To compare the efficacy and safety of flexible ureterorenoscopy (fURS) versus extracorporeal shock wave lithotripsy (ESWL) in managing lower calyceal renal stones ≤15 mm and <1000 HU.

Urolithiasis is a common condition with a steadily increasing global prevalence, and lower calyceal stone treatment is particularly challenging. While stones ≤15 mm and <1000 Hounsfield Units (HU) are generally treatable, lower pole anatomy limits fragment clearance after extracorporeal shock wave lithotripsy (ESWL). Published SFR for ESWL in this location range between 60-80%, which are lower compared to other calyceal sites. Predictive factors such as stone density, size, and skin-to-stone distance are applied to optimize patients selection.

Conversely, flexible ureteroscopy (fURS) with laser lithotripsy achieves more and higher quality SFRs (80-95%) by active fragmentation and retrieval of the stones, thereby bypassing the anatomic barriers. However, It is invasive, requires anesthesia and has complications such as ureteral trauma and infection, including a small but certain risk of sepsis. EAU and AUA guidelines currently recommend either ESWL or URS for stones <20 mm, but note reduced clearance of lower-pole stones by ESWL.

This creates a therapeutic dilemma: should stones ≤15 mm and <1000 HU, theoretically ideal for ESWL, nevertheless to be managed non-invasively, or should fURS be given priority because of increased reliability? We anticipate that fURS will provide a higher 3-month stone-free rate than ESWL, though ESWL may remain a suitable first-line treatment in well-selected patients owing to lower morbidity and non-invasive nature.

Inclusion Criteria:

• Adults (≥18 y)
• Lower-calyx stone
• Less than or equal15 mm
• Mean Hounsfield (HU) <1000

Exclusion Criteria:

• Pregnancy
• Uncorrected coagulopathy
• Active UTI/obstruction
• Anatomical barriers to Flexible Ureteroscopy or extracorporeal shock wave lithotripsy coupling (e.g., prohibitive SSD/BMI).
• Cardiac devices contraindicating ESWL