IS case 532: Thymoma
Imaging Sciences URMC 2010
Publication Date: 2010-09-11
PA and lateral views of the chest demonstrated a smooth, lobulated anterior mediastinal mass that projects over the right hilum. There was no significant tracheal deviation or compression. Calcified granulomas within the right lower lobe were also noted.
In actuality, a large variety of tumors can arise in the the anterior mediastinum, not just limited to the 4T's. However, lymphoma and thymomas comprise the top two most common anterior mediastinal masses, so the mnemonic is certainly useful.
The term thymoma refers to a spectrum of thymic epithelial neoplasms, which possess different proportions of epithelial cells and lymphocytes. In terms of invasiveness and anaplasia, they can range from benign encapsulated thymomas (Class A) to thymic carcinomas (Class C). The latter tend to demonstrate more irregular margins, heterogeneity, necrosis, and calcifications, but benign thymomas may also exhibit these characteristics.
The clinical presentation of thymomas may be related to impingement of mediastinal structures, or occasionally to the development of various autoimmune conditions. About 30-50% of thymoma cases are associated with myasthenia gravis. Grave's disease, hypogammaglobulinemia, Sjogren's syndrome, dermatomyositis/polymyositis, and Cushing's disease have also been reported.
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