Prone Versus Supine Lasix Renal Scan to Assess Surgical Success After Laparoscopic and Robot-Assisted Pyeloplasty

Abstract

Purpose:

Success after laparoscopic pyeloplasty (LP) for ureteropelvic junction obstruction is determined based on renal scan (RS) results and patient symptoms±ultrasonography. The upright or prone position during RS may facilitate drainage. This study reports on outcomes after LP and robot-assisted pyeloplasty (RALP) and determines if patient position (supine vs prone) alters the results of the postoperative RS and surgical “success.”

Patients and Methods:

A retrospective review of LP and RALP performed by one surgeon between 2005 and 2012 was performed. Follow-up consisted of RS±ultrasonography. The paired t test was used to assess for a significant difference between mean T_1/2 for supine vs prone scans in each patient. Linear regression was used to determine if preoperative split renal function on the affected side or degree of preoperative hydronephrosis predicted difference in supine vs prone T_1/2.

Results:

There were 11 LP and 81 RALP performed; 84 had follow-up data. There were four (4.3%) failures. Thirty-eight patients had sufficient supine and prone RS for analysis. The difference in T_1/2 between supine and prone RS was significant (mean difference 10.18±27.28 min, P=0.03). Strict success increased to 65.8% from 44.7% and combined strict plus technical success increasedt o 78.9% from 63.1% on prone vs supine RS. Split function and degree of hydronephrosis were not predictors of difference in RS results.

Conclusions:

LP and RALP have good technical results. Prone position for RS may facilitate drainage and may be a more accurate representation of postoperative outcome after pyeloplasty, particularly in equivocal cases.

Introduction

Ureteropelvic junction obstruction (UPJO) is a common urologic abnormality with an incidence of 1 per 1000 to 1500 newborns.¹ Although UPJO may be asymptomatic, symptoms may include flank pain, nausea and/or vomiting, fever from pyelonephritis, and symptoms related to urolithiasis. In younger patients, there may be nonspecific symptoms such as failure to thrive and diffuse abdominal pain. Symptoms are often precipitated at times of diuresis, such as after drinking alcohol. Surgical management is indicated in patients with symptomatic obstruction, recurrent pyelonephritis, stones, or impaired or worsening renal function, provided that the renal function is worth salvaging. Open dismembered pyeloplasty was first performed by Anderson and Hynes² in 1949 for retrocaval ureter and was later applied to UPJO repair.³ One key factor in successful dismembered pyeloplasty is dependent positioning of the newly reconstructed ureteropelvic junction (UPJ).³

Because of the morbidity associated with open pyeloplasty, minimally invasive treatment options have evolved and include endoscopic treatment (balloon dilation and endopyelotomy using various techniques), laparoscopic pyeloplasty (LP), and robot-assisted laparoscopic pyeloplasty (RALP). Success rates of open pyeloplasty and LP/RALP are excellent and often comparable, in the range of 90% to 100%.^1,4

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Diuretic renal scintigraphy (RS) is often used to confirm the diagnosis of UPJO, detect compromised or worsening renal function during follow-up, and to follow patients postoperatively to determine if the surgery was a success or failure. Pouliot and associates⁸ have categorized successful outcomes after LP into three categories: Strict success (T_1/2<10 min), technical success (T_1/2<20 min with improved postoperative T_1/2), and clinical success, which is defined as the absence of symptoms, but persistence of obstruction on RS (T_1/2>20 min). There has, however, been great variability in the technical performance of diuretic renal scans, which may limit the ability of investigators to interpret outcomes and compare results across various studies.

In an attempt to standardize the technical performance of diuretic renal scan, guidelines⁹ have been proposed by the Consensus Committee of the Society for Radionuclides. Patient positioning has been recommended to be sitting/erect or lying/supine with inclusion of erect films after the study.⁹ The authors state that in the erect position, normal hydrostatic effects on urine flow are recognizable.⁹ Despite these recommendations, the typical standard position for renal scans is the supine position. Because the UPJ is often situated anterior/inferior, however, the upright position and/or prone may facilitate drainage, which has been demonstrated with intravenous pyelography.¹⁰

To our knowledge, there are no studies directly comparing the results of postoperative diuretic renal scan, performed in varying positions, to determine whether patient position during renal scan affects drainage (i.e., T_1/2) and subsequently the documentation of success after surgery. The purpose of this study is to report on outcomes after LP and RALP and to determine if patient position (supine vs prone) during diuretic renal scan alters the results of the postoperative renal scan and rates of surgical success using a previously published categorization of “success.”⁸

Patients and Methods

Patient selection

All LP and RALP cases performed by a single surgeon (RJH), between November 2005 and June 2012 were retrospectively reviewed. Ultrasonography was often the first imaging modality used in the work-up of these patients. Diagnosis of UPJO was confirmed by renal scan and retrograde pyelogram in the majority of cases; triphasic CT of the abdomen and pelvis was performed to identify crossing vessels. Decision to perform pyeloplasty was based on patient symptoms, recurrent infections, stones, and impaired renal function. Patients with poor split renal function (<20%) of the affected side were often counseled that renal function may not be salvageable with surgery, but were offered surgical repair if the patient was symptomatic and desired to proceed with pyeloplasty rather than nephrectomy.

Surgical technique

All cases were dismembered pyeloplasty regardless of whether they were performed laparoscopically or robot-assisted. Most patients had retrograde pyelography with magnified oblique views of the UPJ junction to document the length of the stenotic segment shortly before the procedure (<7 days preoperatively). A long, 26-cm, ureteral stent was inserted at that time, unless a stent had been inserted previously for obstruction, infection or intractable pain, before the retrograde study.

If a limited number of stones were present, they were removed during the pyeloplasty after the renal pelvis was opened, using flexible nephroscopy to access and remove caliceal stones with a tipless nitinol basket. When there was extensive stone disease present, a percutaneous nephrolithotomy was performed 1 week before pyeloplasty.

In all cases, the ureter was spatulated laterally 1 cm beyond the obstructing segment, as demonstrated on the preoperative retrograde pyelogram. In cases with severe hydronephrosis, redundant renal pelvis was excised. The anastomosis was performed with two continuous 4-0 monofilament absorbable sutures. When a crossing vessel was present, the dismembered UPJ was transposed anterior to the vessel before completing the anastomosis. All patients had postoperative urinary drainage with a Foley catheter and the preoperatively placed ureteral stent. In addition, a Jackson-Pratt (JP) drain was left in all cases.

Postoperative management and follow-up

Most patients had the Foley catheter removed on postoperative day 2, followed by removal of the JP drain after ensuring there was adequate voiding and no increased output from the drain. Patients were discharged home after removal of the drain. Ureteral stents were typically removed under local anesthetic using flexible cystoscopy, within 4 to 6 weeks postoperatively. For patients followed exclusively at our institution, follow-up after removal of the stent consisted of a Lasix renal scan approximately 1 month later and every 6 months thereafter up to 2 years postoperatively or longer, depending on the results. Most patients had a standard diuretic renal scan performed in the supine position at one site (Medvue Medical Imaging, Toronto, ON) following the standard technique. Proper hydration is ensured, and patients empty the bladder before the scan. The radiopharmaceutical used is 10 mCi (370 MBq) technetium Tc 99m-diethylenetriaaminepentacetic acid.

Acquisition of data is performed in a number of phases: Flow, dynamic, postvoid, Lasix acquisition after administration of 20 mg Lasix, and Lasix postvoid 60 seconds after the patient voids. Standard data analysis is performed as per institutional protocol. At the request of the senior author, some patients had imaging in the prone position based on the clinical suspicion of a false-positive supine study. For more recent cases, patients had imaging in supine and prone positions during their follow-up. Ultrasonography was performed in some cases to assess for presence and degree of postoperative hydronephrosis.

Outcomes

The primary outcome was the difference between drainage half-life (T_1/2) of supine vs prone renal scans. This was evaluated by comparing, within each patient, the mean T_1/2 of all postoperative supine renal scans with the mean T_1/2 of all postoperative prone renal scans. Accordingly, patients who did not have both supine and prone postoperative renal scans were excluded from calculation of this outcome.

The secondary outcomes included assessment of potential predictors of a difference in supine vs prone T_1/2, as well as evaluation of change in categorization of success between supine and prone renal scans. Degree of preoperative hydronephrosis and split differential renal function of the affected side were the specific predictors assessed. Degree of hydronephrosis was determined by measuring the maximal anterior-posterior diameter of the renal pelvis on preoperative CT scan. Split differential renal function of the affected side was determined from the preoperative renal scan. Categorization of success was based on the previously described categories (strict, technical, and clinical).⁸ We compared the percentage of cases in each of the three categories of success based on supine T_1/2 vs prone T_1/2.

Statistical analysis

Categorical data are presented as frequencies and percentages. Continuous data are presented as median with interquartile range (IQR) or as mean±standard deviation, depending on the distribution of the data. The primary outcome, which was the difference between the mean drainage half-life (T_1/2) of all supine and prone diuretic renal scans for each patient, was determined using the paired t test. Linear regression analysis was performed to determine if preoperative split renal function of the affected side or degree of preoperative hydronephrosis was a predictor of a difference in the supine vs prone T_1/2. The Fisher exact test was used to determine if the percentage of successful pyeloplasty outcomes (ie, categorization of success) differed significantly on supine vs prone renal scans. All statistical analysis was performed using SAS software version 9.2 (SAS Institute, Cary, NC). A P value of <0.05 was used for statistical significance.

Results

A total of 92 minimally invasive pyeloplasties were performed during the study period. Most were RALP (81, 88%). Patient demographic and preoperative data are presented in Table 1. The majority of patients were female (59.8%), and 40.2% were left sided. Twenty-seven percent of patients had urolithiasis, and 13% had recurrent infections preoperatively. Eight patients did not have follow-up data at our institution and were excluded from postoperative review. Two patients had preoperative nephrostomy tube drainage. There were four failures (4.3%), and three patients had a secondary endopyelotomy. Median follow-up was 11.7 months (IQR: 5.5–21.4 months).

Table 1.

Demographic Data and Preoperative Characteristics

Sex, n (%)
Male	37 (40.2)
Female	55 (59.8)
Affected side, n (%)
Left	37 (40.2)
Right	55 (59.8)
BMI kg/m² (mean±SD)	24.0±5.0
Symptomatic flank pain, n (%)	78 (85)
Urolithiasis, n (%)	25 (27.1)
Infections, n (%)	12 (13)
Diagnosis, n (%)
For cause workup	82 (89.1)
Incidental	10 (10.9)
Crossing vessel, n (%)	41 (45.1)
Preoperative stent, n (%)	78 (84.8)
Preoperative nephrostomy tube, n (%)	2 (2.2)
Previous endopyelotomy, n (%)	5 (5.4)
Previous pyeloplasty, n (%)	2 (2.1)

BMI=body mass index; SD=standard deviation.

Thirty-six patients had sufficient postoperative supine and prone renal scans to allow for comparison of these techniques. In this patient subgroup, mean age was 43.6±16.3 years, 66.6% were female, and 52.8% were left sided. Most patients (86.1%) were symptomatic before surgery, and 47.2% had crossing vessels. The difference in T_1/2 between supine and prone renal scans was significant with a mean difference of 10.18±27.28 min (P=0.03). In total, 32% of scans showed an improvement in success classification with the prone position. With prone renal scans, the rate of strict success increased to 65.8% from 44.7% on supine renal scan; however, this difference did not reach statistical significance (P=0.3). Similarly, combined strict plus technical success was higher on prone renal scan at 78.9% vs 63.1% on supine renal scan, which also did not reach statistical significance (P=0.27). Twenty-four (63%) cases yielded the same success classification between supine and prone renal scans. Failure in this subset was applicable to two patients and remained the same regardless of the position used for renal scan.

Linear regression analysis showed that split function of the affected side and degree of preoperative hydronephrosis were not predictors of difference in supine vs prone renal scan T_1/2 (P=0.12 and P=0.59, respectively).

Discussion

Diuretic RS is a technically challenging procedure with a large potential for interobserver variability. This has prompted a number of attempts at standardization of the procedure. In 1992, a report was published from the combined meetings of the Society for Fetal Urology and members of the Pediatric Nuclear Medicine Council regarding the “well tempered” renal scan for examination of asymptomatic neonates with hydronephrosis or hydroureteronephrosis.¹¹ In that report, it is recommended that the patient may be placed prone or briefly in the sitting position after the renogram phase to distribute the radioactive tracer more uniformly throughout the entire collecting system. The prone position is also highlighted as a means to ensure the bladder is dependent so that its position does not slow ureterovesical drainage; it is recommend that the diuretic study be completed prone if that position is required to “fill” the entire system.¹¹

In 1994, the Scientific Committee of the Ninth International Symposium on Radionuclides in Nephrourology established a Consensus Committee on Diuresis Renography. One of the roles of that committee was to produce recommendations for a standardized approach to diuresis renography in an attempt to “improve reproducibility between centers, discourage unacceptable practice and stimulate further discussion between nuclear medicine and urology health care professionals who treat patients with dilated and obstructed upper urinary tracts.”¹² Those recommendations ranged from, but were not limited to, the type of hard- and software used, data acquisition and timing of study, patient preparation and positioning, use of bladder catheterization, and choice of radiopharmaceutical and diuretic. A follow-up article was published in the British Journal of Urology International to highlight the Consensus report and make it more accessible to urologists.⁹

The position for renal scan, according to the Consensus Committee, should be sitting/erect or lying/supine, but including erect films at the end of the study to appreciate the effect of posture on the dilated upper tracts.⁹ Erect postvoid images at the end of the study are also recommended to decrease equivocal results.⁹ Despite these recommendations, there remains variation in the performance of renal scans, and patient position is routinely supine. Improved urinary drainage in the upright position for intravenous pyelography has also been reported.¹⁰

False positive results on renal scan to assess for obstruction can be caused by very poor renal function in which one is unable to determine if absence of response to the diuretic is from obstruction or parenchymal dysfunction, severe hydronephrosis with a “mixing chamber” effect in which emptying of the renal pelvis may not be appreciable, positional effects, full bladder, and hydration status.¹³

LP and RALP have good success rates with only four (4.7%) failures in our report of 84 cases with follow-up data. Prone positioning for renal scan increased the rates of strict and technical success to almost 80%; however, this was not statistically significant. This could be a result of the small size of the study population, which may have been underpowered to detect a difference. The degree of preoperative hydronephrosis and split renal function did not predict for difference in supine vs prone renal scan T_1/2 in our study cohort.

Vitorri and coworkers¹⁴ investigated the effect of MAG3 diuretic renography in an F+10 seated position (F+10SP) for the assessment of hydronephrosis. In that study, a standard F-15 renal scan, where furosemide is administered 15 minutes before the start of the study, which was performed in the supine position, was compared with one in which furosemide was administered 10 minutes after the start of the study with the patient seated. They found the “equivocal” test rate decreased from 16% for the F-15 group to less than 1.5% in the F+10SP group. This lends support to the clinical suspicion of the senior author of this article that postoperative pyeloplasty patients may have a false positive renal scan if the supine position is used.

There are a number of limitations to this study. It is a retrospective review with inherent biases because of the nature of the study. This is a single surgeon study in a tertiary teaching hospital, and the results may not be generalizable to the urology community as a whole. Follow-up data were lacking or short in some patients because of the tertiary nature of this hospital. Many patients were referred from other urologists and saw those urologists for their extended follow-up. Also, only a limited number of patients had both supine and prone studies, which were often performed based on the clinical suspicion of a false positive or equivocal supine study. Degree of postoperative hydronephrosis was also unable to be determined for most patients because they were lacking follow-up ultrasonography examinations, which are now being performed routinely in more recent cases. Severe hydronephrosis is a known cause of false positive diuretic renal scan, and the effect of severe hydronephrosis on prone renal scan T_1/2 is not clearly known.

One strength of the study is that the vast majority of renal scans were performed in one center, which should limit the biases involved in the interpretation of the renal scans. Future prospective studies comparing supine and prone renal scans in patients postpyeloplasty are needed to better characterize and further evaluate the findings of the present study.

Conclusions

Both LP and RALP have good technical and clinical results with a low failure rate. Prone positioning for diuretic renal scan may facilitate drainage and may be a more accurate representation of postoperative outcomes after pyeloplasty, particularly in equivocal cases.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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