A patient undergoes extensive resection of 100 cm of terminal ileum with the ileocecal valve for Crohn's disease. Two years later she has chronic diarrhea and a renal stone composed of calcium oxalate. Which mechanism explains the stone formation?
- A Increased colonic absorption of dietary oxalate because calcium binds fatty acids instead ✓
- B Hyperuricosuria from increased cell turnover
- C Reduced urinary citrate from chronic acidosis
- D Direct secretion of oxalate by the inflamed ileum
Correct answer: A. Increased colonic absorption of dietary oxalate because calcium binds fatty acids instead
Explanation
After terminal ileal resection, impaired bile salt reabsorption causes bile salt loss into the colon, where they irritate the mucosa and cause chloride-rich watery diarrhea. Malabsorbed fatty acids bind intraluminal calcium, leaving oxalate free to be absorbed in the colon, producing hyperoxaluria and calcium oxalate stones. Uricosuria and hypocitraturia are mechanisms for other stone types and are not the dominant process here.
Reference: Schwartz's Principles of Surgery, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.