Enterolith

In equines

Equine enteroliths are found by walking pastures or turning over manure compost piles to find small enteroliths, during necroscopy, and increasingly, during surgery for colic. Therefore, the incidence of asymptomatic enteroliths is unknown.

Equine enteroliths are typically smoothly spherical or tetrahedral, consist mostly of the mineral struvite (ammonium magnesium phosphate), and have concentric rings of mineral precipitated around a nidus.

Enteroliths in horses were reported widely in the 19th century, infrequently in the early 20th century, and now increasingly. They have also been reported in zebras: five in a zoo in California and one in a zoo in Wisconsin. Struvite enteroliths are associated with elevated pH and mineral concentrations in the lumen. In California, struvite enteroliths are associated also with a high proportion of alfalfa in the feed and less access to grass pasture. This association has been attributed to the cultivation of alfalfa on serpentine soils, resulting in high concentrations of magnesium in the alfalfa.

In humans

In humans, enteroliths are rare and may be difficult to distinguish from gall stones. Their chemical composition is diverse, and rarely can a nidus be found. A differential diagnosis of an enterolith requires the enterolith, a normal gallbladder, and a diverticulum.

An enterolith typically forms within a diverticulum. An enterolith formed in a Meckel's diverticulum sometimes is known as a Meckel's enterolith. Improper use of magnesium oxide as a long-term laxative has been reported to cause enteroliths and/or medication bezoars.

Most enteroliths are not apparent and cause no complications. However, any complications that do occur are likely to be severe. Of these, bowel obstruction is most common, followed by ileus and perforation. Bowel obstruction and ileus typically occur when a large enterolith is expelled from a diverticulum into the lumen. Perforation typically occurs within the diverticulum.

On plain X-rays, the visibility of the enterolith depends on its calcium content. Calcium-rich stones usually demonstrate a radiodense rim and a relatively radioluscent core. Choleic acid stones are almost always radiolucent. They sometimes can be visualized on CT scans without contrast; presence of contrast in the lumen may reveal the enterolith as a void. Most often, they are visualized using ultrasound.

Although recent surveys of enterolith composition are lacking, one early review notes struvite (as in equines), calcium phosphate, and calcium carbonate and reports choleic acid. Deoxycholic acid and cholic acid have also been reported.

Treatment

In simple cases of obstruction, where there are no complications, a variety of non-surgical and surgical techniques are used to remove the enterolith. These include crushing the enterolith and milking it back to the stomach or forward to the colon, surgical removal via an uninvolved segment of the gastrointestinal tract, and resection of the involved segment.

References

References

1. Blue MG. (April 1979). "Enteroliths in horses--a retrospective study of 30 cases". Equine Veterinary Journal.
2. (July 1981). "Clinical and structural features of equine enteroliths". Journal of the American Veterinary Medical Association.
3. (April 1987). "Enteroliths in horses". The Cornell Veterinarian.
4. (February 1994). "Enterolithiasis in two zebras". Journal of the American Veterinary Medical Association.
5. (July 1975). "Enterolithiasis in a confined Hartman's mountain zebra". Journal of Wildlife Diseases.
6. (2004). "Dietary risk factors and colonic pH and mineral concentrations in horses with enterolithiasis". Journal of Veterinary Internal Medicine.
7. (December 1992). "Enterolith ileus: a rare complication of duodenal diverticula". The American Journal of Gastroenterology.
8. (August 1993). "Enterolith ileus as a complication of duodenal diverticulosis--one case report and review of the literature". Gaoxiong Yi Xue Ke Xue Za Zhi.
9. (1996). "Small bowel obstruction caused by a medication bezoar: report of a case". Surgery Today.
10. (2003). "Bowel obstruction caused by a Meckel's diverticulum enterolith: a case report and review of the literature". Current Surgery.
11. (2003). "Enterolith ileus as a complication of jejunal diverticulosis: two case reports and a review of the literature". Digestive Surgery.
12. Raper HS. (1921). "A Human Enterolith containing Choleic Acid". The Biochemical Journal.
13. (August 1965). "Chemical analysis of an enterolith". Gut.