By Heather Spain, DVM, DACVR
In the vomiting patient, especially a young animal or one with a tendency for dietary indiscretion, ruling out mechanical obstruction secondary to a gastrointestinal foreign body is a common reason for performing survey abdominal radiographs. The first step is a careful search of the length of the gastrointestinal tract for evidence of abnormal luminal contents. Of course, some foreign objects (e.g., of mineral or metal opacity) will be easier to identify than others (e.g., soft tissue opacity or lucent foreign bodies). When foreign material is identified, or at least suspected, determining the location of this material (gastric, small intestinal, or colonic) is the next important step. Due to inherent superimposition of structures encountered in abdominal radiography, this determination can be challenging, even for experienced practitioners. Identification of concurrent imaging features suggestive of small intestinal mechanical ileus, such as two populations of bowel (with normal bowel segments measuring less than 1.6x the height of L5 in the dog and less than 12mm in the cat)1, supports a small intestinal localization of the foreign body, and exploratory laparotomy may be pursued. However, in cases where the patient has presented soon after ingestion, has been intractably vomiting, has a foreign body that is only partially obstructive, or has received medical management for an apparently nonobstructive foreign body, determining the location of the material may be more difficult. Accurate localization is imperative, as it will drastically change the patient’s treatment plan. Following are three tips for additional radiographs that are easy to perform in the general practice setting and may increase diagnostic yield of a study when a foreign body is suspected.
Tip #1 The Left Lateral View: As a general standard, many practices obtain a two-view study of the abdomen, including right lateral and ventrodorsal (VD) images. Though a recent study suggested that obtaining three views of the abdomen instead of two did not have a statistically significant effect on diagnostic accuracy or confidence in evaluation of studies from patients presented with acute abdominal signs,2 obtaining a left lateral view can still provide diagnostic benefit. On a left lateral projection, the gastric fundus will be dependent and the pylorus will be nondependent; as a result, gas within the gastric lumen will redistribute into the pylorus, potentially into the pyloroduodenal outflow tract, and even into the proximal duodenum. Obtaining a left lateral view as the first image in a three-view abdominal series is more likely to highlight the pylorus and proximal duodenum with gas compared to obtaining it as the second or third view in the series.3 Therefore, if clinical suspicion of an outflow tract obstruction or a linear foreign body is high, planning to obtain the left lateral view first may be beneficial. The presence of an outflow tract foreign body may appear as a distinct object highlighted by surrounding gas or as the lack of gas within the pyloric outflow tract (Figure 1). Because linear foreign bodies must have a proximal anchor point in order to produce their characteristic intestinal plication, the pyloric outflow tract is a very common location for these foreign bodies to lodge; one study reported up to 85% of dogs with linear foreign bodies as having material anchored in the pyloric outflow tract.4
Tip #2 The Pneumocolonogram: The use of contrast media in diagnostic imaging is very common. The most recognizable contrast media, such as barium and iodinated compounds, are designated as “positive” contrast media due to their highly opaque appearance on radiographs. Alternatively, gas is designated as a “negative” contrast medium. Similar to our previous tip where native gas was used to better visualize a particular anatomical region +/- highlight a foreign object, gas can also be infused into a viscous as a negative contrast agent for the same purpose. A pneumocolonogram is an efficient and simple study that can better define the course and luminal contents of the colon. A red rubber or Foley catheter can be used. A red rubber catheter should be advanced into the distal descending colon. The Foley catheter can be positioned more caudally, even within the rectum, as partial inflation of the balloon will reduce retrograde leakage of gas. In either case, the catheter should be left in place following administration of gas. Room air is gently infused, ideally until the entire length of the colon up to the ileocecocolic junction is gas-filled. Published doses range from 1-8mL/kg5-6 for a dog to 20-30mL total for a cat.7 The patient may be more comfortable and less likely to expel administered air if sedated. Additional lateral and VD radiographs are then obtained for comparison to survey radiographs (Figures 2-3). The presence of fecal material within the colon does not preclude performance of a pneumocolonogram, though it may make administration of gas slightly more difficult; when the colon contains a large volume of fecal material, it should be easily identified and a pneumocolonogram is unlikely to add diagnostic information.
Tip #3 The Horizontal Beam: The presence of free peritoneal gas in a patient with a suspected or known GI foreign body is suggestive of GI perforation and an indication for emergency surgery. In larger volumes, free gas may appear as conspicuous angular gas lucencies that highlight the serosal surface of abdominal organs; smaller volumes can appear as multifocal, round, or irregularly shaped gas lucencies not superimposed with a viscous; scant gas may only be evidenced by a subtle, stippled appearance to the mesentery. Pneumoperitoneum of at least 0.5mL in volume can be reliably identified radiographically with increased detection rates on lateral compared to VD projections.8 When the presence of pneumoperitoneum is questionable, the use of a horizontal x-ray beam can help identify gas accumulation in a nondependent portion of the abdomen (Figure 4). Use of this technique may be limited in private practice, as a rotating x-ray tube head is required to obtain the view. The patient should be positioned in left lateral recumbency and a VD radiograph obtained with the horizontal x-ray beam. Free abdominal gas should collect in the nondependent region of the abdominal cavity adjacent to the body wall. Left lateral recumbency is preferred, as collection of gas within the gastric fundus on a right lateral view can complicate interpretation.
Even with the use of these additional radiographic techniques, a definitive diagnosis of a GI foreign body/mechanical ileus may not be possible with radiography alone. In this situation, the use of alternative imaging modalities, such as abdominal ultrasonography or CT scan, may be required.
Figure 1: Right lateral (A) and VD (B) abdominal radiographs of a patient with a foreign body within the pyloric outflow tract. On the left lateral projection (C) the foreign material is outlined by gas and is seen crossing the pyloroduodenal junction.
Figure 2: Right lateral radiograph (A) and VD radiograph of a patient with a soft tissue opaque, striated foreign body in the right cranial abdomen (textile). Following pneumocolonogram, it is clear that foreign body is within the small intestine (C).
Figure 3: Right lateral radiograph (A) and VD radiograph of a patient with a mineral opaque mid-abdominal foreign body (rock). Following pneumocolonogram the location of the rock in the proximal descending colon is confirmed (C).
Figure 4: Right lateral (A) and VD (B) radiographs of a patient with suspected pneumoperitoneum found on thoracic radiographs; there are linear lucencies between the serosal margin of the stomach and the diaphragm on these images. A horizontal beam VD radiograph (C) with the patient in left lateral recumbency demonstrates collection of free gas immediately adjacent to the body wall. The right side of the patient is marked (R).
- Thrall, D (2018). Textbook of Veterinary Diagnostic Radiology. 7th Elsevier: St. Louis, MO.
- Mavromatis M, Solano M, Thelan M (2018). Utility of two-view vs. three-view abdominal radiography in canines presenting with acute abdominal signs. Vet Rad & Ultrasound. 59(4): 542-546.
- Vanderhart D, Berry CR (2015). Initial influence of right versus left lateral recumbency on the radiographic finding of duodenal gas on subsequent survey ventrodorsal projections of the canine abdomen. Vet Rad & Ultrasound. 56 (1): 12-17.
- Hobday MM, Pachtinger GE, Drobatz KJ, Syring RS (2014). Linear versus non-linear gastrointestinal foreign bodies in 499 dogs: clinical presentation, management and short-term outcome. J Small Anim Pract. 55: 560-565.
- Nyland TG and Ackerman N (1978). Pneumocolon: A diagnostic aid in abdominal radiography. Vet Rad. 19(6): 203-209.
- BSAVA Manual of Canine and Feline Abdominal Imaging (2012). Ed. R O’Brien and F Barr. British Small Animal Veterinary Association, Gloucester.
- Wallack, S (2003). The Handbook of Veterinary Contrast Radiography.
- Marlof A, Blaik M, Ackerman A, Watson E, Gibson N, Thompson M (2008). Comparison of computed radiography and conventional radiography in detection of small volume pneumoperitoneum. Vet Rad & Ultrasound. 49(3): 227-232.