CHAPTER 1: AUA GUIDELINE ON MANAGEMENT OF STAGHORN CALCULI: DIAGNOSIS AND TREATMENT RECOMMENDATIONS

Abstract

Staghorn calculi are branched stones that occupy a large portion of the collecting system. Typically, they fill the renal pelvis and branch into several or all of the calices. The term “partial staghorn” calculus designates a branched stone that occupies part but not all of the collecting system while “complete staghorn” calculus refers to a stone that occupies virtually the entire collecting system. Unfortunately, there is no consensus regarding the precise definition of staghorn calculus, such as the number of involved calices required to qualify for a staghorn designation; consequently, the term “staghorn” often is used to refer to any branched stone occupying more than one portion of the collecting system, ie renal pelvis with one or more caliceal extensions. Furthermore, the designation of “partial” or “complete” staghorn calculus does not imply any specific volume criteria. Staghorn calculi are most frequently composed of mixtures of magnesium ammonium phosphate (struvite) and/or calcium carbonate apatite. Stones composed of cystine or uric acid, either in pure form or mixed with other components, can also grow in a “staghorn” or branched configuration, but calcium oxalate or phosphate stones only rarely grow in this configuration. Struvite/calcium carbonate apatite stones also are referred to as “infection stones” because of their strong association with urinary tract infection caused by specific organisms that produce the enzyme urease that promotes the generation of ammonia and hydroxide from urea.1 The resultant alkaline urinary environment and high ammonia concentration, along with abundant phosphate and magnesium in urine, promote crystallization of magnesium ammonium phosphate (struvite), leading to formation of large, branched stones. Other factors play a role, including the formation of an exopolysaccharide biofilm and the incorporation of mucoproteins and other organic compounds into this matrix. Cultures of “infection stone” fragments obtained from both the surface and inside of the stone have demonstrated that bacteria reside within the stone thereby causing the stone itself to be infected in contrast to stones made of other substances where the stones remain sterile inside.2 Repeated urinary tract infections with urea-splitting organisms may result in stone formation, and once an “infection stone” is present, infections tend to recur. Over time, an untreated staghorn calculus is likely to destroy the kidney and/or cause life threatening sepsis.3, 4 Complete removal of the stone is an important goal in order to eradicate any causative organisms, relieve obstruction, prevent further stone growth and any associated infection, and preserve kidney function. Although some studies suggest that it may be possible to sterilize small residual struvite fragments and limit subsequent stone activity,5 the majority of studies indicate that residual fragments may grow and be a source for recurrent urinary tract infection.6, 7 Thus, the AUA Nephrolithiasis Guideline Panel believes that complete stone removal should remain a therapeutic goal, especially when a struvite/calcium carbonate/apatite stone is present. The Panel identified 4 modalities as potential alternatives, on the strength of the evidence, for treating patients with staghorn calculi: