FIP in a cat - an uncommon presentation

An 8-month-old DSH kitten with a history of chronic diarrhoea and vomiting presented with a palpable colonic mass that was surgically resected and submitted for histopathological evaluation. No other lesions were grossly evident at the time of exploratory laparotomy.

Fig 1. This is a section of the submitted formalin-fixed colon that has been opened. The wall of the colon contains a relatively well-demarcated, firm, homogenous white-grey mass.
Fig 2. This is an H&E section of the affected colon. The colonic mucosa and submucosa are infiltrated by nodular to confluent aggregates of a mixed inflammatory population. Similar inflammatory infiltrate was also evident expanding the serosal surface.
Fig 3. On closer inspection, the inflammatory infiltrate is composed predominantly of macrophages and neutrophils.
Fig 4. Immunohistochemistry was performed whereby antibodies against Feline Coronavirus (FCoV) antigen are applied to the sections of affected colon. Several macrophages are positive for FCoV in this section as denoted by a strong brown cytoplasmic staining pattern (arrows).

Final diagnosis

Feline infectious peritonitis (FIP) associated with focal nodular pyogranulomatous colitis


This case is an example of an uncommon but recognised intestinal presentation of a common infectious disease. FIP is an invariably fatal and sporadic viral disease of domestic and wild felids caused by feline corona virus (FCoV).

The majority of cats with non-effusive (dry) FIP present with pyogranulomatous inflammation or granulomas within the brain, kidneys, eye, lymph nodes and/or omentum. Occasionally however, cats affected with noneffusive (dry) FIP may present with chronic vomiting and diarrhoea associated with a palpable mass at the ileocecocolic junction or adjacent colon. On gross examination, the appearance of the mass can resemble that of lymphoma but FIP should remain an important differential diagnosis, particularly in cats of appropriate signalment.