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Imaging is a critical component of the diagnostic workup in patients with suspected foreign body ingestion. Traditionally, abdominal radiographs have served as the initial imaging modality. The improved detail provided by digital (computed) radiography makes it more sensitive than conventional radiography in identifying GI foreign bodies [37]. Radiographic findings may include segmental small intestinal dilation, plication, or detection of a foreign body (Figure 5.2). Objective radiographic criteria for determination of small intestinal obstruction have been evaluated. Adams et al. compared the small intestinal diameter (SID) of cats to the dorsoventral height of the cranial end plate of the second lumbar vertebra (L2) and found that when the SID : L2 ratio was 3.0 or greater, the probability of a mechanical obstruction was greater than 70% [38]. In dogs, a value of 1.6 for the ratio of the 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.