Renal Stones

Question 1

Pathophysiology of renal stones

Answer 1

• Urine becomes supersaturated to the point where precipitation occurs
• Free particle theory – stream of urine that’s so saturated with ions that they join up and make crystals
• Fixed theory – crystals stick to something and can’t move allowing further aggregation
• Stone inhibitors include citrate, magnesium, pyrophosphate and glycoproteins

Question 2

Types of renal stones

Answer 2

• Calcium oxalate forms 80% of stones
• Calcium phosphate
• Uric acid (not visible on xray)
• Struvite (magnesium ammonium phosphate)

Question 3

Staghorn calculi

Answer 3

• Renal calculus that forms the shape of a staghorn
• The body sits in the renal pelvis with horns extending into renal calyxes
• Usually composed of struvite
• In recurrent upper urinary tract infections, the bacteria can hydrolyse the urea in urine to ammonia, creating the solid struvite
• Can be seen on plan xray films

Question 4

Presentation of renal stones

Answer 4

• May be asymptomatic and never cause an issue
• Renal colic
• Excruciating loin to groin pain
• Colicky (fluctuating in severity) as the stone moves and settles
• May have haematuria, nausea, vomiting and oliguria
• May have symptoms of sepsis if infection present (i.e. fever)

Question 5

Diagnosis and management of renal stones

Answer 5

• Diagnosis
  
  • Urine dipstick (haematuria in stones but also exclude infection)
  • Bloods for infection and kidney function
  • CT KUB is gold standard for identifying stones
• Management
  
  • NSAIDs are usually the most effective type of analgesia (i.e. PR diclofenac)
  • Antiemetic if nausea and vomiting
  • Fluids
  • Antibiotics if infection is present
  • Stones less than 6mm have greater than 50% chance of passing without intervention - can take several weeks
  • Tamsulosin (an alpha-blocker) can be used to help aid spontaneous passage of stones
  • Surgical Interventions in large stones or stones that do not pass

Question 6

Surgical interventions for renal stones

Answer 6

• Extracorporeal Shock Wave Lithotripsy
  
  • An external machine generates shock waves and directs them at the stone under xray guidance.
  • Breaks the stone to smaller parts to make them easier to pass.
• Ureteroscopy and Laser Lithotripsy
  
  • Camera inserted via urethra, bladder and ureter
  • Stone identified
  • The stone is broken up by targeted lasers
  • The smaller parts are easier to pass
• Percutaneous Nephrolithotomy
  
  • Performed in theatres under anaesthetic
  • A nephroscope (small camera on a stick) is inserted via a small incision at the patient’s back
  • The scope is inserted through the kidney to assess the ureter
  • Stones can either be removed or broken up to small stones
• Open surgery

Question 7

Management of recurrent renal stones

Answer 7

• One episode of renal stones predisposes patients to further episodes and so advise to:
  
  • Increase oral fluids
  • Reduce dietary salt intake
  • Reduce intake of oxalate-rich foods for calcium stones (i.e. spinach, nuts, rhubarb, tea)
  • Reduce intake of urate- rich foods for uric acid stones (i.e. kidney, liver, sardines)
  • Limit dietary protein