What are staghorn calculi (struvite stones)?

Arthur R. Crowley, MD

Urology

Staghorn stones are stones that involve the renal pelvis and extend into at least 2 calyces of the kidney. Approximately 75% of staghorn calculi are struvite (composed of magnesium, ammonium, phosphate crystals mixed with carbonate-apatite). These stones are associated with urinary tract infections caused by bacteria that produce urease. Urease hydrolyzes (or splits) urea into ammonium and hydroxyl ions resulting in an increase in ammonium and phosphate concentrations leading to an alkaline urine. The alkaline urine leads to precipitation of magnesium ammonium phosphate crystals mixed with varying proportions of carbonate apatite. This stone matrix is believed to protect the bacteria from antibiotics. In essence, antibiotics cannot clear the associated infection unless the stone material is completely removed.

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Kidney Stones

Referred to as "silent stones," kidney stones often do not cause any symptoms. The first indication of a kidney stone is often a sudden feeling of extreme pain as the stone blocks the flow of urine. Kidney stones are one of the most painful urologic disorders and one of the most common disorders of the urinary tract. Most kidney stones - which are hardened masses that develop from crystals that separate from the urine in the urinary tract - are passed out of the body without surgical intervention by a doctor. A less common type of kidney stone, called a struvite or infection stone, is caused by infection in the urinary tract. Doctors are not always able to diagnose the cause of a kidney stone, which is why it's important to learn how to prevent them in the fist place. A person who has had a kidney stone in the past may likely form another one.

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