Stone disease and endourology: size, site and sepsis
What the exam tests
Acute colic management, the size and site rules that determine intervention, stone composition, metabolic prevention, and complications of endourological procedures.
Core rules
- First-line analgesia is an NSAID; non-contrast CT KUB is the imaging standard. Ultrasound is preferred in pregnancy and children.
- Spontaneous passage depends mainly on size: under 5 mm most distal stones pass; 5 to 10 mm distal stones may be helped by medical expulsive therapy with an alpha blocker. Stones above 10 mm, or those failing expulsive therapy, need ureteroscopy or shockwave lithotripsy.
- Renal stones over 20 mm, staghorn calculi and lower pole stones unsuited to lithotripsy are managed with percutaneous nephrolithotomy.
- An obstructed infected system is an emergency: decompress with nephrostomy or stent and give antibiotics. A stent alone does not treat infection; drainage plus antimicrobials does.
- Composition guides prevention: calcium oxalate is commonest; struvite implies urease-producing infection such as Proteus; uric acid stones are radiolucent and dissolve with alkalinisation; cystine stones need high fluid volumes plus penicillamine or tiopronin.
Worked example
A 45-year-old has a 6 mm left distal ureteric stone, is afebrile, has pain controlled with ibuprofen and a normal creatinine. Reasoning: he falls in the observation-with-expulsive-therapy group. Add tamsulosin, counsel on return precautions and arrange review; ureteroscopy is indicated if the stone has not passed by four to six weeks, or sooner if pain or infection supervenes.
Traps
Giving expulsive therapy for a proximal stone; lithotripsy in pregnancy; assuming a stent treats pyonephrosis; treating a staghorn with repeated lithotripsy rather than PCNL; forgetting steinstrasse after lithotripsy.