Staghorn Calculi

Definition

• Complete staghorn: occupies the entire collecting system
• Partial staghorn: extends into some but not all calyces
• Campbell-Walsh-Wein Urology, p. 2754

Composition

• Campbell-Walsh-Wein Urology, p. 2758

Pathogenesis of Struvite Stones

1. Urease-splitting bacteria hydrolyze urea: CO(NH₂)₂ + H₂O → 2NH₃ + CO₂
2. NH₃ + H₂O → NH₄⁺ + OH⁻ → alkalinizes urine (pH >7.2)
3. At alkaline pH, phosphate becomes insoluble and precipitates with Mg²⁺ and NH₄⁺ → struvite (MgNH₄PO₄·6H₂O)
4. CO₂ → CO₃²⁻, which combines with Ca²⁺ and PO₄³⁻ → calcium carbonate apatite
5. Ammonia also damages the glycosaminoglycan layer of the urothelium, allowing bacteria to attach and form a biofilm - which perpetuates stone growth

• Campbell-Walsh-Wein Urology, p. 2736; Goldman-Cecil Medicine, p. 1290; Comprehensive Clinical Nephrology, p. 706

Risk Factors

• Female sex (increased susceptibility to upper UTI)
• Indwelling urinary catheters
• Neurogenic bladder
• Spinal cord injury
• Urinary tract anomalies with stasis
• Prior urologic surgery

Natural History (Why Treatment is Mandatory)

• 50% complete renal function loss in affected kidney within 2 years
• Recurrent UTIs and urosepsis
• End-stage renal disease
• Increased overall mortality (up to 28% in some series)
• Conservative management carries nephrectomy rates up to 50%

• Campbell-Walsh-Wein Urology, p. 2754; Comprehensive Clinical Nephrology, p. 2403

Surgical Management

First-Line: Percutaneous Nephrolithotomy (PCNL)

• Upper pole access is generally preferred for single-tract approach - allows access to upper pole, renal pelvis, and many lower pole stones with the rigid nephroscope; mid-calyceal stones treated with flexible nephroscopy
• Flexible nephroscopy during PCNL improves clearance and reduces the number of access tracts needed
• Multiple tracts are often required for complete calculi
• Retrograde flexible ureteroscopy (URS) can be used as an adjunct (ECIRS - endoscopic combined intrarenal surgery)

SWL (Shockwave Lithotripsy)

• Should not be used as monotherapy for staghorn stones
• High failure rate + risk of steinstrasse (stone street)
• In the only prospective RCT comparing SWL vs. PCNL for staghorn stones, PCNL provided superior stone-free rates (74% vs. 22%), shorter treatment duration, and fewer septic complications
• May be used as adjunct to PCNL (sandwich therapy) for residual inaccessible fragments

Ureteroscopy (URS)

• As sole modality for complete staghorn stones: highly unlikely to succeed and not recommended
• May be considered for simple partial staghorn stones with favorable anatomy or PCNL contraindications, but often requires multiple stages

Laparoscopic/Robotic Approaches

• Described in small series; stone-free rates relatively low (29-67%)
• No obvious advantage over PCNL in routine cases
• May help in ectopic kidneys where percutaneous access is challenging

Open Nephrolithotomy

• Now reserved for rare cases where PCNL is impossible or likely to fail within an acceptable number of procedures
• Stone-free rates up to 85%, but inferior to modern PCNL with respect to length of stay, transfusion risk, renal function loss, and recovery

Nephrectomy

• Indicated for poorly functioning or nonfunctioning kidneys
• Also appropriate when xanthogranulomatous pyelonephritis is present
• Conservative therapy without treatment leads to nephrectomy in up to 50% of patients
• Campbell-Walsh-Wein Urology, pp. 2758-2762; Comprehensive Clinical Nephrology, p. 2403-2405; Brenner & Rector's The Kidney, p. 1252

Prevention and Medical Management

• Treat underlying UTI with appropriate antibiotics
• Surveillance urine cultures
• Urease inhibitor acetohydroxamic acid (AHA) can be used adjunctively but has significant side effects (thromboembolism, neuropsychiatric effects)
• Urine acidification with vitamin C or ammonium chloride to keep pH <6.5
• Address predisposing structural/functional abnormalities (catheterizable channels, neurogenic bladder management)

Summary Box