Presentation: About 17% of type A thymoma patients present with myasthenia gravis (muscle weakness, fatigue, diplopia, drooping eyelids, and dysphagia). The remainder present with symptoms related to compression of anterior mediastinal structures (dyspnea, persistent cough, chest pain, fever, night sweats, and weight loss). Many are discovered incidentally on imaging studies performed for other reasons. Most type A thymomas (about 60%) are diagnosed at Stage I (completely encapsulated) according to the Masaoka-Koga classification system. About 30% of tumors are Stage II (microscopic capsular invasion OR gross invasion into surrounding fat OR adhesions to pleura or pericardium). The image shows a bland spindle cell proliferation with a few scattered lymphocytes in the background.