The mass is firm and covered anterolaterally with a thin translucent membrane, consistent with mediastinal pleura. The cut surface is yellow-tan in color with variably sized lobulation and focal hemorrhagic/degenerative areas in the central portion.
There is extension of the tumor into the surrounding mediastinal fat, outside of the tumor capsule, and this qualifies as an invasive thymoma. The tumor tends to push the mediastinal pleural margin and the pericardial structures. There is no evidence of pericardial involvement.