Feline infectious peritonitis (FIP) causes which type of lesions?

• A. Suppurative, granulomatous, modified transudate
• B. Fibrotic lesions
• C. Necrotizing vasculitis
• D. Granulomatous with caseating necrosis

Answer: (A)

FIP produces granulomatous inflammation that often involves vessels, i.e., pyogranulomatous vasculitis, with inflammatory cells that can include neutrophils (suppurative) and macrophages forming granulomas around small vessels and serosal surfaces. In the classic wet form, this vascular inflammation leads to leakage of protein-rich fluid into cavities, described as a modified transudate. So the tissue lesions reflect mixed inflammatory patterns (suppurative plus granulomatous) and the associated effusion is the high-protein, low-to-moderate cellularity fluid classified as a modified transudate. Other patterns like purely fibrotic lesions, necrotizing vasculitis, or granulomas with caseating necrosis are not typical hallmarks of FIP.