Abdominal Radiology Q & A
by Allison Zwingenberger on February 19, 2008
What are the radiographic signs for free peritoneal gas?
There are a few different signs to look for when you suspect free peritoneal gas. Serosal surfaces, especially ones that you would not normally see (liver lobes) become visible from the high contrast between gas and soft tissue. You will also see gas that is not contained within the gastrointestinal tract. These gas bubbles often have odd, angular shapes. Gas also tends to rise to the highest point in the abdomen, which is under the diaphragm in both projections. Look for the diaphragm to be outlined by gas on both sides. It is usually highlighted by gas (lungs) on the cranial side, but the caudal side should have stomach wall or liver adjacent to it. When outlined on both sides by gas, the diaphragm will appear as a very thin, sharp, soft tissue line.
Signs to look for:
*increased peritoneal detail
*angular gas bubbles not contained in the GI tract
*diaphragm outlined by gas on both sides
Is there any benefit to fasting an animal prior to radiographing in order to see the GI tract better?
Yes, fasting the animal and taking it outside will ensure that the stomach and colon are empty. The stomach can cause a mass effect in the cranial abdomen when it is full. Radiopaque material in the colon can also obscure portions of the abdomen. An empty GI tract as well as urinary bladder makes for a much better study.
How can I identify the different parts of the diaphragm on a radiograph?
Generally, when the animal is in lateral recumbency, the weight of the abdominal organs push on the dependent crus. If the animal is in left lateral, that would be the left crus. So you will usually see the left crus projected in front of the right in left lateral recumbency. The opposite is true for right lateral recumbency. But there is a lot of variation in diaphragm conformation between animals, and where you center the x-ray beam, so you won’t see these changes every time. Just remember the fundus sits under the left crus, and the caudal vena cava enters the right crus for landmarks.
The cupula is sometimes visible on a lateral radiograph, but is seen better on the v/d as the most cranial part of the diaphragm centered on midline. The two crura can look like “Mickey Mouse” ears.