Sonographic characteristics of thymoma compared with mediastinal lymphoma

Thymomas are uncommon neoplasms that are typically located in the cranioventral mediastinum in domestic species, which generally affects older animals. Medical records and sonograms of 50 animals diagnosed with either mediastinal thymoma (n = 35) or lymphoma (n = 15) between January 2005 and February 2012 were reviewed. Cases with definitive cytological and/or histological diagnoses of either thymoma or lymphoma were included in this study. Masses were characterized by echogenicity, presence or absence of cysts, shape, margination, vascularity, and presence of effusion. Many thymomas (57.1%) were sonographically cystic in appearance and nearly all were heterogeneous (94%) in echogenicity compared with lymphoma (P = .0028). Lymphomatous lymph nodes were more likely to be solid (80%) and were equally divided between hypoechoic (47%) and heterogeneous (53%) echogenicities. Sonographic findings of either internal cysts or a heterogeneous echogenicity in mediastinal masses may be suggestive of a thymoma.