What is the treatment for an interpolar kidney stone?

Treatment of Interpolar Kidney Stones

For symptomatic patients with interpolar kidney stones ≤20 mm, shock wave lithotripsy (SWL) or ureteroscopy (URS) should be offered as first-line treatment options, with URS providing a higher stone-free rate in a single procedure. 1

Treatment Algorithm Based on Stone Size

Stones ≤10 mm

• First-line options:
  • SWL or URS (strong recommendation) 1
  • Both have acceptable stone-free rates with lower morbidity than PCNL
  • URS has a higher single-procedure stone-free rate (90% vs 72% for SWL) 2

Stones 10-20 mm

• First-line options:
  • URS is preferred over SWL 1
  • SWL has reduced stone-free rates for interpolar stones in this size range
  • URS is associated with a lower likelihood of requiring repeat procedures 1

Stones >20 mm

• First-line option:
  • PCNL (strong recommendation) 1
  • SWL should not be offered as first-line therapy (moderate recommendation) 1
  • PCNL offers higher stone-free rates (94% vs 75% for URS) 1

Procedural Considerations

For SWL

• Best practices:
  • Decreasing frequency (from 120 to 60-90/min) improves stone-free rates 1
  • Proper acoustic coupling between treatment head and skin is crucial 1
  • Stepwise energy ramping minimizes renal injury 1
  • Normal saline irrigation must be used 1

For URS

• Best practices:
  • Complete stone removal should be the goal 1
  • Ho:YAG laser is the gold standard for lithotripsy 1
  • Normal saline irrigation must be used (strong recommendation) 1
  • Routine post-URS stenting is unnecessary after uncomplicated procedures 1

For PCNL

• Best practices:
  • Flexible nephroscopy should be a routine part of standard PCNL (strong recommendation) 1
  • In uncomplicated cases presumed stone-free, nephrostomy tube placement is optional 1
  • Normal saline irrigation must be used (strong recommendation) 1

Special Considerations

Contraindications

• SWL contraindications: 1

  • Pregnancy
  • Bleeding disorders
  • Uncontrolled UTI
  • Severe obesity
  • Arterial aneurysm near the stone
  • Anatomic obstructions distal to the stone

• PCNL contraindications: 1

  • Use of anti-coagulation or anti-platelet therapy that cannot be discontinued
  • Presence of contractures, flexion deformities, or other anatomic derangements

Infected Stones

• When infection is suspected with ureteral obstruction, the collecting system must be urgently drained with a stent or nephrostomy tube before stone treatment 1

Imaging Considerations

• CT is the gold standard for detecting kidney stones with approximately 97% sensitivity 2
• Motion artifact in CT images can cause warping distortion that makes stones appear larger than they actually are 3
• Correlation with KUB radiograph and ultrasound is critical for optimal surgical planning 3

Follow-up

• Follow-up imaging (KUB X-ray or ultrasound) within 1-2 weeks of treatment to assess stone position 2
• Increase fluid intake to more than 2L/day to help prevent recurrence 2
• Consider metabolic evaluation to prevent recurrence 2

The choice between SWL, URS, and PCNL for interpolar kidney stones should be based primarily on stone size, with consideration of patient factors and stone characteristics. URS generally offers higher stone-free rates with acceptable morbidity for most interpolar stones, while PCNL is reserved for larger stone burdens.