Morphological assessment of paranasal sinuses and teeth in the horse
Sinonasal and dental diseases can be a serious disorder in horses due to the persistence of the former and the common extension of the latter to the supporting bones of the skull. The diagnosis of equine sinonasal and dental disease can be challenging due to the complexity of these and adjacent anatomical structures, and therefore the use of advanced imaging, including computed tomography (CT) has greatly increased recently. A major aim of this study was to improve the morphological characterization of the sinuses and cheek teeth in normal horses of different ages. These studies defined the volumes of the 7 different sinus compartments; showed that the volume of the different compartments increase with age; that in contrast to accepted findings, the Triadan 09 alveoli is located in the caudal maxillary sinus (CMS) in 13% of the youngest group and the Triadan 10 alveoli is fully within the rostral maxillary sinus (RMS) in 53% of cases. The infraorbital canal was found to be susceptible to apical infection-related damage in horses <2 years of age (<2 y.o.) due to the intimate relationship of this canal and the medial aspect of the maxillary cheek teeth alveoli. The mean positions of the clinical crowns and apices of the maxillary Triadan 11s were 2.48 cm (adjusted 5.2% of head height) and 2.83 cm (adjusted 6.2% of head height) more rostral, respectively in horses >16 y.o. compared to horses <6 y.o., consistent with rostral dental drift. Measurements of dental drift could provide further objective radiographic guidelines on ageing horses by dental imaging and also help our understanding of the aetiopathogenesis of cheek teeth diastemata. This study also found that the reserve crown length decreased from a mean of 4.7 cm (adjusted 19.7% of head height) in the youngest (<6y.o.) group of horses to a mean of 2.9 cm (adjusted 10.5% of head height) in the oldest group (>15y.o.), with the 06s and 09s having the shortest reserve crowns. These data are useful reference information for clinicians and radiologists in the diagnosis and treatment of equine sinonasal and dental disease. Morphological characterization of the ventral and dorsal conchal bullae in horses of different age using CT described the age-related difference in sizes of these structures (smaller in younger horses). In the ventral conchal bulla, this reduction in volume was probably related to protrusion of the large dental alveoli in young horses into the nasal cavity and bulla. Bullae linear measurements and volumes were also associated with head size. The anatomical position of both bullae was associated with specific maxillary cheek teeth, thus increasing the diagnostic value of conventional radiography in the investigation of bulla disease and providing landmarks for the surgical treatment of this disorder. Skull shape analyzed with the use of Procrustes statistical analysis showed landmark variability between different age groups and in particular, high landmark variability between young (<5y.o.) and old (>16y.o.) horses and less landmark variability between adult (6-15y.o.) and old horses. Future studies could investigate changes in the equine skull in relation to genotype to characterize breed-related diseases affecting teeth and sinonasal compartments. In the second part of the study, 32 infected maxillary cheek teeth extracted from clinical cases were evaluated grossly and histologically and these pathological results were compared to the pre-extraction radiographic and CT imaging findings. This study showed a high sensitivity (97%) of CT in detecting changes in teeth affected by apical infection. In the third part of the study, 30 cheek teeth assessed as being abnormal based on oral, radiographic and CT examinations were extracted along with their alveoli from 27 cadaver heads. Gross and histological examination findings from these teeth and alveoli were compared to the pre-extraction imaging findings, again showed high sensitivity (96.4%) of CT in diagnosing cheek teeth apical infection. Additionally, CT showed a high correlation with histology in detecting dental infection related alveolar bone changes including alveolar bone lysis, sclerosis and bone thickening. This aspect of the study was also the second largest pathological study of equine apical infection published to date and thus has also improved our understanding of the pathogenesis of this disorder. In conclusion, CT was shown to be an excellent imaging modality for improving the morphological characterization of the sinuses and teeth in normal horses of different ages, and thus also improving the value of this modality in diagnosis and treatment of disease affecting sinonasal and dental structures. This study also objectively showed the high sensitivity of CT in detecting cheek teeth apical infection in horses as compared to radiography, including by assessment of alveolar bone changes. Overall, the results of this project improve morphological knowledge of the equine skull and teeth and will have direct clinical benefits by improving the diagnosis and thus the treatment of equine sinonasal and dental disease.