Computed Tomography (CT) imaging offers more diagnostic information than traditional two- dimensional systems. This enables imaging of greater anatomical detail, with a wide range of tissue attenuation and has the potential to eliminate the confusion that results from superimposition of surrounding structures. Currently at B&W Equine clinic is used for both standing horses, and anaesthetised animals such as foals or horses with neurological signs requiring a cervical myelogram. Patients undergo a CT examination of the head, performed with the horse under carefully monitored standing sedation with an aquisition time of 30-45s. The majority of horses accept the diagnostic procedure extremely well, although like all procedures performed in a conscious horse’s, the horse’s temperament and safety concerns ultimately dictate the feasibility. CT performed in the conscious sedated clinical patient is very helpful to diagnose many lesions localised to the head and cranial part of the neck depending on the conformation of the horse. Indications for Computed tomographic exams of the head are widespread. At our hospital these include investigation of: Horses with head trauma, including mandibular injuries and fractures; Suspected apical dental disease involving the reserve crown or apical areas and Dental fractures; Oral tumours; Paranasal sinus diseases including neoplasia, cysts, PEH, sinus empyema; Periocular lesions; Middle ear disease and Temporomandibular disease; Pharyngeal and Guttural pouch disease and cervical neurological disease. In vitro studies have demonstrated the ability to produce high resolution three-dimensional imagery pf the nternal equine dental structures1, 2. In Ex vivo studies CT, has demonstrated sensitivity for detailed appraisal of occlusal secondary dentinal thickness3, indundibular restoration4, 5. Clinical studies have confirmed the sensitivity for identification of dental alveololitis6 pulpar disease and dental sinusitis7, 8; sinus disease9, 10 and dental fracture11, and it has been shown to be more sensitive than radiography12.

Both helical and cone beam systems have been demonstrated to be diagnostic13 but the resolution of helical systems is preferred diagnostically currently. In many cases CT assists in determination of extent of periodontal disease, the significance of dental fractures, the presence of supernumerary dentition and appraisal of relation of dysplastic and/or fractured teeth to the surrounding structures. Localisation of disease to an individual root or pulp can assist greatly with treatment planning and outcome prediction. CT should be considered essential for determination of the extent of space occupying lesions such as Progressive Ethmoid Haematoma (PEH)14, brain abscess15, and neoplasia. Neoplasia involving the maxilla and mandible are often associated with teeth and CT this enables three-dimensional imaging that will inform the prognosis before undertaking ambitious surgical techniques. Treatment planning for surgical procedures involving the head, such as sinus exploration eg for sinus cysts or mandibular fracture repair, is greatly enhanced with the benefit of 3d CT images.

Like all diagnostic imaging modalities, there are limitations with CT. Horses that are severely ataxic or with acute neurological disease can tolerate the mobility of the air plinth poorly, resulting in excessive movement and non-diagnostic image or excessive anxiety in the patient. Cervical vertebral lesions of the mid- to caudal cervical vertebra only fit in the baryatric coils, and can require general anaesthesia. However, most horses can be managed effectively to enable a diagnostic examination of the head while standing, and in our clinic the costs of the imaging are usually offset by a more precise approach to treatment with improved outcome predictions.

References
1 Windley, Z Weller, R Tremaine, W H Perkins, J D (2009) Two- and three-dimensional computed tomographic anatomy of the enamel, infundibulae and pulp of 126 equine cheek teeth. Part 1: Findings in teeth without macroscopic occlusal or computed tomographic lesions Equine Veterinary Journal, 2009, Vol.41(5), pp.433-440, 2009
2 Kopke S. Angrisani,N, Staszyk, C. (2012) The dental cavities of equine cheek teeth : three-dimensional reconstructions based on high resolution micro-computed tomography,BMC Veterinary Research Vol. 8 173, 2012
3 R. Marshall, D. J. Shaw, P. M. Dixon (2012) A study of sub-occlusal secondary dentine thickness in overgrown equine cheek teeth The Veterinary Journal July 193, 53-57.
4 P. M. Dixon; D. Savill T. Liuti (2014) Critical evaluation of ex vivo restoration of carious equine maxillary cheek teeth infundibulae following high-pressure gas and micro-particle abrasion.The vet Journal 200 368-374.
5 Horbal, R.J.M. Reardon, T. Liuti, P.M. Dixon, (2017) Evaluation of ex vivo restoration of carious equine. Maxillary cheek teeth infundibulae following debridement with dental drills and Hedstrom files. The Veterinary Journal, 230; 30-35.
6 Henninger W., Frame E.M., Willmann M., Simhofer H., Malleczek D., Kneissl S.M., Mayrhofer E. (2003) CT features of alveolitis and sinusitis in horses. Vet. Radiol. Ultrasound 44, 269-276.
7 Casey M.B., Browne W.J. and Tremaine W.H. (2009) The diagnostic value of computed radiography in the investigation of pulpitis of equine cheek teeth. In: Proceedings of the British Equine Veterinary Association Congress, Equine Veterinary Journal, Newmarket. p 102
8 Casey, M.B., Pearson, G.R., Perkins, J.D. and Tremaine, W.H. (2015), Gross, computed tomographic and histological findings with dental apical infection. Equine Vet J, 47: 557-567.
9 Morrow K.L., Park R.D., Spurgeon T.L., Stashak T.S., Arceneaux B. (2000) Computed tomographic imaging of the equine head. Vet. Radiol. Ultrasound 41, 491-497.
10 Dixon et al A multicentre study of computed tomographic and clinical features of 1600 cases of equine sinonasal disease. Part 3. Diagnosed causes of sinonasal disease (in press).
11 Rowley KJ, Townsend NB, Chang Y-MR, Fiske-Jackson AR. A computed tomographic study of endodontic and apical changes in 81 equine cheek teeth with sagittal fractures. Equine Vet J. 2022;54:541–548.
12 Liuti T, Smith S and Dixon PM (2018) A Comparison of Computed Tomographic, Radiographic, Gross and Histological, Dental, and Alveolar Findings in 30 Abnormal Cheek Teeth from Equine Cadavers. Front. Vet. Sci. 4:236.
13 Van Zadelhoff, C, Liuti T, Dixon PM, Reardon RJM. Multidetector CT and cone-beam CT have substantial agreement in detecting dental and sinus abnormalities in equine cadaver heads. Vet Radiol Ultrasound. 2021;62:413–420.
14 Colbourne, C M;Rosenstein, D S;Steficek, B A;+2 more :Journal of the American Veterinary Medical Association, 1997 Aug 01, volume 211, issue 3, pages 335-338
15 Allen, J, Barbee D.; R ;Boulton, C R; Equine veterinary journal, 1987 volume 19, issue 6, pages 552-555 (4p)