Ultrasonography is sexy, but dont rule out abdominal radiography

Positional radiography can be used to evaluate for free gas in the abdomen. Since an air-fluid interface is needed to help to see gas within the peritoneal space, a horizontal beam projection with the patient on its left side and a ventrodorsal projection will put the gas in the right lateral abdomen near the pyloric antrum. Since the pylorus is small, the gas accumulation will be identified caudal to the diaphragm. Radiograph image courtesy of Dr. PeaseIf your veterinary clinic has an ultrasound machine, you probably think that's the go-to when you have an acute abdomen patient. I mean, “swipe right.” Amirite? But if you don't have this miraculous wonder of an imaging machine, you feel guilty. Don't.

Traditional abdominal radiography is a great first modality for patients with acute abdominal pain, says Anthony Pease, DVM, MS, DACVR. Just make sure your protocol is up-to-date with these four tips to make your long-standing relationship with abdominal radiography work.

1. Three is better than two

Pease says that traditionally, right lateral and ventrodorsal projections are taken when evaluating the stomach. A right lateral projection places gas in the fundus of the stomach and fluid in the pyloric antrum. And to evaluate the pylorus, a ventrodorsal projection puts fluid in the fundus and gas in the pyloric antrum. But at Michigan State University, Pease says they take three views of all abdomens: a right lateral to see the fundus, a left lateral to evaluate the pylorus and look for pyloric outflow obstructions, and a ventrodorsal to provide more information about the pylorus, to better evaluate the colon and to complete the three-dimensional aspect of radiography. More information is always better!

2. The guidance of the contrast (a few “highlights”)

If you suspect a luminal obstruction and you don't have an ultrasound machine, don't worry. “Barium or iodinated contrast medium procedures can help you determine if the bowel wall is thick or infiltrated and let you look at overall motility or assess for a rupture,” says Pease. >BIG caveat: If one of these abnormalities is seen, you'd be better off performing an exploratory laparotomy rather than a contrast procedure since the contrast study takes three to six hours to complete.

Pease says barium contrast medium is the most universally used agent for gastrointestinal imaging-and it's safe. The dose is 6 to 10 ml/lb, generally administered through a gastric tube. If aspirated, barium physically obstructs the airways with no inflammatory component and may cause granulomas if it leaks into the peritoneal or pleural cavity. So Pease says not to use it if a ruptured bowel or ruptured esophagus is suspected. Iodinated contrast medium is generally used intravenously but can be administered orally for these studies. Its main limitation, according to Pease, is that it has a bad taste and it is hypertonic (it will draw fluid into the bowel and will cause an inflammatory reaction if aspirated into the lungs).

3. Free gas? Where? I'm driving over …

Pease says positional radiography can also be used to evaluate for free gas in the abdomen. Since an air-fluid interface is needed to help to see gas within the peritoneal space, a horizontal beam projection with the patient on its left side and a ventrodorsal projection will put the gas in the right lateral abdomen near the pyloric antrum. Since the pylorus is small, the gas accumulation will be identified caudal to the diaphragm.

“For a suspected gastric dilatation-volvulus (GDV), you only need to obtain a right lateral radiograph,” says Pease. “Visualization of the pylorus in the craniodorsal abdomen on a right lateral radiograph is pathognomonic for a GDV. Numerous times people have been fooled by the normal appearance of the ventrodorsal projection and missed the volvulus.”

A futile effort

Don't even bother trying to evaluate small intestinal wall thickness on survey radiographs! Since soft tissue and fluid are the same opacity. “It's impossible to know whether the structure you're seeing is a thick wall or just a combination of fluid summating with the small intestinal wall,” says Pease.

4. Look to the colon

The abdomen is divided into two spaces, peritoneal and retroperitoneal. The retroperitoneal space contains the adrenal glands, kidneys and sublumbar lymph nodes, and the peritoneal space contains the remaining organs. Pease says this will help you determine the differentials for a mass or for gas within the abdomen. How? Look to the colon!

The retroperitoneal space is dorsal to the colon. So if a soft tissue mass displaces the colon ventrally, then the mass is likely retroperitoneal, indicating it is either arising from the kidneys, adrenal glands or sublumbar lymph nodes. If gas is present in the retroperitoneum, this is likely secondary to a pneumomediastinum rather than a rupture of the gastrointestinal tract or other causes of pneumoperitoneum.

A final take

“Although technology continues to evolve diagnostic methods, radiographs are still useful to determine if a surgical obstruction or mass is present-or can at least provide a general overview of the abdomen,” says Pease. “And while barium contrast medium has largely been replaced with ultrasonography or exploratory laparotomy, abdominal radiography can work with abdominal ultrasonography to augment and further characterize findings when it comes to patients with acute abdominal pain.”