Definition: Thymoma refers to tumor of thymic epithelial cells. Germ cell tumors, neuroendocrine tumors, and lymphomas can involve thymus, but they are not considered as variants of thymoma. It is a tumor of adult life and is rare in children. The image shows a gross specimen of Thymoma, type AB. The patient was 52 y/o female who presented with breathing difficulty and was found to have a large tumor in the right hemithorax. The tumor is multi-lobulated with an intact capsule. Image copyright: pathorama.ch.