Case reveal » Veterinary Diagnostic Imaging » College of Veterinary Medicine

Radiographic findings:

In the cranial mid-abdomen, in the region of the right dorsal colon, there is a large, well-defined, ovoid, and smoothly marginated mineral opacity (arrowheads).

Ventrally distributed within the ventral colon, outlining the haustrae, there are 2 small collections of fine granular mineral opaque material.

An exploratory celiotomy was recommended and subsequently performed. Intraoperatively, a large enterolith was identified within the right dorsal colon. A pelvic flexure enterotomy was initially made to evacuate the large colon of fecal material. However, attempts to gently mobilize the enterolith toward the pelvic flexure were unsuccessful. Consequently, a second enterotomy was performed directly in the right dorsal colon to facilitate the removal of the enterolith. Further examination of the gastrointestinal tract revealed four small, lipoma-like masses located within the mesentery of the small intestine, large colon, and small colon, all of which were excised.

The patient remained comfortable throughout recovery, with no signs of diarrhea. She tolerated refeeding without any complications and was discharged into the care of her owner in stable condition.

Enterolithiasis, the formation of mineral concretions within the gastrointestinal tract, is a significant cause of colic in equids, particularly in endemic regions such as California. Predisposing factors include diets rich in alfalfa, limited pasture turnout, and breed predispositions (e.g., Arabians, Morgans, American Saddlebreds, and donkeys). Clinical signs are often mild and intermittent, making imaging crucial for diagnosis and management.

Abdominal radiography is a cornerstone in the diagnostic workup of equids with suspected enterolithiasis. The evolution of radiographic technology—from analog to computed radiography (CR) and more recently to direct digital radiography (DR)—has significantly impacted diagnostic accuracy.

In a study of 141 horses (Yarbrough et al., 1994), analog radiography demonstrated:
- Sensitivity: 76.9%
- Specificity: 94.4%
- Positive Predictive Value: 96.4%
- Negative Predictive Value: 67.5%
Detection was more successful for large colon enteroliths (83.2%) than small colon enteroliths (41.6%). Inadequate penetration was the most common cause of false negatives, highlighting the importance of proper exposure settings and technique.

Maher et al. (2011) evaluated 142 horses using CR:
- Sensitivity: 85%
- Specificity: 93%
- Sensitivity by Location:
  - Large colon: 94.5%
  - Small colon: 50%
Impact of Gas Distention: Sensitivity decreased with increased gas (mild: 95%, severe: 60%)
CR improved contrast resolution compared to analog systems, enhancing detection, especially in the large colon. However, small colon enteroliths remained challenging due to their central location and surrounding dense ingesta.

Kelleher et al. (2014) assessed 238 equids using DR:
- Sensitivity: 84%
- Specificity: 96%
- Sensitivity by Location:
  - Large colon: 88.9%
  - Small colon: 61.5%
Impact of Gas Distention: Mild distention yielded highest sensitivity (96.9%), while severe distention reduced it (72.7%)
DR offered superior image quality and better compensation for underexposure, resulting in fewer nondiagnostic images. It also showed improved sensitivity for small colon enteroliths compared to CR, likely due to enhanced image processing capabilities.

Optimal Visualization of the Right Dorsal Colon
- The right dorsal colon is anatomically located on the right side of the abdomen.
- Placing the right side against the cassette minimizes superimposition of other abdominal structures, improving contrast and visibility of enteroliths.
Increased Diagnostic Sensitivity
- In the 1994 JAVMA study, the majority of enteroliths were found in the right dorsal colon (59 out of 94 horses).
- Radiographic views taken from the right side (especially “view 2” in the study) were most effective in detecting enteroliths in this location.
Reduced Motion and Artifact
- Positioning the horse with the right side closest to the cassette stabilizes the area of interest and reduces motion artifacts, which can obscure mineral densities.

Radiographic identification of enteroliths facilitates timely surgical intervention, especially in cases with mild or ambiguous clinical signs.
Exploratory celiotomy remains the definitive treatment, with radiographic findings guiding surgical planning. In all studies, radiography proved to be a cost-effective and reliable tool in high-prevalence areas, reducing unnecessary medical management and improving outcomes.

Yarbrough, Tom B., et al. “Abdominal radiography for diagnosis of enterolithiasis in horses: 141 cases (1990-1992).” Journal of the American Veterinary Medical Association 205.4 (1994): 592-595.
Maher, Omar, et al. “Abdominal computed radiography for the diagnosis of enterolithiasis in horses: 142 cases (2003–2007).” Journal of the American Veterinary Medical Association 239.11 (2011): 1483-1485.
Dutra, Natália Lima Brasil, et al. “Contribution of abdominal radiography to the diagnosis of enterolithiasis in horses.” Semina ciênc. agrar (2024): 1317-1334.
Kelleher, Maureen E., et al. “Use of digital abdominal radiography for the diagnosis of enterolithiasis in equids: 238 cases (2008–2011).” Journal of the American Veterinary Medical Association 245.1 (2014): 126-129.
Blue, M. G. “Enteroliths in horses—a retrospective study of 30 cases.” Equine veterinary journal 11.2 (1979): 76-84.