Computed tomographic description of the highly variable imaging features of equine oromaxillary sinus and oronasal fistulae

Oronasal and oromaxillary sinus fistulae are well-documented complications following removal or loss of a maxillary cheek tooth. Diagnosis is currently based on a combination of oral examination, videoendoscopy, radiography, and computed tomography (CT). The objective of this retrospective, case series study was to describe the CT characteristics of confirmed oronasal and oromaxillary sinus fistulae in a group of horses. Inclusion criteria were a head CT acquired at the authors' hospital during the period of 2012-2017, a CT diagnosis of oronasal or oromaxillary sinus fistulae, and a confirmed diagnosis based on a method other than CT. Signalment, clinical findings, oral examination findings, presence of a confirmed fistula, and method for confirmation of the diagnosis were recorded. A veterinary radiologist reviewed CT studies for all included horses and recorded characteristics of the fistulae. Seventeen horses were sampled. Fourteen oromaxillary sinus fistulae and three oronasal fistulae were identified. All fistulae appeared as variably sized focal defects in the alveolar bone. Defects frequently contained a linear tract of heterogeneous material interspersed with gas bubbles, considered consistent with food. Computed tomographic attenuation of the material (Hounsfield units, HU) varied widely within and between cases. In 16 of 17 cases, there was evidence of concurrent dental disease in addition to the fistulae. Although the gold standard diagnostic test remains identification of feed material within the sinus or nasal passages, findings from the current study support the use of CT as an adjunctive diagnostic test for assessing the extent of involvement and presurgical planning.