Horse with nasal mass and trouble breathing - what caused it?

Abstract

We describe herein the clinical, endoscopic, computed tomography (CT), pathologic, and microbiologic features of an infection caused by an under-recognized fungal pathogen,, in a 25-y-old Australian Quarter Horse. The horse had a unilateral obstructive nasal mass, resulting in stertor and dyspnea. On endoscopy, the mass was tan, multinodular, and completely obstructed the nasal passage. CT analysis revealed a large, soft tissue-attenuating and partially mineralized mass in the right nasal passage and dorsal-conchofrontal sinus, expanding into adjacent paranasal sinuses with associated bone lysis and rhinosinusitis. Histopathology of the mass on 2 occasions revealed suppurative inflammation initially, and pyogranulomatous inflammation subsequently. The inflammatory reaction surrounded numerous spherical fungal structures (~60-80 µm diameter) that stained positively on periodic acid-Schiff and Grocott methenamine silver stains. PCR for the fungal internal transcribed spacer 1 and 2 regions followed by Sanger sequencing on a cultured isolate identified the agent as, which has only been reported previously as pathogenic in one horse in the United States, to our knowledge. Previous reports described this fungus as a nonpathogenic, environmental commensal fungus associated with insects and plants.