Renal Calculi (Kidney Stones)

Precipitates that form from urine due to a high concentration of that particular precipitate in the urine

Aetiology

  • 3:1 male
  • Peak age 20-50

Types of stone

There are 4 types of stone:
  • Calcium oxalate and phosphate - most common (80%)
    • Most patients have idiopathic hypercalciuria but some have hyperparathyroidism and various other underlying metabolic conditions
    • Oxalate is found in brassica and rhubarb and vegetarians can be slightly higher risk
  • Magnesium ammonium phosphate (triple stones or struvite)
    • Usually form irregular staghorn calculi that form casts in the collecting system
    • Often occur after infection - proteus and some staphylococci
  • Uric acid
    • Most are idiopathic but can occur in gout and patients who’ve had aggressive chemo for leukaemia etc.
  • Cystine
    • Uncommon and often a result of genetic defects in reabsorption of amino acids leading to cystinuria and stones forming at low pH

Pathophysiology

  • Stones tend to form in the kidney itself or in the renal pelvis
  • The problems occur when the stone passes down from the renal pelvis into the ureter, and get stuck
  • Smaller stones (usually those <5mm) will pass freely down into the bladder, and then leave the body in the urine, but larger stones (>5mm) can become stuck in the ureter
  • Common sites of obstruction are the:
    • Uretopelvic junction
    • Vesicoureteric junction (VUJ)

Clinical presentation

  • Pain - a classical colicky 'loin to groin' pain
    • Patients often describe it as the worst pain they have ever felt
    • Colicky pain is due to the peristaltic contraction of the ureters
  • Nausea and vomiting
  • Haematuria
  • Sepsis

Investigations

  • Urinalysis - non-visible haematuria
  • AXR - around 85% of stones will be visible
    • Uric acid and cystine stones are radiolucent so won't be visible
  • CT KUB is the initial investigation of choice for diagnosing kidney stones
  • Ultrasound KUB is less effective at identifying kidney stones but is helpful in pregnant women and children

Management

  • Watchful waiting is usually used in stones less than 5mm, as there is a 50-80% chance they will pass without any interventions; may also be suitable for patients with stones 5-10mm, depending on individual factors
    • Patients will need analgesia - NSAIDs e.g. IM diclofenac are preferred, IV paracetamol is an alternative, where NSAIDs are not suitable
    • Antiemetics are used for nausea and vomiting (e.g., metoclopramide, prochlorperazine or cyclizine)
    • Antibiotics are required if infection is present
  • Surgical interventions are required in large stones (10mm or larger), stones that do not pass spontaneously or where there is complete obstruction or infection
  • Indications for emergency kidney de-obstruction: AKI, sepsis, refractory pain

Methods for stone removal

  • Medical expulsive therapy e.g. tamsulosin
  • Extracorporeal shock wave lithotripsy (ESWL)
  • Ureteroscopy and laser lithotripsy
  • Percutaneous nephrolithotomy (PCNL)