Is a 7x6 mm right renal middle calyceal stone with an average density of 778 Hounsfield Units (HU) indicated for Extracorporeal Shock Wave Lithotripsy (ESWL)?

Management of a 7x6 mm Right Renal Middle Calyceal Stone with 778 HU Density

ESWL is an appropriate first-line treatment option for this 7x6 mm middle calyceal renal stone with 778 HU density, as it falls within the recommended size and location parameters for ESWL according to multiple urological guidelines.

Stone Characteristics and Treatment Selection

Size and Location Considerations

• The stone is 7x6 mm in size, located in the middle calyx of the right kidney
• According to guidelines, stones located in the renal pelvis or upper/middle calyces less than 20 mm are appropriate candidates for ESWL 1
• For middle calyceal stones less than 10 mm, ESWL is considered a first-line treatment option alongside flexible ureteroscopy (fURS) 1

Stone Density Considerations

• The stone has an average density of 778 Hounsfield Units (HU)
• While higher stone density (>750 HU) can affect fragmentation success, it is not an absolute contraindication to ESWL 2
• Research shows that stones with lower mean HU values tend to fragment more successfully with ESWL, but satisfactory outcomes can still be achieved with higher density stones 2, 3

Expected Outcomes and Success Rates

• For middle calyceal stones, ESWL has favorable outcomes compared to lower calyceal stones 3
• Success rates for ESWL in middle calyceal stones of this size range from 69-93% 4
• Multiple ESWL sessions may be required for complete stone clearance:
  • 21.3% of patients with high-density stones show clearance after two ESWL sessions
  • 27% after three sessions
  • 51.6% may require four sessions 2

Treatment Algorithm

1. First-line treatment options:

   • ESWL is appropriate for this stone size and location
   • Flexible ureteroscopy (fURS) with laser lithotripsy is an equally valid alternative

2. If choosing ESWL:

   • Pre-stenting is generally not recommended before ESWL 1
   • Consider prescribing alpha-blockers after ESWL to facilitate passage of stone fragments 1
   • Plan for possible multiple sessions (2-3) for complete stone clearance

3. If initial ESWL fails:

   • AUA/ES guidelines recommend switching to an endoscopic approach (ureteroscopy) 1

Important Considerations and Caveats

• Stone heterogeneity matters: The variation coefficient of stone density (VCSD) can be a predictor of ESWL success - more heterogeneous stones (higher VCSD) may fragment better 5
• Patient factors: Body mass index (BMI), skin-to-stone distance (SSD), and renal cortical thickness (RCT) can affect ESWL success rates 5
• Follow-up is essential: Imaging should be performed after treatment to assess stone clearance
• Complications: While generally safe, potential complications include hematuria, pain, fever, and rarely subcapsular hematoma 6

In summary, ESWL is an appropriate treatment option for this 7x6 mm middle calyceal stone with 778 HU density. While the stone density is relatively high, which may reduce fragmentation efficiency, the favorable location in the middle calyx and the modest size make ESWL a reasonable first-line approach. The patient should be counseled that multiple sessions might be required for complete stone clearance.