Case reveal


  • Rostromedial to the right second maxillary molar (110) there is a well-defined focal region of osteolysis (yellow bracket) and the root of this tooth protrudes into the ventral aspect of the right rostral maxillary sinus (green circle).
  • A large amount of mixed granular, soft tissue, fluid, mineral and gas attenuating material (blue arrowheads) is seen within the right rostral and caudal maxillary sinus, right frontal sinus and protruding within the right and left dorsal, and right middle and ventral choncal sinuses with associated mass-effect and multifocal osteolysis (right infraorbital canal, frontal bone, nasal septum, right maxillary septum and conchae). 
    Also, multifocally, the right and left maxillary bone in contact with this intranasal and sinosal material are markedly thin. An oval, irregularly marginated mineral attenuating structure is seen within the right caudal maxillary sinus (red circle).
  • Associated with the focal region of frontal bone osteolysis there is moderate thickening of the soft tissues of the frontal region with minimal gas noted within. 
  • Within the right aspect of the sphenopalatine sinus there is a small amount of fluid-attenuating material.
  • Severe premolar and molar malocclusion is seen, characterized by a markedly undulating occlusal surface (wavemouth).
  • The perialveolar space surrounding multiple premolar and molar teeth is widened with surrounding sclerosis (pink arrowheads). Multiple, small, round, lucent regions are seen associated with the apical region of multiple mandibular teeth. The first right maxillary molar tooth (109) is markedly foreshortened. 209 is missing.
  • Within the left rostral maxillary sinus there are two, well-defined, oval, fluid-attenuating, non-contrast enhancing lesions (green circle).
  • Within the left lateral ventricle, there is a well-defined, soft tissue and mineral attenuating structure with ill-defined margins and mild contrast enhancement. The lateral ventricles are mildly symmetrically dilated.
  • The left thyroid gland included in the filed of view is larger when compared with the contralateral (limited examination for the cervical region).


  • Oromaxillary sinus fistula (in region of tooth 110) with food impaction, associated severe periodontal disease and severe destructive rhinitis/sinusitis.
  • Dental malocclusion and multifocal periodontal/apical disease. Absent tooth 209 with diastema.
  • Small mineralized left lateral ventricular mass, with mild lateral symmetric ventriculomegaly. A cholestrinic granuloma is the primary differential and likely represents an incidental finding.
  • Right rostral maxillary sinus cysts.
  • Asymmetric thyroid glands of unknown clinical significance

A little bit more…

  • Oronasal or oromaxillary sinus fistula: Usually a complication following repulsion or extraction of a maxillary molar (Hargreaves et al., Dixon et al.). Concurrent periodontal disease is often present.
  • Loss of alveolar bone and lack of granulation tissue at diastema results in communication between the oral cavity and either the nasal passages (oronasal fistula- usually at the level of premolar teeth [06–08]) or a maxillary sinus (oromaxillary sinus fistula- usually at the level of molar cheek teeth [09–11]). Both can happen simultaneously (Hargreaves et al.).
  • Reasons for lack of granulation tissue formation (Hargreaves et al.):
    • Sequestration of osseous fragments from the alveolus
    • Retained infected dental material remaining
    • Extension of a temporary alveolar seal placed following extraction into a maxillary sinus
    • Premature loss of a temporary alveolar seal.
  • Oronasal or oromaxillary sinus fistula may form secondary to impaction of food material into a diastema between two maxillary cheek teeth resulting in periapical infection and erosion of the periodontium with subsequent fistula formation (Hargreaves et al., Dixon et al.). Therefore, some chronically infected +/- fractured teeth can have extensive infection (or even sequestration of their alveolar and adjacent supporting maxillary bone) resulting in fistula formation even prior to their extraction (Dixon et al.).
  • Clinical signs include the presence of thick (purulent), malodorous and unilateral nasal discharge +/- missing tooth (Hargreaves et al.).
  • Computed tomography is the preferred modality (more sensitivity and specificity than radiography) for the evaluation of oronasal or oromaxillary sinus fistulae (Hargreaves et al.).
Tooth 109 is absent. Mixed gas and soft tissue attenuating material fills the alveolar space and is seen extending into the right nasal passages. The material tracks caudally along the nasal meatus, obliterating/compressing the ventral nasal conchae.
(Hargreaves et al.)  
  • Key computed tomographic features of oronasal or oromaxillary sinus fistula identified by Hargreaves et al.:
    • Presence of a defect in the alveolar bone plate with formation of a tract of variable size
    • Heterogeneous material with mixed attenuation (food) extending from the oral cavity or alveolus into either a nasal passage or a paranasal sinus.
    • Associated signs of sinusitis/rhinitis.
  • Computed tomography may allow for detection of subtle changes early on. Can also aid in detection of small osseous fragments/possible sequestra within the alveolus or associated sinus (Hargreaves et al.).
  • Surgical debridement of damaged tissues, removal of retained fragments, impacted food and placement of PMMA (acrylic) alveolar plugs is the most common first treatment approach (Dixon et al.).


  • Hargreaves, Laura, and Jonathon J. Dixon. “Computed tomographic description of the highly variable imaging features of equine oromaxillary sinus and oronasal fistulae.” Veterinary radiology & ultrasound 59.5 (2018): 571-576.
  • Dixon, P. M. “Treatment of equine oro‐nasal and oro‐maxillary fistulae.” Equine Veterinary Education 32.9 (2020): 471-478.