Urolithiasis
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Direct answer
Urolithiasis means stones anywhere in the urinary tract; a stone entering the ureter causes sudden severe loin-to-groin colic with haematuria and a restless patient. Non-contrast CT KUB is the investigation of choice. Most small stones pass with analgesia and hydration, whereas larger, impacted or infected obstructing stones need extracorporeal shock wave lithotripsy, ureteroscopy or percutaneous nephrolithotomy.
What you must remember
- Calcium oxalate stones are the commonest; struvite (magnesium ammonium phosphate) stones form in alkaline urine with urease-producing organisms such as Proteus and grow into staghorn calculi; uric acid stones are radiolucent.
- Most urinary stones are radio-opaque on a plain KUB film, but a normal film never excludes a stone — CT is far more sensitive.
- Non-contrast CT KUB is the gold standard, defining stone size, site, hydronephrosis and alternative diagnoses without contrast risk.
- Classical presentation — colicky loin-to-groin pain radiating to the testis or labium, with nausea, vomiting and microscopic or gross haematuria; the patient rolls about and cannot lie still.
- An NSAID such as diclofenac is first-line analgesia, at least as effective as opioids; alpha-blocker medical expulsive therapy may aid selected distal stones of roughly 5-10 mm, though evidence varies.
- Stones under about 5 mm usually pass spontaneously; passage becomes progressively less likely above 6-7 mm.
- Obstruction with fever means infected obstructed hydronephrosis (pyonephrosis) — a urological emergency needing urgent decompression by ureteric stent or percutaneous nephrostomy with antibiotics; staghorn calculi are best treated by PCNL.
Common confusion
Renal colic and peritonitis are opposite in behaviour — the stone patient is restless and rolls around, while the peritonitic patient lies motionless. Radiology trips students too: uric acid (and pure matrix/xanthine) stones are radiolucent on plain films, so a "normal KUB with classic colic" still means CT. Finally, do not confuse staghorn physiology — struvite stones grow in alkaline, infected urine, unlike calcium stones, and they require complete clearance along with infection control.
Exam-focused takeaway
The most frequent stem is the next-best-step — non-contrast CT KUB for acute colic, not an intravenous pyelogram or ultrasound alone. Learn the size thresholds for spontaneous passage, the radiolucent stone list, struvite and Proteus associations, and the emergency pathway for an obstructed infected kidney. Metabolic causes such as hyperparathyroidism and cystinuria appear as one-liners.
Frequently asked questions
Which investigation is chosen for suspected ureteric colic?
Non-contrast CT KUB — the gold standard for diagnosis, sizing and treatment planning. Ultrasound is the first choice in pregnancy and young patients when radiation must be limited.
Which urinary stones are radiolucent?
Uric acid stones, along with xanthine and pure matrix stones. They are invisible on plain films but seen clearly on non-contrast CT.
What is the first-line analgesic for renal colic?
An NSAID such as diclofenac, given by intramuscular, intravenous or rectal route. Opioids are added when NSAIDs are contraindicated or inadequate.
When does a stone need urgent intervention?
When there is obstruction with fever or sepsis (pyonephrosis), renal deterioration, intractable pain or vomiting, or a solitary kidney. Urgent decompression is by stent or nephrostomy.
How are staghorn calculi treated?
Percutaneous nephrolithotomy is first line for struvite staghorn stones, aiming for complete stone-free clearance and treatment of the urinary infection.