Kidney stones are much more common than bladder stones, and can lead to serious complications.

THE body gets rid of some of its waste products through the urine produced in the kidneys. Sometimes, the waste products form crystalline substances which collect inside the kidney, and in the course of time, form hard masses, i.e. stones.

Kidney stones (renal calculi) are common in our country and usually affect people from the third decade of life onwards, with more males being affected. They are much more common than bladder stones.

The vast majority of renal calculi contain calcium with uric acid, with other compounds making up the rest.

The mechanisms that lead to the formation of renal calculus include supersaturation of urine by stone-forming compounds with the formation of microscopic structures on foci of crystals or foreign bodies in the kidney; and the deposition of stone-forming compounds on parts of the kidney, with gradual increase in the deposits by calcium compounds to form calculus. Sometimes the calculus may become large (staghorn calculus).

Flushed out: Most renal stones are small, and it is generally accepted that 80% of patients will pass out urine stones that are up to 4mm in diameter.

Various factors increase the likelihood of calculus formation. They include:

·Hypercalciuria, which is an increased amount of calcium in the urine. This may be related to increased absorption of calcium by the intestines, increased breakdown of calcium in the bones, and an inability of the kidneys to retain calcium during urine formation.

·Small amounts of fluid intake lead to the production of small amounts of urine, which results in high concentrations of stone-forming compounds in the urine. This is an important cause of calculus formation as much water can be lost from the body through sweating and breathing in our tropical climate.

·A decrease in the body’s citrate and magnesium levels increases the likelihood of calculus formation as both compounds are important inhibitors of calculus formation in the urinary tract.

·Medical conditions like cancer and kidney disease increase the likelihood of calculus formation. This is usually due to the treatment of the medical condition.

The body tries to rid itself of the calculus by passing it out in the urine. It is possible for small calculi to traverse the ureters, bladder, and be passed out through the urethra. However, it is not the case with larger calculi.

The problems posed by the calculus are due mainly to obstruction to the flow of urine from the kidneys through the urinary tract. This results in stasis of urine, which increases the likelihood of urinary tract infection. The combination of urinary tract infection and kidney infection poses particular danger as it can lead to kidney damage with resulting loss of renal function and infection of the blood stream (septicaemia), which is potentially life threatening.

Clinical features

Many patients do not have any symptoms, particularly those with small stones.

The clinical features of renal calculi include that of urinary tract infections, particularly recurrent ones, ureteric colic when the stone attempts to traverse the ureter, history of having passed out stones in the urine, and loss of renal function, including renal failure.

Ureteric colic usually present with severe pain in the back or the side of the abdomen, or sometimes in the groin, lasting minutes or hours, with intervals when there is no pain.

The other common symptoms of renal calculi include an inability to lie still, nausea, urine that contains blood or is smelly or cloudy, a burning sensation when passing urine, an urge to pass urine often, and fever.

Management

A diagnosis of renal calculus is usually made from symptoms and the medical history, especially if there had been renal calculus previously.

The laboratory tests include urinalysis to check for infections and stones, renal function tests and estimations of substances that cause stone formation, e.g. calcium. Stones that have been passed out in the urine are also analysed to determine their composition.

Imaging investigations are useful in confirming the diagnosis and locating the precise position of the calculus. They include x-rays, intravenous pyelogram (IVP), ultrasound and computerised tomography (CT) scan. An IVP involves an intravenous injection of a dye which passes through the kidneys into the urine. The x-ray images will locate the calculus and any blockages of the urinary tract.

CT scans are thought to be more accurate than IVPs. However, the imaging technique used will depend on what is available at the hospital or imaging centre.

The treatment modality depends on the size of the calculus. Most renal calculi are small and it is possible to be treated at home. It is generally accepted that 80% of patients will pass out urine calculi that are up to 4mm in diameter. The calculi may still cause pain until after it has been passed out. Painkillers are usually prescribed. Injections will be given if oral medicines do not provide relief. Medicines for nausea and vomiting may also be prescribed.

It is important to drink sufficient water until the urine is colourless. If the urine is yellow or darker, it means that there is insufficient drinking.

If the calculus is 6mm to 7mm in diameter or larger, it is usually removed by surgical procedures, i.e. extracorporeal shock wave lithotripsy (ESWL), ureterorenoscopy, percutaneous nephrolithotomy (PCNL), or traditional surgery. The type of treatment depends on the size and location of the calculus. The indications for surgical treatment include pain, infection, and obstruction. Surgical treatment is not usually performed when there is an untreated urinary tract infection, uncorrected bleeding disorders, or pregnancy.

Extracorporeal shock wave lithotripsy (ESWL) is the least invasive of the procedures available. It involves the delivery of shockwaves by a device called a lithotriptor. The energy released when the shockwave hits the calculus causes it to break up into small fragments, which are then passed out in the urine.

The anaesthesia used depends on the type of lithotriptor used. ESWL is limited by the size and site of the calculus. Treatment is less successful if the calculus is larger than 1.5cm in diameter or is located in the lower part of the kidney. Although there is fragmentation of the calculus, complete passage in the urine is less likely because of the large volume of the fragments or its location in the lower part of the kidney.

The results are also poorer in obese or overweight patients because of the increased distance from the device to the calculus.

ESWL is not done if there is ureteral obstruction below the site of the calculus. There are some patients who require more than one session of EWSL to treat the calculus successfully.

Ureterorenoscopy involves inserting a telescopic instrument called an ureteroscope through the urethra and bladder up into the ureter and kidney where the calculus is stuck. It is sometimes called retrograde intrarenal surgery (RIRS). The calculus, which is either removed with another instrument or is broken up into smaller fragments by ESWL or laser, is passed out in the urine. The procedure is usually performed under general anaesthesia.

Percutaneous nephrolithotomy (PCNL) involves inserting a telescopic instrument called a nephroscope into the kidney through an incision made in the patient’s back. The calculus is either removed or broken into smaller fragments with ESWL or laser.

PCNL is usually performed under general anaesthesia. Because its risks are greater than that of ESWL and ureterorenoscopy, PCNL is usually performed when the calculi are large and/or complex or when ESWL or ureterorenoscopy has failed.

There are occasions (usually less than 10%) when traditional surgery is used to remove the calculus, i.e. when ESWL, ureterorenoscopy and PCNL are unsuitable treatment modalities. This involves making an incision in the back, under general anaesthesia, to access the kidney and/or ureter to remove the calculus or calculi.

The complications of surgical treatment depend on the treatment modality and the size and position of the calculi. They include pain, urinary tract infection, bleeding, injury to the ureter, infection of the blood stream (septicaemia) and steinstrasse, which is blockage of the ureter caused by fragments of the calculus.

Prevention

One should be cognisant that a recurrence is increased by a high protein, low fibre diet, physical inactivity, recurrent urinary tract infections, disease of the small intestine, intestinal bypass surgery, when there is only one functioning kidney, past history of renal calculi, and a family history of renal calculi.

There is also evidence that certain medicines increase the likelihood of a recurrence, e.g. antacids, aspirin, calcium and vitamin D supplements.

The crucial measure that can prevent a recurrence is an increase in fluid intake which would lead to an increase in urine output.

Source: Dr Milton Lum