'Case of the Month' from the University of Santiago de Compostela, Spain: challenging the status quo in percutaneous stone surgery for horseshoe kidneys, the Galdakao-modified supine Valdivia position is a safe alternative for complex cases.

Abstract

Horseshoe kidney (HSK) is the most common renal fusion anomaly, with a reported incidence of approximately one in 500 births. Characteristically, these kidneys have their collecting system anteriorly displaced and usually a high insertion of the ureters in the renal pelvis, which may impair normal urinary drainage. This urine stasis has been proposed as a cause for stone formation, which occurs in around 20–60% of cases, although metabolic abnormalities have also been found in these patients [1]. Several treatment options can be currently offered to patients with stones in HSKs: shockwave lithotripsy, flexible ureteroscopy, percutaneous nephrolithotomy (PCNL), laparoscopy/robot-assisted and, less commonly, open surgery. For large stone burdens, PCNL is the treatment of choice, which has been traditionally performed in prone position. In the present case report, we present a complex stone in a HSK treated with PCNL using the Galdakao-modified supine Valdivia position (GMSVP) and then discuss some key points regarding this different approach for such a special situation. A 42-year-old woman with history of recurrent UTIs over the preceding 5 years attended the emergency department complaining of right loin pain and fever. Ultrasonography (US) revealed right pyonephrosis with severe dilatation of the renal pelvis and calyces due to a staghorn stone, which was radiopaque on X-ray film. A nephrostomy tube was placed, and broad-spectrum antibiotics were administered. Urine cultures revealed an E. coli sensitive to amoxicillin, oral cephalosporins, and quinolones. A CT scan was then carried out, which showed a complete staghorn stone in the right moiety of a HSK. A dimercaptosuccinic acid (DMSA) scan revealed a differential renal function (DRF) of 27% for the right renal unit. (Fig. 1A,B). After a 10-day course of antibiotics a second urine culture had negative results. After a thorough discussion with the patient regarding different treatment alternatives, staggered PCNL was proposed. The patient was aware of the complexity of the stone distribution and the special anatomy of the HSK. She signed an informed consent for endoscopic combined intrarenal surgery (ECIRS), for multiple percutaneous tracts and to undergo several interventions to clear the stone burden entirely. She was also informed about the potential risk of infection, sepsis, and bleeding. Preoperative amoxicillin was started 5 days before surgery, according to the latest antibiogram. In the first surgery, the patient was placed in the GMSVP. Before draping, US was performed to check if it was possible to access the different calyces in this position without puncturing neighbouring organs. The previously placed percutaneous nephrostomy was not used, as it was very close to the large bowel and entered through the infundibulum of the middle calyx. Combining US and fluoroscopy, three punctures were carried out for those possible accesses the surgeon considered would be required. Three guidewires were passed to maintain these tracts and fastened to the operating field. (Fig. 2A,B). The upper pole approach was initially dilatated up to 16 F and a holmium laser was used to make room in the calyx to then dilate up to 24 F using Amplatz serial dilators much more safely. A lithotrite with combined ultrasonic and ballistic energy was employed. After 140 min, with only the upper pole stone having been removed, we decided to stop the procedure and schedule a new surgery. Three nephrostomy tubes were left in place, one for each access. The hospital stay was 7 days due to the advent of fever in the postoperative period. After 2 weeks, a second surgery was performed. We again took the upper pole access to make sure there were no fragments left behind and we used a flexible nephroscope to treat the renal pelvis stone and the remaining calyceal branches. A holmium laser was utilised and fragments from the renal pelvis and lower calyces were taken out using nitinol baskets. As it was not possible to enter into the middle calyx via this access, we took advantage of the tract already in place from the first procedure to dilate it up to 16 F. Through this access all the branches in the middle pole, but one in parallel, were cleared. Here, we made the most of the GMSVP to insert a flexible ureteroscope retrogradely, which very easily entered this calyx, to break and remove all the stones. Therefore, it was not necessary to use the third potential percutaneous access established in the first intervention (Fig. 3). Again, a nephrostomy tube through the upper pole as well as a JJ catheter were left in situ for drainage. The patient did not present any haemodynamic problems during the surgery, which lasted 4 h and 30 min. She was discharged after 4 days with no further complications. Stone analysis revealed a compound composition of struvite (53%) and apatite (47%). A CT scan 2 months later showed small residual fragments in the upper and lower pole and a new DMSA scan revealed a 4% improvement in the DRF of the right renal unit. After discussion with the patient, bearing in mind the infective nature of these residual stones, we agreed to perform a retrograde intrarenal surgery to complete the stone clearance. In this third procedure, a single-use ureteroscope was chosen to reach the most difficult locations in the HSK without putting our disposable endoscope at risk of breakage. Those stones that could not be extracted straightaway with baskets through the ureteric access sheath were fragmented first with a holmium laser. After a 60-min intervention, no stones were endoscopically detected in the pelvicalyceal system. The patient was discharged on day 2 without any complication and 3 months later she was asymptomatic with no further UTIs, and CT did not reveal any residual fragments in the right kidney. Stone treatment in abnormal kidneys is a challenge requiring a comprehensive analysis of the case, of the different alternatives available, and their theoretical outcomes. Overall, PCNL is the treatment of choice for large and/or complex stone burdens. In the special HSK scenario, the PCNL success rate is reported to be around 75–88%, yet a considerable percentage of cases require auxiliary procedures. Conversely, its incidence of complications in the literature ranges from 14.3% to 29.2% and it is similar to that of PCNL performed in normal kidneys [2]. PCNL has been classically carried out prone for HSKs. The abnormal position of the kidneys in the abdomen increases the concern about a potential injury to neighbouring organs when creating the access. However, a supine position has been shown to be a safe and effective approach for PCNL, even in patients with renal abnormalities, whenever there is a clear path to the kidney [3]. Furthermore, the GMSVP offers the opportunity to perform ECIRS in a natural and ergonomic manner, combining instruments retrogradely and anterogradely, minimising the need for multiple tracts. Taking into account the special anatomy of the HSK, it is mandatory to thoroughly analyse the preoperative imaging in these patients. In our opinion, this should always encompass a CT urogram, in which special attention to axial slices should be paid. In cases of large stones, with prior interventions to the kidney and when parenchymal thinning is found, a DMSA scan can add very valuable information to assess the DRF. In our present case, the patient had a suboptimal right kidney function of 27%, which rose to 31% after removing the entire stone burden. This improvement in renal function has been found in other studies assessing the functional impact of PCNL, and it is more often found when there is some degree of obstruction preoperatively. Before surgery, it is compulsory to take a urine sample for culture and, should it be positive, to treat the patient with antibiotics. Staghorn stones, due to their nature, carry a considerable risk of infective complications in PCNL. In this case, although the urine culture was negative, we decided to initiate oral amoxicillin 5 days before the procedure. This decision can be controversial, although it is based on our own experience, as well as that of other groups regarding the discordance between the culture results using voiding urine and those with urine taken straightaway from the renal puncture or performed using the stone itself [4]. The present case gives us lots of food for thought and some interesting technical tricks are worth commenting upon here. First of all, we strongly recommend performing US in the operating room before draping, to preoperatively confirm that there is a safe and clear path to the calyces. Then, when multiple accesses are possibly required in our surgical planning, it is much better to perform all these punctures at the beginning and place guidewires in each access. Puncturing a kidney for an accessory tract once a percutaneous access is created is much more difficult. We decided to start dilating the upper calyx puncture, as this is in general the best approach to have entire access to the pelvicalyceal anatomy. In HSKs, their special anatomy favours this approach, as they lie more posteriorly and are found relatively lower in the abdomen, therefore making it possible to carry out this puncture below the 12th rib. However, endourologists must be aware that the tract length in this situation is usually longer than in normal kidneys. In cases with a large stone burden, patients must be advised that several surgeries will be required to clear all the stones. Operating time is directly related to infective complications, that is why we decided to stop the first procedure after 2 h, which is our time limit in general. However, in the second surgery we exceeded this cut-off time considering that all the kidney cavities were better drained after 2 weeks with the three nephrostomies. Regarding the multiple accesses to the kidney, our policy is to minimise their use and size as much as possible, to reduce the risk of bleeding. This way, we decided to use a standard 24-F sheath for the main tract and 16-F for the second one and flexible ureteroscopy to avoid a third access to the kidney. Finally, the use of flexible endoscopes has been shown to increase success rates by allowing us to reach peripherally located calyces in HSKs [5]. Stone fragments were sent for compositional analysis, which revealed their infective nature. In these cases, a complete removal of the calculi is necessary to prevent the residual fragments re-growth. This led us to recommend a third surgery to complete the stone clearance, which was entirely successful with just retrograde intrarenal surgery. From a technical standpoint, flexible ureteroscopy in HSKs should follow a fragmentation and extraction strategy, in which all the stone pieces are actively taken out with nitinol baskets, bearing in mind the low likelihood of spontaneous passage of dust or small stones in this anatomy. In conclusion, large stone burdens in HSKs are a challenging scenario for endourologists, requiring a comprehensive study of the case and tailored treatments that may include different approaches to render the patient stone free. A supine position is a safe and alternative option to the classical prone approach in this situation, provided that a clear path to the kidney is demonstrated. The author has no conflict of interest to disclose.