This thymoma shows predominance of neoplastic epithelial cells with only an occasional thymocyte (lymphocyte of the thymus). The epithelial cells are mostly round or oval with vesicular nuclei. Thymomas can be associated with other disorders including myasthenia gravis, Grave disease, and red cell aplasia. They usually arise in the anterior mediastinum but can occur in other locations along the pathway of embryonal migration.

These low and high magnification photos of another thymoma show that the number of lymphocytes can be great. The variation in proportions of the non-neoplastic lymphocytes and the neoplastic epithelial cells has little, if any, clinical significance.

From the slide collection of the late Dr. Charles Kuhn.