Kidney Stones

Pathophysiology

• Calcium oxalate +/- calcium phosphate: ~75%
• Struvite (triple phosphate): 15% → mostly in the setting of infection with urease producing bacteria (e.g. Proteus, Klebsiella, Pseudomonas and Enterobacter)
• Pure calcium phosphate: 5-7%
• Uric acid: 5-8%
• Cystine: 1%
• Lithogenic medications: 1%

Presentation

• Most patients present between 30-60 years of age
• Risk factors
  • Low fluid intake
  • Urinary tract malformations (horseshoe kidney, duplex collecting system)
  • Urinary tract infections (especially urease producing bacteria)
  • Cystinuria
  • Hypercalciuria (high sodium intake, primary hyperparathyroidism, hypervitaminosis D, Cushing syndrome, Sarcoidosis, Milk-alkali syndrom)
  • Hyperuricosuria (Gout)

Clinical Features

• Haematuria may be absent in approximately 15% of patients
• Strangury is also present occasionally
• Some patients may have complications of obstructive pyelonephritis and therefore may have a septic clinical presentation
• Children may describe vague abdominal pain

Radiographic Features

Management

• Approximately 90% of stones <4 mm are likely to pass down the ureter and into the bladder, and thus often require no more than analgesia and hydration
• Indications for surgical management include:
  • Larger stones, typically those above 5 mm in size
  • Extended duration of symptoms
  • Location of the stone, with proximal calculi less likely to spontaneously pass
  • Infection or septic features
  • Certain professions (airline pilot, truck driver) due to the risk of renal colic during work
  • Solitary kidney
  • Failed conservative management
• Surgical
  • Typically retrograde ureteric stent with subsequent laser lithotripsy
  • If acutely septic and not fir for anaesthetic percutaneous nephrostomy with an antegrade stent followed by laser lithotripsy is preferred
  • Extracorporeal shock wave lithoripsy is preferred for large proximal calculi in patients unsuitable for invasive management
  • Percutaneous nephrolithotomy for large calculi near the pelviureteric junction (especially staghorn calculi)

Sources

• Urolithiasis | Radiology Reference Article | Radiopaedia.org last revised 25 June 2025. Accessed 24 December 2025