Renal and Ureteric Stones

Overview

Also known as nephrolithiasis, urolithiasis, or ‘kidney stones’, renal and ureteric stones describe the formation of stones (calculi) anywhere in the urinary tract from the kidneys (where most originate) to the ureter and bladder.

Renal/ureteric colic describes acute, severe, crampy pain that occurs when a stone moves through the urinary tract or obstructs the flow of urine through the ureter. It is often described as one of the most painful sensations known.

Pathophysiology

Stone formation

Renal stones form when solutes crystallise out of the urine. This can be due to supersaturation (where there are too many solutes for the urine to hold in solution) which can be due to reduced water available (e.g. due to dehydration) or increased amounts of solutes (e.g. dietary factors, metabolic disorders, or some pathogens).

Stone passage and renal colic

Once the stone is formed, it may stay in place and grow or travel through the urinary tract. As the stone is passed through the urinary tract it leads to severe, colicky pain due to peristalsis of the ureter attempting to expel the stone. The pain often radiates from the loin to the groin due to how the kidneys and ureters are innervated. Some small stones may pass without causing any symptoms.

Complications

In some cases, the stone may obstruct the flow of urine, resulting in swelling of the kidneys. This is known as hydronephrosis is a urological emergency.

Some stones can form staghorn calculi. These are renal stones that are branched in shape which increase the risk of obstruction and hydronephrosis.

Stone Types

Calcium stones

Conditions predisposing to hypercalcaemia (e.g. hyperparathyroidism) can predispose to the formation of calcium stones:

• Calcium oxalate stones are the most common type and make up 80% of cases:
  • Associated with hypercalciuria, hyperoxaluria and hypercitraturia
  • They are radiopaque
• Calcium phosphate stones make up to 10% of cases:
  • Associated with hypercalciuria, hypocitraturia, high urine pH
  • They are radiopaque

Uric acid stones

Uric acid makes up to 10-20% of stones:

• Associated with low urinary pH (<5.5), and hyperuricosuria (e.g. gout)
• They are radiolucent

Struvite stones

Struvite stones (also known as infection stones) make up to 5% of renal stones:

• Associated with Proteus mirabilis infection as it uses the enzyme urease, which converts urea into ammonia and carbon dioxide, increasing urinary pH and making it more alkaline
• They are slightly radiopaque and frequently present as staghorn calculi

Cystine stones

Cystine stones are rare and make up around 1% of stones. They are due to cystinuria, an inherited recessive metabolic disorder that causes cystine to leak out of the kidneys into the urine:

• They are semi-radiopaque

Epidemiology

• Renal stones are common and their annual incidence is around 1-2 per 1,000
• Renal stones are more common in men than women
• Around 12% of men and 6% of women will experience renal colic at some point in life
• Incidence peaks between 40-60 years in men and late 20s for women 

Risk Factors

• Dehydration – increases the risk of supersaturation and stone formation
• Obesity – evidence has shown links between obesity and low urine pH and hypercalciuria
• High dietary oxalate, urate, sodium, and animal protein
• Family history
• Causes of hypercalcaemia – hyperparathyroidism, excess vitamin D supplements, sarcoidosis
• Hyperuricaemia and gout
• Anatomical abnormalities – horseshoe kidney, strictures, polycystic kidney disease, vesicoureteral reflux
• Gastrointestinal disorders – intestinal resection/bypass, Crohn’s disease, malabsorption
• Genetic disorders – cystic fibrosis, renal tubular acidosis, cystinuria, primary hyperoxaluria
• Drug-induced stones make up around 1% of stones:
  • Drugs that can cause hypercalciuria include loop diuretics, corticosteroids, acetazolamide, vitamin D, and theophylline
  • Thiazide diuretics can reduce the risk of calcium stones
• Chronic lead and cadmium exposure

Presentation

Overview

Features of renal stones include:

• Renal colic – severe, episodic, crampy pain that radiates from the loin to the groin:
  • Episodes usually last from minutes to hours with periods of no or dull pain between
  • Many people are restless due to the severity of the pain
• Associated nausea and vomiting:
  • Due to the severity of the pain
• Haematuria may be seen

Features suggesting complications may be present:

• Features of obstruction:
  • Reduced urine output, urine hesitancy, intermittent urinary stream, or urinary retention, costovertebral (renal) angle tenderness
• Fever of coexisting urinary tract infection:
  • Such as fever, rigours, and sweating
  • Features suggestive of sepsis may be present, such as hypotension with/without tachycardia

Investigations

Overview

• Urgent imaging (within 24 hours of presentation) in all people:
  • Non-pregnant adults: non-contrast CT of the kidneys, ureter and bladder
  • Pregnant people or children: ultrasound scan

Other tests include:

• Blood cultures:
  • If the patient is febrile and/or has other signs of sepsis
• Full blood count (FBC):
  • May identify leukocytosis suggesting infection 
• Urinalysis and culture:
  • May identify leukocytes and red blood cells
  • The presence of nitrites suggests coexisting infection
• Urea and electrolytes (U&Es):
  • May identify renal dysfunction
  • May identify hypercalcaemia or hyperuricaemia
• Urine pregnancy test in all people of childbearing age:
  • To screen for ectopic pregnancy
• Clotting panel:
  • If intervention is being planned

Management

Initial management

Initial management involves:

• Analgesia: if not contraindicated, give an NSAID via any route (e.g. IM diclofenac)
  • If NSAIDs are not appropriate, consider IV paracetamol or opioids if they fail
• IV fluids and antiemetics if needed
  • Antispasmodics are not used in renal stones

Further management depends on the size of the stone, how likely it is to spontaneously pass, and if any complications are present.

Obstruction and infection

If features of obstruction with or without infection are present, this is a urological emergency:

• 1^st-line: immediate decompression and stabilisation.
  • Often done with a nephrostomy tube, catheterisation, or ureteric stenting
• If features of infection present: give IV antibiotics

Once the patient is stabilised, the stone is removed as below. 

Non-emergency setting

For renal stones in a non-emergency setting::

• <5 mm: likely to spontaneously pass
• >5mm but<10 mm:
  • Adults: shockwave lithotripsy (SWL) is first-line
  • <16 years old: ureteroscopy (URS) or SWL is first-line
• 10-20 mm:
  • Adults: URS or SWL is first-line
  • <16 years old: URS, SWL or percutaneous nephrolithotomy (PCNL) is first-line
• >20 mm and/or staghorn calculi:
  • Adults: PCNL is first-line
  • <16 years old: URS, SWL, or PCNL is first-line

For ureteric stones in a non-emergency setting:

• <10 mm or 20 mm:
  • Adults: SWL is first-line
  • <16 years old: URS or SWL is first-line

Management steps vary if first-line measures fail or are not practical.

SWL and PCNL are avoided in pregnancy.

Patient Advice

Patients should be given advice regarding the prevention of future episodes:

• Increase fluid intake (2.5-3 L/day for adults, 1-2 L/day for children)
• Reduce salt intake
• Do not routinely restrict calcium intake

Complications

The main complications of renal stones include:

• Obstruction and hydronephrosis:
  • Obstruction of urinary flow can lead to swelling of the kidneys which if prolonged, can lead to reduced renal blood flow and irreversible kidney damage
• Infection and sepsis:
  • Co-existing UTIs can increase the risk of sepsis
  • Obstruction of urinary flow can also increase the risk of infection

Other complications include:

• Increased risk of renal cell cancer:
  • Renal stones are associated with an increased risk compared to the general population
• Chronic kidney disease (CKD):
  • A history of renal stones can increase the risk of CKD
• Renal calyx rupture:
  • This is rare and can lead to the formation of a collection of urine known as a urinoma

Prognosis

• The majority of stones up to 4 mm pass within 40 days
• Stones that are 5-10 mm pass spontaneously in around 50% of people
• Rates of recurrence are high and can be around 50% at 5 years and 80% at 10 years