Evaluation of cytology and histopathology for the diagnosis of canine orbital neoplasia: 112 cases (2004-2019) and review of the literature.

Objective To provide an updated overview of canine orbital neoplasia, to compare diagnostic utility of cytology and histopathology, and to evaluate alternative sampling modalities, particularly image-guided core needle biopsy. Procedures A medical records search was performed to identify dogs with orbital neoplasia. Data were collected regarding signalment, diagnosis, vision status, imaging modalities, and sample collection methods. A reference population with orbital neoplasia was also identified via literature search for comparison with regard to final diagnosis. Results One hundred and twelve dogs met selection criteria. In the study and reference populations, respectively, diagnoses were grouped as follows: mesenchymal tumors 40% and 35%, epithelial tumors 35% and 18%, tumors of neural origin 8% and 37%, and round cell 17% and 10%. The most common diagnoses in the study group were nasal adenocarcinoma, osteosarcoma, lymphoma, and meningioma. Cytology results were available for 47 dogs and histopathology results were available for 95 dogs. Both cytology and histopathology results were available for 30 dogs, in 53% of which results were discordant. Cytology samples were nondiagnostic or provided a diagnosis that was later overturned in 32% of cases in which they were obtained. Results from core needle biopsy samples were nondiagnostic or overturned by surgical biopsy results in only 13% of cases. No significant complications were associated with any sampling method. Conclusions Orbital neoplasia is common in dogs. Histopathology is superior to cytology in providing a definitive diagnosis. Image-guided core needle biopsy appears to be a safe and effective means of obtaining samples.