Kidney Stones

Definition (1,2)

Nephrolithiasis:
“The presence of calculi within the urinary system.”

Calculi are crystalline stones, and can be anywhere along the course of the urinary tract, including the kidneys, ureters, bladder, and urethra.

The terms urolithiasis and nephrolithiasis can usually be used interchangeably (although some specialists have varying definitions).

Epidemiology (2, 3, 9)

• Main ages affected: 30-60 years of age.
• Uncommon and rare in childhood.
• Incidence in childhood is unknown, estimated to be approximately 2 children per million UK population per year.
• The most common types of calculi in children are calcium phosphate and struvite.

Pathophysiology (1, 3, 4, 6, 8)

Unlike in adulthood, when calculi can occur without pre-existing pathology (e.g. due to lifestyle), whenever they occur in childhood it is very important to find out the aetiology.

The urine contains stone formation promoters (calcium and oxalate) and stone formation inhibitors (citrate and magnesium). The balance of these chemicals keeps the urine stone-free, so an imbalance (too much stone promoters and/or not enough stone inhibitors) can precipitate stone formation. Other factors that can ‘tip’ this balance and cause stone formation are urine concentration and urine pH.

Table 1: Shows the different types of renal calculi and their causes.

Risk Factors (2, 4, 6, 8)

• Hypercalciuria (most commonly idiopathic) – NB: most children with hypercalciuria do not have stones!
• Recurrent UTIs
• Genitourinary anomalies
  • Hydronephrosis
  • Duplex ureter
  • Posterior urethral valves
  • Bladder exstrophy
  • Horseshoe kidney
• Metabolic disorders affecting the production or excretion of purines, calcium, uric acid, cystine, citrate, oxalate

Clinical Features (3, 6, 8)

Calculi can present asymptomatically (e.g. incidental finding on USS) or have a range of symptoms, described below:

From history:

• Haematuria (frank or microscopic)
• Loin pain, abdominal pain, pelvic pain
• Vomiting
• UTI symptoms (dysuria, frequency, fever)
• Passage of a visible stone
• Irritable and colicky baby
• Inability to void (if presenting with acute urinary obstruction)

From examination:

Examination is usually unremarkable, but it may be useful to look for signs of metabolic imbalances and other potential causes of calculi e.g. Rickets, malabsorption, dysmorphic features (e.g. William syndrome), gout.

DDx (1)

• Acute pelvic/abdominal pain
  • Appendicitis
  • Ectopic pregnancy
  • Bowel obstruction
  • Gastroenteritis
  • UTI
  • Cholecystitis / cholelithiasis
  • Pneumonia
  • Intussusception
  • Meckel’s diverticulum
  • Mesenteric adenitis
  • …
• Pyelonephritis
  • Urinalysis and culture would be positive for infection and USS/CT would show no stones
• Ureteropelvic junction obstruction
  • Similar symptoms, but diagnosis on USS or CT showing hydronephrosis and absence of calculi
• Baby colic
  • Reassuring imaging and urinalysis

Investigations (6, 7, 9)

Lab tests

• Urinalysis – can give a clue to the cause e.g. UTI, renal tubular acidosis.
• Consider sending urine for culture and sensitivity.
• Stone analysis –  if the stone is collected (either passing spontaneously or with interventional stone retrieval), stone analysis is recommended to understand the aetiology.
• Metabolic review – only after nephrolithiasis has been diagnosed and when recommended by specialist.

Imaging

• 1^st line: urgent (within 24h of presentation) ultrasound scan.
• If diagnosis still uncertain, consider low-dose non-contrast CT scan of kidneys, ureters and bladder.
  • The CT is more likely to pick up stones smaller than 3mm, but due to radiation, USS remains the first line.

Management

Initial management (6, 7)

• Symptom relief
  • NSAIDs (any route) is 1^st line for pain management (even if suspected and not confirmed renal colic)- NICE
  • IV paracetamol if NSAIDs contraindicated or adjunct
  • 3^rd option: consider opioids
• Consider watchful waiting if the renal stones are asymptomatic and either < 5mm, or > 5mm and the patient / their carers have made an informed decision about watchful waiting for the stone to be passed.
  • In this case, strain the urine to try and capture the stone for analysis.
• Consider referral to paediatric nephrologist or urologist for expert advice on assessment and metabolic investigations.

Definitive and long-term management (7)

Stone removal:

• If renal stone < 10 mm, consider the following treatments:
  • Ureteroscopy OR shockwave lithotripsy
  • If they fail, consider percutaneous nephrolithotomy
• If renal stone 10-20mm, consider the following treatments:
  • Ureteroscopy, shockwave lithotripsy OR percutaneous nephrolithotomy
• If renal stone > 20mm, including staghorn type
  • Ureteroscopy, shockwave lithotripsy OR percutaneous nephrolithotomy
  • NB: if shockwave lithotripsy is chosen, consider pre-treatment stenting
• If ureteric stone < 10mm, consider the following treatments:
  • Medical: alpha blockers
  • Ureteroscopy or shockwave lithotripsy
• If ureteric stone 10-20mm, consider the following treatments:
  • Ureteroscopy or shockwave lithotripsy

Preventing recurrence:

• Lifestyle advice
  • Discuss diet and fluid intake with the patient and their carers, as appropriate
  • Drink 1-2 litres of water a day
  • Add fresh lemon juice to drinking water
  • Avoid carbonated drinks
  • Depending on their size and age, recommend daily salt intake of no more than 2-6g
  • Do not restrict calcium intake but ensure normal intake of 350-1000mg per day (depends on age)
• Specific management of the cause of the kidney stones
  • Consider potassium citrate if stones are recurrent and are predominantly of the calcium oxalate type, with hypercalciuria or hypocitraturia
  • Surgical correction of anatomical abnormality
  • Specific treatment of metabolic abnormality (e.g. supplements)

Complications (1)

Complications are not common.

Nephrolithiasis complications include urinary obstruction, ureteric stricture.

Complications arising from interventions (shockwave lithotripsy, ureteroscopy, percutaneous nephrolithotomy) include: bleeding, bruising, infection/sepsis, obstruction needing a nephrostomy, injury to other organs, pneumothorax

Prognosis

Prognosis depends on the aetiology behind stone formation. If there is no anatomical or metabolic cause (e.g. infection), renal calculi are unlikely to reoccur during childhood. Children with metabolic abnormalities and/or anatomical abnormalities which have not been surgically corrected will be more likely to have other episodes.

References