Endourology and Stone Disease
What this domain tests
This domain tests stone composition and metabolic evaluation, imaging choice, medical expulsive therapy, and the selection of shockwave lithotripsy, ureteroscopy, percutaneous nephrolithotomy, laparoscopy, and robotics.
Core rules and concepts
- Calcium oxalate stones are most common; struvite stones form with urease-producing infection; uric acid stones are radiolucent and dissolve with urinary alkalinization; cystine stones suggest cystinuria.
- Noncontrast CT is the standard acute imaging test and reports stone size, location, density, and obstruction. Ultrasound is preferred in pregnancy and children.
- Stones smaller than 5–6 mm may pass with conservative therapy; distal ureteral stones may benefit from alpha-blocker medical expulsive therapy. Infected obstruction requires urgent decompression by stent or nephrostomy, not lithotripsy.
- Shockwave lithotripsy works best for radiopaque stones under 2 cm in the kidney or proximal ureter. Ureteroscopy handles distal and impacted stones. PCNL is first-line for large renal stones, especially staghorn calculi.
- Laparoscopy and robotics are useful for complex reconstruction, large stones, or anatomic abnormalities.
Worked example
A 45-year-old woman has an 8-mm distal ureteral stone, fever 39°C, and hydronephrosis. Reasoning: fever plus obstruction means infected obstructed kidney. Resuscitate, give antibiotics, and decompress urgently with a stent or nephrostomy; definitive stone treatment follows after infection resolves.
Traps
Do not perform lithotripsy in an infected obstructed system. Do not rely on plain radiography for uric acid stones. Do not leave struvite fragments behind, because recurrence is high.