Cats with idiopathic chronic rhinosinusitis that develop clinical signs before two years of age have more severe nasal conchal lysis, sinus malformation, and more severe inflammation on histological examination.

Objective: To evaluate the severity of sinonasal lesions on CT in cats with feline idiopathic chronic rhinosinusitis (FICR) comparing cats who developed the condition at a young age to those who developed it as an adult. And, to assess if CT findings correlate with histopathology.

Animals: 58 cats with FICR confirmed on histopathology.

Methods: Medical records were retrospectively reviewed. Cats were divided into 2 groups based on their age category: juvenile (group 1, n = 30) and adult (group 2, 28), with juvenile cats being 2 years old or younger and adults being older than 2 years at the onset of clinical signs. Computed tomographic findings were recorded and graded (mild, moderate, and severe) by a board-certified radiologist, comparing each group. The CT findings were then compared to the histopathology results.

Results: The overall CT grade was not significantly different between the 2 groups (P = .21). Nasal conchal lysis was more severe in group 1 than in group 2 (P = .002), and group 1 also had a higher incidence of sinusal malformation (OR 2.42). Inflammatory infiltrates were more severe on histopathology in group 1 than in group 2 (OR 4.95), and the overall CT grade was slightly positively associated with the histological severity (κ = 0.2).

Clinical Relevance: Feline idiopathic chronic rhinosinusitis was associated with more severe nasal conchal lysis, sinus malformation, and more severe inflammation on histopathological examination in cats that develop clinical signs before 2 years of age. This finding could have an impact in term of clinical signs severity.