Is a 0.7 cm non-obstructing stone in the right renal lower caliceal region with a density of 700 Hounsfield Units (HU) and no hydronephrosis indicated for Extracorporeal Shock Wave Lithotripsy (ESWL)?

Management of a 0.7 cm Non-Obstructing Lower Caliceal Renal Stone

Extracorporeal Shock Wave Lithotripsy (ESWL) is not recommended as first-line therapy for this 0.7 cm lower caliceal stone with a density of 700 HU due to poor stone-free rates for lower pole stones with high density. 1, 2

Stone Characteristics and Treatment Decision

The key factors influencing treatment choice for this stone include:

• Size: 0.7 cm (≤10 mm)
• Location: Lower calyx
• Density: 700 HU (high density)
• No hydronephrosis (non-obstructing)

Treatment Options Based on Guidelines

For symptomatic lower pole renal stones ≤10 mm, guidelines recommend:

• First-line options: Either ESWL or Ureteroscopy (URS) 1
• Important considerations:
  • Stone density (700 HU) significantly impacts ESWL success rates 2, 3
  • Lower pole location reduces ESWL efficacy compared to other locations 1, 2

Why URS is Preferred Over ESWL in This Case

Despite the AUA/Endourological Society guideline stating that both ESWL and URS can be offered for stones ≤10 mm in the lower pole 1, several factors make URS the preferred option for this specific case:

1. High stone density (700 HU): Stone density >700 HU predicts poor fragmentation with ESWL 2, 3
2. Lower pole location: Anatomically unfavorable for fragment clearance after ESWL 1, 2
3. Better stone-free rates: URS provides higher stone-free rates for lower pole stones compared to ESWL 1

Treatment Algorithm

1. For this 0.7 cm lower pole stone with 700 HU density:

   • Recommend URS as first-line therapy
   • ESWL would likely result in incomplete fragmentation and poor clearance

2. If URS is contraindicated:

   • Consider ESWL with understanding of lower success rates
   • Patient should be informed about higher likelihood of residual fragments

3. Post-procedure considerations:

   • Follow-up imaging to confirm stone clearance
   • Metabolic evaluation to prevent recurrence

Important Caveats and Pitfalls

• Residual fragments after ESWL: Up to 59% of "clinically insignificant residual fragments" after ESWL become clinically significant over time, requiring additional interventions 4

• ESWL limitations for lower pole stones: Even for small stones, fragment clearance is anatomically hindered in lower pole location 1, 2

• Stone density impact: Mean attenuation value (HU) is a stronger predictor of ESWL success than stone size alone 3

• Patient-specific factors: While not mentioned in this case, factors such as obesity, skin-to-stone distance, and collecting system anatomy would further impact ESWL success 1

In conclusion, while both ESWL and URS are technically appropriate for a 0.7 cm stone, the combination of lower pole location and high stone density (700 HU) makes URS the preferred first-line treatment to achieve optimal stone clearance.