EDUCATION 

Contemporary management of renal calculus disease

P. DOWNEY and D. TOLLEY

Department of Urology, Wythenshawe Hospital, Manchester and The Scottish Lithotriptor Centre, Western General Hospital, Edinburgh, UK

Introduction Epidemiology Patient assessment

Patient management Results of stone management Conclusion References

Keywords: Renal calculi, management

The management of renal calculus disease has changed. Non-invasive and minimally invasive techniques of stone disintegration and removal have replaced open stone surgery in managing this condition. In this article we discuss the investigation and management of patients with renal stone disease as currently performed in specialist stone centres

J.R.Coll.Surg.Edinb., 47, October 2002, 668-675 

INTRODUCTION

In the past three decades, major advances have been made in the field of urolithiasis. Risk factors for stone formation have been identified and molecular defects have been clarified. Stones can now be fragmented and removed using minimally invasive techniques (shock-wave lithotripsy, percutaneous nephrolithotomy and ureterorenoscopy with intracorporeal lithotripsy) and effective prophylactic medical therapy can be used to reduce the rates of stone regrowth and recurrence. In this article we review the contemporary management of renal calculus disease as performed in specialist stone centres.

EPIDEMIOLOGY ^1-4

The incidence of urinary stone disease is increasing in the United Kingdom. This is almost certainly due to increased dietary protein intake which increases urinary excretion of phosphates and magnesium and reduces urinary citrate concentration. Symptomatic stones occur in 27-34 per 104 population per annum in adults occurring three times more commonly in the south than in the north of the country. In the adult population males are affected four times more often than females. The incidence is lower in children (1-2 per million per year) and in this age group, boys are more frequently affected than girls. Seventy to 85% of urinary calculi are composed of calcium salts (calcium oxalate in the majority of cases) with the remainder being composed of struvite (3-15%), urate (2-18%) and cystine (1-2%). The incidence of struvite “infection” stones is declining due to the availability of effective antibiotic therapy.

PATHOPHYSIOLOGY

Abnormalities of urine composition^5-7

The crystallisation of stone-forming salts in urine occurs due to abnormalities of urine composition. These can be metabolic or environmental in origin. More than one abnormality often exists in an individual patient. Known abnormalities of urine composition which predispose to stone formation are outlined below:

Low urine volume: A low urine output (< 2L/day) is a predisposing factor

Hypercalciuria: This is found in 50% of stone forming patients. In the majority of these no underlying cause can be identified (idiopathic hypercalciuria). In other cases, it results from increased absorption of calcium in the gastrointestinal tract (absorptive hypercalciuria), impaired tubular calcium reabsorption (renal hypercalciuria) or secondary to hyperparathyroidism.

Hypocitraturia: 20-60% of stone forming patients have reduced urinary citrate concentrations which may occur secondary to urinary tract infection, systemic acidosis, chronic diarrhoeal states and hypokalaemia. Prolonged physical exercise and the consumption of a diet rich in animal protein are also associated with this abnormality.

Hyperoxaluria: Hyperoxaluria may be genetic (primary) or acquired. Primary hyperoxaluria is rare. Acquired hyperoxaluria occurs in l0% of patients with stones resulting from increased oxalate absorption from the gastrointestinal tract. Under normal circumstances, calcium binds to oxalate in the gastrointestinal tract - a reaction which prevents their subsequent absorption. When insufficient dietary calcium is present this binding does not occur and oxalate absorption increases. Thus, a low dietary intake of calcium leads to mild hyperoxaluria

Hyperuricosuria: l0-20% of stone forming patients have gouty diatheses - conditions which predispose to uric acid and calcium oxalate/phosphate formation.

Cystinuria: This is a recognised predisposing factor.

Urinary tract infection: Urinary tract infection by urea-splitting organisms (Proteus sp, Haemophilus sp, Klebsiella sp and ureaplasma urealyticum) produces hydrolysis of urea with hydroxyl and ammonium ion production. This leads to urinary alkalisation, increased dissociation of phosphate and supersaturation of struvite and carbonate apatite which predispose to struvite stone formation.

Nutritional-environmental factors ^8,9

Nutritional-environmental factors may themselves cause urinary stone formation or exaggerate underlying metabolic risk factors. Strenuous physical exercise or excessive sweating may predispose to stone formation by urinary concentration, altering urinary pH and by reducing urinary citrate levels. Dietary factors are also important. The consumption of a diet rich in animal protein, sodium and refined sugars is associated with a high risk of stone formation as it increases urinary calcium and uric acid concentrations and lowers urinary citrate concentration. A high calcium intake does not carry an increased risk of stone formation in patients provided they do not suffer from absorptive hypercalciuria.

PATIENT ASSESSMENT

Investigation of patients with stone disease^10-12

The investigation and management of stone disease is of great economic importance. In the US the cost to the taxpayer for the evaluation and management of urinary tract stone disease in 1993 was $1.23 billion and a further $139 million of wages were lost as a result of the disease. Allowing patients to form new stones without providing preventative medical therapy is an expensive way of managing the problem since each patient will have, on average, 7 stone episodes during their lifetime. Sixty percent of these will require intervention involving shock wave lithotripsy (SWL) or other minimally invasive techniques with an estimated average cost (at current prices) of £9534 per patient over 30 years. A theoretical cost reduction of 33% could be achieved in patients by thorough initial investigation, annual review at a dedicated stone clinic and repeated biennial metabolic investigations of patients (provided preventative medical therapy reduced stone recurrence rates by 20%). This is clearly of great importance and is currently an area of great interest.

Clinical and biochemical evaluation

In order to provide the stone former with adequate medical advice it is essential to identify the mechanisms responsible for stone formation. When this has been achieved it is possible to design efficient treatment programmes to achieve stone clearance and prevent recurrent stone formation or progressive growth of residual fragments.

An essential component of the initial evaluation of stone forming patients is the medical history. This should be structured to identify underlying medical conditions and medication which predispose to stone formation (immobilisation, hyperparathyroidism, hyperthyroidism, chronic enteric disorders, sarcoidosis, recurrent urinary tract infection etc.) and also determine the severity of the stone disease (number of previous-stone events and the frequency of stone formation). These factors are important in determining the extent of subsequent investigations.

Each patient should keep an accurate dietary record of all food and drink consumed each day for seven days prior to attending the stone clinic. This record can then be analysed for fluid and calorie intake; calcium, magnesium, sodium, potassium, phosphate, oxalate, purine, protein, fibre, fat and refined sugar content. Risk factors for stone formation can be identified from this record and appropriate dietary advice given. The main dietary risk factors for stone formation are outlined in Table 1.

Table 1: Dietary factors predisposing to stone formation

Metabolic investigations

With the acceptance of minimally invasive techniques of stone removal there has been a decline in the routine metabolic evaluation of stone forming patients. This has been in part due to the belief that the condition can be managed solely by minimally invasive techniques and in part due to financial constraints and cost cutting imposed by health authorities. Not all stone forming patients require a complete metabolic evaluation. All patients, however, should undergo basic haematological (serum creatinine, urate and calcium levels) and urinary examinations (urinary pH, culture and a spot test for cystine when cystinuria is suspected). Those with a strong family history, chronic enteric disorders, hyperparathyroidism, hyperthyrodism, gout, nephrocalcinosis, multiple, bilateral or recurrent stone disease and those with chronic urinary tract infection require a more thorough assessment. In addition to the basic investigations outlined above, two 24 hour urine collections should be obtained on consecutive days. The first collection, containing an acid preservative is analysed for volume, creatinine, calcium, magnesium, sodium, potassium, phosphate, oxalate and citrate concentrations. The second, containing no acid preservative, is analysed for volume, pH, protein, urate and a qualitative test for cystine. The samples are brought for analysis after completion of the second 24 hour collection and urinary risk factors determined. In the majority of patients the high risk is usually due to more than one of the above ‘abnormalities’.

Stone analysis

Patients are encouraged to filter urine and collect stone fragments for analysis on at least one occasion.

Radiological assessment

Imaging of the urinary tract by intravenous urography is the mainstay of radiological assessment of stone forming patients. It not only provides essential information on stone burden and location within the collecting system but it also identifies co-existing functional and morphological abnormalities such as ureteropelvic junction (UPJ) obstruction, calyceal diverticulae etc. With this information the appropriate method of stone removal can be determined. In circumstances where it cannot be safely or effectively employed (in pregnant patients, those with poor renal function or a history of contrast allergy) plain radiography and ultrasound scans of the renal tracts often provide sufficient information. When renal functional impairment or obstruction is suspected further information can be gained when necessary by isotope renography.

PATIENT MANAGEMENT

The management of urinary stone disease has two equally important aspects: (1) the management of the stone and (2) the prevention of stone recurrence.

The management of renal calculus disease has undergone a remarkable transformation during the past 20 years. The introduction of SWL has revolutionised current practice. Alongside this, instrument miniaturisation now permits stone fragmentation and removal by minimally invasive means in patients when SWL fails or cannot be performed. In specialist stone centres, where an integrated approach is possible, open surgery is now rarely performed unless ablative therapy is being carried out.

Asymptomatic renal calculi <5mm in diameter in unobstructed non-infected kidneys do not require removal, unless this is necessary for professional reasons (pilot, professional driver etc.). Stones such as these can be safely managed by annual review with radiological examination. Increasing stone size, the development of symptoms or the presence of urinary infection would alter the decision for expectant management.

Extracorporeal shock wave lithotripsy (SWL) ^13-17

Chaussy, Brendel and Schmiedt introduced the principle of urinary stone disintegration using shock waves in 1980. The technique was subsequently introduced into clinical practice in 1982 and since then it has revolutionised the management of this condition. The aim of SWL is to pulverise calculi using shock waves that are generated outside the body. The resultant small particles pass spontaneously. Shock waves can be generated by three methods: (1) underwater electrostatic spark-gap discharge, (2) electromagnetic generation and (3) piezoelectric generation The shock wave is generated underwater and focused by an ellipsoid reflector or gantry to a high-energy second focal point. Since water and the human body (which comprises over 65% water) share similar acoustic impedance, shock waves generated in this way can travel through the body without causing tissue damage provided the shock wave is travelling through the same medium. To achieve this, early lithotriptors required patient immersion in water baths but this can now be achieved using compressible water bags that are applied to the skin overlying the targeted kidney. When shock waves encounter abrupt changes of acoustic impedance, for instance at the interface of body tissue and a stone, energy is released. This results in sheer force generation which, together with the formation of cavitation bubbles, lead to stone disintegration.

Stone targeting is achieved by two-dimensional radiographic imaging or real-time ultrasound. The intensity of the shock wave can be adjusted depending on patient tolerance and the characteristics of the stone. The rate of shock wave generation is gated to the heart rate to prevent arrhythmias occurring.

Simple analgesia, with a non-steroidal anti-inflammatory agent and intravenous sedation is all that is required in the majority of cases. In young children, general anaesthesia is required due to the inability of these patients to remain still throughout the course of treatment.

The success rate of lithotripsy treatment is determined by entry criteria, treatment schemes, the lithotriptor used and the experience of the operators. The ability of a lithotriptor to produce stone disintegration in vitro is independent of the method of shock wave generation. In clinical practice, however, electromagnetic and piezoelectric lithotriptors have higher retreatment rates than electrohydraulic systems but are associated with less painful treatment sessions and fewer complications.

Short-term complications associated with SWL include flank pain, transient haematuria, steinstrasse, skin ecchymosis and intrarenal haematoma formation. To prevent steinstrasse, when managing stones >2cm in size, a double pigtail stent should be inserted into the collecting system prior to SWL. Lithotripsy is contra-indicated during pregnancy as the teratogenicity and fetotoxicity of this form of therapy are unknown. Patients receiving anticoagulation therapy should stop it prior to undergoing lithotripsy and care should be exercised when treating patients with cardiac pacemakers.

In general, non-cystine stones <2cm in size in non-obstructed systems are best managed by SWL. Stones between 2 and 3 cm in size can be managed by either SWL (following placement of a double pigtail stent) or by primary percutaneous nephrolithotomy (PCNL). Stones >3cm in size are best treated by primary PCNL with SWL to the residual fragments.

Percutaneous nephrolithotomy (PCNL)

The first percutaneous nephrostomy tract made for the purpose of stone removal was reported by Fernstrom and Johanson in 1976.Other surgeons then adopted the technique. The procedure was initially performed as a salvage procedure following conventional renal surgery. Wickham and Kellett reported the first 31 cases of elective PCNL in 198119 and since then PCNL has become established as a standard procedure in urological practice.¹⁸ Between 1981 and 1983 more than 1500 successful operations were reported. Despite the pervasive role of extracorporeal SWL in current practice, PCNL remains an important procedure in the urological armantarium. The indications for PCNL are outlined in Table 2.

Table 2: Indications for the use of percutaneous nephrolithotripsy

PCNL has two component parts - access and stone removal.

Access: Under general anaesthesia, cystourethroscopy is performed. A ureteric catheter is passed into the ureter of the stone bearing kidney and advanced into the renal pelvis (Figure 1). The patient is then turned to the prone position. A urologist or radiologist, depending on the personnel available, then gains access to the pelvicalyceal system. Under fluoroscopic control, an 18-gauge needle is passed transcutaneously at the posterior axillary line into the pelvicalyceal system (Figure 2). This is usually performed below the twelfth rib through the lower pole calyx. The precise calyceal entrance point, however, depends on the position of the stone within the collecting system and whether other procedures, such as antegrade endopyelotomy, are being performed. Supracostal approaches into the upper pole calyx can also be performed although significant respiratory complications have been reported in approximately 9% of patients following this approach. A guide-wire is then passed into the collecting system (Figure 3). The tract is dilated to 24 Fr. diameter using flexible fascial dilators or concentric steel dilators and a 24 Fr. Amplatz sheath is inserted. (Figure 4) A 22 Fr. nephroscope is passed into the collecting system via the Amplatz sheath and the stone visualised (Figure 5).

Figure 1: Ureteric catheter passed into renal pelvis 

Figure 2: Needle puncture into pelvicalyceal system

Stone removal: The simplest method of stone removal is by extraction via the Amplatz sheath using grasping forceps or stone retrieving baskets. When a 24 Fr. Amplatz sheath is being used this is only possible when stones are <8mm in width. Many stones are larger than this and intracorporeal lithotripsy is required to break them into more manageable fragments. This can be achieved using ultrasonic, electrohydraulic or electrokinetic probes or with lasers (pulsed dye and holmium), depending on the available equipment, the characteristics of the stone and the preference of the surgeon. When stone clearance has been achieved a nephrostomy tube drain is positioned in the collecting system (Figure 6). This can be removed 24-48 hours later.

Figure 3: Guide wire passed into pelvicalyceal system 

Figure 4: Amplatz sheath in position

Flexible ureterorenoscopy

The development of small diameter fibreoptic, flexible ureterorenoscopes (Figure 7) has enabled access to the entire urinary collecting system for diagnostic and therapeutic purposes in 85-96% of patients ²⁰ (Figures 8 and 9). Ureterorenoscopes (6.9 Fr.) are now available with active deflection capabilities of 360° and 3.5 Fr. working channels. These permit inspection of the entire upper urinary tract and allow the passage of electrohydraulic probes (1.9 Fr.) and holmium laser fibres for therapeutic purposes. Stones in the upper urinary tract, therefore, can be accessed and managed endoscopically without the need for percutaneous access.

RESULTS OF STONE MANAGEMENT ^21-31

Overall, stone-free rates of 85% can be expected following SWL at 3 month follow-up. In a meta-analysis of the published literature Lingeman et al (1994) reported success rates of 74%, 56% and 33%, respectively when stones <lcm, 1-2cm or >2cm were treated with primary SWL.21 Results are, therefore, are less favourable with this form of therapy when large stones are being treated. These results need to be compared with the success rates of l00%, 89% and 94%, following PCNL for similar-sized stones.

Results are also poor when lower pole calyceal stones are being treated. Data from the Scottish Lithotriptor Centre, Edinburgh, show an overall stone-free rate, following primary piezoelectric SWL for stones >2cm in size, of 33% (following a mean of 4.1  sessions of lithotripsy) with complications occurring in 31% of patients (unpublished data). Results from other series show stone-free rates of 41-79% and 39%, respectively, following primary SWL for stones <2cm and >2cm in size. Various factors are responsible for this poor outcome (Table 3).

The importance of lower pole caliceal anatomy, pelvicaliceal angle, infundibular length, infundibular diameter and infundibulopelvic angle, in determining stone-free rates following primary SWL, have been recently addressed by several authors. Failure to achieve stone-free status following SWL occurred in 78% of patients with complex caliceal anatomy, in 64% of patients with a pelvicaliceal angle <90º and in 70% of patients with an infundibular diameter <4 mm. On account of the lack of success attributed to SWL in these circumstances it has been suggested that lower pole caliceal calculi >10mm in size should be managed by primary PCNL, since this form of therapy has an overall success rate of 90-98% in specialist stone centres and is independent of stone size.

In expert hands, flexible ureterorenoscopy and intracorporeal lithotripsy is successful in 87-89% of cases. Seventy seven to 88.5% of patients achieve stone-free status following a single treatment session. These results compare favourably with those following SWL (when more than one treatment session is often required) as well as percutaneous nephrolithotomy. Staghorn calculi and large upper tract calculi (>2cm) have also been managed endoscopically using this approach. Success rates of 76% have been reported following a single treatment session increasing to 91% when a second look procedure was performed. Retrograde ureteroscopic management of upper tract stones is particularly useful in obese patients, in whom SWL and percutanous nephrolithotomy cannot be performed, and is associated with few complications.

Figure 5: Nephroscope

Prevention of stone recurrence 32-37

Without medical intervention, the risk of stone recurrence in an individual patient is 40% within 3 years, 74% within 10 years and 98% within 25 years. When prophylactic medical therapy is used recurrence rates fall significantly. This is of considerable benefit to the patient and is all the more important when one considers that minimally invasive techniques of stone removal are associated with higher stone recurrence rates than the previously used open surgical procedures (38%, 41% and 49% following open surgery, PCNL and ESWL, respectively).

Table 3: Factors responsible for the poor outcome after SWL

The efficacy of preventative medical therapy depends on lifelong compliance. Patient motivation, therefore, is important if this form of therapy is to succeed. It has been shown that patients revert to their “bad dietary habits” within 9-12 months, unless they have a second stone event within a few months of commencing prophylactic therapy. Motivation and compliance may be improved by annual review at a dedicated stone clinic with biennial urine testing to verify compliance. Initial investigation will identify 20-25% of patients in whom stone formation occurs secondary to hyperparathyroidism, renal tubular acidosis, primary hyperoxaluria, gouty diatheses, cystinuria and urinary tract infection. Specific medical or surgical intervention can then be structured to correct these underlying disorders.

Figure 6: PC nephrostomy tube insitu 

Figure 7: Flexible ureterorenoscope

In the remaining 70-75% of patients (idiopathic stone formers) dietary, absorptive or renal factors responsible for development of urinary calculi can be identified. Advice can then be given as to how to prevent further calculi. In general patients should be advised to: (1) increase their oral fluid intake (>3L/day); (2) reduce their intake of animal proteins, oxalate, salt and refined sugars; (3) increase their fibre intake and (4) optimise their calcium intake (600/110 mg/day).

Advice on dietary calcium restriction should only be given to patients with absorptive hypercalciuria since restricting dietary calcium in patients who do not suffer from this condition may increase the risk of stone formation by increasing oxalate absorption from the gastrointestinal tract.

Figure 8: Flexible ureterorenoscope in middle pole calyx 

Figure 9: Flexible ureterenoscope in lower pole calyx

The two most commonly prescribed drugs for the prevention of calcium stone formation are thiazide diuretics and tri-potassium citrate. Thiazides reduce hypercalciuria by preventing hyperabsorption of intestinal calcium and by urinary dilution. They should, however, be prescribed with potassium supplements to prevent hypokalaemia. Tri-potassium citrate corrects hypocitraturia. It significantly reduces stone recurrence irrespective of previous treatment modality, stone composition, metabolic abnormalities and stone-free status. Patient compliance and gastrointestinal side-effects, however, may limit it's usefulness in routine practice. An alternative method of correcting hypocitraturia is by the consumption of homemade lemonade. An intake of 2 litres of this preparation per day is known to increase urinary citrate concentrations 2-fold. This may also reduce stone recurrence. Further studies, however, are required to determine whether this is the case.

With good patient compliance preventative medical therapy is effective in reducing stone recurrence rates. Using this form of therapy stone recurrence rate was reduced to 1/7 of its previous rate, in a group of recurrent stone forming patients, and a state of remission was maintained in 83% during a follow-up period of 5.4 years. Other studies have reported reductions in recurrent formation of calculi by as much as 90% using prophylactic medical therapy in groups known to develop recurrent stones.

CONCLUSION

The modern management of renal calculus disease has undergone significant changes in the past 20 years and it is now possible to achieve stone free status in the majority of patients using minimally invasive techniques. This is of great importance since the repeated trauma of conventional open surgery can be avoided in recurrent stone formers. Indeed, open surgery is now rarely performed at specialist stone centres, unless ablative therapy is being performed.

Achieving a stone free state is important in the management of this condition, however, it is becoming clear that the use of metabolic measures to prevent stone recurrence is of equal importance. It is now possible to identify and correct underlying predisposing factors for stone formation in the majority of cases. This requires careful initial investigation and lifelong follow-up at dedicated stone clinics. A reduction in recurrence rates of 90% can be achieved using these methods and this is perhaps an area where more work is required in the future.

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Copyright: 2 July 2000

Correspondence: P. Downey, South Manchester University Hospital Trusts, Wythenshawe Hospital, Southmoor Road, Wythenshawe, Manchester, M23 9LT, UK. E-mail: pauldowneymd@aol.com