One of the subtleties of interpreting abdominal radiographs is peritoneal detail. It’s a difficult region to evaluate, since it is the potential space between all the organs. It is normally filled with fat, including the falciform fat ventral to the liver, and mesenteric fat in the omentum. When we say peritoneal detail, we mean that the contrast between fat and the soft tissue of the organs in the abdomen makes the serosal surfaces visible. Poor peritoneal detail is the loss of this fat-soft tissue interface.
Causes of poor peritoneal detail are loss or apparent loss of fat in the peritoneal space. Thin animals have very little fat, so their detail is poor and the organs are not well seen. Animals with peritoneal effusion (hemoperitoneum, transudate, exudate, urine) have more soft tissue (fluid) opacity than fat because of all the fluid. In this case, the serosal surfaces are also not visible.
How do you tell the difference between lack of fat and effusion? The secret is to look at the abdominal contour and skeleton. Young animals have open vertebral physes, and typically have poor peritoneal detail (lack of fat, small amount of peritoneal fluid) until 2-3 months of age. If the animal is thin, the soft tissues over the vertebral column have an undulating or tented appearance, and the abdomen is concave. Conversely, if there is fluid in the peritoneal space, the abdomen will be rounded. If you consider the animal’s age, body condition and abdominal contour, you should be able to determine if poor detail is due to lack of fat or excess fluid. Tomorrow I’ll address the mottled peritoneum.