Gross Pathology: Thymomas are large, multilobulated, solid tumors that are generally encapsulated (80% of cases). They are yellow-gray to brown in appearance and can show areas of prominent cystic change, hemorrhage, necrosis, and calcification. The cut surface shows prominent fibrous bands separating individual lobules. This feature can be clearly seen in this image as well as several preceding images. The capsule may be breached in about 20% of cases with invasion of contiguous structures.