Gastrointestinal signs, especially acute vomiting, can require medical or surgical intervention. Abdominal radiographs are useful for determining if the cause is a mechanical obstruction and thus which type of intervention is needed. The radiographic features depend on completeness, location, and duration of the obstruction. A series of 3 projections\u2014right lateral, left lateral, and ventrodorsal\u2014is recommended.<\/p>\n
Radiograph evaluation involves subjective and objective analysis for most types of obstruction but differs for obstruction caused by linear foreign bodies. If initial radiographs are inconclusive, follow-up radiographs taken 7 to 24 hours later may be helpful. If radiographs still do not lead to a conclusive diagnosis, serial radiography, abdominal ultrasonography, or computed tomography may be needed.<\/p>\n
Take-Home Points<\/strong><\/p>\n Dogs and cats are frequently presented to veterinary practices for acute vomiting. An accurate diagnosis of the cause of the vomiting<\/a> will determine if the animal should be treated medically or surgically. A common cause is mechanical obstruction of the small intestinal tract.1,2<\/sup> <\/span><\/p>\n Common causes of mechanical obstruction include foreign bodies<\/a>, intestinal neoplasia, and intussusception.3<\/sup> Ingestion of a foreign body accounts for approximately 80% of cases of mechanical obstruction.1<\/sup> Mechanical obstruction results in increased intestinal contractility and increased mucosal secretory activity. The swallowing of air and saliva, increased intestinal secretions, and decreased absorption create a cycle of increased luminal pressure and distention, which ultimately leads to decreased perfusion of the intestinal wall, resulting in ischemia, electrolyte loss<\/a> from secretions, clinical dehydration, and increased intestinal mucosal permeability.1,3<\/sup> As a result, it is imperative to quickly diagnose mechanical obstruction in order to mitigate intestinal damage. <\/span><\/p>\n Diagnostic modalities that aid in diagnosis of intestinal obstruction include radiography, ultrasonography, and computed tomography. Although radiography is reported to have the lowest sensitivity, it is often the only imaging modality available in a general practice setting. Abdominal radiography should be the first-line diagnostic imaging modality performed, even when other imaging modalities are available. <\/span><\/p>\n The standard radiographic series most often used to survey the small bowel are the recumbent right lateral and ventrodorsal projections. The position of the patient will alter the location of gas in the gastrointestinal (GI) tract and influence what can be seen on the radiograph. For instance, in a right lateral view, gas will be seen in the fundus of the stomach and gastric fluid will be in the dependent side (the pylorus) (<\/span>FIGURE 1A<\/b><\/span>). <\/span>On a left lateral view, gas will be seen in the pylorus and duodenum (<\/span>FIGURE 1B<\/b><\/span>).<\/span><\/p>\n Figure 1A. Right lateral radiograph of a canine abdomen.<\/p><\/div>\n Figure 1B. Left lateral radiograph of a canine abdomen, showing the differences in gas in the stomach with positional changes. On the left lateral view (B), gas is seen in the pylorus and descending duodenum (arrowheads).<\/p><\/div>\n Movement of intestinal gas during repositioning of the patient will sometimes result in intestinal tract pathology being seen clearly on only 1 view. Thus, a 3-view abdominal series is recommended.4<\/sup> Although the order for obtaining images in this series was traditionally somewhat arbitrary, it has recently been shown that the best order is left lateral, followed by ventrodorsal, and then right lateral.5<\/sup> When radiographs are obtained in this order, gas is more likely to be present in the pylorus and duodenum. Patient preparation (e.g., fasting, cleansing enema) is not required and often not indicated as it can alter the native appearance of the gas and fluid in the intestinal tract, which could jeopardize the radiographic evaluation.4<\/sup><\/span><\/p>\n In healthy dogs and cats, small intestinal loops within each species, especially cats, are generally similar in diameter. For determining normal size, several methods have been proposed and vary between dogs and cats. In dogs, normal small intestinal diameter should be less than twice the width of a rib6<\/sup> or less than 1.6 times the height of the L5 vertebral body at its narrowest point (<\/span>FIGURE 2<\/b><\/span>).7<\/sup> Because the size of feline intestines is more consistent, direct measurements are often used. For cats, the maximum diameter of the small intestine is 12 mm.8<\/sup> A ratio of small intestinal diameter (serosa to serosa) to the L2 vertebral endplate height of less than 2 is also considered normal (<\/span>FIGURE\u00a03<\/b><\/span>).8<\/sup> <\/span><\/p>\n Figure 2. Right lateral view of a healthy dog. The normal intestine should be uniform in diameter and not significantly dilated. The small intestine should be less than 1.6 times the height of the L5 vertebrae (orange line) at its narrowest point or less than twice the width of a rib (white lines).<\/p><\/div>\n Figure 3. Left lateral radiograph of a healthy young adult cat. The small intestine diameter should be uniform, and opacity should be that of mostly soft tissue with minimal luminal gas. A ratio of small intestinal diameter (serosa to serosa) to the L2 vertebral endplate height of <2 is considered normal (white lines). Maximum diameter of the small intestine should not exceed 12 mm.<\/p><\/div>\n Intestinal wall thickness is not routinely evaluated on survey radiographs. A normal empty segment with a small amount of luminal gas will often appear thick because normal luminal fluid and the intestinal wall are of the same opacity. <\/span><\/p>\n The small intestine should be evenly dispersed throughout the peritoneal cavity. Because the intestine is highly mobile, it is easily displaced by enlarged organs or abdominal masses. In obese patients, it is common for the small intestine to be bunched (contained) into the midabdomen (cats) or into the ventral abdomen (dogs). <\/span><\/p>\n The normal luminal content of intestine can vary, depending on when the patient last ate. In a nonfasted animal, air, granular ingesta, and mineral\/metallic debris are often seen. Gas is more commonly seen in dogs than in cats. Reportedly, 30% to 60% of small intestinal content can appear radiographically as gas in healthy dogs.9<\/sup><\/span><\/p>\n The radiographic features of intestinal obstruction depend on 3 factors: the completeness of the obstruction, the location of the obstruction, and the duration of the obstruction.4<\/sup> The goal of the radiographic examination is to first determine if the cause of the clinical signs requires surgical or medical treatment, which is a subjective evaluation. The last step, which may provide more confidence in the radiographic interpretation, is objective evaluation. <\/span><\/p>\n The most common radiographic sign of intestinal obstruction is dilation of the small intestine, which is especially obvious when there is segmental dilation or 2\u00a0populations of bowel (i.e., 1 section is distended and the other sections are empty) (<\/span>FIGURE 4<\/b><\/span>). Distention is usually indicated by a greater than 50% difference in diameter between the normal and distended bowel or by intestinal segments that are greater than 3 to 4 times the width of a rib.7,10<\/sup> <\/span><\/p>\n Figure 4. Left lateral radiograph of a young dog with mechanical obstruction caused by foreign material. There is marked segmental dilation of the small intestine (asterisks) relative to the normal\/empty small intestine (X). This radiographic appearance is the most reliable sign of a mechanical obstruction. In addition, foreign material is seen in the lumen of the duodenum (arrowheads).<\/p><\/div>\n Other radiographic signs of obstruction include abnormal shape of the intestinal loops (e.g., hairpin bends, stacking of the bowel loops, plication); radiopaque foreign material (<\/span>FIGURES 5\u20138<\/b><\/span>); and potentially the gravel sign,10,11<\/sup> which is seen with more chronic partial obstruction (<\/span>FIGURE 9<\/b><\/span>). The gravel sign is the result of desiccated ingesta that is trapped just orad to the obstruction. It often has the appearance of granular fecal content or a mineral component,4,10<\/sup> which in the authors\u2019 experience is often secondary to primary mural disease, as opposed to a foreign body, causing the obstruction. <\/span><\/p>\n\n
The Normal Small Intestine<\/h2>\n
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<\/a>Intestinal Obstruction<\/h2>\n
Subjective Radiographic Evaluation of Intestinal Obstruction<\/h3>\n
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Figure 5A. Right lateral radiograph of a young dog with a cloth-like foreign body (arrowheads) in the proximal small intestine.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig5B-719x1024.png\")
FIgure 5B. Ventrodorsal radiograph of a young dog with a cloth-like foreign body (arrowheads) in the proximal small intestine. There is segmental dilation of the small intestine consistent with a mechanical obstruction. Within the dilated segment, the luminal content appears heterogeneous and striated, consistent with cloth-like foreign material (sock).<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig6A.png\")
Figure 6A. Right lateral radiograph of a dog with a sock foreign body in the duodenum (arrowheads).<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig6B.png\")
Figure 6B. Ventrodorsal radiograph of a dog with a sock foreign body in the duodenum (arrowheads). The foreign body is easy to overlook because only the duodenum is dilated and its consistency is similar to that of fecal material. The course of the dilated segment, however, is not consistent with the typical course of the colon, a finding that is helpful for diagnosis.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig7A.png\")
Figure 7A. Left lateral radiograph of a cat with a proximal duodenal foreign body (arrows).<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig7B-721x1024.png\"){kind=spacer}
Figure 7B. Ventrodorsal radiograph of a cat with a proximal duodenal foreign body (arrows). With proximal duodenal obstructions, the diameter of most of the small intestine is normal, making these cases more difficult to identify than jejunal obstruction. This case in particular shows the foreign material to have a consistency similar to that of fecal material and to be near the transverse colon.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig8A.png\")
Figure 8A. Right lateral radiograph of a dog with a corn cob foreign body (arrowheads).<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig8B.png\")
Figure 8B. Left lateral radiograph of a dog with a corn cob foreign body.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/06\/Cole_TVPJulAug23_ObstructionImaging_Fig8C-853x1024.png\")
Figure 8C. Ventrodorsal radiograph of a dog with a corn cob foreign body (arrowheads). Similar to cloth-like foreign material, this foreign body has a characteristic appearance: rectangular shape with a stippled opacity, easier to see on the right lateral (8A) than the left lateral (8B) view of this dog, which stresses the value of taking 3 views. Also note the marked segmental dilation of the small intestine, supporting a diagnosis of mechanical obstruction.<\/span><\/a><\/div><\/div>
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