Stones

Urinary stones (calculi) are hardened mineral deposits that form in the kidney. Salt crystals form when the urine becomes highly concentrated and can grow in size if they fail to pass through the urinary tract. If they become large enough they may cause obstruction to the urinary drainage pathway resulting in pain and bleeding. Sometimes this may be complicated by infection and loss of kidney function.

Urinary stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate. These stones are generally visible on plain X-rays making treatment and follow-up more simple.

A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone and it can grow rapidly to fill the renal pelvis (upper end of the ureter). These stones may be associated with permanent loss of kidney function, recurrent urinary infections and widespread sepsis if not treated. These stones may be weakly visible on plain X-ray.

Other important but less common stones are made of uric acid. Uric acid is the same chemical that causes gout (painful inflammation of one or more joints). It is also associated with a high protein diet and obesity. These stones are not visible on plain X-ray.

The rare cystine stone makes up just 1% of all stones but can be more difficult to treat and prevent than other stones. It is due to an inherited problem of amino acid transport in the kidney and therefore makes for a lifelong risk to the affected person. Lifestyle changes to diet and fluid consumption as well as medications are necessary to try and reduce the frequency of recurrence and the need for treatment.

Although some stones do not cause symptoms, the first symptom of a kidney stone is often significant pain. The pain may begin suddenly when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain in the back and side which progresses to the lower abdomen and groin as the stone migrates down the ureter. Sometimes nausea and vomiting occur with this pain. Blood may be visible in the urine (Haematuria).
If the stone is too large to pass easily, the pain continues as the muscles in the wall of the ureter try to squeeze the stone along into the bladder. As the stone moves down the ureter closer to the bladder, a person may feel the need to urinate more often or feel a burning sensation during urination.
If fever and chills accompany any of these symptoms, an infection may be present which necessitates admission to hospital and more aggressive treatment.
Generally laboratory tests, including urine and blood tests are taken to help determine the type of stone and it’s effects on renal function. If a stone has been removed, or one has passed in the urine and been saved, the lab can analyse the stone to determine its composition.
Non-contrast (i.e. without highlighting dyes) CT scan is the standard imaging test for stone disease. Plain X-ray may also be performed for use in treatment and follow-up. Ultrasound can be used to detect stones and urinary obstruction but is a less accurate scan for stone diagnosis than CT. It’s chief advantage is that it does not use radiation which may be important, for example during pregnancy. MRI scans have a very limited role in stone disease.
The factors that lead to the formation of an initial kidney stone will result in further stones forming in up to 50% of people within the next 5 years. Prevention of future stones focuses on lifestyle modification and this may involve:
- A generally healthy lifestyle and weight
- Adequate fluid intake (at least 2L/day)
- Dietary moderation (avoid excessive meat and salt intake)
- Specific medications (e.g. allopurinol for uric acid stones)
People who make multiple stones may require further investigation and tailored treatment of the underlying factors.
Conservative
Almost all stones smaller than 4mm and the majority less than 8mm lodged in the ureter will eventually pass without needing an operation. Particularly in asymptomatic patients a wait-and-see course may be the most appropriate option. Some medications (alpha blockers, calcium channel blockers and steroids) have been shown to improve stone passage rates and are a standard treatment unless there are reasons not to prescribe them. It is important that stone clearance is confirmed with imaging as prolonged kidney obstruction may lead to kidney damage, loss of function and infection.
Pain control
The severe pain of renal colic usually needs to be controlled by potent pain killers. Stones associated with uncontrolled pain, infection or progressive worsening of kidney function will require intervention. Stones too large to pass spontaneously will also require treatment.
Some stones under the right circumstances may be dissolvable using medications. Uric acid stones form in very acidic urine due to high levels of uric acid. Allopurinol may be used to decrease the uric acid levels in the urine and citrate based agents can be taken to remove it’s acid (urine alkalinizing). In this environment the stone may dissolve back into solution over time avoiding the need for intervention.
The “JJ stent” is a thin, hollow tube with coils at either end to hold it in position. It is placed via a cystoscope into the ureter between the kidney and bladder, bypassing obstruction and facilitating the drainage of urine. It is useful to help relieve kidney obstruction related pain, drain infected urine and allow the healing of injured ureteric tissue. It requires a further procedure (often by flexible cystoscopy with local anaesthesia alone) to remove. It may cause symptoms from irritation (urinary discomfort, urgency and frequency) or reflux of urine (flank ache at the time of voiding).
A ureteroscope is a long, thin instrument which is either rigid or flexible and has an inbuilt camera, light and working channel to allow the passage of instruments. It is inserted through the urethra (urinary outflow pipe), into the bladder and up into the ureter (the long funnel connecting the kidney and bladder). A laser fibre is introduced through the working channel to fragment the stone and the fragments retrieved using a grasper or basket retrieval device. It is the preferred choice of intervention for ureteric stones requiring treatment.
This approach avoids the need for an incision, is very successful and can often be performed as day surgery. It does however require an anaesthetic and carries a small risk of introducing infection, or of damaging the ureter (0.5%).
The PCNL is a form of “keyhole” surgery in which a tube is inserted through the back directly into the kidney. Irrigating fluid is used to improve vision while a laser is directed to fragment the stone. It is the preferred choice for large (>2cm) kidney stones.
This approach has replaced open surgery for large and complicated kidney stones in most instances. Recovery time is much quicker and the surgical wound much smaller. It also requires general anaesthesia and is a relatively long procedure that is not usually done as day surgery (hospital stay is often 2-3 days). More than one procedure may be required for complete stone clearance and the risks of infection, bleeding and (rarely) lung or other organ injury exist.
This treatment technique uses a high frequency shock wave produced by a machine outside the body. The shockwaves are focused on the target stone with image guidance (X-ray or ultrasound). The fragments then pass in the urine. It may be useful for smaller (<2cm) stones in the kidney or ureter.
The advantages of ESWL are that it is the least invasive treatment option and can often be done with sedation and pain relief rather than anaesthesia. It is safe but is the least effective stone clearing option (with a single treatment) and the most likely therefore to lead to retreatment. Larger patients, denser stones and unfavourable anatomy of the urinary drainage pathways may lead to the poorest outcomes with this technique.