Use of digital abdominal radiography for the diagnosis of enterolithiasis in equids: 238 cases (2008–2011)

Maureen E. Kelleher William R. Pritchard Veterinary Medical Teaching Hospital, University of California-Davis, Davis, CA 95616.

Search for other papers by Maureen E. Kelleher in
Current site
Google Scholar
PubMed
Close
 DVM
,
Sarah M. Puchalski Department of Surgical and Radiological Sciences, University of California-Davis, Davis, CA 95616.

Search for other papers by Sarah M. Puchalski in
Current site
Google Scholar
PubMed
Close
 DVM
,
Christiana Drake School of Veterinary Medicine, and the Department of Statistics, College of Letters and Sciences, University of California-Davis, Davis, CA 95616.

Search for other papers by Christiana Drake in
Current site
Google Scholar
PubMed
Close
 PhD
, and
Sarah S. le Jeune Department of Surgical and Radiological Sciences, University of California-Davis, Davis, CA 95616.

Search for other papers by Sarah S. le Jeune in
Current site
Google Scholar
PubMed
Close
 DVM

Click on author name to view affiliation information

Abstract

Objective—To evaluate the sensitivity and specificity of direct digital abdominal radiography for the diagnosis of enterolithiasis in equids and to assess the effect of the number and anatomic location of enteroliths and gas distention of the gastrointestinal tract on diagnostic sensitivity of the technique.

Design—Retrospective case series.

Sample Population—238 horses and ponies ≥ 1 year old that underwent digital abdominal radiography with subsequent exploratory celiotomy or postmortem examination.

Procedures—For each case, 3 reviewers independently evaluated radiographic views. Radiographic images were evaluated for presence or absence and location of enteroliths and the degree of gas distention. Signalment, definitive diagnosis based on exploratory celiotomy or postmortem examination findings, and number and anatomic location of enteroliths were obtained from the medical records.

Results—70 of the 238 (29.4%) equids had confirmed enterolithiasis. With regard to diagnosis of enterolithiasis via digital radiography, overall sensitivity and specificity for the 3 reviewers were 84% and 96%, respectively. Sensitivity was lower for small colon enteroliths (61.5%) than for large colon enteroliths (88.9%) and was negatively affected by gas distention of the gastrointestinal tract. Sensitivity was not affected by the number of enteroliths.

Conclusions and Clinical Relevance—Sensitivity and specificity of digital radiography for the diagnosis of large colon enterolithiasis in equids was high. Sensitivity of digital radiography for detection of small colon enteroliths was lower than that for large colon enteroliths, but was higher than that typically associated with computed radiography. In geographic regions in which enterolithiasis in equids is endemic, digital abdominal radiography could be used as a diagnostic test for equids with colic.

Abstract

Objective—To evaluate the sensitivity and specificity of direct digital abdominal radiography for the diagnosis of enterolithiasis in equids and to assess the effect of the number and anatomic location of enteroliths and gas distention of the gastrointestinal tract on diagnostic sensitivity of the technique.

Design—Retrospective case series.

Sample Population—238 horses and ponies ≥ 1 year old that underwent digital abdominal radiography with subsequent exploratory celiotomy or postmortem examination.

Procedures—For each case, 3 reviewers independently evaluated radiographic views. Radiographic images were evaluated for presence or absence and location of enteroliths and the degree of gas distention. Signalment, definitive diagnosis based on exploratory celiotomy or postmortem examination findings, and number and anatomic location of enteroliths were obtained from the medical records.

Results—70 of the 238 (29.4%) equids had confirmed enterolithiasis. With regard to diagnosis of enterolithiasis via digital radiography, overall sensitivity and specificity for the 3 reviewers were 84% and 96%, respectively. Sensitivity was lower for small colon enteroliths (61.5%) than for large colon enteroliths (88.9%) and was negatively affected by gas distention of the gastrointestinal tract. Sensitivity was not affected by the number of enteroliths.

Conclusions and Clinical Relevance—Sensitivity and specificity of digital radiography for the diagnosis of large colon enterolithiasis in equids was high. Sensitivity of digital radiography for detection of small colon enteroliths was lower than that for large colon enteroliths, but was higher than that typically associated with computed radiography. In geographic regions in which enterolithiasis in equids is endemic, digital abdominal radiography could be used as a diagnostic test for equids with colic.

Enterolithiasis in equids is endemic in areas such as California; in such areas, the presence of calculi in the intestines can be a common cause of colic in equids.1 Typical clinical signs of enterolithiasis in equids are signs of mild, intermittent abdominal pain, which are reflected in recumbency, inappetence, and lethargy. Predisposing factors for enterolith formation include feeding > 50% alfalfa in the diet with minimal pasture turnout and breed (Arabian and Arabian crosses, Morgans, American Saddlebreds, and donkeys).1,2 Development of enteroliths in the colon appears to be influenced by colonic pH and mineral content as well as presence of a nidus such as sand.3

Abdominal radiography is commonly performed in horses and ponies with colic in areas where enterolithiasis is endemic.4 Although the limitations of abdominal radiography for detection of enteroliths include insufficient penetration of radiation through the large abdomen of a horse to provide diagnostic images, radiography is currently the best diagnostic tool to enable proper surgical and therapeutic management of affected horses and ponies. A previous study5 revealed that analog radiography has a sensitivity of 76.9% and a specificity of 94.4% for the diagnosis of enterolithiasis in horses and ponies. In a more recent study6 performed at the same institution, computed radiography had a sensitivity of 85% and a specificity of 93% for diagnosis of enterolithiasis in equids.

The use of direct digital radiography is becoming increasingly common in the field of veterinary diagnostic imaging. The accuracy of digital radiography for the detection of enteroliths in horses and ponies is unknown. With all novel technologies, alterations or advances in techniques may lead to an improved capability for accurate diagnoses or a potential increase in inaccurate diagnoses. The purpose of the study reported here was to evaluate the sensitivity and specificity of digital abdominal radiography for diagnosis of enterolithiasis in horses and ponies and to determine whether the technique's sensitivity or specificity was affected by the number or location of enteroliths or gas distention in the gastrointestinal tract. We hypothesized that regarding diagnosis of enterolithiasis in equids via digital radiography, the sensitivity would be greater than and specificity would be similar to reported values for conventional analog or computed radiography.

Materials and Methods

Case selection—Medical records from horses and ponies > 1 year of age evaluated at the Veterinary Medical Teaching Hospital between April 23, 2008, and October 31, 2011, that underwent a complete study of direct digital abdominal radiography (Figure 1) with either subsequent exploratory celiotomy or necropsy were reviewed. Signalment, radiographic findings, definitive diagnosis based on exploratory celiotomy or necropsy findings, and the number and anatomic location of enteroliths were recorded.

Figure 1—
Figure 1—

Representative digital abdominal radiographic view of a horse with colic from an area where enterolithiasis in equids is endemic. Notice the enterolith located in the large colon. The scale marker at the left of the image represents 10 cm.

Citation: Journal of the American Veterinary Medical Association 245, 1; 10.2460/javma.245.1.126

All abdominal radiographic views were obtained with a gadolinium-based scintillation digital detectora (digital radiography). To obtain a complete abdominal image series, at least 4 views were obtained each with a 14 × 17-inch capture plate, in a manner described previously.5 The detectorb was housed in a holder that was linked via an overhead rail system to the x-ray tube. Tube output variables were dependent on the body location undergoing imaging but, in general, settings were as follows: 110 kVp (range, 110 to 140 kVp); 160 mAs (range, 100 to 200 mAs). All images were stored on the hospital's picture archiving and communication system.c

The radiographic views were evaluated on a dedicated image review workstation comprised of 2 liquid crystal display monitors.d The 2 monitorsd were 20.8-inch 3-megapixel, monochrome, medical grade monitors calibrated to the grayscale display function.

Radiographic evaluation—For each case that met the inclusion criteria, all available radiographic views were reviewed separately by 3 reviewers (a board-certified surgeon, board-certified radiologist, and equine surgery resident), who were unaware of the equid's signalment, history, clinical signs, and definitive diagnosis. Each set of radiographic views was reviewed for the absence or presence of single or multiple mineral densities within the gastrointestinal tract (characteristic of enteroliths), the degree of gas distention visible as gas density within the gastrointestinal lumen (determined subjectively as mild [< 1/4 of the dorsal abdominal field is filled with gas], moderate [1/4 to < 1/2 of the dorsal abdominal field is filled with gas], or severe (≥ 1/2 of the dorsal abdominal field is filled with gas]; Figure 2), and whether radiographic penetration of the abdomen was adequate or inadequate. If enteroliths were identified, the number and suspected anatomic location were recorded.

Figure 2—
Figure 2—

Representative digital abdominal radiographic views of 3 horses with colic from an area where enterolithiasis in equids is endemic. Gas distention of the abdomen is present in each horse and is graded as mild (< 1/4 of the dorsal abdominal field is filled with gas; A), moderate (1/4 to < 1/2 of the dorsal abdominal field is filled with gas; B), or severe (≥ 1/2 of the dorsal abdominal field is filled with gas; C). See Figure 1 for remainder of key.

Citation: Journal of the American Veterinary Medical Association 245, 1; 10.2460/javma.245.1.126

Statistical analysis—With regard to detection of enterolithiasis in horses and ponies via digital radiography, sensitivity and specificity were calculated for each of 3 image reviewers. A consensus measure for the 3 reviewers was formed by scoring a positive finding when at least 2 of the 3 reviewers had a positive finding and scoring a negative finding when at least 2 of the 3 reviewers had a negative finding. Sensitivity and specificity were also calculated for these consensus measures. The ability of each reviewer to correctly diagnose the presence or absence of enteroliths was calculated as the κ statistic (a measure of each reviewer's accuracy in making the correct radiographic diagnosis). Sensitivity was also calculated by location of the enteroliths and as a function of the number of enteroliths determined from postmortem or surgical findings. Dependence of sensitivity by location and number of enteroliths and the association between location of enteroliths and degree of intestinal gas distension were assessed by use of χ2 tests of association or the Fisher exact test. The McNemar test was used to assess the nature of the disagreement between presence or absence of enteroliths and the radiographic diagnosis. All results were considered significant at a value of P < 0.05.

Results

Two hundred thirty-eight equids met the inclusion criteria. Breeds included 62 Quarter Horses; 37 Arabians; 22 warmbloods; 20 Thoroughbreds; 16 American Paint Horses; 13 mixed-breed horses; 12 each of American Miniature Horses and Morgans; 8 Appaloosas; 6 each of Friesians, draft horses, and ponies; 4 each of Tennessee Walking Horses and Missouri Foxtrotters, 2 each of Rocky Mountain Horses and Standardbreds; and 1 each of Andalusian, Cleveland Bay, Icelandic, Lippizan, Paso Fino, and Peruvian Paso. Mean age was 13.7 years (median, 13 years; range, 2 to 39 years). There were 109 mares, 105 geldings, and 24 stallions.

Enterolithiasis was confirmed in 70 of the 238 equids; for 62 equids, confirmation was achieved during exploratory celiotomy, and for 8 equids, confirmation was achieved necropsy. A single enterolith was identified in 43 equids, 2 to 5 enteroliths were identified in 19 equids, and ≥ 6 enteroliths were identified in 8 equids. Enteroliths were located in the right dorsal colon in 33 horses, transverse colon in 12 equids, and in the small colon in 13 equids. Enteroliths were detected in > 1 location in 12 equids (right dorsal and transverse colon in 7, right dorsal and small colon in 4, and transverse and small colon in 1). Final diagnoses of the remaining 168 equids were summarized (Table 1). Digital radiographic views were of adequate diagnostic quality in 229 of 238 (96%) of cases.

Table 1—

Diagnoses for 168 equids > 1 year of age that underwent direct digital abdominal radiography with either subsequent exploratory celiotomy or necropsy during which no evidence of enterolithiasis was detected.

DiagnosisNo. of equids
Strangulating small intestinal lesion41
Large colon displacement25
Sand impaction22
Fecalith15
Colitis12
Large colon volvulus11
Large colon impaction10
Nonstrangulating small intestinal lesion6
No notable findings on exploratory celiotomy5
Nonstrangulating cecal lesion3
Foreign body penetration3
Neoplasia3
Peritonitis2
Adhesions1
Strangulating cecal lesion1
Endocarditis1
Esophageal rupture1
Femur fracture1
Gastric impaction1
Strangulating small colon lesion1
Oleander toxicosis1
Small colon impaction1
Ruptured kidney1

In total, 238 equids were evaluated at a veterinary teaching hospital between April 23, 2008, and October 31, 2011. Of those equids, 70 had a diagnosis of enterolithiasis confirmed during exploratory celiotomy or necropsy.

Sensitivity of diagnosis of enterolithiasis in equids by means of digital radiography (Table 2) was high for all 3 image reviewers (83%, 84%, and 88%), as was the specificity (96%, 94%, and 97%). There was good agreement between reviewers. For the comparison of reviewers 1 and 2, κ was 0.81. For the comparison of reviewers 1 and 3, κ was 0.78. For the comparison of reviewers 2 and 3, κ was 0.87. Overall (consensus) sensitivity was 84%, and consensus specificity was 96%. The McNemar test yielded P values of 0.15, 0.82, and 0.24 for reviewers 1,2, and 3, respectively. Sensitivity was not affected by the number of enteroliths (P = 0.106). Sensitivity was significantly (P = 0.049) lower for small colon enteroliths than for large colon enteroliths and was significantly (P = 0.016) negatively affected by the degree of gas distention (Table 1).

Table 2—

Consensus sensitivity of digital abdominal radiography for the detection of enteroliths in equids depending on the number of enteroliths, anatomic location of enteroliths, and associated gas distention of the intestines.

VariableSensitivity (%)P value
No. of enteroliths 0.106
 183.72 
 2–594.74 
 ≥662.5 
Location of enteroliths 0.049
 Large colon88.89 
 Small colon61.54 
 Transverse colon91.67 
Intestinal gas distention 0.016
 Mild96.88 
 Moderate74.07 
 Severe72.73 

Digital radiographic views obtained from 238 equids (70 of which had enterolithiasis) were examined by each of 3 image reviewers. Sensitivity and specificity for detection of enteroliths were calculated for each of the 3 image reviewers. A consensus measure for the 3 reviewers was formed by scoring a positive finding when at least 2 of the 3 reviewers had a positive finding and scoring a negative finding when at least 2 of the 3 reviewers had a negative finding; sensitivity and specificity (data not shown) were calculated for these consensus measures. The degree of gas distention visible as gas density within the gastrointestinal tract lumen was subjectively graded as mild (< 1/4 of the dorsal abdominal field is filled with gas), moderate (1/4 to < 1/2 of the dorsal abdominal field is filled with gas), or severe (≥ 1/2 of the dorsal abdominal field is filled with gas).

Discussion

In the present study, digital radiography provided high sensitivity and high specificity with excellent agreement among image reviewers for the diagnosis of enterolithiasis in adult equids evaluated at our hospital. The sensitivity of digital radiography for detecting enteroliths was higher (84%) than that of conventional radiography (76.9%) determined in a previous study5 conducted at the same hospital. With regard to detection of enteroliths, sensitivity of digital radiography was similar (84%) to the sensitivity of computed radiography (85%) recently reported from the same institution.6

Other similarities between the present study and the study of computed radiography6 performed previously include both the lack of effect of the number of enteroliths and degree of gas distension on the ability of these 2 techniques to detect enteroliths in equids. It has been proposed that a higher number of enteroliths implies the presence of smaller stones and that the smaller size impedes the ability to visualize them radiographically. Additionally, severe gas distension causes compression and distortion of intra-abdominal organs, which could contribute to increased false-negative results. In both studies, enteroliths were also more likely to be detected in the large colon than the small colon. In the present study, 2 of the 3 image reviewers were the same individuals who had participated in the previous study6 of computed radiography; yet, despite the change in the third reviewer, the 3 inter-reviewer agreements were similar between the 2 studies. Results of the present study suggested that digital radiography is indicated as a diagnostic test for equids with colic in geographic areas where enterolithiasis among equids is endemic.

Underexposure was the most common cause of nondiagnostic radiographic views in both the present study and the previous computed radiography retrospective evaluation.6 In the present study, the percentage of digital radiographic views that were nondiagnostic was lower than that for the computed radiographic views, which suggested that the digital radiography system may better compensate for underexposure through image processing mechanisms that allow change in contrast after the image is acquired.

In the present study, enterolithiasis was diagnosed for 70 of the 238 (29%) equids that underwent direct digital abdominal radiography. In the previous study6 at this institution, 83 of 142 (58%) equids had enterolithiasis, as determined via computed radiography. Factors that may have contributed to the apparent decrease in the percentage of equids with colic that received a diagnosis of enterolithiasis include increased owner awareness and management changes in endemic regions, particularly avoidance of feeding a strict alfalfa diet. Additionally, the time period of the present study coincided with a major economic downturn that decreased the number of equids with colic that were brought to the hospital for evaluation, which may have altered the case distribution in the study population.

In the present study, breed distribution of the affected equids was somewhat different than that of the previous studies involving abdominal radiography (analog and computed) and enterolithiasis in equids. The percentage of Quarter Horses among the affected equids remained relatively static across studies, whereas there was a much smaller percentage of Arabian horses in the present study, compared with the percentages in the previous studies. The present study also had a comparatively higher percentage of warmbloods and Thoroughbreds. In the previous studies, the breed distribution indicated an overrepresentation of Arabian horses, compared with the hospital's general population of equids. In the present study, the higher percentage of warmbloods and Thoroughbreds was representative of an overall shift in the hospital's general population of horses and ponies.

On the basis of the results of the present study in equids, caution should be exercised when the digital radiographic results are negative for enterolithiasis because the sensitivity for detection of small colon enterolithiasis was low (61.5%). Although the sensitivity was improved, compared with that for computed radiography (50%),6 the results of the present study were based on a smaller number of equids with small colon enteroliths (8/70 [11%] equids) than the other study6 (12/83 [14%] equids). It was previously proposed that the lack of contrast with intraluminal gas and midabdominal location were factors in the reduced sensitivity for computed radiographic detection of small colon enteroliths. Although these factors were still present, image processing and overall acquisition of a higher percentage of diagnostic images may also have had a role in the increased sensitivity of digital radiography for detection of small colon enteroliths in equids, compared with that of computed radiography.

Findings of the present study indicated that the overall sensitivity and specificity of abdominal radiography by means of a digital radiography system for detection of large colon enteroliths in equids are high, and similar to previously reported values obtained via conventional and computed radiography. The sensitivity of digital radiography for detection of small colon enteroliths in equids was increased, compared with the sensitivity of computed radiography; furthermore, digital radiography was associated with a greater percentage of images deemed diagnostic. Abdominal radiographic views obtained with a digital radiography system that has technical components similar to those of the system used in the present study has the potential to be an important part of the diagnostic workup of horses and ponies with colic and abdominal disease in endemic areas.

a.

EDR-6, Eklin Medical Systems Inc, Santa Clara, Calif.

b.

CXDI-50G, Canon, Tokyo, Japan.

c.

Sound-Eklin, Carlsbad, Calif.

d.

Totoku (ME351i), North American Inc, Irving, Tex.

References

  • 1. Hassel DM, Langer DL, Snyder JR, et al. Evaluation of enterolithiasis in equids: 900 cases (1973–1996). J Am Vet Med Assoc 1999; 214: 233237.

    • Search Google Scholar
    • Export Citation
  • 2. Hassel DM, Aldridge BM, Drake CM, et al. Evaluation of dietary and management risk factors for enterolithiasis among horses in California. Res Vet Sci 2008; 85: 476480.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Hassel DM, Rakestraw PC, Gardner IA, et al. Dietary risk factors and colonic pH and mineral concentrations in horses with enterolithiasis. J Vet Intern Med 2004; 18: 346349.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Rose JA, Rose EM, Sande RD. Radiographic diagnosis of equine enterolithiasis, in Proceedings. 26th Annu Meet Am Assoc Equine Pract 1980;211220.

    • Search Google Scholar
    • Export Citation
  • 5. Yarbrough TB, Langer DL, Snyder JR, et al. Abdominal radiography for diagnosis of enterolithiasis in horses: 141 cases (1990– 1992). J Am Vet Med Assoc 1994; 205: 592595.

    • Search Google Scholar
    • Export Citation
  • 6. Maher O, Puchalski SM, Drake C, et al. Abdominal computed radiography for the diagnosis of enterolithiasis in horses: 142 cases (2003–2007). J Am Vet Med Assoc 2011; 239: 14831485.

    • Crossref
    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 215 0 0
Full Text Views 714 573 235
PDF Downloads 393 210 24
Advertisement