Pediatric cystine stone successfully treated by mini‐percutaneous nephrolithotripsy and antegrade ureteroscopy

Introduction Cystinuria is often diagnosed by large renal stone for pediatric patients. The patients suffer from recurrence of stone disease, develop the chronic kidney disease and fall into end‐stage renal failure. Total removal of stone at the first intervention and prevention of recurrence are essential. Although, it is difficult to treat the pediatric stone patients for their anatomical feature. Case presentation We report three cases of pediatric cystine stone patients (two 4‐year‐old boys and a 9‐year‐old girl) successfully treated by mini‐percutaneous nephrolithotripsy and antegrade ureteroscopy. We could remove stones completely in all three cases, and the patients did not suffer from major complications. Conclusion It is essential to select the surgical approach, the endourological device, and the patient's position which is suitable for the age, the body size, and the condition of stones at the initial intervention of pediatric cystine stone.


Introduction
Cystinuria is an inherited disorder of dibasic amino acid transport system in the renal proximal tubule and the small intestine, consisting of 1% to 2% in adult urolithiasis and 10% in pediatric urolithiasis. 1 Some cases of cystinuria were associated with chronic kidney disease and fell into end-stage renal failure. 2 The patients of cystinuria often reveal the large volume stone at the initial diagnosis. This is the case report of three pediatric cystine stone patients successfully treated by mini-PNL and antegrade URS.

Case report Case 1
A 4-year-old boy performed urethroplasty for hypospadias got fever and vomiting. He did not have family history of cystinuria. Abdominal X-ray showed a 9 9 8 mm stone at right kidney area and a 20 9 12 mm stone at right proximal ureter area. Non-contrast-enhanced computer tomography (NCCT) showed a 10 9 6 mm stone at right lower calices and a 13 9 8 mm stone at right proximal ureter. He was diagnosed as obstructed pyelonephritis and the status of inflammation was improved by antibiotics. Then, we performed mini-PNL of twice procedures (146 and 95 min, 8 days-interval).

Case 2
A 4-year-old boy with family history of cystinuria got fever and abdominal pain. Abdominal X-ray showed a 28 9 12 mm stone at right proximal ureter area and a 15 9 10 mm at right distal ureter area. NCCT showed a 13 9 12 mm stone at right proximal ureter, a 11 9 8 mm stone at right distal ureter, right hydronephrosis, and abscess at the upper pole of right kidney. The status of inflammation was improved after antibiotics. Then, we performed antegrade URS of three times of surgeries (128, 182, and 163 min, 4 and 11 days interval).

Case 3
A 9-year-old girl with family history of cystinuria was detected a staghorn stone in right kidney, which was shown 49 9 31 mm in abdominal X-ray and a 35 9 19 mm in NCCT without symptoms. Mini-PNL of twice procedures (134 and 163 min, 5 days interval) were performed (Fig. 1). Fig. 1 Images of all three cases before and after treatment.
Patient's characteristics and laser settings of three cases are shown in table 1. The results of infrared spectroscopy were pure cystine component in all three cases. They did not suffer from major complications and have no recurrence of the stone with oral administration of the thiol drug and urine alkalization agent (follow-up period were 60 months in case 1, 30 months in case 2, and 12 months in case 3).
Surgery was performed as follows. Mini-PNL (cases 1 and 3): the patient was set in the prone position after induction of general anesthesia. The 18-gage Chiba needle was punctured into the dorsal middle calices under the guidance of ultrasonography and fluoroscopy and a 0.035 inch guidewire was took into the collecting system. After the dilation of the access tract, the renal stone was visualized by the miniaturized nephroscopy (16 Fr outer sheath, Karl Storz) and treated by Holmium laser dusting (Versa Pulse Select 30 Lumenis).
We closed the procedure about 100-180 min and a 14Fr nephrostomy tube was inserted. The fragment migrated into ureter was removed by antegrade flexible URS. Antegrade URS (case 2): the patient was set in the flank position after induction of general anesthesia. The procedure of puncture and tract dilation is same as mini-PNL. The stones were visualized by the flexible URS (P6 or P7 4.9/7.95 Fr Olympus) through the 15 Fr outer sheath. Holmium laser lithotripsy and removal of the fragment by N Circle Basket (1.5 Fr Cook) were performed and 14 Fr Nephrostomy tube was inserted (Fig. 2).

Discussion
Treatment of pediatric urinary stone needs high-quality care and sophisticated surgical technique for the smaller size of  the body and visceral organs. We should choose minimally invasive approach based on the patient factors (age, gender, and body size) and the stone factor (location, size, and the composition). In >2 cm stones, PNL were reported higher success rate than retrograde URS and shock wave lithotripsy (SWL). 3,4 It is advantage of the prone position that we can get large operating space for puncture, dilation of the tract and endoscopy. Case 1 was performed urethroplasty for hypospadias with urethral stenosis, so we avoided retrograde URS and SWL. case 2, retrograde URS was another option, but we considered the pressure elevation of the collecting system and obstruction by postoperative fragments caused by large stone burden. Severe hydronephrosis and dilated proximal ureter were preferable for puncture and approach. URS could be approached by both antegrade nephrostomy and retrograde urethral access. In the third procedure we performed laser lithotripsy toward fragments migrated to urinary bladder by antegrade URS with saline flush and discharge by urethral catheter. In our institution, the adult patients are often performed endoscopic combined intrarenal surgery in the modified Valdivia position, but we chose the prone and flank position to obtain the working space widely.
We could investigate some reports about Japanese patients of cystinuria. Takahashi et al. reported about 22 cases of long-term follow-up (median 160 months). Primary intervention was four SWL cases, five URS cases, and 13 PNL cases but the most patients were adults (median age: 46 years, range: 12-82 years). 5 Inoue et al. reported about bilateral cystine stones of 2-year-old boy successfully treated by super ultra-mini endoscopic renal surgery (sheath 8.5/9.5Fr). 6 Currently, miniaturized nephroscopy and URS, improvement of laser technology and fine retrieval instruments have revolutionized minimally invasive surgery in children. 4

Conclusion
We could get the stone free status for three cases of pediatric cystine stone by mini-PNL and antegrade URS with 15-16Fr tract size. Any patients did not suffer the complications such as bleeding and septic shock. Mini-PNL and antegrade URS are effective for large stone burden (>2 cm). It is essential to select the endourological device and the patient position for age, body size, stone burden, and stone location.