What is a staghorn calculus?

Staghorn Calculus: Definition, Composition, and Management

A staghorn calculus is a branched kidney stone that occupies a large portion of the collecting system, typically filling the renal pelvis and extending into several or all of the calices, which if left untreated can destroy the kidney and cause life-threatening sepsis. 1

Definition and Classification

• Terminology:

  • "Partial staghorn" refers to a branched stone occupying part but not all of the collecting system
  • "Complete staghorn" refers to a stone occupying virtually the entire collecting system 1
  • No consensus exists regarding the precise definition, such as the number of involved calices required to qualify as a staghorn calculus 1

• Appearance:

  • Branched configuration resembling a deer's antlers
  • Conforms to the shape of the renal collecting system
  • Visible on imaging as a branching calcification within the kidney 1

Composition and Etiology

• Primary composition (most frequent):

  • Magnesium ammonium phosphate (struvite)
  • Calcium carbonate apatite 1
  • These are commonly referred to as "infection stones" due to their association with urinary tract infections 1

• Less common compositions:

  • Cystine stones
  • Uric acid stones
  • Rarely calcium oxalate or calcium phosphate stones 1, 2

• Formation mechanism:

  • Strongly associated with urinary tract infections caused by urease-producing organisms (e.g., Proteus, Klebsiella) 1, 3
  • Urease enzyme converts urea to ammonia and hydroxide, creating an alkaline environment 1
  • High ammonia concentration with abundant phosphate and magnesium promotes struvite crystallization 1
  • Exopolysaccharide biofilm formation and incorporation of mucoproteins contribute to stone growth 1
  • Bacteria reside within the stone itself, making the stone infected (unlike other stone types that remain sterile inside) 1

Clinical Significance and Complications

• Untreated staghorn calculi can lead to:

  • Kidney destruction
  • Life-threatening sepsis 1
  • Renal cirrhosis 4
  • Pyonephrosis (pus-filled kidney) 5

• Radiological signs of complications:

  • Fragmented staghorn calculus may indicate pyonephrosis requiring urgent surgical attention 5

Management Principles

• Treatment goal: Complete stone removal is essential to:

  • Eradicate causative organisms
  • Relieve obstruction
  • Prevent further stone growth
  • Preserve kidney function 1, 6

• First-line treatment: Percutaneous nephrolithotomy (PNL) is the recommended first-line treatment 1, 6, 7

• Treatment options:

  1. PNL monotherapy
  2. Combination of PNL and shock wave lithotripsy (SWL)
  3. SWL monotherapy
  4. Open surgery (typically anatrophic nephrolithotomy) 1

• Multitract approach: For complex staghorn calculi, multiple percutaneous access tracts may be required to achieve complete stone clearance 6

• Conservative management: Associated with 28% mortality over 10 years and 36% risk of significant renal impairment 7

Important Considerations

• Perioperative antibiotics: Essential to prevent bacteremia and sepsis when crushing infection stones, as bacteria can be released from the stone during fragmentation 2

• Stone composition affects treatment approach:

  • Struvite stones: Fragile due to wide crystal interstices and rich organic matrix
  • Whewellite and uric acid stones: Hard with compact structure, refractory to crushing
  • Cystine stones: Very hard, may benefit from combination of crushing and alkali solution irrigation 2

• Recurrence prevention:

  • Complete stone removal is crucial to prevent recurrent urinary tract infections
  • Residual fragments may grow and serve as a source for recurrent infection 1