Renal calculi are formed when the urine is supersaturated with salt and minerals such as calcium oxalate, struvite (ammonium magnesium phosphate), uric acid and cystine. 60-80% of stones contain calcium.They vary considerably in size from small 'gravel-like' stones to large staghorn calculi. The calculi may stay in the position in which they are formed, or migrate down the urinary tract, producing symptoms along the way. Studies suggest that the initial factor involved in the formation of a stone may be the presence of nanobacteria that form a calcium phosphate shell.[3, 4]
The other factor that leads to stone production is the formation of Randall's plaques. Calcium oxalate precipitates form in the basement membrane of the thin loops of Henle; these eventually accumulate in the subepithelial space of the renal papillae, leading to a Randall's plaque and eventually a calculus.
Bladder stones (calculi) account for around 5% of urinary tract stones and usually occur because of foreign bodies, obstruction or infection.The most common cause of bladder stones is urinary stasis due to failure of emptying the bladder completely on urination, with the majority of cases occurring in men with bladder outflow obstruction.Approximately 5% of bladder stones occur in women and are usually associated with foreign bodies such as sutures, synthetic tapes or meshes, and urinary stasis, so bladder stones should always be considered in women investigated for irritable bladder symptoms or recurrent urinary tract infections.
Patients with indwelling Foley catheters are also at high risk for developing bladder stones and there appears to be a significant association between bladder stones and the formation of malignant bladder tumours in these patients.
- Renal stones are common, being present at some time in one in ten of the population, although a significant proportion will remain asymptomatic.
- The annual incidence is about 1-2 cases of acute renal colic (or ureteric colic) per 1,000 people and the average lifetime risk around 5-10%.
- Men are more commonly affected than women, with a male:female ratio of 3:1. The difference between the sexes is gradually being eroded. This is thought to be due to lifestyle-associated factors, such as obesity and a Western diet.
- The peak age for developing stones is between 30 and 50 and recurrence is common.
Several risk factors are recognised to increase the potential of a susceptible individual to develop stones. These include:
- Anatomical anomalies in the kidneys and/or urinary tract - eg, horseshoe kidney, ureteral stricture.
- Family history of renal stones.
- Relative dehydration.
- Metabolic disorders which increase excretion of solutes - eg, chronic metabolic acidosis, hypercalciuria, hyperuricosuria.
- Deficiency of citrate in the urine.
- Cystinuria (an autosomal-recessive aminoaciduria).
- Drugs - eg, diuretics such as triamterene and calcium/vitamin D supplements.
- More common occurrence in hot climates.
- Increased risk of stones in higher socio-economic groups.
- Contamination - as demonstrated by a spate of melamine-contaminated infant milk formula.
- Many stones are asymptomatic and discovered during investigations for other conditions.
- The classical features of renal colic are sudden severe pain. It is usually caused by stones in the kidney, renal pelvis or ureter, causing dilatation, stretching and spasm of the ureter. In most cases no cause is found:
- Pain starts in the loin about the level of the costovertebral angle (but sometimes lower) and moves to the groin, with tenderness of the loin or renal angle, sometimes with haematuria.
- If the stone is high and distends the renal capsule then pain will be in the flank but as it moves down pain will move anteriorly and down towards the groin.
- A stone that is moving is often more painful than a stone that is static.
- The pain radiates down to the testis, scrotum, labia or anterior thigh.
- Whereas the pain of biliary or intestinal colic is intermittent, the pain of renal colic is more constant but there are often periods of relief or just a dull ache before it returns. The pain may change as the stone moves. The patient is often able to point to the place of maximal pain and this has a good correlation with the current site of the stone.
- Other symptoms which may be present include:
- Rigors and fever.
- Urinary retention.
- Nausea and vomiting.
- The patient with colic of any sort writhes around in agony. This is in contrast to the patient with peritoneal irritation who lies still.
- The patient is apyrexial in uncomplicated renal colic (pyrexia suggests infection and the body temperature is usually very high with pyelonephritis).
- Examination of the abdomen can sometimes reveal tenderness over the affected loin. Bowel sounds may be reduced. This is common with any severe pain.
- There may be severe pain in the testis but the testis should not be tender.
- Blood pressure may be low.
- Full and thorough abdominal examination is essential to check for other possible diagnoses - eg, acute appendicitis, ectopic pregnancy, aortic aneurysm.
This depends upon the position of the pain and the presence or absence of pyrexia and includes:
- Biliary colic.
- Dissection of an aortic aneurysm: beware the patient who presents with features of renal colic for the first time over the age of 60. This may be dissection of aortic aneurysm leading to ruptured aortic aneurysm.
- Pyelonephritis: very high temperature. Pain is unlikely to radiate to the groin.
- Acute pancreatitis.
- Acute appendicitis.
- Perforated peptic ulcer.
- Epididymo-orchitis or torsion of the testis: very tender testis.
- Sinister causes of back pain: usually tender over vertebrae.
- Drug addiction: there are reports of people with fictitious stories of renal colic, designed to obtain an injection of pethidine. These patients tend to be abusive when offered anything other than pethidine.
- Münchhausen's syndrome.
- Basic analysis should include:
- Stick testing of urine for red cells (suggestive of urolithiasis), white cells and nitrites (both suggestive of infection) and pH (pH above 7 suggests urea-splitting organisms such as Proteus spp. whilst a pH below 5 suggests uric acid stones).
- Midstream specimen of urine for microscopy (pyuria suggests infection), culture and sensitivities.
- Blood for FBC, CRP, renal function, electrolytes, calcium, phosphate and urate, creatinine.
- Prothrombin time and international normalised ratio if intervention is planned.
- Non-enhanced CT scanning is now the imaging modality of choice and has replaced intravenous pyelogram (IVP).Ultrasound scanning may be helpful to differentiate radio-opaque from radiolucent stones and in detecting evidence of obstruction.
- Plain X-rays of the kidney, ureter and bladder (KUB) are useful in watching the passage of radio-opaque stones (around 75% of stones are of calcium and so will be radio-opaque).
- The European Association of Urology's guidelines on urolithiasis recommend stone analysis for:
- All first-time stone formers.
- All patients with recurrent stones who are on pharmacological preventing therapy.
- Patients who have had early recurrence after complete stone clearance.
- Late recurrence after a long stone-free period (stone composition may change).
Initial management can either be done as an inpatient or on an urgent outpatient basis, usually depending on how easily the pain can be controlled.
Indications for hospital admission
- Solitary kidney.
- Known non-functioning kidney.
- Inadequate pain relief or persistent pain.
- Inability to take adequate fluids due to nausea and vomiting.
- Poor social support.
- Inability to arrange urgent outpatient department follow-up.
- People over the age of 60 years should be admitted if there are concerns on clinical condition or diagnostic certainty (a leaking aortic aneurysm may present with identical symptoms).
Indication for urgent outpatient appointment
- Pain has been relieved.
- The patient is able to drink large volumes of fluid.
- Adequate social circumstances.
- No complications evident.
Initial management of acute presentation
- Non-steroidal anti-inflammatory drugs (NSAIDs), usually in the form of diclofenac IM or PR, should be offered first-line for the relief of the severe pain of renal colic. NSAIDs are more effective than opioids for this indication and have less tendency to cause nausea. However, if parenteral morphine is required in severe renal colic pain, this works quickly and can provide pain relief in the time taken for an NSAID to work. If opioids are needed then a Cochrane review concluded that it should not be pethidine.
- Provide antiemetics and rehydration therapy if needed.
- The majority of stones will pass spontaneously but may take 1-3 weeks; patients who have not passed a stone or who have continuing symptoms should have the progress of the stone monitored at a minimum of weekly intervals to assess the progression of the stone.
- Conservative management may be continued for up to three weeks unless the patient is unable to manage the pain, or if he or she develops signs of infection or obstruction.
- Medical expulsive therapy may be used to facilitate the passage of the stone. It is useful in cases where there is no obvious reason for immediate surgical removal. Calcium-channel blockers (eg, nifedipine) or alpha-blockers (eg, tamsulosin) are given. A corticosteroid such as prednisolone is occasionally added when an alpha-blocker is used but should not be given as monotherapy.
Managing patients at home
- All patients managed at home should drink a lot of fluids and, if possible, void urine into a container or through a tea strainer or gauze to catch any identifiable calculus.
- Analgesia: paracetamol is safe and effective for mild-to-moderate pain; codeine can be added if more pain relief is required. Paracetamol and codeine should be prescribed separately so they can be individually titrated.
- Patients managed at home should be offered fast-track investigation initiated by the hospital on receipt of a letter or email completed by the general practitioner.
- Patients should ideally receive an appointment for radiology within seven days of the onset of symptoms.
- An urgent urology outpatient appointment should be arranged for within one week if renal imaging shows a problem requiring intervention.
- Approximately 1 in 5 stones will not pass spontaneously and will require some form of intervention.
- If the ureter is blocked or could potentially become blocked (eg, when a larger stone will fragment following other forms of therapy), a JJ stent is usually inserted using a cystoscope. It is a thin hollow tube with both ends coiled (pigtail). It is also used as a temporary holding measure, as it prevents the ureter from contracting and thus reduces pain, buying time until a more definitive measure can be undertaken.
- Procedures to remove stones include:
- Extracorporeal shock wave lithotripsy (ESWL) - shock waves are directed over the stone to break it apart. The stone particles will then pass spontaneously.
- Percutaneous nephrolithotomy (PCNL) - used for large stones (>2 cm), staghorn calculi and also cystine stones. Stones are removed at the time of the procedure using a nephroscope.
- Ureteroscopy - this involves the use of laser to break up the stone and has an excellent success rate in experienced hands.
- Open surgery - rarely necessary and usually reserved for complicated cases or for those in whom all the above have failed - eg, multiple stones.
- Several options are available for the treatment of bladder stones. The percutaneous approach has lower morbidity, with similar results to transurethral surgery while ESWL has the lowest rate of elimination of bladder stones and is reserved for patients at high surgical risk.
- Complete blockage of the urinary flow from a kidney decreases glomerular filtration rate (GFR) and, if it persists for more than 48 hours, may cause irreversible renal damage.
- If ureteric stones cause symptoms after four weeks, there is a 20% risk of complications, including deterioration of renal function, sepsis and ureteric stricture.
- Infection can be life-threatening.
- Persisting obstruction predisposes to pyelonephritis.
- Most symptomatic renal stones are small (less than 5 mm in diameter) and pass spontaneously.
- Stones less than 5 mm in diameter pass spontaneously in up to 80% of people.
- Stones between 5 mm and 10 mm in diameter pass spontaneously in about 50% of people.
- Stones larger than 1 cm in diameter usually require intervention (urgent intervention is required if complete obstruction or infection is present).
- Two thirds of stones that pass spontaneously will do so within four weeks of onset of symptoms.
- A stone that has not passed within 1-2 months is unlikely to pass spontaneously.
- The following features predispose to recurrent stone formation:
- First attack before 25 years of age.
- Single functioning kidney.
- A disease that predisposes to stone formation.
- Abnormalities of the renal tract.
Recurrence of renal stones is common and therefore patients who have had a renal stone should be advised to adapt and adopt several lifestyle measures which will help to prevent or delay recurrence:
- Increase fluid intake to maintain urine output at 2-3 litres per day.
- Reduce salt intake.
- Reduce the amount of meat and animal protein eaten.
- Reduce oxalate intake (foods rich in oxalate include chocolate, rhubarb, nuts) and urate-rich foods (eg, offal and certain fish).
- Drink regular cranberry juice: increases citrate excretion and reduces oxalate and phosphate excretion.
- Maintain calcium intake at normal levels (lowering intake increases excretion of calcium oxalate).
- Depending on the composition of the stone, medication to prevent further stone formation is sometimes given - eg, thiazide diuretics (for calcium stones), allopurinol (for uric acid stones) and calcium citrate (for oxalate stones).
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