Determination of tissue tracer transit of Technetium-99m-mercaptoacetyltriglycine diuretic renography in infants with suspected ureteropelvic junction obstruction - A multicenter prospective observational study

INTRODUCTION

There is an ongoing controversy regarding management of ureteropelvic junction obstruction in infants, with a shift towards a non-operative approach. However, precise predictors of outcome are lacking. Recent studies postulated a high prognostic value of Technetium-99m-mercaptoacetyltriglycine tissue tracer transit with regard to the development of an impaired differential renal function and its potential improvement following pyeloplasty.

OBJECTIVE

To evaluate the prognostic value of Technetium-99m-mercaptoacetyltriglycine tissue tracer transit for the occurrence of changes in differential renal function in infants with suspected unilateral ureteropelvic junction obstruction in a prospective observational multicenter study.

STUDY DESIGN

Infants below 3 months of age with a unilateral isolated hydronephrosis ≥ grade 3 received ultrasound and Technetium-99m-mercaptoacetyltriglycine diuretic renography at two different time points (timepoint 1 and timepoint 2). Data were analyzed at local centers and at the study center and were collected in an internet-based database system. Tissue tracer transit was determined for each diuretic renography, inter-observer variation for tissue tracer transit and standard parameters for judgement of differential renal function development were assessed.

RESULTS

Thirty-seven patients were analyzed. Median age was 11 weeks (7-15) at timepoint 1 and 26 weeks (19-33) at timepoint 2. A delayed tissue tracer transit at timepoint 1 was not associated with deterioration of differential renal function at timepoint 2 in both, locally (10/37 cases) and centrally (4/37) analyzed cases. However, sensitivity and specificity were poor. The intraclass correlation coefficient comparing local and central findings of tissue tracer transit and renal drainage demonstrated poor or fair agreement. Analysis of standard parameters for differential renal function development revealed a prognostic value only for the dichotomized anteroposterior renal pelvic diameter (APD, p = 0.03, 95%-CI 1.2-22.2).

DISCUSSION

Regarding the primary endpoint of our study, we could not confirm the hypothesis that delayed tissue tracer transit reliably predicts a subsequent decline in differential renal function in the cohort of patients studied. Whether the low age of the patients, technical problems in the correct assessment of tissue tracer transit by the investigator in early infancy, the study design, or the parameter itself played a role is debated.

CONCLUSION

In the presented setting tissue tracer transit was not useful as a predictive parameter for deterioration of differential renal function in infants with suspected unilateral ureteropelvic junction obstruction. Sensitivity and specificity of tissue tracer transit were not sufficient for risk stratification. Improved utility of tissue tracer transit as a marker might be achieved using a different study setting.

Management dilemma in pelvi-ureteric junction obstruction: is transit time the answer?

PURPOSE

Pelvi-ureteric junction obstruction (PUJO) is the leading cause for hydronephrosis in children. Diuretic renography used in the pre- and post-operative evaluation of pyeloplasty may not be reliable in predicting the outcome.

METHODS

A prospective study was conducted from October 2018 to November 2020, including all children with unilateral PUJO undergoing Pyeloplasty. Renal diuretic renography scans done in the pre and post operative periods were assessed for transit time. The time taken for the isotope to reach the renal pelvis was noted by a single observer as the transit time, from the dynamic frames of the diuretic renogram.

RESULTS

Of the 65 children, 74% were boys. The transit time (median) in the preoperative renography was 10 min, whereas the same was 4 min 45 s in the postoperative period, the decrease was statistically significant. On evaluation of transit time with ROC (receiver operating characteristics) curve, a cut-off of 4 min and 25 s was arrived at, which could identify the delayed drainage reliably.

CONCLUSION

Improvement in transit time is a reliable predictor of renal function improvement after pyeloplasty, comparing favorably in relation to split renal function.

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.

The role of Plasma Renin Activity in prenatally diagnosed non-obstructed hydronephrosis at risk for surgery-an observational study

BACKGROUND

Patients with asymptomatic prenatally diagnosed hydronephrosis may progress to needing surgery; no biomarker supporting the identification of these cases is currently available. The aim of the study was to assess the role of Plasma Renin Activity (PRA) as a discriminatory factor to identify patients with asymptomatic prenatally diagnosed hydronephrosis who require close monitoring and are at-risk for surgery.

METHODS

The study group consists of 30 children prenatally diagnosed with asymptomatic unilateral hydronephrosis, initially managed with medical follow-up. Pyeloplasty was indicated if patients became symptomatic or if there was a significant drop in split renal function (SRF) during follow-up. An association was sought between PRA and renal parameters in post-hoc analysis.

RESULTS

During the mean follow-up of 55.5 ± 8.2 months, 13/30 (43.3%) patients developed delayed drainage and 8/30 (26.6%) underwent pyeloplasty. Mean PRA was higher at presentation in the group which later presented with a drop in differential kidney function  ≥ 10%, while it was within the normal range for age in the other patients. Before pyeloplasty, progression to delayed drainage coincided with a drop in SRF and a rise in PRA. While PRA levels normalized after pyeloplasty, SRF improved but did not reach initial values. A mean rise of 68.9% in PRA preceded current indications for surgery by 27.5 ± 9.5 months.

CONCLUSIONS

A progressive increase in PRA in children with asymptomatic prenatally diagnosed hydronephrosis reflects obstructive stress in the tubulo-interstitial compartment. This stress is relieved by pyeloplasty and is reflected by a drop in PRA after surgery. PRA can, thus, serve as the discriminatory factor to identify hydronephrosis patients 'at-risk' for surgery even before the current criteria for pyeloplasty are met.

Head to head comparison of [99mTc]Tc(CO)3(NTA) and [99mTc]Tc-MAG3 in patients with suspected obstruction

PURPOSE

^99mTc-tricarbonyl-nitrilotriacetic acid, [^99mTc]Tc(CO)₃(NTA), is a new ^99mTc-renal radiopharmaceutical with a clearance equal to that of ¹³¹I-ortho-iodohippuran, [¹³¹I]I-OIH. Our purpose was to compare the performance of [^99mTc]Tc(CO)₃(NTA) and [^99mTc]Tc-MAG3 in patients with suspected obstruction.

METHODS

[^99mTc]Tc(CO)₃(NTA) was prepared with commercially available NTA ligand and CRS Isolink kit, and isolated by HPLC. Eighteen adult patients referred for diuretic renography received an intravenous injection of approximately 40 mg of furosemide 15 min prior to either [^99mTc]Tc(CO)₃(NTA) or [^99mTc]Tc-MAG3 (mean activity of 47 ± 4.4 MBq). Data were acquired for 24 min followed by an anterior image of the liver and gall bladder and a measure of voided volume. Patients received a second furosemide injection equal to one third of the original dose followed fifteen minutes later by administration of the alternate tracer, mean activity of 320 ± 34 MBq. Clearances were measured using a camera-based technique.

RESULTS

The clearance of NTA was greater than that of MAG3, 331 ± 146 versus 271 ± 105 mL/min/1.73 m², respectively, p < 0.0001. The kidney to background ratio for NTA was greater than that of MAG3 for both left and right kidneys, p < 0.001; the 20 min/maximum count ratio was significantly less, p < 0.0001. There was no significant difference in the voiding volumes following NTA and MAG3 administration, 598 ± 237 mL versus 498 ± 170 mL, respectively, p = 0.07. Gall bladder activity was not observed with NTA but was present in 6/17 MAG3 studies. Images and renogram curves were comparable except for two patients where the NTA study excluded obstruction but the MAG3 study suggested an indeterminate or obstructed kidney.

CONCLUSIONS

Unlike MAG3, NTA is not eliminated via the hepatobiliary track. Moreover, NTA has a higher kidney to background ratio and more rapid clearance than MAG3. These advantages should allow more robust camera-based clearance measurements and may lead to better discrimination between obstructed and non-obstructed kidneys.

The different elements of the Urinary Tract Dilation (UTD) Classification System and their capacity to predict findings on mercaptoacetyltriglycine (MAG3) diuretic renography

INTRODUCTION

The UTD Classification System risk stratifies postnatal UTD into three groups: low risk (UTD P1), intermediate risk (UTD P2), and high risk (UTD P3). In the original consensus document, a functional scan is not recommended for UTD P1 and is left to the discretion of the clinician for UTD P2 and P3.

OBJECTIVE

This study aims to understand which patients with postnatal urinary tract dilation would benefit from a functional study. We investigated how different elements of the UTD classification system predict differential renal function (DRF) and diuretic half-life (T½) on MAG3 scan in infants undergoing evaluation for prenatally detected UTD.

STUDY DESIGN

This is a multicenter retrospective chart review of infants 6 months of age or younger evaluated for prenatal UTD, correlating their first MAG3 scan and first postnatal renal ultrasound (RUS). Multivariable logistic regression was used to find UTD elements predictive of DRF < 40% and/or T½ > 20 min.

RESULTS

A total of 517 patients met study criteria. Median age at time of RUS and MAG3 renal scan was 48 days (IGR 31-81) and 63 days (IQR 45-98), respectively. DRF < 40% was found in 6% of kidneys with UTD P2 and 35% of kidneys with UTD P3. T½ > 20 min was found in 31% of kidneys with UTD P2 and 79% of kidneys with UTD P3. An abnormal ureter (OR 2.7, 95% CI 1.2-6.0) and parenchymal thinning (OR 16, 95% CI 5.8-41.4) were significant at predicting DRF < 40%. Parenchymal thinning (OR 3.0, 95% CI 1.5-6.1) also predicted T½ > 20 min, as did each cm increase in the anterior-posterior renal pelvic diameter (APRPD) (OR 4.8, 95% CI 3.0-7.7).

DISCUSSION

The UTD system discriminates well and correlates with the likelihood of finding adverse features on diuretic renography. Patients in the UTD P3 high-risk category had a significantly higher incidence of decreased differential renal function and delayed drainage than those in UTD P1 and P2. Of the individual components of the UTD Classification system, the presence of parenchymal thinning was the most important factor in predicting both decreased differential renal function and delayed drainage.

CONCLUSION

Given the high incidence of poor function and delayed drainage seen in the UTD P3 group, we believe a functional study should be recommended in the evaluation of these patients. Our findings support leaving the performance of a functional study at the discretion of the physician for UTD P2.

The search for the definition, etiology, and effective diagnosis of upper urinary tract obstruction: the Whitaker test then and now

INTRODUCTION

Robert Whitaker, inspired by Dr William W Scott at the Brady Institute at Johns Hopkins and by Sir David Innes Williams at Great Ormond Street Hospital for Children in the late 1960s, spent much of his career exploring the meaning of persistent dilatation of the upper urinary tract, in an attempt to define obstruction and to find a means of diagnosing it accurately.

OBJECTIVE

This is a historical review of Bob Whitaker's journey from his definition of obstruction to the inception of his eponymous test.

RESULTS

In 1975, he proposed a theory to explain the pathophysiology behind obstructive hydronephrosis and megaureter. He was among the first pediatric urologists to observe that 'it is wrong… to assume that dilatation necessarily indicates obstruction', a statement that was widely stated and even appeared in the textbooks at the time. He defined obstruction as 'an increased pressure in the pelvicalyceal system of the kidney at normal physiological flow rates such that the renal function is adversely affected'. This realization led to the development of a percutaneous pressure-measuring technique at controlled flows, later referred to as the Whitaker test. It predated and later assisted in the interpretation of diuretic renograms.

DISCUSSION

Whitaker questioned the etiology of 'hydronephrosis' and challenged other hypotheses proposed at the time, which often included causes of mechanical occlusion at the ureteropelvic junction (UPJ) or ureterovesical junction (UVJ). Whitaker's hypothesis is that 'obstruction' at UPJ and UVJ levels is not mechanical but the result of a failure of normal peristalsis to form and propagate a bolus. This, in turn, depends on the potentially abnormal distensibility of the renal pelvic and ureteric wall whether it be congenital or acquired. The aim of this review is to recall the history of the development of a technique to evaluate dilated upper urinary tracts and to re-evaluate various theories that might explain the etiology of the dilatation in the light of more recent evidence. Robert (or Bob, to his colleagues) Whitaker was among the founder members of the British Association of Paediatric Urologists, which now has more than 50 members, in 1992. Together with his colleagues Philip Ransley and David Thomas, Whitaker established the annual pediatric urology course for pediatric surgery and urology trainees in Cambridge, U.K., which still runs to this day. He retired from his surgical practice in 1990 and up until the present time has taught clinical anatomy in the Cambridge University School of Medicine.

Is it Always Necessary to Treat an Asymptomatic Hydronephrosis Due to Ureteropelvic Junction Obstruction?

The postnatal treatment of asymptomatic unilateral hydronephrosis due to ureteropelvic junction obstruction remains controversial, and the timing of and indications for surgical intervention are continuously debated. There is no consensus on the best follow-up during expectant management. The various modalities and parameters have been discussed along with their pros and cons and an attempt has been made to clear up the controversies.

Benefit of F-15 protocols in equivocal F + 20 MAG3 renography in children with upper tract dilatation and symmetric split function: Results and outcomes

PURPOSE

In children with upper tract dilatation, diuretic renography, which includes application of mercaptoacetyltriglicin-99 mTc (MAG3), is the standard examination. Ordinarily, furosemide is applied 20 min after tracer injection (F + 20). In children with persistent hydronephrosis and preserved split function, this protocol may lead to further examinations with repeatedly equivocal washout curves. The present study evaluated the potential of MAG3 (F-15) scans in this subgroup of children to achieve a conclusive result avoiding additional equivocal MAG3 (F + 20) scans.

OBJECTIVE

To evaluate whether the washout curve using the F-15 protocol is a helpful criterion with which to clarify results in patients with equivocal patterns in the F + 20 protocol.

PATIENTS

31 children (male/female 22/9, median age at time of examination 42 months, mean anterioposterior diameter 2.1 cm, left/right 14/18) underwent MAG3 F-15 renography at the present department because of upper urinary tract dilatation and (repeatedly n ≥ 2 F + 20 = 28) equivocal results in MAG3 F + 20 examinations.

RESULTS

In 10/31 children (32.2%), MAG3 F-15 revealed an obstructive pattern, indicating a pyeloplasty in 9/10 of them (90%). In 16/31 children (51%), the F-15 protocol showed a non-obstructive curve, leading to further uneventful follow-up in 15/16 of them (93.7%). In 5/31 children (16%), MAG3 F-15 led to equivocal results, resulting in no pyeloplasty and further uneventful follow-up in all the children (mean follow-up 1.46 years).

DISCUSSION

In children with persistent high-grade hydronephrosis on ultrasound and preserved split function, multiple scans were prompted and further management was sometimes difficult. Although there was proven evidence that the F-15 protocol reduced the frequency of equivocal pattern, there was no indication for primary F-15 investigation, due to the risk of over diagnosis of obstruction. The F-15 scan was considered to be a stress test of the upper tract leading to a diuretic challenge without any opportunity to investigate normal washout curve. In these cases, partial obstruction could lead to false positive obstructive results. A stepwise approach, in which the traditional F + 20 technique allows observation of the rate of washout of radiopharmaceuticals before forced diuresis followed by a F-15 protocol, could reduce the child's additional radiation burden and stress.

CONCLUSION

After equivocal results in MAG3 F + 20 protocols, performing a MAG3 F-15 exam lead to a conclusive result in 80.6% (25/31 patients) of the cases. Thus, performing a MAG3 (F-15) exam can be recommended in children with persistent hydronephrosis and preserved split function after equivocal results on MAG3 (F + 20) scans.

Role of ureteric stents in relieving obstruction in patients with obstructive uropathy

Purpose:

The aim of this study is to evaluate the role of ureteric stents in relieving obstruction and improvement of kidney function in patients with obstructive uropathy.

Materials and Methods:

This study involved 138 patients with obstructive uropathy with age ranged from 2 months to 73 years. Patients classified into two groups: Group (I): Includes 57 patients (41.3%), ureteric stents fixed to them; and Group (II): Includes 81 patients (58.6%) managed by other treatment modalities. All patients underwent clinical assessment, Laboratory and radiologic investigations: At presentation and postoperative. These included: Complete urine analysis, urine culture and sensitivity, serum creatinine, serum urea nitrogen, serum uric acid, serum sodium (Na), serum potassium (K), Fasting blood glucose level and blood picture and plain X-ray (KUB), abdominal ultrasonography (US), diuretic renography and retrograde pyelography.

Results:

Renal glomerular filtration rate (GFR) was used as an indicator for improvement of renal function after fixation of ureteric stent. In group I: 56 (71.8%) kidneys showed significant recovery compared to 61 kidneys (66.3%). In group II, there is statistically significant relation between renal perfusion and renal recovery (P < 0.004), statistically significant relation between parenchymal thickness and recovery in both groups (P < 0.0002), statistically significant relation between degree of corticomedullary differentiation and recovery (P < 0.0003) and statistically significant relationship between hemoglobin levels at presentation and the recoverability (P < 0.002).

Conclusion:

The predictors of renal recoverability revealed that ureteral stents alone can help in regaining renal function and significant improvement of clinical condition in patients with obstructive uropathy.