1. F 49, anterial mediastinal mass with myasthenia gravis

2. Normal Thymus Fibrous septa Tumor border

3. Type B2 Thymoma Epithelial tumor cells and background immature T lymphocytes

4. Type B2 Thymoma Epithelial tumor cells (arrows)

5. large, polygonal tumour cells that are arranged in a loose network

6. Type B2 Thymoma Definition: Type B2 thymoma is an organotypical thymic epithelial neoplasm composed of large, polygonal tumour cells that are arranged in a loose network and exhibit large vesicular nuclei, closely resembling the predominant epithelial cells of the normal thymic cortex. A background population of immature T cells is always present and usually outnumbers the neoplastic epithelial cells Synonyms: Cortical thymoma Lymphocytic thymoma (obsolete) Mixed lymphocytic and epithelial thymoma (obsolete)