Thymomas, while rare, are the most common primary tumors of the mediastinum ¹. They arise from thymic tissue. Most patients are between 40 to 60 years of age with an annual incidence of 0.15 per 100,000 person years ^{1, 2}. There is a strong association with myasthenia gravis and paraneoplastic syndromes².

Histology 

Macroscopic:
Yellow adipose tissue 220 x 170 x 75 mm, 513 g, containing a firm multinodular tumor. On one side the specimen is lined by a shiny smooth membranous pericardial surface with multiple bulging exophytic brown nodules.

Sectioning reveals a variegated solid pale pink tumor 90 x 75 x 50 mm which extends to involve the roughened area of resection, together with multiple solid dark brown nodules up to 30 mm. No necrosis or hemorrhage is seen. The thymic fat shows yellow adipose tissue with several 5-10 mm tumor nodules immediately adjacent to the main tumor

Microscopic:
Invasive thymoma. WHO Types A & B3. 90 mm maximum dimension and incompletely excised. Involves chest wall inked resection surface over a distance of at least 10 mm. Tumor bulges into pericardial cavity but with intact pericardium. Lymphatic invasion identified. No perineural invasion identified.