Notice that this specimen is being viewed at low power as was the previous slide of a normal thymus. However, in this slide the lobulated structure of the thymus is not seen. Rather the entire field appears homogeneous with no apparent cortex or medulla.
A thymoma is a neoplasm of the epithelial-reticular cells of the thymus. These are considered to be the stromal cells of the thymus. The parenchymal cells of the thymus are the T-cells. In a thymoma the T-cells are normal and do not contribute to the neoplasm. The mean age of patients with a thymoma is 50. Thymoma is often associated with other disorders. For example, 40% of patients with myasthenia gravis have a thymoma. 90% of thymomas are benign.