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Urinary tract calculi have affected humans since antiquity and treating patients with nephrolithiasis is commonplace in urological practice. The lifetime risk for developing urinary tract stone disease is in the region of 5-to-10 per cent; however the lifetime recurrence risk is as high as 50 per cent.
International epidemiological data demonstrates that the incidence of stone disease is increasing globally, primarily due to increased triglyceride intake and increasing age. Other pathological risk factors for the development of nephrolithiasis include metabolic syndrome, diabetes mellitus, vitamin D supplementation and hyperuricaemia.
At the recent European Association of Urology (EAU) Annual Meeting in Madrid (March 2015), Prof Reis Santos introduced the term ‘diabesity’ to describe the metabolic overlap of diabetes and obesity. He predicted an epidemic of stones, either due to uric acid stone formation from obesity or calcium oxalate stone formation from malabsorptive bariatric procedures. Furthermore, there was a sustained increase in the incidence of kidney stones in the paediatric population between 1996 and 2007.
Important preventative measures include appropriately high fluid intake (to produce a daily urine output of at least 2-to-2.5 litres urine/24 hours), alkanising beverages, fruit and vegetables and a balanced diet (a Mediterranean diet has been shown to be effective in reducing risk of stone formation, ie, rich in vegetables, fruits and cereals with 0.8-to-1g protein/kg body weight per day, maximum of 6g sodium chloride per day, 1-to-1.2g calcium per day and restriction of oxalate).
A variety of recently developed technological advances have improved the treatment of urinary tract calculi.
Guidelines for symptomatic renal calculi
Minimally-invasive urological procedures have almost completely replaced open surgery for treating patients with kidney stones. The EAU recommends percutaneous nephrolithotomy (PCNL) for the treatment of renal calculi >20mm. PCNL is associated with excellent stone-free rates; however these are counterbalanced by higher complication rates compared to less invasive urological procedures. Recent advances have resulted in the miniaturisation of PCNL, with smaller-calibre nephroscopes to reduce complications associated with large-diameter dilatations.
Conventional PCNL involves a renal tract dilated to 28-to-30Fr. Excellent results using more novel techniques such as the mini Perc (18Fr), ultra-mini Perc (11-13Fr) and micro Perc (5Fr) are also emerging.
Flexible ureterorenoscopy, also known as retrograde intrarenal surgery (RIRS), is an alternative to the percutaneous approach. RIRS was initially proposed as a method to treat lower pole stones resistant to extracorporeal shock-wave lithotripsy (ESWL) and current EAU guidelines also recommend RIRS as a first-line modality with lower pole stones not suitable for ESWL.
Notably, recent studies have demonstrated that RIRS is effective for treating larger urinary tract calculi throughout the pelvicalyceal system. The potential disadvantages with RIRS and larger stones include limited visibility, requirement for flexible scopes (which are less durable), decreased size of fragment removal and cost (particularly in developing countries). In expert hands, stone-free rates are very good.
In the 1980s, this modality revolutionised the urological approach to kidney stones and widespread use of this technology continues today. Stone-free rates with lower pole stones are approximately 50-to-60 per cent; however, this figure increases to 80-to-90 per cent for upper and middle pole calyces.
Clearance rates with ESWL and lower pole stones are dependent on stone size, as clearance rates of 74 per cent are described with lower pole stones <10mm. This decreases to 56 per cent and 33 per cent for lower pole stones that are 11-to-20mm and >20mm, respectively. Ureteric stenting prior to elective ESWL should be considered in patients with stones >2cm as the rate of steinstrasse after ESWL is 10 per cent for stones >2cm.
Although ESWL is still utilised as the initial approach for treating most patients with lower pole stones ≤1cm, it is undeniable that worldwide, treatment rates for ESWL are declining as surgeons and patients alike increasingly opt for endourological or minimally-invasive percutaneous procedures.
Adverse predictors for lower pole stone clearance with ESWL include the following:
- Lower pole infundibular angle <70°
- Infundibular length >3cm
- Infundibular width >5mm
- A comprehensive nomogram developed by Wiesenthal et al demonstrated the following factors as predictors for effective stone clearance with ESWL:
- Patient age
- Body mass index (BMI)
- Stone location
- Stone size
- Mean stone density
- Skin-to-stone distance
At the beginning of the 21st Century, the field of endourology was treated to novel technological refinements such as improved endoscopic manoeuvrability, advanced accessory instrumentation and modified scope profile.
Access to the entire collecting system is possible with modern flexible ureteroscopes and stone fragmentation with the holmium: YAG laser provides efficient stone clearance with minimal thermal effects on adjacent tissue.
At present, commercially available flexible ureteroscopes have a mean tip diameter of 6.9-to-7.5 French (Fr) and a mid-shaft diameter of 7.5-9Fr.
In 2005, the ‘Lower Pole II’ study compared RIRS with ESWL for the treatment of isolated lower pole stones ≤1cm in 78 patients. The operative durations were significantly shorter with ESWL and intraoperative complication rates were also lower. However, the study demonstrated a 15 per cent better stone clearance rate with RIRS compared to ESWL and it is widely believed that greater statistical significance will be demonstrated with RIRS compared to ESWL in this setting in the near future, as ureteroscopic technology continues to improve at an exponential rate. The flexible ureteroscopes used at the time the ‘Lower Pole II’ study was performed were of larger calibre, had a more limited degree of flexion and poorer optics compared to newer scopes available today.
Currently, RIRS is proposed as the primary treatment modality for patients with lower pole stones that have failed ESWL therapy, as the stone clearance rate with this modality for lower pole calculi is approximately 96 per cent for lower pole stones >20mm in diameter. Indeed, in many countries, flexible ureterorenoscopy is used first-line to treat intrarenal stones in all calyceal locations up to 20mm.
PCNL therapy originated in the 1980s where a 28-to-30Fr working sheath facilitated effective irrigation during the procedure and extraction of larger stone fragments. These features allowed PCNL to facilitate excellent clearance rates for large stones and lower complication rates compared to traditional open stone surgery. Currently, PCNL represents the most invasive procedure for patients with significant stone burden. The UK Health Episode Statistics database reviewed complications for >5,700 PCNL surgeries over years and identified rates for haemorrhage (1.4 per cent), urinary tract infection (3.8 per cent), pyrexia (1.7 per cent), sepsis (0.7 per cent) and 30-day readmission rates (9 per cent).
Over the last decade, there has been increasing interest in modifying the traditional PCNL procedure to less-invasive ‘mini percutaneous’ techniques. One recent meta-analysis by De et al compared stone clearance rates and complication rates between RIRS, conventional PCNL and minimally-invasive percutaneous procedures (MIPPs). The authors demonstrated that conventional PCNL is associated with higher stone clearance and complication rates compared to RIRS.
However, RIRS provided higher stone-free rates than MIPPs. The authors concluded by suggesting that RIRS should be considered standard therapy for renal stones <2cm. When flexible instruments are unavailable, it is suggested that standard PCNL should be performed due to the low efficacy associated with MIPPs. The future of PCNL lies in the miniaturisation of the procedure, with narrower punctures and smaller nephroscopes.
Robotic-assisted surgery is now established in the field of urology and is increasingly being used for index operations of the kidney, prostate and bladder. The aim of robotic surgery in endourology and nephrolithiasis is to provide safer and more consistent outcomes with less variability in surgeon performance and reduced exposure to intraoperative radiation. In addition, robotic surgery provides fine movement control of the endoscopy, which is vital for preforming complex endourological stone procedures.
Other potential advantages with robotic ureterorenoscopy include instrument stability, improved ergonomics and increased range of motion. A preliminary study on 18 patients by Desai et al demonstrated the feasibility for robotic flexible ureteroscopy, as no procedures were converted to manual and the complete stone clearance rate was 89 per cent at three months.
The incidence of nephrolithiasis is increasing in the developed world and appropriate management strategies require a thorough understanding of stone characteristics and developing technologies.
ESWL represents the least invasive treatment option for nephrolithiasis; however stone-free rates with ESWL are generally lower than more invasive treatment modalities such as RIRS and PCNL.
In the near future, it is likely that robotic-assisted procedures will develop to offer additional advances and alternatives to the currently performed RIRS and PCNL procedures.
References available on request
A 58-year-old lady is referred to the urology outpatients department complaining of intermittent right sided flank, recurrent urinary tract infections and non-visible haematuria. A plain film KUB x-ray is performed on the day of her appointment, which shows a lower pole left-sided calculus measuring 2cm. Routine bloods are within normal limits and a mid-stream urine (MSU) is positive for red blood cells (RBCs) only. The patient has a prior history of a right-sided ureteric calculus five years previously that was treated with laser lithotripsy. She has no other relevant past medical or surgical history and takes no regular medications. She also mentions that her father also complained of recurrent urinary tract calculi during her childhood. As she is symptomatic, she enquires what management options are available for treating her right-sided kidney stone and for treating kidney stones in general.