average pre-injection signal.

RESULTS

For the healthy mice, the time activity curves of both kidneys were nearly identical and displayed rapid excretion of contrast. For the UUO mice, the dynamic CEST curves for the obstructed kidneys displayed prolonged time to peak (TTP) values and delayed contrast excretion compared with the contralateral (CL) kidneys. Renal pH maps of the healthy animals showed similar acidic values for both kidneys (pH 6.65 ± 0.04 vs 6.67 ± 0.02), whereas in the obstructed kidneys there was a significant increase in pH values compared with the CL kidneys (pH 6.67 ± 0.08 vs 6.79 ± 0.11 in CL and UUO kidneys, respectively).

CONCLUSION

Our findings indicate that DCE-MR-CEST urography can detect changes in renal uptake/excretion and pH homeostasis and distinguish between obstructed and unobstructed kidney as early as 1 day after UUO.

Quantitative renal magnetic resonance imaging: magnetic resonance urography

The goal of functional renal imaging is to identify and quantitate irreversible renal damage and nephron loss, as well as potentially reversible hemodynamic changes. MR urography has evolved into a comprehensive evaluation of the urinary tract that combines anatomical imaging with functional evaluation in a single test without ionizing radiation. Quantitative functional MR imaging is based on dynamic contrast-enhanced MR acquisitions that provide progressive, visible enhancement of the renal parenchyma and urinary tract. The signal changes related to perfusion, concentration and excretion of the contrast agent can be evaluated using both quantitative and qualitative measures. Functional evaluation with MR has continued to improve as a result of significant technical advances allowing for faster image acquisition as well as the development of new tracer kinetic models of renal function. The most common indications for MR urography in children are the evaluation of congenital anomalies of the kidney and urinary tract including hydronephrosis and renal malformations, and the identification of ectopic ureters in children with incontinence. In this paper, we review the underlying acquisition schemes and techniques used to generate quantitative functional parameters including the differential renal function (DRF), asymmetry index, mean transit time (MTT), signal intensity versus time curves as well as the calculation of individual kidney glomerular filtration rate (GFR). Visual inspection and semi-quantitative assessment using the renal transit time (RTT) and calyceal transit times (CTT) are fundamental to accurate diagnosis and are used as a basis for the interpretation of the quantitative data. The importance of visual assessment of the images cannot be overstated when analyzing the quantitative measures of renal function.

The roles of protein load test in quantitatively evaluating renal function after severe unilateral ureteral obstruction in adult rabbits

Background

The accuracy of dynamic renal scintigraphy in evaluating the function of hydronephrotic kidneys is controversial. This study sought to investigate the effects of ureteral obstruction on renal function and the role of the protein load test (PLT) in evaluating hydronephrotic kidneys' function.

Methods

A ureteral obstruction model was generated with New Zealand white rabbits. The baseline glomerular filtration rate (GFR) and the GFR during the PLT were measured by dynamic renal scintigraphy at weeks 6, 9, and 12 after obstruction and the renal reserve GFRs were calculated. The renal GFR differences between different time points and between the PLT and baseline status were compared.

Results

(I) Both the baseline GFRs (t=11.287, P=0.000) and the GFRs during the PLTs (t=16.235, P=0.000) of the hydronephrotic kidneys were significantly lower than those of the contralateral kidneys. (II) The baseline GFRs of the obstructed kidneys were not significantly different 6, 9, and 12 weeks after obstruction (F=0.122, P=0.887), but their net reserve GFRs (F=8.419, P=0.004) and relative reserve GFRs (F=3.770, P=0.049) gradually decreased over time. (III) There was no significant correlation between the net reserve GFRs (r=-0.006, P=0.977) or the relative reserve functions (r=-0.022, P=0.920) of the obstructed kidneys and their baseline GFRs. However, there was a significant negative correlation between the net reserve GFRs (r=-0.590, P=0.002) or the relative reserve functions (r=-0.546, P=0.006) of the obstructed kidneys and the duration of obstruction. (IV) The reserve GFRs of the obstructed kidneys were not proportional to their baseline GFRs.

Conclusions

The functional changes in hydronephrotic kidneys are not sensitively reflected by baseline GFRs. GFRs during the PLTs and the reserve GFRs play important roles in the early and accurate evaluation of the function of obstructed kidneys.

Renal cortical transit time in the evaluation of prenatally detected presumed pelvi ureteric junction like obstruction: A systematic review

Introduction

Differentiating nonobstructive from obstructive dilatation of the kidney is a clinical dilemma in prenatally detected hydronephrosis. Many radionuclide renogram parameters have been used to differentiate obstructed from non-obstructed units, including cortical transit time (CTT). We evaluate the role of CTT in identifying obstruction through a systematic review.

Methods

A literature search of the MEDLINE, MEDLINE In-Process, and MEDLINE Epub Ahead of Print, EMBASE, Google scholar, Pub Med, and Cochrane Library was done using key words - radionuclide renogram, CTT, parenchymal transit time, cortical transit, renography to identify articles on the subject. The identified articles were assessed for appropriateness and reviewed.

Results

The initial search yielded a total of 1583 articles, after adding the articles from references and applying the inclusion and exclusion criteria a total of 28 articles were selected. CTT showed good inter observer agreement in identifying obstruction. The use of CTT as a single parameter for determining the need for surgery and to identify those kidneys which will have functional improvement after surgery has been evaluated and has been found to be useful. CTT is best used in conjunction with ultrasonography to make clinical decisions.

Conclusion

The commonly used visual method of estimating the CTT, is a promising parameter for the evaluation of prenatally detected pelviureteric junction obstruction. Further well-designed multicenter prospective studies are needed to establish it as the most specific parameter to differentiate obstructive from nonobstructive dilatation of the pelvicalyceal system.

Intraobserver and interobserver variations in cortical transit time measurement in children with pelviureteric junction obstruction

Cortical transit time (CTT) has recently been shown to be a useful parameter in the management of children with pelviureteric junction obstruction (PUJO). The aim of this study was to assess intraobserver and interobserver variations in the qualitative and quantitative assessment of CTT in children with PUJO. A retrospective study was performed, and ^99mTc-MAG3 renogram images of all children with PUJO performed from January 2016 to December 2017 were retrieved. The images were assessed by three observers at two different time points. CTT was qualified as delayed if CTT was more than 3 min else; it was noted as normal. The intraobserver and interobserver variations in the results of the CTT of the normal kidney and affected kidney both before and after surgery were studied. The kappa statistic was used to compare the interobserver variation of qualitative interpretation of CTT. The Bland–Altman plot was used to evaluate the intraobserver and interobserver variations of the quantitative interpretation of CTT. A total of 57 ^99mTc-MAG3 renal scintigraphies were evaluated. Overall, 114 renal units were evaluated with 51 normal renal units and 63 renal units with PUJO. Of these, 63 renal units with PUJO, 31 renal units had been operated upon, whereas the remaining 32 renal units had no intervention at the time of the study. The kappa statistic in the normal, affected operated, and affected unoperated kidneys was interpreted as almost perfect, substantial to almost perfect, and moderate to substantial level of agreement, respectively. The Bland–Altman plot revealed a large mean difference and wide 95% limits of agreement in affected kidneys (both operated and unoperated). The study concludes that the qualitative CTT interpretation in the affected renal unit which is most commonly used in recent studies is a reliable and reproducible parameter in children with PUJO. The quantitative measurement had wide inter- and intraobserver variation for clinical use.

Cortical transit time: understanding utility and pitfalls in children with pelviureteric junction obstruction

INTRODUCTION

Delayed cortical transit time (CTT) has been recently studied and proposed as a parameter that can predict the need for surgery in children with pelviureteric junction obstruction (PUJO).

AIM

The aim of this study was to study the change in CTT, after surgery, in children with PUJO and to correlate CTT with intrapelvic pressure of the kidney.

MATERIAL AND METHODS

A prospective study was performed, and all children who underwent pyeloplasty from January 2016 to December 2017 were included. Pre-operative and postoperative renal ultrasonography and Technetium-99m mercaptoacetyltriglycerine Tc-MAG3 renal scintigraphy were performed. Cortical transit time was measured by a visual method by two different observers. The renal intrapelvic pressure of the kidney was also measured during surgery after giving a diuretic to replicate the diuresis induced during the renal scan. The correlation was studied between the pre-operative CTT and intrapelvic pressures and between the pre-operative CTT and the renal function of the affected kidney.

RESULTS

Thirty-one children were included in the study. The median age of children who underwent surgery was 50 months (2-168). In 71% of patients, the CTT was prolonged before surgery, whereas only 22.5% had delayed CTT after surgery. The mean CTT before surgery was 226.1 ± 74.8 s and decreased to 165.4 ± 55.9 s after surgery (p= <0.001). The mean intrapelvic pressure was 21 ± 7.5 cm H₂O. There was no correlation noted between the intrapelvic pressure and the CTT. A significant negative correlation was noted between the CTT and the different renal function of the kidney.

DISCUSSION

This is the first prospective study that studies the changes in CTT after surgery. Only retrospective studies had been conducted to date which concluded that CTT was delayed in most of the patients who had been operated. It has been proposed that the prolonged CTT is due to raised pressure in the kidney secondary to obstruction. This study did not find any correlation between the pressure and CTT. The significant negative correlation between CTT and renal function also emphasizes the need to take the renal function into consideration before interpreting and using the absolute value of CTT for guiding treatment.

CONCLUSION

Cortical transit time assessment by the visual method is a useful parameter in the management of children with PUJO. There is a significant improvement in CTT after surgery.

Managing Ureteropelvic Junction Obstruction in the Young Infant

In the last decade, management of congenital UPJ obstruction has become progressively observational despite the lack of precise predictors of outcome. While it is clear that many children will have resolution of their hydronephrosis and healthy kidneys, it is equally clear that there are those in whom renal functional development is at risk. Surgical intervention for the young infant, under 6 months, has become relatively infrequent, yet can be necessary and poses unique challenges. This review will address the clinical evaluation of UPJO in the very young infant and approaches to determining in whom surgical intervention may be preferable, as well as surgical considerations for the small infant. There are some clinical scenarios where the need for intervention is readily apparent, such as the solitary kidney or in child with infection. In others, a careful evaluation and discussion with the family must be undertaken to identify the most appropriate course of care. Further, while minimally invasive pyeloplasty has become commonly performed, it is often withheld from those under 6 months. This review will discuss the key elements of that practice and offer a perspective of where minimally invasive pyeloplasty is of value in the small infant. The modern pediatric urologist must be aware of the various possible clinical situations that may be present with UPJO and feel comfortable in their decision-making and surgical care. Simply delaying an intervention until a child is bigger may not always be the best approach.

Predictors of Renal Functional Improvement After Pyeloplasty in Ureteropelvic Junction Obstruction: Clinical Value of Visually Assessed Renal Tissue Tracer Transit in 99mTc-mercaptoacetyltriglycine Renography

OBJECTIVE

To determine the clinical value of visually assessed renal tissue transit time (TTT) in ^99mTc-mercaptoacetyltriglycine (^99mTc-MAG3) renography for patients undergoing pyeloplasty.

MATERIALS AND METHODS

Medical records of 164 patients who underwent dismembered pyeloplasty were retrospectively reviewed. Baseline and postoperative renal ultrasonography and ^99mTc-MAG3 renography were performed. Two urologists blinded to clinical data evaluated the renography and classified TTT as timely or delayed based on visualization of the tracer in the kidney pelvis between 2 and 10 minutes. Renal functional change after pyeloplasty was compared between patients in the timely and delayed groups.

RESULTS

A total of 126 patients (median age, 9 months) were evaluated after excluding patients with bilateral ureteropelvic junction obstruction, a single functioning kidney, duplicated ureter, or <3 months of follow-up. There were no differences between 89 patients with timely TTT and 37 patients with delayed TTT in mean preoperative hydronephrosis grade (3.7 vs 3.8) and pelvic diameter (3.1 cm vs 3.4 cm). Although the pre- and postoperative mean values of differential renal function (DRF) were significantly higher in the timely group than in the delayed group (47.2% vs 38.3% and 47.9% vs 44.6%), DRF change was greater in the delayed group (6.3% vs 0.6%). In multivariate analysis, delayed TTT was the only significant predictor of >5% improvement in renal function after pyeloplasty.

CONCLUSION

Delayed TTT in ^99mTc-MAG3 renography was a significant predictor of renal functional improvement after pyeloplasty in ureteropelvic junction obstruction. Because substantial improvement of renal function is anticipated, we recommend immediate pyeloplasty in patients with delayed TTT and decreased DRF.

Interobserver agreement on cortical tracer transit in 99mTc-MAG3 renography applied to congenital hydronephrosis

OBJECTIVE

This study aims to evaluate interobserver agreement on visual analysis of technetium-99m mercaptoacetyltriglycine (Tc-MAG3) renal tissue transit used for the evaluation of antenatal hydronephrosis.

MATERIALS AND METHODS

Thirty-eight Tc-MAG3 diuretic renograms were retrospectively collected between 1 and 31 December 2015. The 1-min reframed images were presented to four nuclear medicine consultants and to two nuclear medicine residents, one in the first year of the training program and the others in their fourth and final year. These observers were asked to classify the radiotracer cortical transit (normal/delayed) based solely on visual assessment of the images. For the interobserver agreement, modified Fleiss' kappa (κ) analysis for multiple raters was carried out. For both groups, percentages of agreement were also calculated.

RESULTS

A total of 69 kidneys were evaluated. All four nuclear medicine consultants agreed on the classification of 88.4% of the kidneys. When the agreement of at least three of the four observers was considered, the percentage of agreement reached 98.6%. The two nuclear medicine residents agreed on the classification of 69.6% of the kidneys. The modified Fleiss' κ-value was 0.88 (95% confidence interval: 0.79-0.95) for the group of nuclear medicine consultants, indicating almost perfect agreement. For the residents, it was 0.39 (95% confidence interval: 0.16-0.59), suggesting fair agreement.

CONCLUSION

Our results seem to indicate that there is an almost perfect agreement in the qualitative identification of delayed cortical transit among physicians with experience at observing renographic images.

Delayed renal tissue tracer transit in Tc-99m-DTPA renography correlates with postoperative renal function improvement in UPJO patients

OBJECTIVE

The aim of the study was to explore the potential parameters for evaluating the improvement in relative renal function (RRF) in patients with unilateral ureteropelvic junction obstruction (UPJO) who underwent surgery. In this regard we observed the RRF expressed as the obstructed kidney's percentage contribution to overall renal function in technetium-99m diethylenetriaminepentaacetic acid (Tc-99m-DTPA) diuretic renography.

MATERIALS AND METHODS

Data on 47 patients, who underwent Anderson-Hynes pyeloplasty for diagnosed unilateral UPJO during the period of February 2003 to October 2014, were retrospectively collected. Tc-99m-DTPA diuretic renography was performed on all patients before and after surgery, and no morphological or functional abnormalities were detected on the contralateral kidney. Several parameters, especially renal tissue tracer transit (TTT), the response to furosemide stimulation, and RRF, were evaluated. All data were analyzed with the statistical software SPSS, 17.0, and a value of P less than 0.05 was considered statistically significant.

RESULTS

Data on 42 patients were eventually retained for further analysis; five patients were excluded because of indeterminate TTT. All patients showed obstructive response to furosemide stimulation with a preoperative RRF of 41±12%. Postoperative RRF of the obstructed kidneys was 47±11%, significantly higher than the preoperative RRF (P<0.05). Postoperative RRF improvement (absolute increment≥5%) was seen in 18/42 (43%) patients, and 24/42 (57%) of them manifested with postoperative drainage improvement. After surgery, both the RRF increment and the percentage of patients with postoperative RRF improvement in the preoperative delayed TTT group were significantly higher than those in the normal TTT group (12±7 vs. 2±4%, and 81 vs. 19%, respectively; P<0.05), but no significant difference in postoperative drainage improvement was detected between the two groups (56 vs. 54%, P>0.05). None of the other factors, including the preoperative RRF, obstructed kidney location, surgical method, sex, and age, had a significant influence on postoperative RRF improvement (P>0.05).

CONCLUSION

Preoperatively delayed TTT of Tc-99m-DTPA diuretic renography was an independent factor that correlated with RRF improvement of unilaterally hydronephrotic kidneys, and might provide valuable information for surgical decisions pertaining to UPJO patients.

Radionuclides in nephrourology, Part 2: pitfalls and diagnostic applications

Radionuclide renal scintigraphy provides important functional data to assist in the diagnosis and management of patients with a variety of suspected genitourinary tract problems, but the procedures are underutilized. Maximizing the utility of the available studies (as well as the perception of utility by referring physicians) requires a clear understanding of the clinical question, attention to quality control, acquisition of the essential elements necessary to produce an informed interpretation, and production of a report that presents a coherent impression based on data contained in the report and that specifically addresses the clinical question. To help achieve these goals, part 1 of this review addressed the available radiopharmaceuticals, quality control, and quantitative indices, including the measurement of absolute and relative renal function. Part 2 assumes familiarity with part 1 and focuses on the common clinical indications of suspected obstruction and renovascular hypertension; part 2 also summarizes the status of radionuclide renal imaging in the evaluation of the transplanted kidney and the detection of infection, discusses potential pitfalls, and concludes with suggestions for future research. The series of SAM questions accompanying parts 1 and 2 has been designed to reinforce and extend points made in the review. Although the primary focus is the adult patient, aspects of the review also apply to the pediatric population.

Assessment of renal function in mice with unilateral ureteral obstruction using 99mTc-MAG3 dynamic scintigraphy

Background

Renal scintigraphy using ^99mTc-mercaptoacetyltriglycine (^99mTc-MAG3) is widely used for the assessment of renal function in humans. However, the application of this method to animal models of renal disease is currently limited, especially in rodents. Here, we have applied ^99mTc-MAG3 renal scintigraphy to a mouse model of unilateral ureteral obstruction (UUO) and evaluated its utility in studying obstructive renal disease.

Methods

UUO mice were generated by complete ligation of the left ureter. Sham-operated mice were used as a control. Renal function was investigated on days 0, 1, 3, and 6 post-surgery using dynamic planar imaging of ^99mTc-MAG3 activity following retro-orbital injection. Time-activity curves (TACs) were produced for individual kidneys and renal function was assessed by 1) the slope of initial ^99mTc-MAG3 uptake (SIU), which is related to renal perfusion; 2) peak activity; and 3) the time-to-peak (TTP). The parameters of tubular excretion were not evaluated in this study as ^99mTc-MAG3 is not excreted from UUO kidneys.

Results

Compared to sham-operated mice, SIU was remarkably (>60%) reduced in UUO kidneys at day 1 post surgery and the TACs plateaued, indicating that ^99mTc-MAG3 is not excreted in these kidneys. The plateau activity in UUO kidneys was relatively low (~40% of sham kidney’s peak activity) as early as day1 post surgery, demonstrating that uptake of ^99mTc-MAG3 is rapidly reduced in UUO kidneys. The time to plateau in UUO kidneys exceeded 200 sec, suggesting that ^99mTc-MAG3 is slowly up-taken in these kidneys. These changes advanced as the disease progressed. SIU, peak activity and TTPs were minimally changed in contra-lateral kidneys during the study period.

Conclusions

Our data demonstrate that renal uptake of ^99mTc-MAG3 is remarkably and rapidly reduced in UUO kidneys, while the changes are minimal in contra-lateral kidneys. The parametric analysis of TACs suggested that renal perfusion as well as tubular uptake is reduced in UUO kidneys. This imaging technique should allow non-invasive assessments of UUO renal injury and enable a more rapid interrogation of novel therapeutic agents and protocols.

Captopril renography as a prognostic factor in obstructive hydronephrosis with preserved renal function

Hydronephrotic kidney with a differential renal function greater than 55% is defined as supranormal. The signification of this finding remains controversial. In this article, the authors reported a case of supranormal function in obstructive hydronephrosis. Differential renal functions were evaluated after administration of captopril and after pyeloplasty. The role of captopril renography as a prognostic factor for surgery is discussed.

Diuretic renography in hydronephrosis: renal tissue tracer transit predicts functional course and thereby need for surgery

PURPOSE

The recognition of those hydronephrotic kidneys which require therapy to preserve renal function remains difficult. We retrospectively compared the 'tissue tracer transit' (TTT) of (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG(3)) with 'response to furosemide stimulation' (RFS) and with 'single kidney function < 40%' (SKF < 40%) to predict functional course and thereby need for surgery.

METHODS

Fifty patients with suspected unilateral obstruction and normal contralateral kidney had 115 paired (baseline/follow-up) (99m)Tc-MAG(3) scintirenographies. Three predictions of the functional development were derived from each baseline examination: the first based on TTT (visually assessed), the second on RFS and the third on SKF < 40%. Each prediction also considered whether the patient had surgery. Possible predictions were 'better', 'worse' or 'stable' function. A comparison of SKF at baseline and follow-up verified the predictions.

RESULTS

The frequency of correct predictions for functional improvement following surgery was 8 of 10 kidneys with delayed TTT, 9 of 22 kidneys with obstructive RFS and 9 of 21 kidneys with SKF < 40%; for functional deterioration without surgery it was 2 of 3 kidneys with delayed TTT, 3 of 20 kidneys with obstructive RFS and 3 of 23 kidneys with SKF < 40%. Without surgery 67 of 70 kidneys with timely TTT maintained function. Without surgery 0 of 9 kidneys with timely TTT but obstructive RFS and only 1 of 16 kidneys with timely TTT but SKF < 40% lost function.

CONCLUSION

Delayed TTT appears to identify the need for therapy to preserve function of hydronephrotic kidneys, while timely TTT may exclude risk even in the presence of an obstructive RFS or SKF < 40%.