Subconjunctival mycetoma caused by Scedosporium apiospermum infection in a horse

An 11-year-old American Saddlebred gelding was presented for evaluation of a nonpainful subconjunctival mass involving the lateral canthus of the left eye. Other findings included a central corneal scar and a small central cataract of the lens in the left eye. Fine-needle aspiration of the mass was performed and cytologic examination revealed marked pyogranulomatous inflammation with intralesional fungal hyphae, consistent with mycetoma. The fungal structures were elongated and characterized by nonstaining walls; several bulbous yeast-like structures were also observed. The mycetoma was surgically removed and submitted for histopathologic examination and fungal culture. The histopathologic diagnosis was subconjunctival phaeohyphomycosis. Scedosporium apiospermum was identified based on macroscopic and microscopic features of the organism in culture. Scedosporium spp. have been reported as causes of mycetomatous and nonmycetomatous infections in both immunocompromised and immunocompetent people and animals. S. apiospermum and Pseudallescheria boydii, which is its teleomorphic counterpart, have been implicated as potentially emerging human and veterinary pathogens. Timely diagnosis is essential as the organism is often resistant to commonly used antifungal drugs. This report provides a detailed cytologic description of the organism and recent information on the taxonomy of this fungus and the diagnostic peculiarities of this particular infection.