Renal Parenchymal Damage After Percutaneous Nephrolithotomy with One-Stage Tract Dilation Technique: A Randomized Clinical Trial

Abstract

Purpose:

To compare the effects of one-stage vs gradual dilation techniques during percutaneous nephrolithotomy (PCNL) on postoperative renal scar formation and overall renal function.

Patients and Methods

: Of 152 adult patients who underwent surgery during the study period, 48 were randomized into two groups. In group 1 (n=19), gradual tract dilation with Alken metallic dilators was used, and in group 2 (n=29), one-stage tract dilation was used. We compared patient demographics, intraoperative and preoperative parameters, postoperative overall renal function, and renal scar formation on the target renal pole.

Results:

Access time (P=0.001; 95% confidence interval [CI]: 3.19–6.30) and radiation exposure during access (P=0.03; 95% CI: 0.03–0.66) were significantly shorter in group 2. In group 1, the decrease in mean technetium-99m dimercaptosuccinic acid (99m-Tc DMSA) uptake from 44.1±20.1% to 43.4±19.6% 4 weeks postoperatively (–0.7%±0.5%; P=0.27; 95% CI: –0.56–1.93) was not significant. In group 2, however, there was a significant decrease in post-PCNL 99m-Tc DMSA uptake 2 (–2.4±0.3%, from 50.1±13.5% to 47.7±13.8%; P=0.001; 95% CI: 1.13–3.66). Four weeks after surgery, new scar formation or progression of the preoperative scar at the site of access were seen in 14 of 29 (48.3%) patients who were treated with one-stage dilation whereas only 2 of 19 (11.0%) patients who were treated with gradual dilation developed new scarring at the access site (P=0.007).

Conclusion:

Although the one-stage tract dilation technique reduced radiation exposure and access time, in the short term, it may cause more parenchymal damage than the gradual dilation technique.

Introduction

I n the era of minimally invasive surgery, percutaneous nephrolithotomy (PCNL) is the standard of care for the surgical management of large renal stones. The creation of the nephrostomy tract is one of the main steps in this technique. Three standard dilation instruments are available: Amplatz fascial dilators, metal telescopic dilators, and balloon dilators.¹ To reduce access time and radiation exposure during access, however, one-stage dilation techniques have become popular in recent years at many centers.

In this technique, unlike sequential dilation, the tract is rapidly dilated to 28F–32F with a single 28F–32F dilator in one step. Although the safety, efficacy, and potential advantages of the principle of rapid one-step tract dilation have been shown in case series,^2

–7 concerns remain about possible damage to the renal microvasculature with single-step dilation compared with the standard gradual dilation technique.

We designed a randomized clinical trial to compare the effects of one-stage vs gradual dilation techniques on postoperative renal scar formation and overall renal function to evaluate the extent of renal trauma with these two procedures.

Patients and Methods

Patients

Between March 2009 and March 2010, all adult candidates for PCNL at Faghihi Hospital in Shiraz (Iran) were considered for enrollment. Those who had no history of renal surgery or shockwave lithotripsy (SWL) and who had no renal anomalies or solitary kidney were randomized into two groups with a block randomization method. In group 1, gradual tract dilation was performed with Alken metallic telescopic dilators, and in group 2, one-stage tract dilation was performed. We excluded patients with a failed first access, those needing more than one access or those who had clinically significant (ie, >4 mm) post-PCNL residual stone in postoperative renal ultrasonography and plain radiography images, and those who needed post-PCNL auxiliary procedures, such as SWL or re-PCNL. The data for the remaining patients (n=48) were analyzed statistically (Fig. 1).

FIG. 1.

Patient allocation for a trial of a one-stage vs gradual tract dilation technique for percutaneous nephrolithotomy (PCNL). SWL=shockwave lithotripsy.

All procedures were performed by the same operator (AA), and a single radiologist (MA) reviewed all the renal scans. The surgeon and radiologist were blinded to the results of the renal scan and the type of surgery, respectively.

The purpose of the study was explained to all patients, and their written informed consent was obtained. This study was approved by the ethics committee of Shiraz University of Medical Sciences.

Surgical technique

With the patient under general anesthesia, a single dose of intravenous ceftriaxon was administered as a prophylactic antibiotic. With the patient in the lithotomy position, the operator advanced a 6F ureteral catheter to the renal pelvis under direct cystoscopic vision. The patient was repositioned to the prone position, and the collecting system was visualized by retrograde injection of about 50 mL room air (air pyelography) or diluted contrast via the ureteral catheter. Then the target calix was punctured with an 18-gauge access needle with fluoroscopic triangulation or the bull's-eye technique.⁸

After the correct position of the nephrostomy needle was verified, an 0.035-inch J-tipped guidewire was passed into the targeted calix, over which the Alken guide was introduced into the collecting system under fluoroscopic guidance. Tract dilation was then performed in patients in group 1 by sequential insertion of Alken metallic telescopic dilators over the Alken guide to gradually dilate the access tract up to 28F. A 30F Amplatz sheath was then advanced over the dilators. In patients in group 2, a single 28F Amplatz dilator was advanced over the Alken guide, and a 30F Amplatz sheath was placed in the collecting system. All steps in tract dilation and Amplatz sheath placement were performed under fluoroscopic control in all patients.

Nephroscopy with stone localization, pneumatic lithotripsy, and stone extraction were accomplished in all patients, and an 18F nephrostomy tube was placed in the collecting system at the end of the procedure. On postoperative day 1, the ureteral catheter was removed, and the nephrostomy tube was clamped. If neither fever nor urine leakage occurred, the nephrostomy tube was removed on postoperative day 2, and the patient was discharged from the hospital on the same day.

Outcome variables

Patient demographic characteristics, intraoperative information such as entrance calix, access time (from needle puncture to the start of nephroscopy), and radiation exposure during access (radiation exposure time before insertion of the access needle to the start of nephroscopy) were compared between the two groups.

To evaluate blood loss during the procedures, the rate of hemoglobin decrease was assessed by comparing the preoperative hemoglobin level with 24-hour postoperative hemoglobin level. All patients underwent preoperative technetium-99m dimercaptosuccinic acid (99mTc-DMSA) renal scan, and split renal function of the target renal unit was recorded 1 week before the operation. The presence, size, and location of any scarring (photopenic areas) on the target kidney were recorded. The same scan was repeated 4 weeks postoperatively, and special attention was paid to changes in renal function of the treated kidney and the formation of a new scar on the targeted pole. The renal scar was measured and compared to the area of the corresponding renal pole. The scar was considered small, moderate, or large when the photopenic area on the 99mTc-DMSA renal scan covered less than 1/6, between 1/6 and 1/4, or more than 1/4 of the corresponding renal pole surface, respectively.

To compare the outcomes of one-stage and gradual tract dilation and their ultimate effect on the renal junction and scar formation of the involved kidney, the preoperative, intraoperative, and postoperative data were analyzed statistically with the Kolmogorov-Smirnov test, t test and chi-square test. All data were analyzed with SPSS v. 14 software (Chicago, IL).

Results

After excluding patients on the basis of the criteria reported above, 48 patients remained in the two groups, and their data were included in the statistical analysis. In group 1 (n=19), gradual dilation was used, and in group 2 (n=29), one-stage dilation was used. These groups were age- and sex-matched, and there were no significant differences in preoperative variables, such as mean stone burden and location (Table 1). In all patients, PCNL was performed through a single access, with no access failures. All stones were successfully removed in both groups. Analysis of the data with the Kolmogorov-Smirnov test confirmed the normal distribution of all variables. Access time (P=0.001; 95% confidence interval [CI]: 3.19–6.30) and radiation exposure during access (P=0.03; 95% CI: 0.03–0.66) were significantly shorter in group 2 (one-stage dilation) than in group 1.

Table 1.

Patient Characteristics

	Total (n=48)	Group 1 (gradual dilation) (n=19)	Group 2 (one-stage dilation) (n=29)	P value
Mean age±SD (years)	43.5±15.5	42.5±18.2	44.1±1 3.7	> 0.05
Male/female	28/20	9/10	19/10	> 0.05
Mean stone burden±SD (mm)^a	28.5±11.1	30.9±12.9	26.9±9.7	> 0.05
Stone side (right/left)	19/29	8/11	11/18	> 0.05
Stone location
Renal pelvis (%)	15 (31.3%)	7 (36.8%)	8 (27.6%)	> 0.05
lower calix+pelvis (%)	6 (12.5%)	3 (15.8%)	3 (10.3%)
Lower calix (%)	13 (27.1%)	3 (15.8%)	10 (24.5%)
Upper calix (%)	3 (6.2%)	1 (5.3%)	2 (6.9%)
Staghorn (%)	11 (22.9%)	5 (26.3%)	6 (20.7%)

Largest diameter.

SD=standard deviation.

Table 2 summarizes the intraoperative data in both groups. There was no statistically significant difference between groups in the decrease in postprocedural hemoglobin (−1.98±1.20 g/dL vs –1.59±1.23 g/dL; P=0.28; 95% CI: –1.11–0.34). None of the patients needed blood transfusion.

Table 2.

Intraoperative Data

	Total (n=48)	Group 1 (gradual dilation) (n=19)	Group 2 (one-stage dilation) (n=29)	P value
Entrance calix				>0.05
Lower (%)	42 (87.5%)	17 (89.6%)	25 (86.2%)
Middle (%)	3 (6.25%)	1 (5.2%)	2 (6.9%)
Upper (%)	3 (6.25%)	1 (5.2%)	2 (6.9%)
Mean access time^a±SD (min)	7.60±2.23	10.47±2.97	5.72±1.75	0.001
Mean time of radiation exposure during access^b±SD (min)	0.91±0.51	1.12±0.68	0.77±0.41	0.03

Calculated from getting access by needle to starting nephroscopy.

Defined as the time of radiation exposure elapsed before the insertion of access needle to starting nephroscopy.

SD=standard deviation.

In group 1 patients, the mean decrease in 99m-Tc DMSA uptake from 44.1±20.1% before surgery to 43.4±19.6% 4 weeks postoperatively (–0.7%±0.5%; P=0.27; 95% CI: –0.56–1.93) was not statistically significant. In group 2 (one-stage dilation) patients, however, there was a significant decrease of –2.4±0.3% in post-PCNL 99m-Tc DMSA uptake (from 50.1±13.5% to 47.7±13.8% (P=0.001; 95% CI: 1.13–3.66).

Fourteen of 48 (29.2%) patients had a small scar on the access site in their preoperative 99m-Tc DMSA renal scan. Four weeks after the procedure, new scar formation or progression of the preoperative scar at the access site was seen in 14 of 29 (48.3%) patients who underwent one-stage tract dilation, whereas new scarring at the access site was seen in only 2 of 19 (11%) patients who underwent gradual dilation (P=0.007) (Table 3).

Table 3.

Preoperative and Postoperative Cortical Renal Scar on the Targeted Renal Pole

	Total (n=48)	Group 1 (gradual dilation) (n=19)	Group 2 (one-stage dilation) (n=29)
	Preoperative/postoperative	Preoperative/postoperative	Preoperative/postoperative
No scar	34 (70.8%)/21 (43.8%)	13 (68.4%)/11 (57.9%)	21 (72.4%)/10 (34.5%)
Small scar^a	14 (29.2%)/24 (50%)	6 (31.6%)/8 (42.1%)	8 (27.6%)/16 (55.2%)
Moderate scar^a	0 (0%)/3 (6.3%)	0 (0%)/0 (0%)	0 (0%)/3 (10.3%)
Large scar^a	0 (0%)/0 (0%)	0 (0%)/0 (0%)	0 (0%)/0 (0%)

The renal scar was considered small, moderate, and large when the photopenic area on the technetium-99m dimercaptosuccinic acid renal scan covers less than 1/6, between 1/6 and 1/4, or larger than 1/4 of the corresponding renal pole surface, respectively.

No major complications, such as visceral, pleural, or vascular injuries, were seen.

Discussion

The introduction of PCNL as the standard of care for the management of large renal stones has revolutionized surgical treatment, with minimally invasive procedures now being preferred over open surgical approaches. The central step in percutaneous renal surgery is tract creation, which is performed classically with three dilation methods (metal telescopic Alken dilators, incremental Amplatz dilators, or balloon dilators). All methods are intended to create a 28F–34F tract over which an Amplatz sheath can be passed.^8,9 Although balloon dilation can be considered a safe approach for one-step tract dilation, its high cost precludes its routine application, especially in centers with limited resources.^3,9

In view of the growing use of one-stage tract dilation for PCNL, we aimed to investigate the effect of this method of tract dilation on overall renal function and regional scar formation. We hypothesized that compared with gradual expansion of the cortical tissue, one-step acute dilation might cause greater trauma to the cortical microvasculature.

The controlled randomized clinical trial reported here enrolled patients with no history of SWL or renal surgery. All patients had an uncomplicated operation through a single access, and all stones were removed successfully without the need for any ancillary procedures. To prevent overestimation of postoperative renal scarring, we scanned all patients before the operation.

Our findings support the safety and efficacy of one-stage tract dilation in PCNL and document its potential advantages, which include reduced radiation exposure time and access time, a result consistent with previous reports.^2

–5

To avoid potential problems associated with the repeated insertion and withdrawal of incremental dilators, such as prolonged access time, excessive radiation exposure, and the possibility of tract displacement, rapid, one-stage tract dilation with a 28F Amplatz dilator^2

–5 has been tried and shown to be safe and effective. In large series, one-stage tract dilation was found to be feasible in almost all adult patients, with a success rate similar to that of standard techniques. Moreover, one-stage tract dilation is not associated with more hemorrhagic complications than multiple incremental techniques^4,5 and can reduce access time and radiation exposure during access.^3
–5

Since the introduction of PCNL, its associated renal parenchymal damage has always been a concern. 99m-Tc DMSA is taken up by the proximal tubular cells, and its cortical uptake depends on the renal blood flow and healthy cortical tissue. These characteristics make 99m-Tc DMSA renal scan the preferred modality for evaluating renal cortical scars and measuring split renal function.¹⁰ Several groups have shown that the detrimental effect of PCNL on overall and regional renal function is generally insignificant or minimal.^11,12 Experimental trials have shown that PCNL may lead to a cortical focal scar averaging 0.15% to 0.9% of the total cortical surface.^13,14 The size of the access and the use of incremental vs balloon dilation had no significant influence on the amount of scar formation.^13

–16

Four weeks after the operation, significantly more patients with one-stage tract dilation developed a new scar on their access site (48.3%) compared with patients who underwent gradual dilation (11%) (P=0.007). This finding was consistent with our results for the overall function of the operated kidney in 99m-Tc DMSA renal scans performed 4 weeks after the procedure. Dilation with a rapid taper from 8F to 28F may result in a larger radial force vector being imparted into the renal tissue than with gradual tapering. Although our results showed more parenchymal and microvasculature damage during one-stage tract dilation than during gradual dilation, the clinical significance of these photopenic hypovascular areas in the long term remain to be determined.

One long-term follow-up study showed that split renal function in 99m-Tc DMSA renal scans improved in patients who underwent selective renal angioembolization.¹⁷ This may be because of the development of an intrarenal collateral blood supply in ischemic areas. Ischemic scars tend to shrink with time. Poulakis and associates¹⁸ and Chaziioannou and colleagues¹⁹ separately showed that scar size after angioembolization shrank by 50% over 12 to 40 months.

Nevertheless, the evidence summarized above falls short of confirming that rapid, single-stage dilation is a suitable option for most patients, so further long-term studies are needed to document the degree of parenchymal damage after PCNL with one-stage tract dilation. We intend to follow patients in group 2 for 1 year after their surgery to determine the long-term effects of one-stage dilation on their renal function and the size of their renal scar.

To our knowledge, no published clinical trials have addressed renal parenchymal damage after PCNL with one-stage vs gradual tract dilation. Some limitations of this study, however, deserve mention. Our sample size in both arms was admittedly small. This was a result of our specific selection criteria to obviate confounding factors as much as possible. Obviously, enrolling more patients in the two groups would enhance the power of the study.

We were also aware of the differences in the number of patients in each group. We randomized the patients before the operation and, to eliminate possible confounding factors, our exclusion criteria were based mainly on intraoperative and postoperative events (eg, failed first access, the need for more than one access, the need for any ancillary procedures such as SWL, etc), and this may explain this difference in the final number of patients in each groups.

In addition, we used a planar technique for 99m-Tc DMSA renal scans, which produces two-dimensional images, so we cannot rule out the possibility that some small scars were overlooked with this imaging modality. Obviously, the use of a three-dimensional imaging technique such as 99m-Tc DMSA single-photon emission CT may be a more sensitive, but less specific, approach to determining the extent of renal scarring.

Conclusions

One-stage tract dilation seems to be a safe and efficient technique for creating the access tract in PCNL. Although it reduces radiation exposure and access time, in the short term, it may cause more parenchymal damage than gradual dilation. The long-term clinical significance of this potentially detrimental effect remains to be studied.

Footnotes

Acknowledgments

This study was supported by Shiraz University of Medical Sciences. We thank K. Shashok (AuthorAID in the Eastern Mediterranean) for improving the use of English in the manuscript, A. Salehi, M.D., for his assistance with the methodology, and E. Ghanbarifard for drawing .

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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