Digital Radiographs Beat Analog for Enterolith Detection

Veterinarians have known for many years that analog radiography is an efficient means of diagnosing enteroliths in adult horses, but computed, or digital, radiography has since replaced many analog machines. Researchers at the University of California, Davis (UC Davis) recently put the newer technology to the test and found it outperformed its predecessor in the task at hand.

Enterolith stones are made up of minerals, such as magnesium ammonium phosphate salts, that build up around an object that a horse eats but does not digest, such as a small chunk of wood, pebble, wire, twine, or other foreign object. These masses can become quite large, sometimes weighing in at 10 to 15 pounds or more.

"A 1994 study of horses evaluated at (UC Davis') William R. Pritchard Veterinary Medical Teaching Hospital, analog radiography was reported to have a mean sensitivity of 76.9% and a mean specificity of 94.4% for the diagnosis of enterolithiasis," relayed Sarah le Jeune, DVM, Dipl. ACVS, study author and assistant professor of Clinical Equine Surgical Emergency and Critical Care at UC Davis.

Sensitivity is the probability that the radiograph will indicate a horse has an enterolith when in fact it does, while specificity is the probability the radiograph will indicate a horse does not have an enterolith when in fact it does not.

Le Jeune continued, "Computed radiography has become more common in veterinary diagnostic imaging in recent years and is generally assumed to improve the capabilities of radiography as a diagnostic technique. However, the effect of computed radiography systems on the diagnostic accuracy of abdominal radiography for the specific identification of enterolithasis is not known."

To test the efficacy of computed radiography in identifying enteroliths, the research team conducted a retrospective study using medical records from 142 horses presented to UC Davis for colic between January 2003 and February 2007. All horses underwent abdominal computed radiography and subsequent laparotomy or necropsy to confirm the diagnosis of enterolithasis. The number and location of enteroliths were also noted.

Upon reviewing the results of their evaluation, the team found that computed radiography outperformed analogue radiography for identifying enterolithasis. Key findings included:

  • The overall sensitivity and specificity were 85% and 93%, respectively;
  • Sensitivity was not significantly impacted by the number or enteroliths present;
  • Sensitivity was lower for identifying enteroliths in the small colon; and
  • Sensitivity decreased as the amount of gas distention present increased.

"In the present study, computed radiography provided high sensitivity and high specificity ... for the diagnosis of enterolithiasis in adult horses at our hospital," le Jeune concluded.

She cautioned that veterinarians should use care when evaluating results that are negative, as sensitivity dropped when enteroliths were located in the small colon or when gas distention was present.

The study, "Abdominal computed radiography for the diagnosis of enterolithiasis in horses: 142 cases (2003-2007)," appeared in the Dec. 2011 issue of the Journal of the American Veterinary Medical Association. The abstract can be viewed online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.