Pyeloplasty effectiveness in cases of ureteropelvic junction obstruction in children: methodology and assessment parameters

Hydronephrosis is the most common abnormality of fetal development revealed antenatally in 1 – 5% of pregnant women [1][2]. Ureteropelvic junction obstruction (UPJO) is the most common cause of antenatal hydronephrosis, which is registered in one of every 750 – 1500 neonates. Every third neonate with postnatal hydronephrosis associated with ureteropelvic junction obstruction requires surgical treatment [3][4].

Pyeloplasty in children with hydronephrosis is a highly effective surgical intervention that is successful in 83 – 97% of cases [5]. However, presently, there is no consistency in the definition of “success” in terms of the results of pyeloplasty.

The most common evaluation criteria include the dynamics of the renal collecting system (RCS) reduction and postoperative renal functional status. However, there are no consistent values of the projection of RCS dilatation measurement and functional renal status that could be used as assessment criteria in a certain period after pyeloplasty indicating success as soon as they are registered.

The lack of such criteria creates problems not only in the preparation of medical reports but also in further patient follow-up. As a rule, patients and their parents expect complete resolution of RCS dilatation. Since there are no criteria for sufficient reduction of RCS, the residual dilatation creates indications for active surgical interventions or suggestions of these actions by specialists that observe the patient.

It should be noted that the tools used to estimate RCS reduction are not standardized in terms of research techniques, projection of RCS dilatation measurement, and the locations between which renal and pelvic anatomic structures are measured.

Single publications on the development of standardized criteria for the evaluation of pyeloplasty effectiveness were dedicated to the analysis of the dynamics of isotope and ultrasonic (US) parameters after the surgery in comparison with the initial condition.

Since there is no unification in the US investigation parameters in patients with hydronephrosis, specialists unnecessary expand the indications to additional examinations based on the widely variable results of the dynamic observation.

In some cases, axial anterior-posterior renal pelvis measurement is performed between the edges of the parenchyma at the kidney hilum (Fig. 1А). In other cases, axial maximum measurements of the extrarenal pelvis are made (Fig. 1В). Fig. 1 shows the renal pelvis dimensions in one patient depending on the approach to the measurement.

Figure 2 shows axial anterior-posterior diameter (APD) in children with hydronephrosis taken from a publication of Babu and Sai [6], wherein the maximum APD in the coronal section was 40 mm (Fig. 2А). At the same time, Walker et al. [7] measure the renal pelvis APD between the edges of the parenchyma at the kidney hilum (Fig. 2B – white arrow), when the extrarenal pelvis is delated (Fig. 2B – blue arrow).

To clarify the terminology of the studied parameter, the direction of the scanning is specified and the measured dimension of the renal pelvis is indicated in each case.

It is known that the volume of the renal pelvis significantly changes under the influence of such factors as the volume of the residual urine, degree of hydration before the study, and the position of the patient during the study, which is not mentioned in the reviewed publications either.

Unfortunately, the lack of illustrative material in most available publications on the methodology of the renal pelvis APD measurement complicates the evaluation of the results of pyeloplasty. Some authors analyzed the effectiveness of pyeloplasty in children with renal pelvis reduction, other authors did not analyze it. Thus, a question arises on the possibility of the application of similar criteria for the evaluation of the effectiveness of surgery for hydronephrosis with a renal pelvis reduction or without it.

In the majority of cases, the ultrasound investigation is performed with a simultaneous study of the bladder. For this procedure, the patients are asked to drink before it for a fast filling up of the bladder. This tactic is wrong because any volemic load affects the real dimensions of the renal pelvis.

Since the degree of bladder filling in the conditions of enhanced diuresis can affect the degree of RCS dilatation, the authors of this article find it important to standardize the methodology of ultrasound measurement of the renal pelvis in patients with an empty bladder.

The differences in the approach to the measurement of PCS dimension in children with hydronephrosis affect the statistical analysis and blur the real picture of the pyeloplasty results.

Considering the above-mentioned facts, to provide adequate evaluation of the pyeloplasty results, it is necessary to standardize the methodology of the US investigation and to determine the projection of scanning and anatomical landmarks that are used for the measurement. The authors of this article propose to discuss the following suggestions on the methodology of US investigation in patients with hydronephrosis and the unification of the terminology of the studied parameter.

Based on the analysis of the available publications and their own experience, the authors of this article find it feasible to make the following measurements:

1) APD of the renal pelvis at the kidney hilum between the edges of the kidney parenchyma (Fig. 1А, 2В (white arrow))

2) maximal axial measurement of the extrarenal pelvis (Fig. 1В, 2В (blue arrow))

3) maximal sagittal measurement of the renal pelvis (Fig. 3 (dark blue arrow)).

The dynamics of the RCS dilatation reduction were also studied by Park et al. [8]. They showed that the average time to the beginning of the reduction of RCS dilatation after pyeloplasty was eight months. Such clinical manifestations as obstruction or lack of positive dynamics of the renal pelvis APD within the first six months after the surgery are unfavorable prognostic factors for the development of obstruction recurrence. It should be mentioned that these authors did not perform renal pelvis reduction and did not provide the method of the renal pelvis APD measurement.

Romao et al. [9] proposed to use the dynamics of the renal pelvis APD three months after the stent removal for the evaluation of the effectiveness of surgery for hydronephrosis (2012). These authors believe that the success of pyeloplasty is guaranteed when three months after the stent removal, a 38% and more reduction of the renal pelvis APD is observed in comparison with pre-operation values or a decrease in the absolute value of the renal pelvis APD more than 11.5 mm. In this study, the measurement of the renal pelvis APD measurement was performed between the edges of the kidney parenchyma. However, the conditions of the US investigation were not specified.

A similar study was conducted by Fernandez-Ibieta et al. [10]. These authors stated that the reduction of the renal pelvis APD by less than 15% three months after open Anderson-Hynes pyeloplasty was a predictor of an unsuccessful surgery and obstruction recurrence. The average reduction of the renal pelvis APD three months after pyeloplasty was 29% in their series. In this study, the measurement of the renal pelvis APD was performed between the edges of the kidney parenchyma. However, the conditions of the US investigation were not specified either.

SanniVa¨rela et al. [11] studied a prospective group of 125 patients with UPJO. The criterion of the resolution of hydronephrosis was the reduction of the renal pelvis APD < 10 mm or not less than 50% of the pre-operation values. They recommended post-operative follow-up of children with UPJO by measuring the renal pelvis APD within the first year after the surgery. The follow-up had to be prolonged to 24 months if the renal pelvis APD < 10 mm was revealed within the first 12 months. These measures were recommended because of the high risk of UPJO recurrence. These authors performed an US investigation in patients with an empty bladder in the condition of a volemic rest. However, it was not specified how the measurements of the renal pelvis APD were made. It was not mentioned either if renal pelvis reduction was performed.

Rickard еt al. [12] conducted a study on the evaluation of the renal pelvis APD in 138 patients with UPJO after pyeloplasty with renal pelvis reduction. In this study, the renal pelvis APD was measured between the edges of the kidney parenchyma at the kidney hilum. However, the method of US investigation was not described. The criterion of successful pyeloplasty and hydronephrosis resolution was the reduction of the renal pelvis APD < 15 mm. It was defined that the reduction of the renal pelvis APD by 40% and more from the pre-operation values three months after surgery without a stent or three months after the stent removal indicated successful pyeloplasty. UPJO recurrence is expected in patients with the reduction of the renal pelvis APD less than 20% three months after surgery and requires additional examination. These authors believe that during the measurement of the renal pelvis APD, it is necessary to consider its dimensions between the edges of the kidney parenchyma. The proposed parameter is a reliable prognostic parameter for the evaluation of pyeloplasty success in the post-operative follow-up regardless of the surgeon’s preferences to perform pyeloplasty with reduction of the dilated renal pelvis or without it.

Carpenter et al. [13] conducted a similar study and performed the analysis of 105 renal units. Unlike Canadian colleagues Rickard et al. [11], these authors considered the reduction of the renal pelvis APD to 0 mm to be the criterion of hydronephrosis resolution. The authors declared that the reduction of the renal pelvis APD < 43% was a predictor of UPJO recurrence and indication to repeated surgical intervention. In this study, the measurement of the anterior-posterior reduction of the renal pelvis was performed between the edges of the kidney parenchyma. However, the methodology of the US investigation was not specified. It was not mentioned either if renal pelvis resection was performed.

Gharpure et al. [14] proposed to use the ratio of the calyx depth to the thickness of the kidney parenchyma (CP-index) as a predictor of pyeloplasty success. These authors believe that CP-index has an advantage in the fact that the measurement of the depth of calyces and thickness of the parenchyma does not depend on the surgeon unlike the measurement of the renal pelvis APD, wherein subjectivism in the measurements cannot be excluded. These authors recommend CP-index in the pre-operative and post-operative observation of children with UPJO. It will prevent unfeasible radioisotope studies indicated because of the remaining high values of the renal pelvis APD in the post-operative period.

Babu and Sai [6] performed a prospective analysis of 24 patients with UPJO in 2010. The patients underwent splitting pyeloplasty without renal pelvis reduction. These authors measured three parameters for the postoperative evaluation of pyeloplasty: renal pelvis APD, renal parenchyma thickness (RPT), and APD to RPT ratio (APD/RPT). The measurements were performed in three-time intervals: before surgery, three, and 12 months after surgery. The statistical analysis showed that a significant reduction of the renal pelvis APD and increase in RPT was observed only 12 months after surgery. A different picture was observed for APD/RPT parameter; its statistically significant decrease was registered both three and 12 months after surgery (p < 0.01). These authors specified that a small sampling was a limitation of their study and concluded on the necessity of further larger-scale study for the standardization of the proposed APD/RPT parameter. It can be a useful, non-invasive, and simple criterion for the evaluation of early results of pyeloplasty.

The results of the isotopic study play a key role in the preparation of indications to pyeloplasty; while in the evaluation of the surgery outcome, its significance is minimal and feasibility is doubtful.

Almodhen et al. [15] believe that if the renal pelvis dimension reduces three months after surgery, a radioisotopic study is not feasible for the registration of the improvement of urine passage via a ureteropelvic anastomosis. The study of differential renal function is not feasible either in patients with preoperative levels of more than 45% and a decrease in the renal pelvic dimension by the results of renal ultrasound investigation because none of the patients had significant changes in the differential renal function revealed.

Cost et al. [16] concluded that isotopic renography should be used only when obstruction recurrence is suspected in a patient by the results of the US study.

The analysis of modern publications demonstrates that the data on the effectiveness of pyeloplasty are based on a subjective and non-standardized assessment of the degree of renal pelvis dimension reduction and differential renal function. The authors who publish the results of pyeloplasty tend to search for a standard creating their system of assessment of the main parameters that characterize the post-operative period.

A lively illustration of ambiguity in the widespread opinion on pyeloplasty success are reports of insurance companies in the USA that are dedicated to the analysis of medical interventions after pyeloplasty. According to these reports, in 10% of cases, children with hydronephrosis that underwent surgery require medical manipulations that are not present in the protocol of treatment [17]. In some cases, the reliability of medical reports on the rate (5.9%) of patients’ refusal from post-operative follow-up is doubtful. The described group of patients might not have complaints. However, symptomless development of UPJO recurrence cannot be excluded in these patients [18].

Hopewell et al. [19] described a phenomenon that favorable results of surgery are more likely to be published than unsuccessful, which negatively affects the reliability of the provided data on the extremely high effectiveness of pyeloplasty.

Thus, the is a paradoxical situation when a wide consensus in the medical society on the high effectiveness of surgical treatment for UPJO was formed in the lack of generally accepted criteria of successful outcome and standardization of the principles and duration of postoperative follow-up. The above-mentioned facts determine the relevance of the studies on the development and standardization of the methodology for the monitoring of the dynamics of the renal pelvic dimensions, functional conditions of the kidneys, and the assessment of pyeloplasty results.