Use of magnetic resonance imaging for the investigation of orbital disease in small animals

Twenty-five small animal patients presenting with signs of orbital disease were investigated using magnetic resonance imaging (MRI) in an attempt to assess the value of this imaging technique for diagnosis. All patients were also examined using ultrasonography, and skull radiography was performed in 20 of these animals. The final diagnoses included neoplasia, inflammatory disease and foreign body penetration. MRI produced detailed images of orbital tissues and provided more information about the extent of pathology than the other imaging techniques; a correct diagnosis based solely on the MRI scan was made in 22 cases. Radiography was found to be helpful only in cases in which neoplastic disease extended markedly beyond the confines of the orbit into the nasal chamber and paranasal sinuses. Radiographic changes other than soft tissue swelling were not evident in other orbital disease processes. Ultrasonography gave both false negative and false positive diagnoses for neoplastic masses, although it allowed the correct diagnosis of both cases of foreign bodies and one of the three cases of retrobulbar abscesses in this series. MRI is recommended for patients in which radiography and ultrasonography fail to produce a confident diagnosis or for which surgery is proposed.