What type of stones are associated with Proteus infection and urease production, and what is their typical appearance?

• A. Struvite stones (magnesium ammonium phosphate); often form staghorn calculi.
• B. Calcium oxalate stones; smooth, radiopaque.
• C. Cystine stones; hexagonal crystals.
• D. Uric acid stones; rhomboid crystals.

Answer: (A)

Proteus infection with urease production causes urine to become alkaline, because urease splits urea into ammonia. In this alkaline environment, magnesium, ammonium, and phosphate precipitate to form magnesium ammonium phosphate, known as struvite stones. These stones can grow quickly and often become large, branching structures that fill the renal pelvis and calyces, producing a staghorn appearance on imaging. On X-ray, struvite stones are typically radiopaque. In urine, they may show coffin-lid shaped crystals under microscopic examination.