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Veterinary Medicine International
Volume 2010, Article ID 386378, 4 pages
Case Report

Thymic Epithelial Tumor with Heart Metastasis in a Horse

California Animal Health and Food Safety Laboratory, San Bernardino Branch, University of California, Davis, 105 West Central Avenue, San Bernardino, CA 93408, USA

Received 19 April 2010; Revised 6 July 2010; Accepted 13 July 2010

Academic Editor: Carolyn J. Henry

Copyright © 2010 Farshid Shahriar and Janet Moore. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Thymic malignancy is rare in horses. Thymic epithelial tumor was diagnosed in an 18-year-old mare with invasion and metastasis to the pericardium and heart. At necropsy, the cranial thoracic cavity was obliterated by a large mass located in the thymic region and the right atrium was also expanded and effaced by a similar mass. Histologically, the neoplasm was composed of sheets of spindle cells with intraparenchymal Hassall's corpuscles and formation of pseudorosettes around blood vessels compatible with type A thymic epithelial tumor according to World Health Organization classification. The neoplastic cells were diffusely immunoreactive for cytokeratin and negative for vimentin, S100, neuron specific enolase, glial fibrillar acidic protein, chromogranin A, synaptophysin, CD3 and CD79a markers. To the authors' knowledge, cardiac invasion and distinct histological pattern of pseudorosette formation have not been described in equine thymic epithelial tumors previously.