Stones that form in the urinary tract (kidney, ureter, bladder) are urinary stones. Pain from kidney stones is one of the most painful conditions, often being described as worse than childbirth.
The management of kidney and ureteric stones has evolved in the past two decades due to the advent of minimally invasive surgical options. Major open surgery is now rare, and most cases can be managed with no-scalpel surgery. More is known about why stones form and some patients can be managed successfully without surgery. Prevention is also an option in certain patients.
Bladder stones are covered in further detail in another section (see Bladder Stones).
How common are kidney stones?
Unfortunately, kidney stones are quite common; the lifetime risk of developing kidney stones is about 1 in 10 for Australian men and 1 in 35 for women. Kidney stones account for about 1 of every 100 hospital admissions. 10% of all first-time stone formers will get another episode within 1 year and 50% within 10 years.
What are the various kinds of kidney stones?
Kidney stones are composed of:
- Calcium salts (70% of cases).
- Struvite or magnesium ammonium phosphate (15%).
- Uric acid (8%).
- Cystine (3%).
- Miscellaneous material.
What are the causes of kidney stones?
Industrialised countries have an increased incidence of kidney stones due to high dietary protein intake. The prevalence increases in countries with more exposure to sunlight. Excessive fluid loss and dehydration, which can be related to occupation is also a factor.
Diet and fluid intake
A diet high in meat (purines), sodium (salt), oxalate and calcium are associated with an increased risk of stone formation. Adequate fluid intake is very important to avoid dehydration. Insufficient citrus fruit (oranges, lemon) intake can result in low amounts of citrate in the urine, which increases the rate of stone formation.
Cystine stones can run in the family. These stones form in acidic urine and can be dissolved with urinary alkalinisation. These stones are very hard and are often resistant to external shockwave treatment.
High calcium levels in the urine
This can be caused by increased absorption in the gut or increased excretion in the kidneys. Excess hyperparathyroid hormone as seen in sarcodoisis can also cause this. Those with sedentary lifestyles or those who are bed-bound from other medical problems (e.g., spinal cord injury patients) have higher calcium resorption from the bones, which increases urine calcium.
High oxalate levels in the urine
Causes include an enzyme deficiency, and bowel conditions which increase oxalate absorption in the gut (e.g., inflammatory bowel disease).
High cystine levels in the urine
This is a congenital defect that causes impaired kidney reabsorption of cystine.
High uric acid levels in the urine
Uric acid can be excessively excreted in conditions like gout or during cancer chemotherapy.
Low citrate levels in the urine
The cause is unknown but inflammatory bowel disease, chronic diarrhoea and malabsorption have been associated.
Urinary tract infections
UTIs encourage struvite stone formation, and the bacteria can ‘hide’ in the stones and make treatment with antibiotics difficult. Anatomical or functional abnormalities like urinary obstruction or stasis (inability to empty), can predispose one to getting UTIs.
What are the symptoms?
Patients have presentations ranging from no symptoms to vague pain, to severe colicky pain. Pain is caused by the stone getting lodged in the ureter (the tube that drains the kidney to the bladder) and causing an obstruction. A stone in the upper ureter classically presents with pain that radiates from the loin to the groin. Pain from a stone in the lower ureter may be felt in the testicle, tip of the penis, or labia and may also cause the frequent urge to urinate.
Some patients may present with associated urinary infections, blood in the urine, nausea or vomiting. More uncommonly, an infection can be severe enough that it spreads to the blood system (sepsis), making the patient so unwell to warrant intensive care support. Some stones do not cause pain and may go unnoticed for many years, resulting in a shrivelled, non-functioning kidney with potential kidney failure.
What are the investigations?
The aims of investigations are to:
- Make the diagnosis.
- Assess kidney function and anatomy.
- Identify causative factors, especially in those with recurrent presentations.
A CT scan of the abdomen is the most useful way to confirm the diagnosis and assess the kidney anatomy. It can also look at the size, position, and number of stones as well as other intra-abdominal abnormalities. It can identify some stones that are not seen on plain X-rays like uric acid stones. Information on kidney anatomy is important when planning the surgical approach.
An ultrasound is a useful way to look for kidney obstruction and anatomy. It can detect stones but is not as accurate as a CT scan. The advantage is that it does not involve any radiation and is suitable for certain patients (e.g., pregnant women).
Kidney nuclear scan
This test is not performed routinely but can provide information about reflux (backflow) of urine up the ureters from the bladder, how much each kidney is contributing to the overall function (differential function) and scarring in the kidneys.
Blood tests can be done to assess kidney function, and look for metabolic abnormalities (e.g., high calcium or uric acid levels in the blood).
A simple urine dipstick is done to look for the presence of blood cells which is often present when there is a kidney stone. It can also test for a concurrent urine infection. For patients with recurrent stone formation, a 24-hour urine collection is done to check for metabolic abnormalities.
What are the treatments?
For patients in acute pain from kidney stones, strong analgesia is often necessary. Often a combination of analgesic medications is needed to control the pain.
Medical dissolution therapy
Some stones can be dissolved with medications instead of treatment with surgery. For example, uric acid stones can often be dissolved successfully with allopurinol medication and alkalinisation of the urine. Penicillamine is also used in the treatment of cystine stones.
Antibiotics are needed to treat documented infections.
Decompression of the kidney
A patient with signs of infection and kidney obstruction can potentially become very ill. Such a patient would require urgent kidney drainage or decompression. This can be done either with a JJ stent (plastic hollow tube which is placed alongside the stone and drains the kidney internally down to the bladder, see JJ stent insertion) or a nephrostomy tube (a plastic tube that is inserted directly through the skin on the flank into the kidney to drain it).
Observation / medical expulsion therapy
Some stones that are small (< 5 – 6mm) are likely to spontaneously pass without needing surgery. These patients are often discharged home with analgesia. Patients are often given up to a month of medical expulsion therapy. If the stone still has not passed by then, surgery may be needed.
Moderate size stones (6 - 8mm) may have a small chance of spontaneously passing. Stones larger than 8mm are unlikely to pass and would most likely need surgery.
Minimally invasive surgery
Nowadays, surgical treatment of kidney stones is effective and minimally invasive. There are a few such surgical options:
Extracorporeal Shockwave Lithotripsy (ESWL)
Extracorporeal Shockwave Lithotripsy (ESWL) uses ultrasound to fragment the stones.
- Shock waves are applied externally targeted at the stone, to fragment it within the urinary tract.
- Usually done as an outpatient with the patient having sedational or general anaesthesia.
- Considered as less invasive compared to ureteroscopic laser stone extraction.
- Not as effective if the stone is big (>2.5cm), located in the lower part of the kidney or made of cystine (very hard).
- Sometimes a stent is pre-inserted to prevent pain when it is anticipated the stone fragments can line up in the ureter to cause obstruction.
- Generally suitable for stones in the kidney or upper ureter.
- Possible complications include bruising of the kidney, bleeding, infection caused by the release of bacteria from stone fragmentation or obstruction of the ureter by the stone fragments. Very rarely, severe bleeding can result in loss of the kidney.
Kidney or Ureteric Laser Stone Surgery
Kidney or Ureteric Laser Stone Surgery uses ureteroscopic or flexible pyeloscopic for stone extraction.
- When a stone is in the ureter, a small-diameter, rigid, long instrument with an attached camera (ureteroscope) is inserted via the ureteric opening in the bladder, up the ureter to treat the stone in the ureter.
- If the stone is in the kidney, a flexible scope (pyeloscope) can be used to go around the angles within the kidney to locate the stone.
- Stone fragmentation can be done with a laser fibre.
- The fragments can then be removed with a small basket.
- Sometimes if the stone is impacted in the ureter leaving no space to work around it, a JJ stent may first be inserted to dilate the ureter. The definitive surgery is then done a few weeks later.
- Possible complications are infection, mild bleeding, and ureteric injury.
Percutaneous Nephrolithotomy (PCNL)
- For bigger stones (>2.5cm or staghorn stones), PCNL is the treatment of choice as it has the highest stone clearance rates (95%) amongst the other surgical options. However, it is relatively more invasive compared to the other options.
- A direct puncture is done through the skin in the patient’s flank into the kidney. A rigid scope (nephroscope) is then passed through the tract to visualise the stone in the kidney.
- Fragmentation is usually done with either a laser fibre, mechanically with compressed air or with ultrasound.
- At the end of the surgery, a tube may be left to drain the kidney to the outside of the body (nephrostomy tube).
- The length of hospitalisation is about 2 to 3 days.
- Possible complications are bleeding (severe in 0.5%), infection, and adjacent organ damage (lung, liver, spleen, bowel).
In the modern era, open surgery for the removal of urinary tract stones is very uncommon. This may be indicated in the patient with a high stone volume that may not be removed with a reasonable number of ESWL or PCNL treatments. Sometimes a kidney may be removed completely, if it is already non-functioning from the long-term damage associated with the kidney stone.
How can we change our diet to reduce the risk of kidney stone formation?
View Dietary Advice for Kidney Stone Formers
Read A/Prof Gani’s publication:
Download Alpha blocker prescribing trends for ureteral stones - PDF (1700 Kb)