Background: Pituitary tumors in dogs can be adenomas, invasive adenomas, or adenocarcinomas. In people, invasive adenomas and pituitary adenocarcinomas carry a worse prognosis than adenomas. Hypothesis/Objective: To identify differentiating features on cross-sectional imaging in dogs with pituitary adenomas, invasive adenomas, and adenocarcinomas. Animals: Thirty-three dogs that had computed tomography (CT) or magnetic resonance imaging (MRI) performed and a necropsy diagnosis of pituitary adenoma (n = 20), invasive adenoma (n = 11), or adenocarcinoma (n = 2). Methods: Medical records were retrospectively reviewed for signalment, history, and diagnosis. CT and MR images were reviewed for characteristics of pituitary tumors. Results: Mean (standard deviation) age for dogs with pituitary adenomas (10.6 ± 2.9 years) was greater than that of those with invasive adenomas (8.3 ± 2.7 years, P =.04). Eighteen out of 20 (90%) dogs with adenomas had contrast-enhancing masses. Thirteen out of 20 (65%) had homogeneous enhancement. Mean adenoma height was 1.2 ± 0.7cm. Eight out of 20 (40%) adenomas were round and 8/20 (40%) compressed surrounding brain. Eleven out of 11 dogs (100%) with invasive adenomas had contrast-enhancing masses. Seven out of 11 (64%) masses were homogeneous. Mean invasive adenoma height was 1.8 ± 0.7cm, which was significantly greater than adenomas (P =.03). Mass shape varied from round to oval to irregular. Six out of 11 (55%) masses compressed surrounding brain. Clinical and imaging features were variable for 2 dogs with adenocarcinomas. Conclusions and Clinical Relevance: Invasive adenoma should be suspected if a dog with a pituitary tumor is o7.7 years of age and has a mass 41.9cm in vertical height. Adenocarcinomas are uncommon and metastatic lesions were not seen with imaging.
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