Outcomes of Robot-Assisted Laparoscopic Pyeloplasty Based on Degree of Obstruction on Preoperative Tc-99 MAG-3 Renal Scintigraphy

Introduction

Ureteropelvic junction (UPJ) obstruction is a condition defined as the failure of antegrade urine flow from the renal pelvis into the ureter owing to an intrinsic or extrinsic obstruction. ¹ At present, the standard diagnosis of a UPJ obstruction is assessed using half-life (T1/2) after administration of a diuretic and differential renal function on Tc-99m mercaptoacetyltriglycine (MAG-3) renal scintigraphy. ¹ Patients who present with symptoms of UPJ obstruction (i.e., Dietl's crisis) and discordant MAG-3 renal scintigraphy represent a significant treatment dilemma for urologists.

In instances where patients' symptoms of UPJ obstruction and degree of hydronephrosis on CT scan are discordant with MAG-3 scintigraphy, urologists are often conflicted whether to manage these patients conservatively or with operation. This diametric presentation questions the accuracy of MAG-3 scintigraphy in ruling in or out UPJ obstruction and its usefulness in identifying appropriate candidates for surgical correction. As previously documented in the literature, results of MAG-3 scintigraphy are impacted by multiple factors including imaging too early after tracer injection, movement artifact, impaired renal function, and institutional variation in study performance. ²

Historically, symptomatic UPJ obstruction has been managed with various techniques including endopyelotomy, open pyeloplasty, laparoscopic pyeloplasty, and robot-assisted laparoscopic pyeloplasty. At present, there is limited research regarding the management of patient's whose symptoms are discordant with MAG-3 scintigraphy, with only two previous studies by Ozayar et al ³ and Fontenot Jr et al, ⁴ which reported opposing results without consensus. Our objective was to evaluate outcomes of robot-assisted laparoscopic pyeloplasty for UPJ obstruction at our single institution and stratify results based on preoperative renal scintigraphy with the intent to evaluate the relationship between documented obstruction and surgical success.

Methods

Results

A total of 125 robot-assisted laparoscopic pyeloplasties performed between 2009 and 2021 who had preoperative MAG-3 scintigraphy were included in our analysis (Table 1). Sixty-seven women and 58 men with a median age of 35 years old were included (Table 1). Pain was the presenting symptom in 90.4% of patients and 5.6% had a documented history of UTI. Twenty-two (17.6%) patients had a previous UPJ procedure on the ipsilateral kidney, including pyeloplasty (n = 11), balloon dilation (n = 4), and endopyelotomy (n = 7) (Table 1). Right-sided pyeloplasty was performed in 60.8% patients and 20% patients had a ureteral stent placed before operation to facilitate drainage of the obstructed UPJ (Table 1). Median preoperative split renal function on MAG-3 scintigraphy was the only statistically significant (p = 0.003) difference in preoperative characteristics between groups, with all patients who underwent preoperative nuclear imaging having a median split renal function of 45% (Table 1).

Median operative time was 210 minutes and median EBL was 30 mL (p = 0.026) (Table 2). Dismembered pyeloplasty technique was performed in 98.4% of cases and Y–V or flap pyeloplasty was performed in 0.8% of patients (Table 2). Stented robot-assisted laparoscopic pyeloplasty was performed in 97.6% of patients, with 46.7% of patients having the ureteral stent placed in a retrograde manner before robotic docking (range: 1–118 days) (Table 2). Median ureteral stent duration was 30 days after operation (Table 2). Jackson–Prat drains were placed in 79.5% of patients, with a median duration of 1 day (range: 1–37 days) (Table 2). Intraoperatively, a crossing vessel causing UPJ obstruction was identified in 40.0% of cases (Table 2). There were no intraoperative complications (Table 2). There were 15 (12.0%) postoperative complications, with 3 patients having urine leaks, and 6 having grade III or greater Clavien–Dindo complications (Table 2). EBL was the only statistically significant difference in perioperative characteristics, postoperative complication rates, or 30-day readmission rates.

Follow-up data were obtained for 125 patients for a median of 12 months (range: 1–60 months) (Table 3). All patients who underwent postoperative CT imaging were noted to have improved or stable hydronephrosis on imaging (Table 3). About 86.4% of patients rated their pain as improved, without statistically significant differences between groups (p = 0.239). Robot-assisted laparoscopic pyeloplasty was successful in 92.8% of cases, with the lowest success rate (90.0%) being among patients whose preoperative MAG-3 scintigraphy was consistent with obstruction (T1/2 Lasix >20 minutes) (Table 3). There was no statistically significant difference (p = 0.202) in pyeloplasty success rates between groups (Table 3).

A total of 9 (7.2%) patients experienced pyeloplasty failure. Failures were managed in the following ways: 2 patients required chronic stent exchanges, 2 patients underwent balloon dilation, 2 patients underwent endopyelotomy, 1 patient underwent repeat pyeloplasty, and 2 patients elected to have nephrectomy owing to persistent pain or significantly reduced renal function (Table 3). In patients undergoing nephrectomy for pyeloplasty failure, the median ipsilateral split renal function was 26.5% and median time to nephrectomy of 42.9 months. The median time to pyeloplasty failure was 21.5 months, with statistically insignificant differences (p = 0.630) across the three groups (Table 3).

Discussion

Consistent with previously published data, ^{3 –10,11} our results demonstrated a high overall success rate for robot-assisted laparoscopic pyeloplasty, with a 92.8% success rate across all patients. About 86.4% of our patients had improvement of their UPJ obstruction-associated pain and 100% of patients had improved or stable hydronephrosis on postoperative CT imaging. Furthermore, when stratified by degree of preoperative UPJ obstruction based on MAG-3 scintigraphy, we demonstrated that patients with discordant, equivocal, or obstructive imaging had similar overwhelmingly positive outcomes with procedure, indicating that degree of obstruction on MAG-3 scintigraphy is not predictive of surgical success.

Patients with no obstruction on preoperative nuclear imaging demonstrated the highest rate of pyeloplasty success across all groups, at 100% (15/15), with those in the equivocal obstruction and obstruction groups demonstrating success rates of 97% (32/33) and 90% (69/77), respectively. Although not statistically significant, the relatively higher success rates in the no obstruction and equivocal obstruction groups may be attributed to their overall better preoperative split renal function relative to the obstructed group. Patients in the equivocal obstruction group saw the highest level of pain improvement at 97%, whereas those in the no obstruction group and obstruction group saw symptom improvement at rates of 86.7% and 81.8%, respectively. Given our results, one could argue preoperative MAG-3 scintigraphy may not be a consistently reliable indicator for appropriate selection of candidacy for successful pyeloplasty.

Overall, clinical pyeloplasty success rates of patients in the obstruction and equivocal groups (100% and 97% respectively) were similar to success rates of patients with equivocal MAG-3 scintigraphy demonstrated by Ozayar et al, who showed clinical pyeloplasty success rates of 95.7%. ³ Similar to Ozayar et al, our study did not demonstrate a statistically significant difference in pyeloplasty success, resolution of symptoms, or changes in postoperative split renal function across groups. The results of our study and the study performed by Ozayar et al ³ are in contrast to results published by Fontenot Jr et al ¹⁰ who noted statistically significant lower rates of symptom improvement (47%) and robotic pyeloplasty success (75%) in their equivocal cohort relative to the control.

When comparing the results of our study with those published by Ozayar et al ³ and Fontenot Jr et al, ⁴ it should be mentioned that our study divided patients into three groups (no obstruction—Lasix T1/2 clearance <10 minutes, equivocal obstruction—Lasix T1/2 clearance 10–20 minutes, and obstruction—Lasix T1/2 clearance >20 minutes), whereas the other two studies defined all patients whose Lasix T1/2 was <20 minutes as equivocal. ^3,4 Furthermore, the definition of pyeloplasty success across our study and studies performed by Ozayar et al ³ and Fontenot Jr et al ⁴ varied, as our study did not use changes in postoperative Lasix T1/2 as the sole marker of objective pyeloplasty success.

As previously mentioned, the results of our study suggest that MAG-3 scintigraphy may not be as vital before selecting patients for robotic pyeloplasty if hydronephrosis, symptomatology, or retrograde pyelogram suggesting UPJ obstruction is present. Accuracy of MAG-3 scintigraphy can be confounded by multiple factors: tracer timing, movement artifact, impaired renal function, and institutional variation in study performance. ² Review of previously published data estimates the reporting of equivocal results in most series is 15%. ^3,11,12 A recently published article by von Rundstedt et al examining sensitivity of T1/2 Lasix clearance in identifying UPJ obstruction found the sensitivity in their series to be only 49%; however, this value increased to 73% when using the percentage of radiotracer present at 40 minutes (P₄₀) as the diagnostic variable. ¹³ The high percentage of symptom resolution in patients who underwent robotic pyeloplasty in our series suggests that despite nonobstructive or equivocal MAG-3 scintigraphy findings, these patients remained good candidates for surgical repair.

Preoperative scintigraphy remains important in establishing split renal function, identifying duplicated systems and unusual renal anatomy, and affirming suspected obstruction in many cases. However, owing to its established limitations, equivocal MAG-3 results are common and should be used in conjunction with other variables in surgical decision making. Thus, our results suggest that if obstruction is highly suspected by either the patient's symptoms and/or findings on other imaging modalities (CT, Whitaker's test, retrograde pyelogram, magnetic resonance urography) and the patient is a good surgical candidate, pyeloplasty may be indicated irrespective of renal scan results.

These findings harbor important clinical significance as urologists are often conflicted on management for patients when preoperative symptoms and/or CT imaging are discordant with their renal scan. As a result, these patients are often subjected to prolonged periods of observation, stent trials, and second and third opinions before finally settling on a committed treatment plan that can be frustrating for both patient and clinical provider. Hopefully, our study gives practitioners more confidence to perform pyeloplasty in these challenging scenarios, given our results demonstrate that good surgical outcomes can be expected.

Limitations of our article include overall sample size, length of follow-up, retrospective design, and surgical technique. When stratified by degree of obstruction on preoperative functional imaging, the sample sizes of the groups were relatively small, limiting the study's overall power. Furthermore, a large proportion of patients were lost to follow-up after 12 months. This is in large part owing to our institution's function as a quaternary referral center, as most patients resumed care with their local urologist after 12 months. To compensate for this, long-term follow-up data were obtained through telephone surveys; however, many patients were still unable to be contacted. This could have led to negative selection bias, in that those patients who failed pyeloplasty were more likely to seek urological care at our institution or elsewhere.

In addition, although our study can draw conclusions regarding patients whose symptoms of UPJ obstruction are discordant with functional imaging relative to all patients who undergo robot-assisted laparoscopic pyeloplasty, conclusions cannot be made regarding long-term outcomes and patient satisfaction in those who undergo robot-assisted laparoscopic pyeloplasty despite discordant functional imaging compared with similar patients who elect observation. Finally, all patients in the analysis received robotic pyeloplasty. Alternative procedures such as “mini lap pyeloplasty” and endoscopic techniques, which have demonstrated success were not included in the analysis and may have affected the results. ¹⁴ These limitations notwithstanding, our article demonstrates that patients who undergo robotic pyeloplasty have high success rates irrespective of the presence of obstruction on their preoperative MAG-3 renal scan.

Conclusion

Robot-assisted laparoscopic pyeloplasty is a safe and efficacious surgical intervention for correcting UPJ obstruction, with results similar to those published previously in the literature. Patients whose preoperative MAG-3 scintigraphy is discordant or equivocal with symptoms and/or other diagnostic studies documenting obstruction can expect to undergo definitive surgical repair with high success rates. Based on these findings preoperative renal scan, although useful for surgical planning, may not be reliable in the appropriate selection of candidacy for successful pyeloplasty.