Nephrolithiasis

 

• Pathophysiology

  • Stones can form anywhere in the urinary tract, but common sites are: vesicoureteric junction (60%), ureteropelvic junction in kidney, and sacroiliac joint (where ureter crosses iliac vessels).
  • 80% are calcium stones, which also contain oxalate (commonest), phosphate, or both. Other stone types include struvite (magnesium ammonium phosphate) – forming staghorn stones – and urate.

• Signs and symptoms

  Renal colic:

  • Sudden onset of severe, intermittent pain, due to peristalsis against the obstruction.
  • Ureteric stone pain radiates from loin to groin. Midureteric stones can mimic appendicitis or diverticulitis.
  • Patient writhing, trying to get comfortable, unlike peritonitis where they are still.
  • Generally unwell: sweaty, nausea and vomiting.

• Risk factors

  • Dehydration
  • Hypercalciuria (and hence hypercalcaemia).
  • Family history.
  • Kidney disease: renal tubular acidosis, medullary sponge kidney, polycystic kidney disease.
  • Gout (urate stones).
  • Proteus infection (struvite stones).
  • Drugs: furosemide, steroids, acetazolamide, theophylline. Thiazides reduce the risk via tubular reabsorption of calcium.

• Investigations

  Diagnosis:

  • Urine dip: 90% will have haematuria. Confirm on microscopy.
  • CT KUB (non-contrast) is the definitive test. Will identify stones as well as other causes of renal colic – e.g. transitional cell carcinoma, retroperitoneal lymph nodes – and other differentials such as appendicitis. Shows 99% of stones vs. 60% on an XR KUB.
  • XR KUB can be used to monitor passage of a stone.

  Other tests:

  • FBC and CRP to look for infection.
  • U&E
  • Check Ca2+, PO43-, and urate if recurrent.

• Management

  Initial management:

  • Analgesia: NSAIDs are 1st line, commonly diclofenac IM or PR.
  • Antiemetics and fluids may also be needed.
  • If pain resolves and no obstruction, patients can be discharged with outpatient follow up if needed.
  • If pain continues or there is obstruction: ureteric stent via cystoscopy, done under general anaesthesia. Temporizing measure until definitive stone removal.
  • If there is sepsis: antibiotics IV and urgent nephrostomy.

  Most stones are <5 mm and pass spontaneously:

  • Encourage good fluid intake.
  • Offer regular analgesia e.g. paracetamol or codeine.
  • Try and urinate into container to catch stone.
  • Usually takes 1-3 weeks to pass. Review if not passed after 3 weeks.

  Stones >1 cm usually require removal:

  • Extracorporeal shock wave lithotripsy (ESWL) is the commonest method. Uses electromagnetic energy to destroy the stone, targeted using XR and US, with the fragments then passed in the urine.
  • In rarer cases, ureteroscopy is used and the stone broken up with a laser, or percutaneous removal is used for large stones (>2 cm) in the renal pelvis.

  Stones 5-10 mm are intermediate:

  • 50% pass spontaneously, though this is rare if ≥7 mm.
  • Passage of distal ureteric stones can be aided by α-blockers, calcium channel blockers, or (for men) regular sexual intercourse (3-4 times/week).

• Complications

  • Obstructive nephropathy.
  • Infection
  • Renal failure if presentation delayed.