Headshaking is a common problem in horses. The etiology is unknown but thought to involve sensory input from branches of the trigeminal nerve, some of which are within the infraorbital canal.The objective of this retrospective cross-sectional study was to describe the CT anatomy and variations of the infraorbital canal in horses with local disease processes and normal horses, and to examine associations between those findings and headshaking. Computed tomography scans were reviewed and morphological changes of the infraorbital canal were described. Presence of changes was then tested for association with headshaking prevalence, presence of disease processes in the region of the infraorbital canal, age, and sex. Nonparametric tests were used and a P-value of .05 was considered significant. A total of 218 horses were included, 9% of which had headshaking and 45% had CT lesions in the region of the infraorbital canal. Morphological changes to the bone of the infraorbital canal were found in 121 horses (56%) and included the following: increased mineralization 39 (18%), decreased mineralization 89 (41%), deformed shape 51 (23%), displaced position 43 (20%), and disruption 11 (5%). All changes of the infraorbital canal significantly increased in frequency with the presence of adjacent disease. Increased mineralization and disruption of the infraorbital canal were significantly associated with headshaking in horses with adjacent disease; the latter only reached significance after exclusion of dentally immature horses.No other changes were significantly associated with the presence of headshaking. No association was found between headshaking and the age or sex of the horse. K E Y W O R D Sequine head, maxillary, neurological, sinusitis, trigeminal nerve

BackgroundSpinal cysts are rare findings in veterinary medicine, but they are increasingly recognized due to the availability of advanced imaging techniques. Extradural meningeal cysts in French Bulldogs have not been reported previously and arachnoid cysts (diverticula) have not been reported at the caudal lumbar (L6–L7) region in dogs.Case presentationTwo French Bulldogs, aged 5 and 8 years, were referred for evaluation of lower back pain and bilateral hind limb neurological deficits. Neurologic examination revealed ataxia and postural deficits in both dogs. Magnetic resonance imaging (MRI) showed cauda equina compression due to a cyst-like lesion at the level of L6–L7 in both cases. The dogs underwent dorsal laminectomy and the meningeal cyst was completely removed in one dog and in the other dog the spinal arachnoid diverticula was marsupialized. In Case 1, histopathology of the cysts was performed and MRI was repeated. Both dogs were pain free during follow-up evaluations.ConclusionsBased on radiological, intra-operative and histopathological findings, the first case was diagnosed as a meningocele connected by a pedicle to the caudal tip of the dural sac forming a dural diverticulum categorized as an extradural spinal cyst type Ib, and Case 2 as a type III intradural arachnoid diverticula. It is concluded that spinal cysts should be included in the differential diagnosis of cauda equina syndrome and lower back pain in French Bulldogs. Results of these cases may be useful for diagnostic and treatment management.