Safety and Efficacy of Minimally Invasive Percutaneous Nephrolithotomy in Treatment of Calculi in Horseshoe Kidneys

Introduction

The most common renal fusion anomaly is horseshoe kidney (HK) with an incidence of 0.25%. ¹ HKs are thought to be associated with an increased incidence of stone disease. The prevalence of urolithiasis in HKs has been reported to be 20%–60%. ^2,3

The treatment of calculi in HK is considered to be a challenge for urologists due to abnormal caliceal orientation and aberrant vasculature. In recent years, minimally invasive treatment modalities, including extracorporeal shock wave lithotripsy (SWL), ⁴ retrograde intrarenal surgery (RIRS) with flexible ureteroscopy, ⁵ and percutaneous nephrolithotomy (PCNL), ^{6 –8} have been used in the treatment of stones in HK. Whereas small stones (<2 cm) can be managed by SWL or RIRS, several investigators have suggested that, for stones larger than 2 cm in a HK, PCNL should be considered as a first-line option. ^{6 –8}

Minimally invasive PCNL (MPCNL) is a modified PCNL technique using a miniaturized endoscope through a smaller (20F or less) nephrostomy tract, which has been shown to achieve compatible stone-free rates (SFR) and minimize complications compared with conventional PCNL. ^9,10

In this study, we present our experience in the treatment of HK associated stones using MPCNL with semirigid ureteroscopy. The outcome of our management showed an acceptable SFR and minimal complications.

Materials and Methods

Preoperatively, urinalysis, urine culture, ultrasonography, kidney, ureter, and bladder radiograph (KUB) or intravenous urography (when serum creatinine <2 mg/dL), and noncontrast spiral computed tomography (CT) were performed in all patients. The stone burden and location were recorded according to KUB and CT results, which were determined by multiplying the stone length by the width in millimeters squared (results are shown in Table 1). The average stone burden is 657±510.9 mm² (range 134.7–2460.1). Prophylactic antibiotics were administered to all patients. Sterile urine was ensured in patients with positive urine culture results before they underwent surgery following a complete course of culture-specific antibiotics.

All patients received MPCNL (F18–20) for stones in HK. The detailed methodology has been stated in our previous publication. ^10,11 Briefly, patients were given either general anesthesia or combined spinal–epidural anesthesia; then, an open tip 5F ureteral catheter was inserted retrogradely, to inject contrast material to facilitate renal puncture and prevented stone fragments dropping from the renal collecting system down to the ureter. With the help of C arm or B ultrasound, a preferred calix puncture was performed. In most of our cases, upper polar accesses were usually chosen due to downward displacement of HKs. The dilatation of the percutaneous tract was conducted over the guidewire with a fascial dilator from 8F to 18F or 20F. The stone was fragmented by the holmium:yttrium aluminum garnet (Ho:YAG) laser or ballistic lithoclast through an F8/9.8 semirigid ureteroscope (RichardWolf, Knittlingen, Germany). Most of the fragments were flushed out with an endoscopic pulsed perfusion pump ^10,12 and few removed by stone grasper forceps. Finally, a 5F Double-J stent was placed, and an 18/20F nephrostomy tube was left in place at the end of the procedure. The operating time of MPCNL was calculated from starting the puncture to placing the nephrostomy tube. When necessary, new percutaneous tracts would be performed during the same procedure or a second-stage MPCNL, which would be performed 5–7 days later, during which existing tracts were used or new tracts were created.

The intra- and postoperative complications were recorded based on the modified Clavien classification. ¹³ Ultrasound and KUB/or noncontrast CT were used to evaluate the stone clearance of MPCNL within 48 hours postoperatively. Success was defined as the stone-free status or the presence of only residual fragments <4 mm without any clinical symptoms, as measured at the largest dimension of the stone. ⁵ The composition of stone samples obtained from operation was also analyzed using Thermo Nicolet 380 infrared spectroscopy. Stones were washed with distilled water, dried, and powdered. A small portion of each sample mixed with potassium bromide was analyzed, and the predominant stone component was recorded—a method consistent with previous work in stone analysis. ¹⁴

Results

From 2006 to 2012, 32 patients with HK stone underwent MPCNL in our hospital. The average age was 38.2±7.3 years (range 14–72), with the average body mass index of 23.3±2.77 (range 17.6–25.2). The male/female ratio was 2.2 (22:10). Relevant comorbidities included diabetes mellitus (4/35, 11.5%) and hypertension (5/35, 14.3%). Twenty-nine patients had unilateral renal stones, and three patients had bilateral renal stones. Among the patients, five had a previous history of kidney surgery and six patients had a history of failed SWL. The patient demographics and characteristics are listed in Table 1.

A total of 42 percutaneous tracts were set up in 35 kidney units. A single tract was used in 29 kidneys (29/35, 82.8%), two tracts were used in 5 (5/35, 14.4%), and three tracts were used in 1 (1/35, 2.8%). Puncture to HKs was 35 tracts (35/42, 83.3%) in upper pole, 5 (5/42, 11.9%) in interpolar region, and 2 (2/42, 4.8%) in lower pole. Second-stage MPCNL was performed in five kidney units due to residual stone burden. The operative time ranged from 53 to 152 minutes (mean 93.4±17.6). A complete stone-free rate was 82.9% (29/35) after first-stage procedures and 91.4% (32/35) after second-stage procedures, in a total of 35 kidney units, respectively. Residual stones were left in three renal units. The characteristics of the operation and results of the treatment are listed in Table 2.

The average hospital stay was 8.6 days (range 6–18). There were no intra-abdominal or pleural complications. Minor complications (Clavien grades I and II) were seen in six patients, in which one patient (3.1%) required transfusion after PCNL. A single patient (3.1%) was treated for urosepsis (Clavien grade IVa) with intensive care unit monitoring and resolved after several days without long-term consequences (see in Table 2).

Stone composition analysis was also performed in our study. Stone composition was calcium oxalate (27/35, 77.1%), calcium phosphate (4/35, 11.5%), uric acid (2/35, 5.7%), and struvite (2/35, 5.7%).

Discussion

Urolithiasis is commonly seen in patients with HKs. ² Many urologists advocate PCNL for large stones in these kidneys based on an aberrant anatomy and the low success rates of SWL and ureteroscopic approaches. ¹⁵ Since most of the calices in HKs are either directed dorsomedially or dorsolaterally, ¹⁶ which usually facilitate the puncture, PCNL remains the preferred method for stones >2 cm or following other failed manipulations. In this study, six patients had a history of failed SWL.

In patients with a HK, upper pole percutaneous access is often recommended, because upper pole access allows reaching upper pole calices, renal pelvis, lower pole calices, pelviureteral junction, and proximal ureter. ^16,17 However, when stones are in the lower caliceal and medial calices, the nephroscope might not reach the stone, either due to length limitations or because of the angulation present within the pelvicaliceal system. ^3,6 The relatively immobile anomalous kidney may also present difficulties with maneuverability of the rigid nephroscope. For that reason, we prefer performing PCNL in HKs using a semrigid ureteroscope. This instrument, 8/9.8F in diameter, is 42.5 cm long and may provide advantages in this patient population for reaching all parts of the collecting system during PCNL in HKs. ¹¹ Our results revealed that MPCNL is effective for HK stones, with compatible complications, to conventional PCNL.

In patients with normal renal anatomy, access to the upper pole calices during PCNL often requires a supracostal approach that may cause thoracic complications. ¹⁸ However, in a HK, the position of the kidney is relatively lower than the normal position, so upper pole puncture can be achieved with a lower risk of pleural injury. Whereas 83.3% of our punctures were upper pole in this series, we did not observe any thoracic complications. The complete stone-free rate was 82.9% after first-stage and 91.4% after second-stage MPCNL procedures, which is comparable to other reports. ^6,17,19 Skolarikos et al. reported a relatively lower stone-free rate in HKs but with staghorn stones and larger burden, ²⁰ although there are 15 semi-staghorn or staghorn stones in our study, the stone burden is smaller compared with their study.

Because residual fragments are an important risk factor for stone growth and recurrence, especially in congenitally anomalous kidney, the complete removal of stones from the kidney is recommended by many authors. ^7,21,22 Auxiliary flexible endoscopy was reported to attribute to the clearance rates of post-PCNL residual stones. ²³ However, the cost of flexible endoscopy is the limiting factor for not using it routinely, especially in developing countries. A multiple tract is an alternative choice to treat post-PCNL residual stones. ²⁴ In our study, we created more than one tract in six kidney units in an effort to render patients stone free. We feel strongly that urologists should be prepared to use multiple tracts to remove the stone during PCNL in HKs as necessary. ²⁵

Our hospital stay was much longer than those reported in other studies. ^9,26 This difference, however, was not a reflection of higher complications, but our culture and customs. In the United States and certain other countries, removal of the nephrostomy tube is often managed in the outpatient setting, but in China, it may be socially unacceptable to discharge a patient with a nephrostomy tube. Patients generally prefer to stay until they are well recovered from surgery. Furthermore, according to the policy of the Chinese medical system, all preoperative evaluations, including blood examination, have to be conducted during hospitalization before being reimbursed.

Conclusion

In this retrospective study, MPCNL is a safe and effective treatment modality in HK stones with acceptable results. The anatomic abnormalities in HK do not appear to adversely affect stone-free rates. In skilled hands, MPCNL complications in HK are similar to the normal anatomy kidney. However, further studies with a larger sample size are required.