The appearance of the gastrointestinal tract in clinically normal pediatric1 and adult2 dogs has been described; the descriptions have included weight-correlated references for total wall thickness. Thickness of the mucosal layer for the stomach, duodenum, and jejunum has been reported1 in pediatric dogs up to 12 weeks of age; however, to our knowledge, these values have not been reported in adult dogs, nor have they been correlated with body weight. These measurements have been applied in pediatric dogs with parvovirus infection, whereby there is thinning of the mucosa but the total wall thickness remains unaffected.3 It is the authors’ clinical impression that hemorrhagic gastroenteritis in adult dogs may yield an ultrasonographic appearance for the wall layers similar to the appearance of the wall layers in pediatric dogs with parvovirus infection. Thus, determination of the thickness for individual wall layers may assist clinicians when evaluating intestinal disorders in adult dogs.
The purposes of the study reported here were to measure the thickness of individual wall layers of the duodenum, jejunum, and colon of dogs and to determine associations between these values and body weight. Our hypotheses were that the mucosal layer would be the thickest layer of the duodenum and jejunum; there would be a significant difference in the thickness of the mucosal layer of the duodenum and jejunum for small, medium, and large dogs; the submucosa, muscularis, and serosa of the duodenum and jejunum would not differ significantly among small, medium, and large dogs; and all wall layers would contribute equally to the total colonic wall thickness.
Materials and Methods
Animals—Dogs included in the study were client-owned animals undergoing an abdominal ultrasonographic examination for reasons unrelated to the present study. Ultrasonographic examinations were conducted between September 2010 and April 2012. The ultrasonographic images were part of the standard ultrasonographic examination during the diagnostic evaluation of each dog; therefore, owner consent for use of the images in the present study was not deemed necessary.
Adult dogs (≥ 12 months old) were included in the study provided they had no signs of gastrointestinal tract disease (vomiting, diarrhea, anorexia, or weight loss) during the 2 months preceding the abdominal ultrasonographic examination and had not received corticosteroids, NSAIDs, antimicrobials, or chemotherapeutics within 30 days preceding the abdominal ultrasonographic examination. Dogs included in the study had no ultrasonographic evidence of gastrointestinal tract disease.
Data initially were obtained for 203 dogs. After review of the medical records, 118 dogs were excluded on the basis of the aforementioned inclusion criteria. Therefore, 85 dogs met the inclusion criteria and were included in the study. Dogs were classified into 3 groups on the basis of body weight: small (< 15 kg [n = 26]), medium (15 to 30 kg [25]), and large (> 30 kg [34]).
Procedures—Ultrasonographic examinations were performed with an ultrasonographic systema and a curvilinear transducerb or linear-array transducer.c All abdominal ultrasonographic examinations were performed by a resident in a veterinary radiology training program or a board-certified veterinary radiologist.
Briefly, each dog was positioned in dorsal recumbency. Hair was clipped on the ventral portion of the abdomen, and acoustic coupling gel was applied. The stomach was examined, and images of the fundus and pylorus were obtained to confirm the presence or absence of gastric contents. A transverse image of the duodenum was obtained at a location ventral to the right kidney. Transverse images of the jejunum were obtained in the left cranial and left caudal aspects of the abdomen. A transverse image of the descending portion of the colon was obtained.
Measurements of wall layers were obtained by one of the authors (NEG) using electronic calipers on a picture archiving and communication systemd with a resolution of 0.05 mm. Measurements were obtained from a single transverse image of the duodenum, jejunum, and colon and included total wall thickness and thickness of the mucosa, submucosa, muscularis, and serosa (Figures 1 and 2). For the colon, measurements of the individual wall layers were obtained only when the layers could be visually distinguished.
Transverse ultrasonographic image of the duodenum of a representative dog with no clinical signs or ultrasonographic evidence of gastrointestinal tract disease. An electronic calipers (white line near the center of the image) was used to measure total wall thickness. Bar = 10 mm.
Citation: American Journal of Veterinary Research 75, 4; 10.2460/ajvr.75.4.349
Transverse ultrasonographic images of the duodenum of a representative dog with no clinical signs or ultrasonographic evidence of gastrointestinal tract disease. An electronic calipers (white line near the center of each image) was used to measure the thickness of the mucosa (A), submucosa (B), muscularis (C), and serosa (D). Bar = 10 mm.
Citation: American Journal of Veterinary Research 75, 4; 10.2460/ajvr.75.4.349
Statistical analysis—The mean, SD, maximum, and minimum values were calculated for each of the duodenal, jejunal, and colonic variables for small, medium, and large dogs; these data were normally distributed as determined by comparing the mean and median, which were equal, and plotting a histogram. An ANOVA was performed for each duodenal, jejunal, and colonic variable, and a Tukey honestly significant difference post hoc test was used to detect significant differences among small, medium, and large dogs. For all analyses, significance was set at values of P < 0.05.e
Results
Mean, SD, maximum, and minimum values for each of the duodenal variables for each group were summarized (Table 1). There was a significant difference in thickness of the mucosal layer (P < 0.05) and total wall thickness (P = 0.01) between small and large dogs. No significant difference was detected for submucosal, muscularis, or serosal thickness among the 3 groups.
Mean ± SD and range values for thickness of the doudenall wall layers in small, medium, and large dogs.*
| Small (n = 26) | Medium (n = 25) | Large (n = 34) | ||||
|---|---|---|---|---|---|---|
| Layer | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) |
| Mucosa | 2.4 ± 0.5a | 1.6–3.5 | 2.6 ± 0.6 | 1.5–3.7 | 2.8 ± 0.5b | 2.0–3.9 |
| Submucosa | 0.6 ± 0.1 | 0.3–0.8 | 0.6 ± 0.2 | 0.3–1.0 | 0.6 ± 0.2 | 0.3–1.2 |
| Muscularis | 0.5 ± 0.1 | 0.2–0.8 | 0.5 ± 0.1 | 0.3–0.8 | 0.6 ± 0.2 | 0.2–0.9 |
| Serosa | 0.4 ± 0.1 | 0.2–0.6 | 0.4 ± 0.1 | 0.3–0.6 | 0.4 ± 0.1 | 0.2–0.7 |
| Total wall | 3.8 ± 0.5a | 2.9–4.7 | 4.1 ± 0.7 | 3.0–5.5 | 4.4 ± 0.7b | 3.1–5.7 |
Range represents the minimum to the maximum value.
Dogs were classified on the basis of body weight as small (< 15 kg), medium (15 to 30 kg), and large (> 30 kg).
Within a row, values with different superscript letters differ significantly (P < 0.05).
Mean, SD, maximum, and minimum values for each of the jejunal variables for each group were summarized (Table 2). There was a significant difference in thickness of the mucosal layer between small and large dogs (P = 0.01) and a significant difference in total wall thickness between small and medium dogs (P = 0.01), small and large dogs (P = 0.01), and medium and large dogs (P < 0.05). No significant difference was detected for submucosal, muscularis, or serosal thickness among the 3 groups.
Mean ± SD and range values for thickness of the jejunal wall layers in small, medium, and large dogs.*
| Small (n = 26) | Medium (n = 25) | Large (n = 34) | ||||
|---|---|---|---|---|---|---|
| Layer | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) |
| Mucosa | 1.8 ± 0.4a | 1.2–2.6 | 2.0 ± 0.4 | 1.5–3.2 | 2.2 ± 0.5b | 1.1–3.2 |
| Submucosa | 0.5 ± 0.1 | 0.3–0.9 | 0.6 ± 0.2 | 0.3–1.0 | 0.6 ± 0.1 | 0.3–0.8 |
| Muscularis | 0.5 ± 0.1 | 0.2–0.7 | 0.5 ± 0.1 | 0.3–0.8 | 0.5 ± 0.2 | 0.3–0.9 |
| Serosa | 0.4 ± 0.1 | 0.2–0.6 | 0.4 ± 0.1 | 0.3–0.6 | 0.4 ± 0.1 | 0.3–0.6 |
| Total wall | 3.0 ± 0.5a | 2.2–4.1 | 3.5 ± 0.5b | 2.4–4.8 | 3.8 ± 0.4c | 2.7–4.7 |
Within a row, values with different superscript letters differ significantly (P < 0.05).
See Table 1 for remainder of key.
Mean, SD, maximum, and minimum values for each of the colonic variables for each group were summarized (Table 3). The individual wall layers were clearly visible and could be measured in 14 small dogs, 14 medium dogs, and 17 large dogs; total wall thickness could be measured in all 85 dogs. For each group, all wall layers contributed equally to total wall thickness, and there were no significant differences for the thickness of the individual wall layers among the 3 groups. There was a significant difference in total wall thickness between medium and large dogs.
Mean ± SD and range values for thickness of the colonic wall layers in small, medium, and large dogs.*
| – | Small (n = 26) | Medium (n = 25) | Large (n = 34) | |||
|---|---|---|---|---|---|---|
| Layer | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) | Mean ± SD (mm) | Range (mm) |
| Mucosa | 0.4 ± 0.1 | 0.2–0.6 | 0.4 ± 0.1 | 0.2–0.5 | 0.5 ± 0.1 | 0.3–0.7 |
| Submucosa | 0.4 ± 0.1 | 0.2–0.6 | 0.3 ± 0.1 | 0.2–0.4 | 0.4 ± 0.1 | 0.2–0.5 |
| Muscularis | 0.4 ± 0.1 | 0.2–0.7 | 0.3 ± 0.1 | 0.2–0.5 | 0.4 ± 0.1 | 0.2–0.7 |
| Serosa | 0.4 ± 0.1 | 0.2–0.5 | 0.4 ± 0.1 | 0.2–0.5 | 0.4 ± 0.1 | 0.2–0.5 |
| Total wall | 1.5 ± 0.3 | 1.0–2.0 | 1.4 ± 0.5a | 1.1–1.9 | 1.6 ± 0.4b | 1.1–2.6 |
See Table 1 for key.
Discussion
Values determined in the present study for the individual wall layers may provide a reference for future clinical evaluation of intestinal disorders in dogs. As we hypothesized, the mucosal layer was the thickest layer in the duodenum and jejunum and contributed to 63% to 64% of the total duodenal wall thickness and 57% to 60% of the total jejunal wall thickness. There was also a significant difference in thickness of the mucosal layer between small and large dogs for both the duodenum and jejunum. The submucosa, muscularis, and serosa of the duodenum and jejunum were similar in thickness and did not differ significantly among the 3 groups.
Hemorrhagic gastroenteritis is a syndrome in adult dogs that is characterized by acute onset of hemorrhagic diarrhea and vomiting and marked hemoconcentration.4,5 Similar to parvovirus infection in pediatric dogs, hemorrhagic gastroenteritis is thought to result in necrosis and destruction of the mucosal villi.5 In a study3 conducted to determine the ultrasonographic appearance of the intestinal tract in pediatric dogs with parvovirus infection, findings included thinning of the duodenal and jejunal mucosa with preservation of the total wall thickness, fluid-filled intestinal segments with decreased or no motility, an irregular luminal-mucosal margin, increased mucosal echogenicity, and ill-defined wall layers. The authors of that study3 hypothesized that the reason total wall thickness was preserved, despite thinning of the mucosa and a fluid-filled lumen, was subserosal hemorrhage, which may have extended into the muscularis and submucosal layers. It is the clinical impression of the authors that hemorrhagic gastroenteritis may cause an ultrasonographic appearance similar to that for parvovirus infection. Clinicians and researchers can use the reference values generated for the individual wall layers in the study reported here to determine whether the ultrasonographic appearance of the intestinal tract of adult dogs with hemorrhagic gastroenteritis is similar to that for pediatric dogs with parvovirus infection.
Total wall thickness for the present study is similar to the result for 231 clinically normal dogs in another study.2 In clinical studies6–8 of dogs with inflammatory bowel disease, the thickness of the duodenum and jejunum often overlaps with the upper portion of the reference range. Reference values for the individual wall layers determined in the present study may be used in clinical studies of dogs with inflammatory bowel disease to increase the sensitivity for detecting dogs with subtle thickening of the small intestines. Additionally, it is important to consider other ultrasonographic features, such as alteration of the wall layers and size of adjacent lymph nodes, when evaluating a suspected underlying intestinal disorder.
The reference value for the thickness of the colon of clinically normal dogs is reportedly 2 to 3 mm.9 That value represents measurements obtained for 12 dogs by use of a 5- or 7.5-MHz transducer with a 1-mm resolution limit. The present study included 85 dogs, and we found that total colonic wall thickness exceeded 2.0 mm in only 3 (3.5%) dogs, all of which were large dogs. We suggest a new reference range of 1 to 2 mm for total colonic wall thickness. We did detect a significant difference in mean total colonic wall thickness between medium and large dogs. However, this may not be clinically relevant because the mean total colonic wall thickness was 1.5 mm for small dogs, 1.4 mm for medium dogs, and 1.6 mm for large dogs. In agreement with our hypothesis, all wall layers contributed equally to total colonic wall thickness.
One limitation of the present study was that histologic examination was not performed to confirm a lack of abnormalities in the gastrointestinal tract of each dog. However, endoscopic biopsy specimens are limited to the mucosal layer of the stomach, duodenum, and colon,10 and we could not justify performing invasive surgical biopsies in 85 dogs. Therefore, we opted to use strict inclusion criteria to exclude dogs with known gastrointestinal tract disease. A second limitation of the present study was the small sample size in each group, which may have affected the statistical power of the reference values. Another limitation of the study was that all measurements were made by only 1 investigator who used still images. This was done to standardize the way in which measurements were obtained because several ultrasonographers at our institution contributed images. The study design did not address interobserver variation.
In the study reported here, reference values were determined for the individual wall layers of the duodenum, jejunum, and colon in adult dogs. The mucosal layer was the thickest layer of the duodenum and jejunum, and there was a significant difference in thickness of the mucosal layer between small and large dogs. The submucosa, muscularis, and serosa of the duodenum and jejunum were similar in thickness for the 3 groups. The layers of the colon contributed equally to the total wall thickness, and total colonic wall thickness ranged from 1.0 to 2.6 mm.
IU22 xMATRIX ultrasound system, Philips Healthcare, Andover, Mass.
C8–5 transducer, Philips Healthcare, Andover, Mass.
L12–5 transducer, Philips Healthcare, Andover, Mass.
Vue Solutions software, version 11.3, Carestream Health Inc, Rochester, NY.
VassarStats, Vassar College, Poughkeepsie, NY.
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