Feline orbital mycosis: A report of 11 cases.

Invasive fungal infections in cats can result in sinonasal or sino-orbital disease, with brachycephalic breeds reported to be predisposed. However, a subset of cases exhibits isolated orbital signs without clinically evident sinonasal involvement, raising questions about whether the sinonasal component is genuinely absent or subclinical at the time of presentation. This retrospective study describes 11 cats with orbital mycosis lacking overt sinonasal disease, identified through the Comparative Ocular Pathology Laboratory of Wisconsin between 1998 and 2024. All 11 cats were mesocephalic breeds (10 domestic shorthair, 1 domestic longhair), with no apparent sex predilection and ages ranging from 1.5 to 17 years (median, 7 years). All cases presented with orbital disease, most commonly exposure keratitis and exophthalmos, without documented upper respiratory signs. Histologically, lesions were characterized by eosinophilic and granulomatous orbital cellulitis with central necrosis. Aspergillus sp. were the most common organisms identified morphologically (8/11), followed by oomycetes (2/11) and Mucorales (1/11). Panfungal polymerase chain reaction confirmed Aspergillus sp. in 3 cases but frequently amplified suspected contaminants. Review of published feline orbital mycosis cases revealed that mesocephalic breeds predominantly present with orbital signs, whereas brachycephalic breeds more commonly exhibit concurrent sinonasal disease. These findings suggest that orbital mycosis in mesocephalic cats may represent subclinical sinonasal infections with preferential orbital extension, potentially reflecting anatomical differences in skull conformation.