Anatomopathological characterization of hepatic lesions of feline infectious peritonitis in cats.

Feline infectious peritonitis (FIP) is one of the most important infectious diseases and a significant cause of death in cats. While the pathology of FIP has been well documented, there is little information on the hepatic lesions. The aim of this study was to characterize the macroscopic, microscopic and immunohistochemical patterns of the liver lesions in cats with FIP. A retrospective study was conducted on 131 cats with FIP, of which 59 had histological inflammatory lesions in the liver and were immunopositive for feline coronavirus. Four major gross patterns were defined: perihepatitis (21/59); nodular with perihepatitis (18/59); nodular multifocal (13/59); and diffuse (7/59). Four histological patterns were observed: (1) random pyogranulomas; (2) random multifocal to coalescent caseous necrosis surrounded by pyogranulomatous inflammatory infiltrate, fibrin and cellular debris; (3) perihepatitis; and (4) random multifocal to coalescent caseous necrosis surrounded by neutrophils, macrophages, lymphocytes and plasma cells. Most cats had more than one histological pattern. FIP virus antigen was detected in macrophages in the pyogranulomas and around the necrotic areas. The diagnosis of FIP remains challenging, especially in cats without effusion. The liver can be considered a suitable site for biopsy when feasible.