SID to the height of the body of the fifth lumbar vertebra (L5) at its narrowest point was reported as the upper limit of normal intestinal diameter [39]. In that report, dogs with SID : L5 ratio equal to or greater than 1.95 had a greater than 80% probability of being obstructed [39].
Elser et al. evaluated utility of serial radiography in dogs and cats for identification of a foreign body obstruction when the initial radiographic images are inconclusive for the presence or absence of GI mechanical obstruction [40]. In that prospective cohort study, four blinded reviewers (two radiologists, one radiology resident, one criticalist) separately assessed the initial and the follow‐up radiographic studies, taken 7–28 hours after the initial set, for diagnosis of mechanical obstruction. An ultrasound served as the gold standard. For all reviewers, there was no significant change in accuracy for the diagnosis of mechanical obstruction using serial radiographs, suggesting that alternative imaging should be pursued in those patients where the suspicion of obstructive foreign body remains high [40].
Positive or negative contrast radiography can be used to identify GI foreign bodies when standard radiographic views are equivocal. While the use of positive contrast agents may be helpful, in many cases of complete obstruction the contrast material may not reach the foreign body either because of a lack of forward flow of ingesta or because of vomiting. In addition, these studies are time dependent and require repeated radiographs to document flow of contrast through the GI tract. If there is suspicion of perforation, positive contrast materials such as barium sulfate are contraindicated; iodinated contrast materials may be a better choice with respect to the impact of leakage of the material into the abdomen. Pneumogastrography, using air or carbonated beverages as the negative contrast medium, can also be useful for identifying intragastric foreign material [41]. Contrast radiography to aid foreign body elucidation has largely been replaced by ultrasound when available.
Figure 5.2 (a) A right lateral radiograph of a dog that ingested pebbles. Note the focal accumulations of pebbles in the pylorus and at the ileocolic junction (arrow) plus multiple gas‐distended small intestinal segments. (b) A right lateral radiograph of a dog with a linear foreign body, note the plication of the small intestine and gas segmentation.
Ultrasound
Ultrasound has become widely used as a means of identifying foreign objects or GI obstruction in animals, with some suggesting ultrasound may be preferred over survey radiography [42, 43]. Availability of ultrasound in practice and ultrasonographer skill play key roles in determining whether radiography or ultrasound is the preferred imaging modality.
Ultrasonography has been shown to be an effective means of identifying GI foreign bodies and obstruction, even when radiographs are inconclusive. Sensitivity of ultrasound has been reported as high as 100% [42, 44] for identifying foreign bodies. Tyrell and Beck reported that 16 of 16 objects were identified by ultrasound in dogs and cats suspected of having GI foreign bodies, compared with only 9 of 14 detected by survey radiography [42]. In another study by Manczur et al., ultrasonography was reported to have a sensitivity of 85% and specificity of 94% for identifying intestinal obstruction based on findings of surgical or medical management, but results of radiographic findings were not compared [45]. In a veterinary study by Sharma et al., radiography definitively identified obstructed versus non‐obstructed dogs in 58 of 82 cases (70%), while ultrasonography produced a definitive result in 80 of 82 (97%) dogs [43]. In animals with suspected obstruction, ultrasound was able to rule out a small intestinal obstruction in 74% and correctly identify obstruction in 23% of cases, the majority of which were due to foreign bodies [46]. This yielded a sensitivity of 100%, specificity of 95.8%, and positive and negative predictive values of 87.5 and 100%, respectively [46]. In addition to successfully identifying objects and obstruction, ultrasonography may also provide additional information not identified on plain radiographs, including free abdominal fluid, evidence of perforation, free gas, GI wall thickening, loss of layering to the small intestine, and lymphadenomegaly [42, 44].
Ultrasonographic findings consistent with a foreign body include distal acoustic shadowing and surface reflection that vary with type of foreign body (Figure 5.3a) [42]. Intramural hematoma marked by septated, hypoechoic, mural expansion of the small intestine has also been reported [47]. Ultrasound may be especially helpful in identifying non‐radiopaque objects, such as wood. Ultrasonographically, wood appears as a linear, echogenic surface associated with uniform acoustic shadowing [48, 49]. Adjacent soft‐tissue swelling may also be present if the wood has migrated out of the stomach [48]. Small intestinal obstruction is suggested by identification of the actual obstruction, intestinal plication, or segmental dilation (Figure 5.3b). Sharma et al. suggested that finding a jejunal diameter greater than 1.5 cm should prompt a search for a small intestinal obstruction (Figure 5.3c) [43].
Figure 5.3 (a) Transverse sonogram of the duodenum at the level of the duodenal papilla. The lumen is filled with a foreign body (right of the image) and anechoic fluid (left of the image). The foreign body (cloth) is characterized by a convex hyperechoic interface in the near field and creates an acoustic shadow in the far field due to attenuation of the ultrasound beam. This is the most common appearance of gastrointestinal foreign bodies. (b) Sagittal sonogram of a plicated small intestinal segment. This image demonstrates the severe folding or pleating of the intestinal wall that occurs with linear foreign bodies. The linear hyperechoic foreign body is not seen as this image was obtained slightly off midline to the luminal center. (c) Transverse sonogram of the small intestine proximal (oral) to a foreign body. Note that the luminal diameter > 1.5 cm should prompt search for an obstruction.
Source: Dr. A. Sharma, University of Georgia, Athens, GA. Reproduced with permission of Dr. A. Sharma.
It may also be possible to identify GI perforation via ultrasonography. The most common ultrasonographic findings in dogs and cats with perforation include focal or regional hyperechoic fat, peritoneal effusion or pneumoperitoneum, fluid‐filled stomach or intestines, and thickening or loss of GI wall layering. Additional findings reported concurrently with foreign body perforation included corrugated or undulating intestine, regional lymphadenopathy, hypomotility, pancreatic changes, the presence of a mass or foreign object, gastroduodenal junction “crumpling,” and gastric wall mineralization [50, 51]. Ultrasonography has also been shown to be superior to computed tomography (CT) for the identification of hypoperfused lesions of the bowel [52].
Computed Tomography
CT is becoming a more commonly used modality because it is fast and easy to perform, and is more readily available. Contrast‐enhanced and non‐contrast CT have been shown to accurately identify GI foreign material and obstruction as well as to differentiate surgical from nonsurgical acute abdomen patients [52–54]. Additionally, while the diagnostic accuracy for surgical versus non‐surgical conditions is high for radiographs, ultrasound, and CT (94%, 94%, and 100%, respectively), median CT acquisition time was far faster than ultrasonography (2.5 and 26.0 minutes, respectively) [54].
Surgical Techniques
Removal of foreign material from the GI tract is primarily performed when the material has not yet reached or is unable to reach the colon. See Chapter
