Karyn A. Labbe1, Kimberly A. Allshouse1, Lindsey J. Gilmour1, Carolyn E. Arnold1, Canaan M. Whitfield-Cargile1, Cleet E. Griffin11College of Veterinary Medicine, Texas A&M University, College Station, Texas . There are no reports in the literature describing the incidence of headshaking/facial rubbing behavior with infraorbital canal (IOC) pathology due to only primary and secondary dental sinusitis. Given the impact that these behaviors can have on the horse's return to previous intended ridden use, an investigation is warranted. The objectives are (1) determine the occurrence of IOC disease in primary or secondary dental sinusitis, (2) describe IOC changes on CT and (3) report the frequency of head-shaking behavior between the sinusitis groups CT scans were assessed for IOC pathology (unilateral or bilateral) and description of IOC disease including displacement, deformation, periosteal proliferation, hyperostosis, osteolysis and infraorbital nerve exposure. Long-term outcome was determined by client questionnaire. Hyperostosis, periosteal proliferation and osteolysis were common CT findings. Hyperostosis was frequently found to involve both the infraorbital canal and the supporting bone structure. Follow-up was obtained in 48/61 cases, with three horses showing headshaking behavior and 2 horses exhibiting facial rubbing during ridden work. Infraorbital canal pathology is commonly detected on CT scans of secondary dental sinusitis. Hyperostosis may be an incidental finding within the paranasal sinuses. Infraorbital nerve histopathology was not performed on any case. The limited number of cases with no infraorbital canal pathology prevented direct comparison between the 2 groups. Client questionnaire carries a memory bias. Computed tomographic changes involving the infraorbital canal do not predict headshaking or facial rubbing behaviors. This finding is important in the context that these behaviors render some horses unusable for their intended riding discipline.
