Renal · Year 2 · from Renal
Case 3: Struvite Staghorn Calculus
Patient Presentation
Demographics: 62-year-old female with paraplegia
Chief Complaint: Recurrent urinary tract infections and malodorous urine
History of Present Illness: The patient has T12 paraplegia from a motor vehicle accident 15 years ago and requires intermittent catheterization. She has had multiple UTIs over the years treated with antibiotics. She now presents with persistent foul-smelling urine, low-grade fevers, and flank discomfort despite recent antibiotic course.
Past Medical History:
- T12 paraplegia (wheelchair-bound)
- Neurogenic bladder requiring intermittent catheterization
- Recurrent UTIs (>5 per year)
- No prior kidney stones
Physical Examination:
- Blood pressure: 118/74 mmHg
- Temperature: 38.2C
- General: Wheelchair-bound, mild distress
- Abdomen: Right CVA tenderness
- GU: Clean intermittent catheterization site
Workup and Results
Laboratory Studies:
- Creatinine: 1.4 mg/dL
- WBC: 14,200/mcL
- Urinalysis: Alkaline pH (8.0), numerous WBC, bacteria, ammonia odor
- Urine culture: Proteus mirabilis >100,000 CFU/mL
CT Abdomen:
- Large staghorn calculus filling right renal pelvis and extending into calyces
- Right kidney enlarged with cortical thinning
Clinical Image
CT scan demonstrating a staghorn calculus (struvite stone) filling the renal pelvis and branching into the calyces, resembling the antlers of a stag. These stones form in the setting of urease-producing bacterial infections.
Diagnosis
Infected Struvite Staghorn Calculus with Proteus UTI
Features:
- Staghorn morphology on CT
- Alkaline urine (pH 8.0)
- Urease-producing organism (Proteus mirabilis)
- Risk factors: neurogenic bladder, recurrent UTIs
Discussion
This case illustrates struvite stone formation:
- Urease Requirement: The lecture states that struvite stones form exclusively in the presence of urease-producing bacteria. Urease hydrolyzes urea to ammonia, alkalinizing the urine and promoting struvite (magnesium ammonium phosphate) crystallization.
- Common Urease Producers: The lecture notes that Proteus species are the most common cause, followed by Klebsiella, Pseudomonas, and some Staphylococcus species. Notably, E. coli does NOT produce urease.
- Staghorn Morphology: Struvite stones grow rapidly in infected urine and fill the renal collecting system, creating the characteristic "staghorn" appearance.
- Complete Removal Required: The lecture emphasizes that complete surgical stone removal is essential - antibiotics alone will not cure the infection while stone material remains as a nidus.
Treatment Plan
- Antibiotics:
- Culture-directed therapy
- Initial broad-spectrum coverage, then narrow based on sensitivities
- Surgical Removal (Essential):
- Percutaneous nephrolithotomy (PCNL)
- Complete stone removal required
- May require multiple procedures
- Post-operative Care:
- Prolonged antibiotic course (4-6 weeks)
- Repeat cultures to confirm sterilization
- Prevention:
- Optimize bladder management
- Consider acetohydroxamic acid (urease inhibitor) if recurrent
- Low threshold for UTI treatment
Teaching Points
- Struvite stones form only with urease-producing bacteria (Proteus, Klebsiella, Pseudomonas)
- E. coli does NOT produce urease and does not cause struvite stones
- Complete surgical removal is essential - antibiotics alone are insufficient
- Staghorn calculi require PCNL for definitive management
- Risk factors include neurogenic bladder, indwelling catheters, recurrent UTIs
Image Reference
For visual reference of nephrolithiasis concepts, see:
- Radiopaedia: Kidney stone disease - Overview and imaging
- Wikimedia Commons: Kidney stones - Stone types
- Radiopaedia: Staghorn calculus - CT findings
Learning Points
- CT is Gold Standard: Non-contrast CT >95% sensitive; Hounsfield units help determine composition
- Stone Passage Rates: <5 mm = >90%; 5-10 mm = ~50%; >10 mm usually requires intervention
- Uric Acid Stone Key: Acidic urine (pH <5.5) is primary risk factor; can dissolve with alkalinization
- Struvite = Infection Stones: Require urease-producing bacteria; complete removal essential
- Prevention for All: Fluid intake >2.5 L urine output daily; stone analysis guides specific interventions