A 40-year-old woman with recurrent urinary tract infections has a plain radiograph showing a large branching calculus filling the renal pelvis and extending into all the major calyces. Which organism is classically responsible for this stone, and what is the preferred treatment?

• A E. coli, extracorporeal shock wave lithotripsy
• B Pseudomonas aeruginosa, dissolution therapy with potassium citrate
• C Klebsiella pneumoniae, open nephrolithotomy
• D Proteus mirabilis producing urease, percutaneous nephrolithotomy ✓

Explanation

Staghorn calculi are typically struvite (magnesium ammonium phosphate) stones caused by urease-producing organisms, most classically Proteus mirabilis; urease splits urea, alkalinising urine and precipitating struvite. Untreated, they destroy the kidney and cause sepsis. Percutaneous nephrolithotomy is the preferred first-line treatment because shock wave lithotripsy alone leaves fragments that perpetuate infection. Dissolution therapy is ineffective for established struvite stones.

Reference: Campbell-Walsh Urology, 12th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.