Kidney stone disease

Kidney stone disease, also called nephrolithiasis or urolithiasis, refers to the presence of symptomatic kidney stones in the urinary tract. When stones are present in the ureter it may be called ureterolithiasis, while stones in the bladder are usually simply called bladder stones or bladder calculi. It's a relatively common condition, with a lifetime prevalence of 10 - 20 percent.

Many have asymptomatic kidney stones (which is not considered kidney stone disease), but in some cases stones can cause urinary obstruction (obstructive uropathy) and resulting damage to the kidney, as well as episodes of severe pain called renal colic. The vast majority of kidney stones pass without intervention within a few days or weeks, but there are options for treatment, including using radiowaves to crush them (ESWL) and removing them surgically.

Epidemiology

Kidney stone disease more commonly affects males than females, and mostly affect people in the 30 - 60 years age group.

Etiology

Certain risk factors are known for certain stone types:

• Any type
  • Low fluid intake
  • Family history
  • Hyperparathyroidism
• Calcium oxalate stone
  • Hypercalcuria
  • Crohn disease
• Uric acid stone
  • Hyperuricaemia and gout
• Struvite stone
  • UTI with urease-producing bacteria

Pathology

Kidney stones are usually small (2-3 mm). 80% of kidney stones are formed of calcium oxalate. 10% are so-called struvite stones, which are formed of magnesium ammonium phosphate. The remaining types are formed of uric acid and cysteine.

Stone formation occurs when the urine is supersaturated with the components of the stone . In some cases other factors will contribute to the formation of stones as well, like abnormal pH.

Calcium oxalate stones are the most common type. This type of stone is radiopaque.

Struvite stones occur in people with alkaline urine. Alkaline urine is a result of a urinary tract infection, especially one caused by bacteria that produce urease, like Proteus and Staphylococcus. Struvite stones grow quickly and can sometimes make a “cast” of the renal pelvis, called staghorn calculi.

Uric acid stones occur in people with acidic urine and increased excretion of uric acid. The latter can be idiopathic or in combination with gout or diseases that cause rapid cell turnover, like leukaemia. This type of stone is radiolucent.

Cysteine stones occur in people with genetically determined defects in renal transport of cysteine. Acidic urine also increases the risk for cysteine stones.

The renal colic pain associated with kidney stones is thought to occur when stones enter the ureter, causing distension of the kidney capsule due to urinary obstruction, and due to ureteric spasm. Stones in the renal pelvis themselves are usually asymptomatic.

Clinical features

Kidney stones may be asymptomatic, especially if they are in the renal pelvis. Kidney stones may also cause haematuria. Concurrent fever with renal colic is a sign of infection together with urinary obstruction, which may be severe.

Renal colic

When a kidney stone passes from the renal pelvis into the ureter, it may get stuck. This causes episodes of severe flank pain. This pain is typically colicky, meaning that it starts and stops abruptly. There may be visible haematuria. The pain may radiate to the ipsilateral testicle or labium. The patient usually has a severe urge to move.

Other pain

A kidney stone may also present with pain other than renal colic. Pain may be mild and not localised to the flank. In these cases, the diagnosis is difficult.

Diagnosis and evaluation

A presumptive diagnosis may be made when the patient has typical renal colic, as kidney stone is highly likely in that case.

Haematuria on urine analysis is seen in most cases of kidney stone (90%), but absence of haematuria does not exclude the diagnosis. It may be necessary to measure the serum calcium and uric acid level to look for underlying cause. A first episode of renal colic should be investigated with kidney function tests to rule out acute kidney injury as a complication.

Whether imaging is necessary in case of uncomplicated (no fever or sign of infection, pain can be controlled with NSAIDs, mild-moderately decreased kidney function) is controversial. In Norway, no imaging is obtained during the initial presentation; imaging is obtained after 3 - 4 weeks. According to most other guidelines however, CT is indicated urgently to assess for obstruction.

Imaging

A low-dose non-contrast CT is usually the first choice as this has little radiation exposure and can detect the majority of stones. Ultrasonography is a reasonable alternative first choice, especially in pregnant and children, but many stones are not visible on ultrasound (70% sensitive and specific). Kidney, ureter, bladder (KUB) radiography was previously widely used, but it is not sensitive and so is rarely used nowadays.

If the stone causes urinary obstruction, one may see hydronephrosis and dilated proximal ureters.

Management

Asymptomatic stones need no management or follow-up. Uncomplicated small (< 5 mm) stones need only symptomatic treatment and follow-up imaging after 4 - 6 weeks to see if the stone has passed. These cases can be treated out-patient.

Consider hospital admission and treatment to remove or crush the stones in:

• Complicated stones (causing obstruction, acute kidney injury, infection)
• Larger stones (> 5 mm)
• Stones which haven't passed after 4 - 6 weeks

For stones in the distal ureter, an alpha blocker like tamsulosin may be considered as it may fascilitate passage of the stone.

Symptomatic treatment for renal colic

An NSAID like ketorolac or diklofenac is the best first choice for renal colic. In addition to relieving pain they also decrease ureteral smooth muscle tone. Hydration, preferably intravenous, is important. A spamsolytic like butylscopolamine may be used as well.

Extracorporeal shockwave lithotripsy (ESWL)

• First choice to remove stones in most cases
• Procedure
  • The stone is located by x-ray or US
  • Uses shockwaves to fragment the stones into fragments which can pass spontaneously
  • May have to be repeated
• Indications
  • Kidney stone < 20 mm
  • Ureter stone < 10 mm
  • Uric acid stones
• Contraindications
  • Non-urological
    • Untreated hypertension
    • Pregnancy
    • Uncorrected bleeding disorder
    • Aortic aneurysm
  • Urological
    • Kidney dysfunction
    • Untreated UTI
    • Obstruction distal to stone
• Complications
  • Generally very safe
  • Perirenal or intrarenal haematoma
  • Haematuria

Percutaneous nephrolithotomy (PCNL)

• Percutaneous access into the renal pelvis -> stones fragmented by shockwaves or laser -> fragments are removed by forceps
• Indications
  • Stones unsuitable for ESWL
  • ESWL treatment failure
• Contraindications
  • Uncorrected bleeding disorder
  • Untreated UTI
• Complications
  • Injuries of adjacent organs
  • Haematoma
  • AV fistula

Ureterorenoscopy (URS)

• Indications
  • Ureteric stones
  • Ureteral strictures
• Complications rare

Open surgery

• For complex stones (staghorn calculi), or if other methods have failed