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There are numerous conditions that may result in a patient presenting with gastrointestinal signs. In an otherwise healthy patient with an acute presentation of GI symptoms, it is impractical to perform a full diagnostic work-up to rule out all possible conditions. In these cases, radiographs are a great place to start the diagnostic process.
The most basic utility of radiographs in a vomiting patient is to determine whether medical management or urgent surgical intervention is indicated. In cases where radiographs do not provide a clear answer between medical or surgical management, they may also help guide further diagnostics, including specific bloodwork, abdominocentesis, or additional imaging studies (i.e., ultrasound and contrast radiography).
When taking abdominal radiographs, it is always incredibly important to take three views: a right lateral, a left lateral, and a ventrodorsal view. This is crucial because gas and fluid may redistribute between views in such a way that a significant lesion may only be clearly appreciable on a single view. For example, a left lateral view is sometimes the only view where a gastric outflow obstruction may be appreciated. This is because the gastric antrum and pylorus are right-sided, so on a left lateral view, they have the potential to fill with gas, which may highlight foreign material. On a right lateral view, the gastric antrum and pylorus are often filled with fluid, which may obscure foreign material. One exception to the “three views” rule would be a patient with clinical signs highly suggestive of gastric dilatation-volvulus, as described later in this article.
Radiographs can be used to diagnose small intestinal mechanical obstruction in dogs and cats. When evaluating these images, there are three is considerations to keep in mind: whether there are two populations of the small intestine; whether the dilated segments are pathologically dilated; and whether there is confidence that the dilated segments are not the colon.
Two populations of small intestine can be determined when there are both normal segments of small intestine and dilated segments present. Generally, a patient with small intestinal segments that are at least twice the diameter of other segments can be classified as having two populations of small intestine. This metric is easy to apply visually and may not even require measurements in some patients.
Once two populations have been identified, a determination can be made as to whether the apparent dilated segments are pathologically dilated. In dogs, pathologic dilation can generally be considered for small intestinal segments that are at least 1.4-1.6 times the height of the fifth lumbar vertebra (L5). In cats, pathologic dilation can generally be considered for small intestinal segments that are greater than 12 mm.
Finally, it is important to be confident that the dilated intestinal segments are, in fact, small intestinal segments, rather than the colon. In cases where the colon cannot be confidently identified, additional imaging may be required, such as ultrasound or pneumocolonogram.
It is essential to remember that these aforementioned metrics are guidelines only, and not all cases will conform to them. For example, in cases of proximal small intestinal mechanical obstruction, there may be no small intestinal dilation. Meanwhile, in cases of distal small intestinal mechanical obstruction, there may be diffuse dilation of the small intestine.
For both gastroenteritis and pancreatitis, radiographs are often normal. In some cases of gastroenteritis, diffuse small intestinal dilation and mild decreased peritoneal serosal detail may be appreciated. In some cases of pancreatitis, mass effect and decreased serosal detail in the right cranial abdomen, widening of the gastroduodenal angle, and gas-dilation of the duodenum may be appreciated. More severe cases of pancreatitis may develop noticeable peritoneal effusion or peritonitis.
Cases of peritonitis will typically have a mottled, hazy, or irregular loss of serosal detail. This appearance is typically different from that of patients with a large volume of peritoneal effusion, which generally results in a more uniform loss of serosal detail, although the distinction can be challenging in some cases.
Peritonitis can be sterile or septic, and the determination between the two cannot always be made radiographically. In patients without body wall trauma or recent surgery, the presence of free peritoneal gas typically indicates gastrointestinal perforation and subsequent septic peritonitis. In cases of peritonitis without clearly appreciable free peritoneal gas, abdominocentesis and blood work can help diagnose septic peritonitis.
In patients with the typical signalment and presentation for gastric dilatation-volvulus, a single right lateral radiograph is often sufficient to make the appropriate diagnosis. Severe gastric dilation will be evident, accompanied by a “double bubble” appearance resulting from the dorsal and leftward displacement of the pylorus. If there is any uncertainty on the initial right-lateral radiograph, do not hesitate to take additional views.
Mesenteric torsion is typically characterized by severe, diffuse small intestinal dilation, often accompanied by gas dilation. Severe acute clinical signs generally accompany this, and, although uncommon, it is often fatal.
Colonic torsion can present with severe clinical signs (hypovolemic shock) or milder clinical signs (abdominal discomfort, vomiting, diarrhea), and the history can be acute or subacute. Although challenging to diagnose, radiographic findings include segmental distension and focal narrowing of the colon, displacement of the descending colon, and displacement of the cecum. Barium enema or CT is generally required for definitive diagnosis.
