Findings: This intravenous pyelogram demonstrates a large staghorn calculus filling the entire collecting system in the atrophic right kidney. No contrast was seen filling the right ureter. The left kidney is enlarged and demonstrates a duplicated collecting system. There is no evidence of hydronephrosis.
Diagnosis: Staghorn calculus in the atrophic right kidney and compensatory hypertrophy of the left kidney.
Discussion: The staghorn calculus is formed by a rapidly growing stone which tend to fill the pelvocalyceal system. These stones are composed of magnesium ammonium phosphate (struvite) which represents a common sequela of urinary tract infections. The radiographic density is determined by the amount of calcium that is incorporated in the magnesium ammonium phosphate.
Proteus mirabilis is the most common organism associated with urolithiasis, but organisms such as pseudomonas aeruginosa, Klebsiella species, Escherichia coli, and staphylococcus aureus are also known to promote stone formation. These bacteria produce urease, which catalyzes the formation of ammonia from urea as a result of hydrolysis of ammonia, rendering the infected urine alkaline, which promotes crystallization of hydroxyapatite, commonly incorporated in the struvite stone.
References:
Davidson AJ, Hartman DS. Radiology of the Kidney and Urinary Tract, 2nd Edition.
W. B. Saunders Co., Philadelphia; YEAR :438-446.
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