The purpose of this study was to identify signs seen in computed tomographic (CT) examination of the nasal cavities of dogs that can help differentiate between fungal rhinitis, neoplasia and non-specific rhinitis.

The records of the Queen Mother Hospital for animals were reviewed for the period between February 2004 and August 2007 and cases that had nasal CT and final diagnosis of nasal disease were retrieved. The original CT study was reviewed by 2 board certified radiologists that had no prior knowledge of the case or the final diagnosis. Signs identified in each case, level of aggression and also the CT diagnosis was recorded after a consensus was achieved by the two radiologists. Positive predictive values were calculated, and significant associations between CT signs and final diagnosis were identified using the chi-square test.

Fifty seven cases (22 with primary neoplasia, 14 with fungal rhinitis and 21 with non-specific rhinitis) that satisfied the inclusion criteria were selected and reviewed.

Neoplasia was significantly associated with a higher incidence of loss of turbinate detail, mineralisation, invasion of the surrounding bone, presence of external soft tissue mass, patchy contrast uptake, pathology of the surrounding bone and soft tissue structures, increased soft tissue density of the sinuses and higher mean attenuation values in the affected areas (P <0.05). Cases with final diagnosis of neoplasia were mostly characterised (P<0.05) by the reviewers as 'mass-like' and 'destructive'. Fungal rhinitis was significantly associated with loss of turbinate detail and abnormal lucency within the nasal cavity (P <0.05), and the findings were mostly characterised by the reviewers as 'destructive'. Non-specific rhinitis was significantly associated with increased soft tissue density and bilateral mucosal thickening within the nasal cavity and absence of: bone invasion, external soft tissue mass, missing teeth, pathology involving the surrounding bone or soft tissue structures and increased soft tissue density of sinuses (P < 0.05). When statistically significant signs per disease category were used in combination, the positive predictive value was up to 100 % for neoplasia, 75 % for fungal rhinitis and 72 % for non-specific rhinitis.

These results indicate that CT examination of the nasal cavities can assist in differentiating nasal diseases. Differentiation between nasal neoplasia, fungal rhinitis and non-specific rhinitis should be based on a combination of findings that together have a high positive predictive value.