Urinary Stone Formation After Terminal Ileum Resection

Pathophysiology of Oxalate Stone Formation

Enteric (secondary) hyperoxaluria occurs following ileal resection due to fat malabsorption and consequent elevation of intestinal oxalate absorption, as seen in patients with Crohn's disease undergoing intestinal resection 1, 2
The presence of an intact colon is a critical factor, as oxalate remains available for colonic absorption because of concomitant fat malabsorption and its binding of calcium, leading to increased urinary oxalate excretion 1, 2
Urinary oxalate excretion directly correlates with fat excretion, as demonstrated in studies of patients undergoing intestinal resection, with longer resections leading to greater oxalate absorption and excretion 1, 2

Decreased reabsorption of conjugated bile acids in the terminal ileum leads to excess transmission to the colon, where deconjugation by bacteria occurs, enhancing oxalic acid absorption in both large and small intestine 1, 2
Calcium, which normally binds to oxalate in the intestine preventing its absorption, instead binds to fatty acids due to fat malabsorption, leaving more free oxalate available for absorption, primarily in the colon 2, 3

A diet low in fat and oxalate and high in calcium is recommended for patients with hyperoxaluria following ileal resection, as suggested by the Clinical Nutrition guidelines 1, 2
Restriction of dietary oxalate is warranted particularly in those with recurring urinary tract stones, with teas and fruits being main sources of oxalate 1
Cholestyramine can help reduce oxalate absorption by binding bile acids, though it may worsen fat malabsorption in severe cases, as reported in the Gut journal 3
Adequate hydration to achieve urine volume of at least 2.5 liters daily is critical for stone prevention, as recommended by The Journal of Urology 4

Calcium supplements, unlike dietary calcium, may actually increase the risk of stone formation and should be used cautiously, as noted in The Journal of Urology 4
Pediatric patients typically have lower urinary oxalate excretion than adults, likely due to shorter disease history and fewer bowel resections, as observed in Clinical Nutrition studies 1