Should Percutaneous Nephrolithotripsy Be Considered the Primary Therapy for Lower Pole Stones?

Introduction

T he management of lower pole calculi is a challenging issue even today. There is still a controversy for the exact determination of the indications for the use of percutaneous nephrolithotripsy (PCNL), extracorporeal shockwave lithotripsy (SWL), or even retrograde ureteroscopy. Many critical factors are under evaluation, such as the effectiveness of each method, as described by the stone-free rate, the stone size, the spatial anatomy of the lower pole, the morbidity, the cost, the hospital stay, and the recurrence rate. In this retrospective study, we compare various techniques, focusing mainly on PCNL, which is advocated as the most effective method by the current literature, when stratified by stone burden and lower pole location, even if SWL is considered the first-line treatment for renal stones less than 20 mm in diameter. ^{1 –3}

Materials and Methods

The files of 144 consecutive patients with lower pole calculi who underwent PCNL from one surgeon after a previous, single, unsuccessful session of extracorporeal shock wave lithotripsy (SWL), over a period of 10 years, were included in this study. The patients had solitary, staghorn, multiple, or impacted lower pole stones as shown by the intravenous urography preoperatively. Patients' characteristics are shown in Table 1. They were previously informed about the SWL stone clearance of 55% for lower pole stones in our center using the Dornier MFL 5000 lithotripter, thus deciding in case of one failure to proceed with PCNL for clearance of stones.

The patients with calculi larger than 20 mm after one failed session of SWL were referred to our department, because they remained symptomatic. Those who had radiolucent stones were also included in the study. Successful treatment was considered when no evidence of stones larger than 2 mm was observed immediately after the removal of the nephrostomy tube either in the postoperative kidneys, ureters, and bladder radiograph film or in the nonenhanced computed tomography for the radiolucent stone evaluation.

With the patient in a supine position on a C-arm compatible table, general anesthesia was induced and a 6F ureteral catheter was inserted. Then, the patient was turned to prone position and the contrast material was injected, to delineate the anatomy of the kidney and identify the appropriate calix for puncture. Using the method of triangulation, determination of the direction of an 18-gauge translubar angiography needle was accomplished. The needle was advanced into the calix directly. A floppy J-tip guidewire was inserted into the needle and reached the calix and the renal pelvis if possible. The needle was removed and the dilatation of the nephrostomy tract with the Amplatz dilator or high-pressure nephrostomy balloon set was performed. Then nephrolithotripsy was performed to all accessible calices with the 26F rigid nephroscope (Wolf, Athens, Greece). We used the flexible cystonephroscope (Olympus, Athens, Greece) through the Amplatz sheath to reach nonaccessible calices with the rigid instrument using basketing to either remove the stone or perform laser lithotripsy and then basketing the caliceal fragments. A nephrostomy tube was inserted at the end of the procedure in all the cases. None of the patients had a Double-J stent postoperatively. We evaluated the stone size in relation to the stone clearance rate and also recorded stone composition.

Results

The mean operating time was 72 minutes (42–118 minutes). There was no need for blood transfusion. All of the puncturing attempts for access to the kidney were successful followed by stone removal. No patient needed second-look PCNL. The mean hospital stay was 2.3 days (2–5 days). Nephrostomy tubes remained in place for 2.1 days (2–3 days) postoperatively. Minor complications were encountered, such as fever with negative urine cultures in 10 patients (6.9%), which was managed conservatively. Two patients with struvite stones developed fever with positive urine cultures and were managed with antibiotic treatment effectively. Septicemia or urinoma was not encountered postoperatively. There were minimal analgesic requirements with only one dose of nonsteroid antiinflammatory agents, which were administered intravenously immediate postoperatively. No patient needed any other analgesic medication during the hospital stay. However, they suffered instantly during nephrostomy removal, without any need for further therapy. After being discharged they were given oral analgesics.

Hydronephrosis due to obstruction of the proximal ureter by residual stone fragments was observed in four patients (2.7%) and this resolved after spontaneous passage of these fragments. Analysis of stone composition showed that the majority of the cases, 128 out of the 144 cases (89%), had calcium oxalate stones, 6 (4%) had uric acid stones, 6 (4%) had cystine stones, and 4 (3%) had struvite stones.

After a 3-month follow-up, we were able to demonstrate excellent stone-free rates in all the three categories of patients. The stone-free rate for stones less than 10 mm was 95%. A 97% rate was accomplished for stones between 11 and 20 mm and a 98% rate for stones larger than 20 mm. Further, the stone-free rate for cystine stones was 100%.

Discussion

There was a tremendous pool of patients with urolithiasis, especially the decade 1983–1993, because of the rapid proliferation of SWL units worldwide. Despite the significant amount of data reported, the indications of the various methods such as PCNL and SWL for the treatment of lower pole calculi remain unsettled. ¹ The effectiveness of each method was evaluated by the stone-free rate. The overall stone-free rate according to Netto et al ⁴ was 95.6% for PCNL and 79.2% for SWL. Lingeman et al ¹ presented a 90% success rate achieved with PCNL, a result significantly better than that achieved with SWL (59%). In another study by Cass, ⁵ the rates were 70.5% to 100% and 71.2%, respectively. Dore et al ⁶ reported a 90.2% stone-free rate for solitary inferior caliceal stone using PCNL. Albala et al ⁷ reported a 3-month overall 95% stone-free rate for PCNL versus 37% for SWL.

The advantage of PCNL relative to SWL is prominent, when the stone size increases. Numerous articles have investigated the stone-free rates of these two techniques, stratified by stone size. For stones 10 mm or less, the stone-free rate for SWL is 74% compared with 100% for PCNL. ^4,7 For stones 11 to 20 mm, the rates are 56.3% for SWL and 89% for PCNL, respectively. ¹ Finally, for stones more than 20 mm the difference is even greater: 32.6% for SWL and 93.7% for PCNL. ¹ Havel and colleagues ⁸ also demonstrated the advantage of PCNL with larger stones.

However, we should mention that the SWL stone-free rates can be as much as 30% increased, if immediately after therapy, Phyllanthus niruri (Uriston®), a plant used in Brazilian folk medicine, is administered. Celia et al ⁹ reported a 94.1% stone clearance versus 64.28% without the Phyllanthus niruri therapy. This plant seems to act on urinary excretion of endogenous inhibitors of lithogenesis, namely citrate, magnesium, and glycosaminoglycans, although the exact mechanism of action remains unclear.

Moreover, researchers have reported different percentages of stone clearance using different types of lithotriptors. ^{10 –12} Li et al ¹³ recently reported that stone breakage tends to be more effective when urine specific gravity is about 1.040 than at higher or lower values. Another major parameter that affects the effectiveness of SWL is the spatial anatomy, which was first described by Sampaio and Aragao. ¹⁴ Spatial anatomy of the lower pole, as defined by the infundibulopelvic angle (LIP angle), infundibular length (IL), and infundibular width (IW), plays an influential role in the stone-free rate after SWL. A wide LIP angle, a short IL, and a broad IW, individually or in combination, favor stone clearance, whereas an LIP angle of <70 degrees, an IL of >3 cm, or an IW of ≤5 mm is individually unfavorable. When all three unfavorable factors or unfavorable LIP and IL coexist, the post-SWL stone-free rate falls to 50% or less. ¹⁵ On the contrary, PCNL is not affected by the lower pole spatial anatomy, which is another advantage of this technique. ¹⁶

Complications, cost, and hospital stay are the criteria which offer advantage to SWL and make it the first-choice therapy for stones under 20 mm. PCNL, on the other hand, as an invasive and technically challenging procedure has not yet been well accepted as routine for the management of lower pole kidney stones because the procedure is accompanied by a higher (23%) complication rate (urinary tract infection, obstruction, ileus, sepsis, hematoma, perforation, transfusion, and arteriovenous fistula) versus 12% for SWL (infection, obstruction, colic, hematoma, and Steinstrasse). ⁷ To minimize hemorrhage, which is the most worrisome complication of PCNL, the puncture should pass through the Brodel avascular line. ^17,18 With this approach, we can avoid damage to major blood vessels, especially the posterior segmental artery, which is the artery most commonly damaged during endourologic procedures. ¹⁹ Safest access is also through a lower pole calix, because it eliminates the risk of pleural injury and allows for observation of the entire collecting system with flexible instruments. A promising new attempt for obviating the complications of PCNL and reducing the patients' discomfort due to nephrostomy tube is the use of tubeless access technique. ^{20 –22} The use of fibrin sealant for the closure of the nephrostomy tract appears to make this procedure safe and feasible. ^23,24

Alternative methods in the management of urinary lithiasis in general are progressing constantly. Lower pole stones less than 20 mm can be primarily treated by ureteroscopic means in patients who are obese, who have a bleeding diathesis, with complicated intrarenal anatomy, or with stones resistant to SWL, or as a salvage procedure after failed SWL. Ureteroscopic management of lower pole calculi is a safe and effective as well as a reasonable alternative to SWL or PCNL in patients with low-volume stone disease. ²⁵ However, for patients with stone less than 1 cm undergoing ureteroscopic stone lithotripsy the stone-free rate was 50%. ²⁶

Although SWL remains the first choice of therapy for kidney stones <20 mm, PCNL has urged urologists globally to advocate this kind of procedure. Its indications are expanding, because of its excellent effectiveness, which outclasses SWL, when stratified by stone burden and lower pole location, as shown in our study.

In our study, we found that PCNL is an effective procedure regardless stone size, with an average stone-free rate of 96.7%, which is slightly better than that of previous published studies. Based on these data, the use of PCNL should be considered the first-line treatment in the management of noncomplicated lower pole calculi, regardless of stone size.

With the improvement and evolution of PCNL techniques, as minimally invasive PCNL emerges with the use of miniaturized instruments that reduce the invasiveness of conventional PCNL and use of tubeless technique, we expect a great decreased rate of complications, combined with excellent results. ²⁷