Introduction

The horseshoe kidney (HSK) is the most common renal fusion anomaly, with a prevalence of 0.25% in the general population.^1,2 In most cases, this fusion occurs at the lower end or base, and it is associated with lack of ascent and malrotation, which cause a high incidence of urinary tract infections and stone formation (around 21%–60% of patients).² Percutaneous nephrolithotomy (PCNL) is currently considered the first line of treatment in HSK with stones greater than 2 cm in diameter due to its higher stone-free rate.³ The colon has been reported to be posterior or posterolateral to the renal units in 3%–19% of patients with HSK. The incidence of colonic injury during PCNL in horseshoe kidneys is 5.9%, compared to less than 1% in patients with orthotopic kidneys.^2,4,5 In this case report, we present a patient with an HSK, staghorn kidney stone and retrorenal colon.

Case Presentation

A 52-year-old male patient from the Peruvian jungle was referred to our hospital due to a left renal lithiasis found on ultrasound. The patient had no significant background and a 3-month illness time, characterized by intermittent left lumbar pain without urinary infections. Noncontrast computerized tomography showed a left staghorn kidney stone on an HSK with fusion at the lower poles, with a volume of 3,456 mm³ (12×24×24 mm) and a density of 1,100 HU. In addition, a retrorenal colon and multiple bilateral renal cysts were evidenced (fig. 1). Nephrolithometric scale scores were as follows: Guy’s, III; STONE (stone size, tract length, obstruction, number of involved calyces and essence/stone density), 8; CROES (Clinical Research Office of the Endourological Society), 230. Admission laboratory results included hemoglobin 14 gm/dl, platelets 280,000/ml, leukocytes 7,500/ml, creatinine 0.56 mg/dl, sodium 142 mEq/l, potassium 4.2 mEq/l and urinalysis without alterations.

Faced with the possibility of colon injury, we initially performed flexible ureteroscopy, treating only 40% of the stone, near the renal pelvis. Since the desired stone-free rate was not obtained, a consensus meeting was held with the Urology Department, and it was decided to perform a mini-PCNL with ultrasound support to minimize the risk of colonic injury and to be able to access all renal cavities.

Figure 1. Anteroposterior computerized tomogram without contrast. A, coronal plane shows calculus spanning lower calyx. B, axial plane shows the interposition of the colon (white arrow) on the way to the upper calyx (yellow arrow). C, 3-dimensional reconstruction of the staghorn calculus.

The patient was scheduled for mini-PCNL 1 week after the first surgery. He underwent general anesthesia and was placed in a prone position. After placing the ureteral catheter retrogradely by cystoscopy, we performed pyelography. The puncture was performed with a bull’s-eye technique, directing the puncture toward the upper calyx using fluoroscopic guidance. An ultrasound scan was performed using a 4 mHz curved ultrasound transducer (BK Medical®) to define the adjacent structures to the puncture area and avoid possible inadvertent colonic injury. After puncturing with a Chiba 18 gauge needle (Rocamed®) and passing through it a 0.035 inch × 145 cm hydrophilic guidewire (Roadrunner®), a 1-step candle dilator (Karl Storz, Tuttlingen, Germany) was placed, through which a second guide was passed (safety guidewire), and the 16.5Ch/17.5Ch surgical sheath (Karl Storz) was passed over the latter (fig. 2). After identifying the exit of liquid through the sheath, we proceeded to place the mini-percutaneous 12Ch equipment, with a 6Ch/7Ch working channel and 12° optics (Karl Storz). Nephroscopy was performed and a clear medium was evidenced, with the presence of the residual stone, which was located mainly in the lower calyx. Laser lithotripsy was then performed using high-power holmium P100 equipment (Lumenis®) with a 365 micron laser fiber and laser settings of 0.6 J and 15 Hz, respectively, for energy and frequency. The last stone fragments were removed with an extractor forceps or spontaneously expelled (Venturi phenomenon). The immediate radiological stone-free status was verified under fluoroscopy and by mininephroscopy, navigating all the cavities (fig. 3). Finally, the sheath was removed under vision, leaving the safety guide, and since no bleeding was observed along the way or in the Foley drainage catheter, we opted for a total tubeless procedure.

Figure 2. Fluoroscopy. A, retrograde pyelography during placement of the left ureteral catheter. B, elements of renal approach. Black arrow indicates goat needle. Red arrow indicates ureteral catheter. Blue arrow indicates hydrophilic guide to ureter. C, mini-percutaneous approach with the patient in the prone position.

Figure 3. A, mini-percutaneous access nephroscopy. B, laser lithotripsy. C, extracted stone fragments.

The postoperative course was unremarkable and the patient was discharged on postoperative day 2. After 3 months, during followup, noncontrast computerized tomography was requested in his city of origin, verifying the stone-free status, which was defined as the presence of no fragments or residual fragment <4 mm.

Conclusions

It is a challenge for the urologist to perform PCNL through a path that has a retrorenal colon interposed. Initially, flexible ureteroscopy was considered to be the best approach, but ultimately PCNL with ultrasound guidance yielded a stone-free outcome. Using intraoperative ultrasonography during mini-PCNL reduces the risk of colon injury, especially in the case of a retrorenal colon.