Case Report Parotid salivary gland carcinoma in a geriatric horse E. J. McConnell*, M. G. Sanz § , U. C. M. Kafka † and N. M. Duncan ‡ Section of Equine Medicine, † Section of Diagnostic Imaging, Department of Companion Animal Clinical Studies, and ‡ Department of Pathology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa; and § Maxwell H Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, Kentucky, USA. Keywords: horse; parotid; salivary; carcinoma; neoplasia Summary This case report describes a geriatric gelding with a 2 month history of fast-growing masses within the parotid and submandibular regions. The horse was dyspnoeic on presentation and upper airway endoscopy revealed partial airway obstruction at the level of the pharynx, secondary to a space-occupying mass. Cytological evaluation of multiple fine-needle aspirates obtained from the masses were suggestive of salivary gland neoplasia, therefore the horse was subjected to humane euthanasia. A computed tomographical scan was obtained post mortem and revealed a large multi-lobulated mass involving both guttural pouches, resulting in 80% occlusion of the naso- and oropharynx. Histopathology confirmed a parotid salivary gland carcinoma (papillary-cystic type). Salivary gland tumours are extremely rare in horses, with only a few cases reported in the literature. Treatment of these malignancies proves to be challenging, requiring complete parotidectomy or surgical debulkment, in combination with adjunctive therapy. Introduction The number of geriatric horses and ponies (age 15 years) in the equine population is steadily rising, probably due to improvements in nutrition and an increasing willingness by owners to seek veterinary care and prolong life (Brosnahan and Paradis 2003; Ireland et al. 2011). Ageing has been identified as a risk factor for the development of numerous conditions including chronic laminitis and neoplasia (Ireland et al. 2011), resulting in a growing number of reports involving equine tumours. A study of disease prevalence in 467 geriatric horses, revealed an incidence of neoplasia (excluding pituitary adenomas and lipomas) of 10%, with the most common neoplasia being squamous cell carcinoma (Brosnahan and Paradis 2003). No mention of neoplasia affecting the salivary glands was made, highlighting the infrequent occurrence of such a condition. Salivary gland tumours are rare in domestic species, with an overall incidence of 0.17% in dogs and cats (Carberry et al. 1988). Currently, the incidence of salivary gland neoplasia in horses is unknown; however, given the scant number of reports available in the equine literature, it is deemed to be low. The horse has 3 pairs of major salivary glands (parotid, submandibular and sublingual) and 4 minor salivary glands (buccal, labial, lingual and palatine), responsible for the production of serous and mucous salivary secretions. Of these, the parotid salivary glands are the largest and the most frequently affected by disease (Schumacher and Schumacher 1995). The most common neoplasia associated with the major salivary glands in horses is melanoma, although lymphoma, adenocarcinoma and acinic cell carcinoma have also been reported (Stackhouse et al. 1978; Schumacher and Schumacher 1995; Cole MacGillivray et al. 2002). To our knowledge, this is the first case of computed tomographic (CT) imaging of a salivary gland tumour in a horse. Case history A 25-year-old crossbreed gelding weighing 423 kg was presented to the Onderstepoort Veterinary Academic Hospital of the Faculty of Veterinary Science, University of Pretoria for further investigation of fast-growing masses within the left parotid and submandibular regions. The lesions were first noted 2 months prior to presentation and were reported to grow steadily throughout this period. The horse was observed to have a decreased appetite for roughage and was reluctant to graze. No abnormalities were detected on skull and pharyngeal radiographs, obtained by the attending veterinarian prior to referral. *Corresponding author email: emma.mcconnell@up.ac.za EQUINE VETERINARY EDUCATION 1 Equine vet. Educ. (2012) •• (••) ••-•• doi: 10.1111/j.2042-3292.2012.00423.x © 2012 EVJ Ltd