The Veterinarian will likely recommend x-rays to view the size and shape of internal organs, silhouette of the lungs, and whether there looks like free fluid in the abdomen. (vrcc.com)
An ultrasound revealed he had free fluid around the left kidney and enlarged lymph nodes. (austinpetsalive.org)
With the wet form of FIP, there is typically a collection of free fluid within the body cavities (abdomen and chest). (web-dvm.net)