The large intestine of dogs can be affected by various conditions, including inflammation, tumors, motility disorders, strictures, herniation, foreign bodies, torsion, and intussusception.1 Colitis is the most commonly diagnosed disorder, and it is responsible for intestinal disease in up to 45% of affected dogs. Malignancies such as adenocarcinomas, lymphomas, and gastrointestinal stromal tumors can develop in the large intestine and are more common than tumors in the stomach or small intestine.2 In most diseases involving the large intestine, thickness and layering of the wall, luminal contents, and lumen (intact without narrowing or obstruction) as well as diffuse or focal changes of the mucosal, muscular, and serosal layers should be investigated to determine the extent of pathological changes and formulate a treatment plan.
Colonoscopy is the most sensitive diagnostic tool for large intestinal disease in human medicine; however, the success of colonoscopy is highly dependent on the operator's skill and experience.3 Adverse effects related to colonoscopy (eg, colonic perforation, laceration of blood vessels, and translocation of microflora through the mucosa) have been reported.4 Moreover, colonoscopy has limitations when it comes to estimating function of the colon, measuring luminal diameter, or investigating diseases associated with the submucosal, muscular, and serosal layers of the colon.5
Most diseases of the large intestine are associated with structural changes involving the lumen or intestinal wall. Diagnostic imaging can detect and clarify the extent of lesions on the basis of structural changes.6 Some conditions (eg, foreign bodies, intestinal torsion, intussusception, or extraluminal mass effects) can be detected with survey radiography when the lesions accompany typical radiographic findings. Use of positive or negative contrast agents can improve the sensitivity of radiography, but the inherent limitation of radiography, namely superimposition of the large intestine by the surrounding organs, interferes with detailed examination of intestinal lesions, even when contrast agents are used.6
Ultrasonography, which allows cross-sectional imaging, can be used to assess intestinal lesions without overlap of adjacent structures being an issue. Ultrasonography is extremely useful for examination of wall layers and can be used to investigate any loss of wall layering, which is a good predictive factor in tumor management.7 In particular, this modality can be used to define the origin and extent of a mass originating from the gastrointestinal tract. Ultrasonography is also useful for diagnosing intussusceptions or identifying thickening of the intestinal wall. Thickening of the intestinal wall can occur with inflammation, infection, ischemia, edema, hemorrhage, and neoplasia. In particular, neoplasia can cause diffuse, symmetric wall thickening in the colon.8 Ultrasonography is typically used as an adjunct to radiography because it has lower spatial resolution than radiography, and image quality is limited because of critical artifacts caused by gas and fecal material within the intestine.6
Hydrograms, which are obtained by use of fluidfilling techniques, are used to overcome problems associated with gas-related artifacts and to provide a good acoustic window for examination of the gastrointestinal tract.9 The stomach is dilated with fluid in hydrogram ultrasonography, and the collapsed stomach in fasting human patients can be easily distinguished from any tumor. Hydrograms can be helpful to identify wall layers and the lumen of the intestine and to clarify the extent of a tumor originating from the gastrointestinal tract. Therefore, hydrogram ultrasonography is considered to be complementary to endoscopy for use in the diagnosis of submucosal tumors and an alternative to other expensive imaging techniques such as endoscopic ultrasonography.9 In addition, a modified double-contrast barium enema with carboxymethylcellulose administered into the rectum has been shown to be useful for immediate radiographic and ultrasonographic evaluation of the morphology and mucosal layers of the colon in dogs.10
Computed tomography can eliminate the superimposition of organs adjacent to the large intestine and provide a 3-D representation of the intestinal tract through postprocessing reformatting. However, fecal material in the colon can mask underlying lesions, and emptying the colon leads to collapse of the colonic lumen and contraction of the muscular wall, even on CT images. Computed tomographic examinations with orally administered contrast agents (eg, iodine, diluted barium, neutral contrast agents, room air, or CO2) have been used to overcome these shortcomings, but it is difficult to optimize visualization of the distal part of the large intestine.11,12
Radiographic colonography, ultrasonography, and CT after administration of an enema are primarily used for diagnostic imaging of the large intestine, and each method has its strengths and weaknesses. The purpose of the study reported here was to identify the best contrast agent (room air, diluted barium, or tap water) for diagnostic imaging of the colon and to compare the relative benefits of ultrasonography and CT for this purpose. The hypothesis was that hydrogram ultrasonography could be easily applied to the large intestine and used to clearly indicate the lumen and wall layers of the colon through uniform filling of the colon with contrast agents. In addition, hydrogram ultrasonography would be suitable for examining the wall layers of the colon, and hydrogram CT would be suitable for examining the colonic lumen. The effects of contrast agents on image quality and intestinal filling were investigated in clinically normal dogs to determine the protocol that would optimally provide luminal distention and intestine layering and a minimal amount of artifacts during ultrasonography and CT of the colon.
Supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT, and Future Planning (grant No. 2015R1A2A2A01003313).
Colyte, Taejoon Pharmaceutical Co, Seoul, Korea.
Zoletil, Virbac, Carros, France.
Domitor, Orion Corp, Espoo, Finland.
Omnihexol 300, Korea United Pharm Co, Sungnam, Korea.
Siemens Emotion 16, Siemens, Forchheim, Germany.
ProSound Alpha 7, Hitachi-Aloka, Tokyo, Japan.
SPSS for Windows, release 22.0, standard version, SPSS Inc, Chicago, Ill.
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