Modality choice — SWL, ureteroscopy, or PCNL — is driven by stone burden, location, composition, and patient factors. Non-contrast CT is obtained before intervention: it defines burden, density, and anatomy and (unlike ultrasound) guides the choice between SWL and URS. For operative detail see the procedure pages: Shock Wave Lithotripsy, Ureteroscopy and Laser Lithotripsy, and Percutaneous Nephrolithotomy.
Pre-Treatment Investigations
- Mandatory: urinalysis ± culture — treat infection first, and obtain intra-operative cultures from urine proximal to the stone if infection is suspected (voided cultures may be discordant).
- Selective: serum electrolytes/creatinine (suspected renal impairment), CBC (PCNL or suspected anaemia/infection), and coagulation studies (only with a clinical indication).
- Imaging: non-contrast CT before PCNL and to select SWL vs URS; ultrasound should not be used to choose (no density, inaccurate sizing). Functional imaging (DTPA/MAG-3) if loss of split function is suspected; contrast studies for complex anatomy.
Worse SWL outcomes are predicted by stone attenuation >900–1000 HU and a skin-to-stone distance >10 cm.
General Principles
Weigh symptoms, stone factors (burden, location, composition), and patient factors (anticoagulation, BMI, renal function, anatomy). If purulent urine is encountered endoscopically, abort, drain, and treat the infection. Send stone material for analysis (unless the composition is reliably known from prior identical stones).
Ureteric Stones
| Scenario | Recommended approach |
|---|---|
| Uncomplicated <10 mm | Observation ± medical expulsive therapy (α-blocker — recommended for distal, an option for mid/proximal) |
| Distal or mid, >10 mm or failed conservative | URS first-line (SWL second-line) |
| Proximal, >10 mm or failed conservative | URS or SWL (URS superior for <10 mm; equivalent for >10 mm) |
- The chief determinant of spontaneous passage is axial stone diameter, then location; ~50% of distal stones <10 mm pass spontaneously, and α-blockers add an absolute ~23% (77% vs 54%). MET is off-label, and SUSPEND (2015) found no benefit of tamsulosin or nifedipine (this trial was not included in the AUA meta-analysis).
- Intervene if conservative treatment fails by 4–6 weeks, or earlier for intractable pain, worsening renal function, or infection (continued obstruction beyond ~6 weeks risks permanent damage). Re-image before surgery if passage is suspected.
- SWL is the least morbid option with the lowest complication rate, but URS has the higher single-procedure stone-free rate and is the most cost-effective. URS is first-line for mid/distal stones (and preferred for women of childbearing age, given uncertain shock-wave effects on the ovary) and for suspected cystine or uric acid stones (poor SWL targeting and fragmentation).
Renal Stones
| Stone | Recommended approach |
|---|---|
| Asymptomatic, non-obstructing caliceal | Active surveillance |
| Symptomatic <20 mm, non-lower-pole | SWL or URS (preferred over PCNL) |
| Lower pole ≤10 mm | SWL or URS |
| Lower pole 10–20 mm | PCNL (first-line) or URS; not SWL |
| >20 mm (any location) | PCNL (first-line) or URS (option); not SWL |
- Active surveillance — ~50% of asymptomatic stones progress and ~10–20% need surgery by 3–4 years (lower-pole and ≥4 mm stones fail observation more often). Treat asymptomatic stones in a solitary kidney, women considering pregnancy, infection, vocational settings (pilots, military), poor healthcare access, children, or with rapid growth. The Sorensen trial (2022) showed removing small asymptomatic secondary stones cut relapse to 16% vs 63%.
- SWL success is location-dependent — renal pelvis/UPJ 80–88%, upper/middle calyces ~70%, lower pole 35–69%. Unfavourable lower-pole anatomy (infundibulum <4 mm, infundibulopelvic angle <90°, multiple infundibula) reduces clearance.
- PCNL gives the highest single-procedure stone-free rate (least affected by stone size) but the most morbidity (~15% complications, mostly Clavien I; transfusion ~7% is the commonest).
Special Scenarios
- Stone composition mainly affects SWL (URS/PCNL are largely unaffected); most resistant: cystine > brushite > calcium oxalate monohydrate > matrix. PCNL is preferred for matrix stones.
- Anticoagulation — URS can be performed safely on anticoagulant/antiplatelet therapy.
- BMI — URS and PCNL outcomes are BMI-independent; SWL success falls with obesity.
- Renal function — a unit with <15% split function should be considered for nephrectomy rather than stone-specific treatment; SWL, multiple URS, and single-tract PCNL do not impair long-term function.
- UPJ obstruction — treat stone and obstruction together: PCNL with antegrade endopyelotomy, URS with retrograde endopyelotomy, or pyeloplasty with pyelolithotomy.
- Calyceal diverticulum — PCNL (direct puncture) is first-line; URS for small (<2 cm) upper/middle or anterior diverticula (PCNL carries a bleeding risk for anterior calyces); SWL is seldom effective.
- Horseshoe / ectopic kidney — SWL if <1.5 cm with no UPJO; URS (basket the fragments out) for <2 cm; PCNL or laparoscopy for ≥2 cm. A retrorenal colon warrants preoperative CT.
- Renal transplant — SWL <1.5 cm, URS (antegrade or retrograde), or PCNL (preferred for >1.5 cm); the denervated graft presents like rejection or ATN rather than colic.
- Staghorn calculi (mostly struvite) — remove them (observation is discouraged; 50% lose renal function by 2 years untreated); PCNL is the method of choice via polar access. Open/laparoscopic surgery is reserved for anatomic abnormalities needing reconstruction, and nephrectomy for a negligibly functioning kidney (avoid in pregnancy).
Self-Test
1. What stone size threshold indicates PCNL in a renal transplant? Greater than 1.5 cm.
2. First-line treatment for a distal ureteric stone <10 mm, and for one that fails or is >10 mm? Observation ± α-blocker MET for <10 mm; ureteroscopy (first-line, SWL second-line) for failure or stones >10 mm.
3. First-line treatment for a lower-pole renal stone of 10–20 mm? PCNL (preferred) or ureteroscopy — not SWL.
4. Which stone compositions are most resistant to SWL? Cystine, brushite (calcium phosphate), and calcium oxalate monohydrate.
5. When should an asymptomatic renal stone be treated rather than observed? Solitary kidney, women considering pregnancy, infection, vocational reasons (pilots/military), poor healthcare access, children, or rapid growth.