A 42-year-old woman with recurrent urinary tract infections has a complete staghorn calculus filling the left renal pelvis and all calyces. Urine culture grows Proteus mirabilis. What is the composition of this stone and the preferred definitive treatment?

• A Calcium oxalate stone; extracorporeal shock wave lithotripsy
• B Struvite stone; percutaneous nephrolithotomy ✓
• C Uric acid stone; oral chemolysis with potassium citrate
• D Cystine stone; open nephrolithotomy

Explanation

Staghorn calculi are typically struvite, magnesium ammonium phosphate, formed in alkaline urine infected with urease-producing organisms such as Proteus. Untreated, they cause progressive renal destruction and recurrent sepsis, so active removal is indicated. Percutaneous nephrolithotomy is the standard first-line modality because it achieves the highest stone-free rates for large branched calculi; shock wave lithotripsy alone leaves fragments behind. Uric acid stones are radiolucent and chemolysable, and cystine stones are unrelated to infection.

Reference: Campbell-Walsh Urology, 12th ed.

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