Urolithiasis

Description

• Urolithiasis is the occurrence of calculi (stones) within the urinary tract, including the kidney, ureter, or bladder.
• Stones may be composed of calcium oxalate, calcium phosphate, uric acid, cystine, magnesium ammonium phosphate, xanthine, indinavir, or triamterene.

Epidemiology

The incidence of stones in children of both sexes has increased over the last 25 years. In the adolescent population, the prevalence is about 50 per 100,000.

Risk Factors

• Poor fluid intake
• Immobility
• Urinary tract obstruction
• Urinary tract infection (UTI) (Proteus mirabilis or Escherichia coli)
• Bladder augmentation
• Dumping syndrome
• In children, 50% have a metabolic syndrome associated with urolithiasis.
• 75% have a metabolic predisposition to forming stones.

Pathophysiology

• The urine contains multiple solutes; some help prevent crystallization and some contribute to crystal formation.
• The likelihood of a solute crystalizing varies with the pH of the urine (e.g., uric acid crystal formation is more likely at lower pH).
• When enough crystals form in the urine and urine flow out of the kidney is slow or obstructed
• Crystals then coalesce into a small nidus upon which more crystals will form. This process then leads to stone formation.

Commonly Associated Conditions

Children who present with urolithiasis age <6 years are more likely to develop hypertension (HTN) and diabetes mellitus (DM) later in life.