In 2002, a 27-year-old captive female Przewalski’s wild horse (Equus caballus przewalskii) at the Denver Zoological Foundation presented with a decreased appetite, epistaxis, and clinical signs of sinusitis similar to those observed in the domestic horse. These include facial asymmetry, chronic to intermittent unilateral nasal discharge, exophthalmia, abnormal respiratory noise, ipsilateral ocular discharge, and fistula formation.1 Following 3 weeks of empirical oral antimicrobial therapy, the horse was immobilized for an examination, blood work, and radiographs. Trephining to explore the caudal right maxillary sinus revealed extensive bony necrosis as well as a large, firm, space-occupying mass within the sinus. Due to the likelihood of neoplasia and a poor prognosis for recovery, the horse was humanely euthanatized. Histopathologic results on the large sinus mass removed at necropsy revealed a squamous cell carcinoma (SCC).
In 2006, a 15-year-old captive male Przewalski’s wild horse presented with a decreased appetite, epistaxis, and clinical signs compatible with sinusitis. The horse was immobilized for an examination, blood work, and radiographs. Radiographs revealed a large, soft tissue density occupying the left frontal sinus. The horse died due to complications during anesthetic recovery. At necropsy, a 900 g sinus tumor was discovered, and histopathology again confirmed SCC.
To the authors’ knowledge, these are the first reports of sinus neoplasia in this species. Squamous cell carcinomas are the most common sinus tumors in domestic horses and prognosis is generally poor due to cases typically presenting after there is already advanced localized invasion and destruction.2
1. Honnas, C.M., and J.R. Pascoe. 2002. Diseases of the paranasal sinuses: sinusitis. In: Smith, B.P. (ed.). Large Animal Internal Medicine, 3rd ed. Mosby, St. Louis, Missouri. 53.
2. Laverty, S., and J.R. Pascoe. 1997. Sinusitis. In: Robinson, N.E. (ed.). Current Therapy in Equine Medicine 4. WB Saunders, Philadelphia, Pennsylvania. 419–421.