Table II.

Masaoka-Koga staging system of thymoma.

STAGE	DESCRIPTION
I	Macroscopically completely encapsulated and microscopically no capsular invasion.
II	Macroscopic invasion into surrounding fatty tissue or mediastinal pleura Microscopic invasion into pleura
III	Macroscopic invasion into neighboring organs (pericardium, great vessel, or lung)
IV	Pleural or pericardial dissemination Lymphogenous or hematogenous metastasis