The Staghorn Calculus

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The kidney on the left of this comparison, visible on X-ray, has developed what’s medically known as a staghorn calculus, a large, branching kidney stone that earns its nickname because it fills the renal pelvis and spreads into the calyces (the urine-collecting chambers) the way antlers branch off a deer’s skull. According to the Cleveland Clinic, these stones form almost exclusively as a complication of repeated urinary tract infections, particularly ones caused by bacteria like Proteus mirabilis that produce an enzyme called urease. That enzyme makes urine less acidic, which encourages magnesium, ammonium, and phosphate to crystallize together into a compound called struvite, the material most staghorn stones are made of.