Endourology and Urolithiasis
This domain tests stone imaging, the choice between observation, shockwave lithotripsy, ureteroscopy and percutaneous surgery, and metabolic prevention. Expect questions built around stone size, location and whether the system is infected or obstructed.
Imaging and emergency rules
- Non-contrast CT of the kidneys, ureters and bladder is first line, with high sensitivity and the ability to report Hounsfield density and skin-to-stone distance, both of which predict shockwave success.
- Ultrasound is preferred in pregnancy and children; intravenous urography is largely obsolete.
- An obstructed, infected system with fever is an emergency: decompress with a nephrostomy or stent and give antibiotics, then treat the stone definitively later. Retrograde stenting through pus is inferior to nephrostomy.
Treatment by size and site (EAU framework)
- Ureteric stones under 10 mm: observation with medical expulsive therapy using an alpha-blocker, mainly for distal stones above 5 mm; intervene after 4-6 weeks of failure or persistent pain.
- Renal stones under 10 mm: shockwave or flexible ureteroscopy, with shockwave favoured when density is below 1000 HU and skin-to-stone distance under 10 cm.
- 10-20 mm: shockwave, retrograde intrarenal surgery, or percutaneous nephrolithotomy for lower-pole stones with unfavourable anatomy.
- Above 20 mm and staghorn calculi: percutaneous nephrolithotomy, standard or mini, prone or supine.
Metabolic evaluation and prevention
- Stone analysis on every stone; 24-hour urine studies for recurrent, paediatric, bilateral or high-risk patients.
- Fluid intake to achieve urine output of 2-2.5 L; normal dietary calcium of 1000-1200 mg, not restricted; low sodium; limited oxalate.
- Hypercalciuria: thiazide. Hypocitraturia: potassium citrate. Uric acid stones: alkalinisation to pH 7.0-7.2 plus allopurinol. Cystine stones: high fluid intake plus alkalinisation to pH 7.0-7.5 and penicillamine or tiopronin if needed.
- Struvite stones require complete clearance and treatment of infection; urease inhibitors are an adjunct.
Worked example
A 45-year-old has a 14 mm lower-pole stone of 900 HU, skin-to-stone distance 8 cm, no obstruction and sterile urine. At 10-20 mm the EAU options are shockwave, retrograde intrarenal surgery or percutaneous nephrolithotomy. Favourable density and distance make shockwave reasonable, with counselling that clearance may need more than one session and that lower-pole stones clear less well; percutaneous nephrolithotomy offers the highest single-procedure clearance and is offered if shockwave fails.
Traps that cost marks
Restricting dietary calcium, which increases oxalate absorption and stone risk; offering shockwave in pregnancy, coagulopathy or untreated infection; using an alpha-blocker for all stone sites; assuming a stent controls infection; forgetting stone analysis; forgetting that uric acid stones can be dissolved but cystine stones generally cannot.