Advanced Management of Complex Transplant Lithiasis: Low Lithotomy and Boot Stirrups Technique
Transplant lithiasis is a rare complication, with a reported incidence ranging from 0.1% to 6.3%. It is often diagnosed 1 year after transplantation . However, there may be an under-diagnosis since denervation of the grafts reduces symptomatology of the kidney stones, which also leads to spontaneous passage or delayed management . Therefore, recipients can present with complex pathologies leading to acute kidney injury, such as ureteral obstruction from intrinsic stricture formation, vesicoureteral reflux that can progress to urinary tract infection, and fistulation . Therefore, management should be prompt, despite an asymptomatic presentation. Nephrostomy tube placement or double-J stent implantation are the first-line treatment in cases of obstruction . Extracorporeal shock wave lithotripsy, percutaneous nephrolithotomy (PCNL), and antegrade and retrograde ureteroscopy are minimally-invasive surgical methods for transplant lithiasis <15 mm, >20 mm, and <20 mm, respectively . Management is multimodal and tailored according to patient conditions . Patient positioning is an important factor that contributes to perioperative outcomes . The lithotomy position is commonly used in urological procedures . Modifications can be made to adjust patient position that favors the surgical approach. The addition of stirrups can provide greater comfort to the patient and allows for a more precise positioning . Although stirrups are more commonly used in gynecological procedures and less in benign urological operations, they can serve as an important facilitation for transplant lithiasis management, as transplant kidneys have a disturbed anatomy. We report 2 cases of complex transplant lithiasis managed with staged PCNL and flexible ureteroscopic lithotripsy (FURSL), using the very low lithotomy position with boot stirrups. The perioperative outcomes were favorable, and complete stone clearance was achieved. 

Case 1 A 42-year-old man with obesity was immediately admitted after biochemical results from a routine follow-up showed elevated serum creatinine (SCr) levels (753 μmol/L). Urgent computed tomography (CT) identified a right ureteral stone and allograft hydronephrosis. Emergent right percutaneous nephrostomy was performed under ultrasound guidance, which led to approximately 2 L of drainage per day. He received his living-donor kidney from his mother 3 years before, which was placed in the right iliac fossa. Post-transplantation complications included ureterovesical anastomotic stenosis from prolonged indwelling stent, which required frequent re-stenting, BK polyomavirus infection, and recurrent fever (maximum body temperature 38.5°C) accompanied by oliguria. Comorbidities included hyperlipidemia, hypertension, hyperuricemia, and chronic glomerulonephritis. A CT review was performed once his SCr levels lowered to 253 μmol/L and urine culture was negative, revealing a right renal stone (6×5×5 mm) and 4 ureteric stones distributed from the middle to distal segment near the bladder orifice (maximum diameter: 14×8×6 mm; maximum stone density: 846 Hounsfield units [HU]) in the allograft ( ). He was scheduled to undergo staged elective surgery, to proceed with transplant lithiasis removal. Under general anesthesia, the patient was placed in a very low lithotomy position with direct overbed boot stirrups ( ). The nephrostomy tube was trimmed prior to routine disinfection. The indwelling double-J stent was removed to allow for guidewire insertion. However, retrograde access of the flexible ureteroscope was limited and therefore abandoned. A new 5 Fr double-J stent (Polaris Ultra Ureteral Stent; Boston Scientific Corp, MA, USA) was placed, and the guidewire was withdrawn. In turn, the guidewire was inserted via the nephrostomy tract prior to tube removal. A working channel was established using a small-caliber 16 Fr peel-away sheath (Lithotripsy balloon catheter kit, Create Medic Dalian International Trading Co, Ltd, Liaoning, China). Ballistic lithotripsy (Swiss LithoClast Master, EMS Urology, Switzerland) was performed to pulverize the renal stone. Antegrade introduction of the 7.5 Fr FURS (HU30S; Shenzhen HugeMed Medical Technical Development Co, Ltd, Guangzhou, China) identified the first mid-segment ureteric stone that was pulverized. After clearance, the FURS could not be advanced, due to a difficult angle, which led to its deformation. This deformation allowed the scope to turn and facilitate clearance of the subsequent stones. However, upon switching into a new disposable scope, the FURS was unable to reach the final distal stone, despite multiple attempts. Since the total operative time lasted 3 h, the procedure was halted. The patient made an uneventful recovery. SCr levels were stable, measuring 254 μmol/L after surgery. Follow-up CT found no residual stones where the final distal segment stone may have passed spontaneously ( ). He was discharged on postoperative day 8, after surveilling of his renal function after nephrostomy tube and Foley catheter removal. Stone composition analysis returned as calcium phosphate. He was followed up regularly, and his SCr levels remained around 250 μmol/L at 3 months after surgery. Case 2 A 39-year-old man was referred to our tertiary institute after the local hospital revealed elevated SCr levels (372 μmol/L). He was asymptomatic, and vitals were stable. His medical history was significant for coronary atherosclerosis, hypertension, hyperuricemia, and renal transplant received 8 years prior. CT scan revealed 2 renal stones (maximum diameter 4×3×3 mm) and 4 ureteric stones (maximum diameter: 9×8×6 mm; maximum stone density: 501 HU) in the left allograft, accompanied by hydronephrosis ( ). He recalled the earliest lithiasis formed 6 months after transplantation but was managed conservatively. Upon admission, SCr levels reached 417 μmol/L, and he required left percutaneous nephrostomy with ureteral stent insertion under ultrasound guidance. He received antibiotics and observation of SCr levels before undergoing elective transplant lithiasis removal. The procedure was conducted in the same manner as for the patient in case 1. However, the lower segment of the ureter was accessible without complication. Stone fragments in the middle ureteric segment were retrieved using a stone basket. After the guidewire was advanced into the bladder, a 5 Fr Ultra double-J stent was placed, and a 14 Fr nephrostomy tube was placed before successful conclusion. The patient made an uneventful recovery. His postoperative SCr level was 214 μmol/L. CT review on postoperative day 3 showed complete stone clearance ( ). The nephrostomy tube and Foley catheter were subsequently removed prior to discharge. Stone composition analysis revealed calcium oxalate. 

A 42-year-old man with obesity was immediately admitted after biochemical results from a routine follow-up showed elevated serum creatinine (SCr) levels (753 μmol/L). Urgent computed tomography (CT) identified a right ureteral stone and allograft hydronephrosis. Emergent right percutaneous nephrostomy was performed under ultrasound guidance, which led to approximately 2 L of drainage per day. He received his living-donor kidney from his mother 3 years before, which was placed in the right iliac fossa. Post-transplantation complications included ureterovesical anastomotic stenosis from prolonged indwelling stent, which required frequent re-stenting, BK polyomavirus infection, and recurrent fever (maximum body temperature 38.5°C) accompanied by oliguria. Comorbidities included hyperlipidemia, hypertension, hyperuricemia, and chronic glomerulonephritis. A CT review was performed once his SCr levels lowered to 253 μmol/L and urine culture was negative, revealing a right renal stone (6×5×5 mm) and 4 ureteric stones distributed from the middle to distal segment near the bladder orifice (maximum diameter: 14×8×6 mm; maximum stone density: 846 Hounsfield units [HU]) in the allograft ( ). He was scheduled to undergo staged elective surgery, to proceed with transplant lithiasis removal. Under general anesthesia, the patient was placed in a very low lithotomy position with direct overbed boot stirrups ( ). The nephrostomy tube was trimmed prior to routine disinfection. The indwelling double-J stent was removed to allow for guidewire insertion. However, retrograde access of the flexible ureteroscope was limited and therefore abandoned. A new 5 Fr double-J stent (Polaris Ultra Ureteral Stent; Boston Scientific Corp, MA, USA) was placed, and the guidewire was withdrawn. In turn, the guidewire was inserted via the nephrostomy tract prior to tube removal. A working channel was established using a small-caliber 16 Fr peel-away sheath (Lithotripsy balloon catheter kit, Create Medic Dalian International Trading Co, Ltd, Liaoning, China). Ballistic lithotripsy (Swiss LithoClast Master, EMS Urology, Switzerland) was performed to pulverize the renal stone. Antegrade introduction of the 7.5 Fr FURS (HU30S; Shenzhen HugeMed Medical Technical Development Co, Ltd, Guangzhou, China) identified the first mid-segment ureteric stone that was pulverized. After clearance, the FURS could not be advanced, due to a difficult angle, which led to its deformation. This deformation allowed the scope to turn and facilitate clearance of the subsequent stones. However, upon switching into a new disposable scope, the FURS was unable to reach the final distal stone, despite multiple attempts. Since the total operative time lasted 3 h, the procedure was halted. The patient made an uneventful recovery. SCr levels were stable, measuring 254 μmol/L after surgery. Follow-up CT found no residual stones where the final distal segment stone may have passed spontaneously ( ). He was discharged on postoperative day 8, after surveilling of his renal function after nephrostomy tube and Foley catheter removal. Stone composition analysis returned as calcium phosphate. He was followed up regularly, and his SCr levels remained around 250 μmol/L at 3 months after surgery. 

A 39-year-old man was referred to our tertiary institute after the local hospital revealed elevated SCr levels (372 μmol/L). He was asymptomatic, and vitals were stable. His medical history was significant for coronary atherosclerosis, hypertension, hyperuricemia, and renal transplant received 8 years prior. CT scan revealed 2 renal stones (maximum diameter 4×3×3 mm) and 4 ureteric stones (maximum diameter: 9×8×6 mm; maximum stone density: 501 HU) in the left allograft, accompanied by hydronephrosis ( ). He recalled the earliest lithiasis formed 6 months after transplantation but was managed conservatively. Upon admission, SCr levels reached 417 μmol/L, and he required left percutaneous nephrostomy with ureteral stent insertion under ultrasound guidance. He received antibiotics and observation of SCr levels before undergoing elective transplant lithiasis removal. The procedure was conducted in the same manner as for the patient in case 1. However, the lower segment of the ureter was accessible without complication. Stone fragments in the middle ureteric segment were retrieved using a stone basket. After the guidewire was advanced into the bladder, a 5 Fr Ultra double-J stent was placed, and a 14 Fr nephrostomy tube was placed before successful conclusion. The patient made an uneventful recovery. His postoperative SCr level was 214 μmol/L. CT review on postoperative day 3 showed complete stone clearance ( ). The nephrostomy tube and Foley catheter were subsequently removed prior to discharge. Stone composition analysis revealed calcium oxalate. 

Simultaneous PCNL and FURS has been reportedly effective in the literature for the treatment of complex renal stones [ – ]. The 2 cases presented in this study were conducted on transplanted kidneys, and management was complicated by the disturbed anatomy, which makes conventional access challenging. The procedural combination, as well as the very low lithotomy position with direct overbed boot stirrups, made transplant lithiasis removal manageable. Support stirrups are often needed to help with proper dorsal lithotomy positioning, including flexed and abducted thighs, flexed knees, and minimal external rotation . Boot stirrups, as used in this case report, allow weight from the lower extremity to be placed on the sole of the heel, without pressure on the lateral fibular head . A very low lithotomy position allows for the allograft to be pushed more forward, even in a patient with obesity, which would also require boot stirrups in a direct over-bed fashion for better positioning. Very few reports, especially in the field of urology, have discussed the necessity of boot stirrups. Zhang et al compared 3 different methods for placing and repositioning patients in the lithotomy position over the bed using stirrups and found that the direct over-bed method required significantly shorter time for placement, repositioning, and overall . Such placement was also preferred by nurses and doctors. In the first case, boot stirrups were considered due to the patient’s size, which made initial access smooth. Despite being able to advance the guidewire, the FURS could reach only a 2-cm distance, due to the stricture formed at the ureterovesical anastomosis and altered ureter angle (120°), which also forms a natural pressure ladder . During FURS, stones in the distal segment can recoil to the middle or upper segment under irrigation pressure. Supposedly, a new PCNL channel would be established, since the current working port offered limited angulation. However, doing so would increase the risk of bleeding . Therefore, ultrasound was performed to confirm that no residual stone was found in the distal ureter, and the operation was concluded. Follow-up CT showed complete stone clearance. Previous studies comparing the outcomes between PCNL and FURSL found no difference in postoperative renal function . For patients with advanced chronic kidney disease, transplantation is the best option. Yet, with the limited donor kidney pool, most patients would still require dialysis before referral . The past medical histories of the 2 patients were significant for hypertension, hyperuricemia, and dialysis, all of which were high-risk factors for renal stone formation . Even after transplantation, the regular use of tacrolimus, an immunosuppressant and calcium-phosphatase inhibitor, can cause hypocitraturia, which also increases the risk of stone formation . However, evidence is still low, as the cause of stone formation is multifactorial . Nonetheless, for transplant patients, stone formation can be recurrent and missed. The allograft is a very precious organ for the recipient and would require a timely treatment. PCNL, FURSL, or a combination are all feasible strategies. Due to limitations in angle adjustment, PCNL offers limited applicability for middle and lower renal calyces or ureteral stones. These limitations can be addressed with FURS, which provides greater flexibility in angle changes . Therefore, the simultaneous use of PCNL and FURSL was a secure option for management of transplant lithiasis. Since the angle between the retrograde FURS and reconstructed ureteral orifice is often 120°, more emphasis should be put on antegrade FURS treatment . Nonetheless, this study has several limitations, including its design as a retrospective case report. No comparison was made between conventional lithotomy and very low lithotomy with or without boot stirrups, which also has reported concerns of postoperative neuropathy . However, both patients made an uneventful recovery. Transplant lithiasis is a rare phenomenon, and comparison between surgical techniques would be difficult to fulfill based on single-center efforts. With the increasing incidence of lithiasis, transplant patients should be reminded to undergo frequent imaging follow-up to rule out the diagnosis of transplant lithiasis. Prompt management should also be offered, as even early clearance of asymptomatic or seemingly insignificant stones can largely influence patient prognosis by preventing relapse . 

Combined PCNL and FURSL in a very low lithotomy position with boot stirrups is a safe and feasible method for transplant lithiasis. 

