A 10-year-old cat was diagnosed with chyloperitoneum based on the effusion
characteristics. Feline coronavirus serology was positive. The owner declin
ed further evaluation and elected euthanasia. Necropsy revealed vasculitis
with multifocal areas of necrosis and lymphocytic-plasmacytic inflammation
in multiple solid organs, most likely due to feline infectious peritonitis
(FIP). Immunohistochemistry was negative for FIP antigen. Notwithstanding,
the final diagnosis of FIP was based on the characteristic histopathologica
l lesions. Underlying causes of chyloperitoneum in cats and humans are disc
ussed, and possible pathogenesis of the chyloperitoneum in association with
a vasculitis such as FIP is discussed.