Thymoma/ Lungs, Mediastinum, Heart

Contrast-enhanced coronal (left) and sagittal (right) reformatted CT images of the thorax demonstrate a lobulated mass in the anterior mediastinum (white and red arrows) with mixed attenuation consistent with a thymoma. The aorta is labeled Ao.

This computed tomography (CT) scan clearly illustrates the mass in the right anterolateral mediastinum.


A Thymoma is the most common neoplasm of the anterior mediastinum which originates within the cells of the thymus. The thymus gland is located behind the sternum in front of the great vessels and the pericardium. Thymomas are classified into three histologic types based on the predominant cell type: lymphocytic, epithelial, and lymphoepithelial. Thymomas affect men and women equally, they are most common in individuals in their fifth and sixth decades of life around age 52. They are rare in children. People with thymomas commonly have other diseases of the immune system.

The cause of thymoma is unknown, and the risk factors have not been identified. There is no clear histologic distinction between benign and malignant thymomas. The propensity of a thymoma to be malignant is determined by the invasiveness of the thymoma. Most benign thymomas are asymptomatic and most malignant thymomas are symtomatic. Symptoms include: cough, chest pain, dyspnea, dysphagia, hoarseness, superior vena caval syndrome, and about one-third of thymomas can present with systemic symptoms related to myasthenia gravis, such as muscle weakness.

Thymomas are usually diagnosed based on posterior and lateral chest x-rays, and CT images of the chest. If x-ray or CT images reveal the presence of a thymoma with uncommon features, or if there is a question of invasion into other nearby structures in the chest, it may be necessary to obtain a tissue sample of the mass or biopsey for examination.

Treatments for thymomas are surgery, radiation therapy, and chemotherapy depending on if the tumor is malignant or not. If malignant, treatment depends on the staging of the thymoma. Relapse after primary therapy for a thymoma may occur after 10 to 20 years. Therefore, long-term follow up should continue to be performed throughtout the patients life. The 15 year survival rate of a person with an invasive thymoma is 12.5%, and it is 47% for a person with a nonivasive thymoma. Death usually occurs from cardiorespiratory complications. The prognosis is based largly on the stage of the thymoma.