Hyalohyphomycotic chronic rhinosinusitis caused by <i>Microascus cirrosus</i> in a cat

Abstract A 13‐year‐old, male, neutered, indoor‐only, domestic long‐haired cat was presented with an 8‐month history of sneezing and a 2‐month history of epistaxis. Computed tomography demonstrated an irregular contrast‐enhancing soft tissue opacity within both nasal cavities and osteolysis of surrounding bony structures. Round to oval structures interpreted as yeasts were identified during cytological and histological assessment of blind nasal biopsies. The cat experienced ongoing clinical signs during empirical treatment for cryptococcosis, which prompted repeat computed tomography, rhinoscopy and fungal culture of nasal biopsies. Microascus cirrosus was cultured from these samples, with it suspected to have been the cause of this patient's chronic fungal rhinosinusitis. Treatment with oral terbinafine was initiated, which resulted in no overt improvement in clinical signs, leading to the patient's euthanasia.