Restricted Diffusion on Diffusion-Weighted MRI in a Cat With Orbital Lymphoma and Presumptive Pulmonary Lymphoma

A 10-year-old Turkish Angora cat presented with left conjunctival swelling and exophthalmos. Ultrasound and computed tomography revealed an orbital mass and a well-defined pulmonary mass in the left cranial lobe. Magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI), demonstrated restricted diffusion in the orbital (apparent diffusion coefficient [ADC] = 0.56 × 10^-3 mm²/s) and pulmonary masses (ADC = 0.53 × 10^-3 mm²/s), suggesting high cellularity. Histopathology confirmed orbital lymphoma, and pulmonary lymphoma was suspected on the basis of cytology. To our knowledge, this is the first report to describe restricted diffusion on DWI MRI in a feline case of orbital lymphoma and presumptive pulmonary lymphoma, highlighting the potential utility of this imaging modality in distinguishing lymphoma from other tumor types.