Thymoma

September 14, 2005
Naveen Verma, MD

,
Terence M. Brady, MD

For the past year, a 45-year-old man experienced dull, aching chest pain and breathlessness following routine work. He had no history of fever, cough, dysphagia, or change in voice.

For the past year, a 45-year-old man experienced dull, aching chest pain and breathlessness following routine work. He had no history of fever, cough, dysphagia, or change in voice.

A chest film revealed a large anterior mediastinal mass. This was confirmed by CT, which showed a 12 × 9-cm invasive mass that displaced the mediastinal structures to the left, invaded the superior mediastinum, and showed focal areas of calcification. Drs Navin Verma, Terence M. Brady, and Sonia Arunabh of Flushing, NY, write that CT-guided biopsy of the lesion confirmed the diagnosis of thymoma.

Anterior mediastinal masses are often asymptomatic and are found on routine screening. When they are symptomatic, they are associated with coughing or breathlessness and, on occasion, superior vena cava syndrome. The differential diagnosis encompasses the “Four Ts:” ectopic thyroid, teratoma, thymoma, and T-cell lymphoma. An x-ray study and CT furnish the radiologic diagnosis, but the final diagnosis is by biopsy.

An ectopic thyroid is usually located superiorly and is contiguous with the thyroid gland; the patient may present with dysphagia or dyspnea. A teratoma occurs mainly in younger patients, and the mass shows calcification and fat planes. The presence of calcification in an untreated patient makes the diagnosis of lymphoma unlikely (calcification is seen in lymphomas only after radiotherapy).

Although thymomas are rare, they are the tumors most commonly resected from the anterior mediastinum. They are most often detected near the junction of the heart and the great vessels, occur slightly more often in women, are usually seen in the fifth or sixth decade, and rarely develop before age 20. Compared with thymic hyperplasia, which is symmetric and diffuse, thymoma usually distorts the gland's normal shape. In 40% to 70% of cases, thymoma is associated with parathymic syndromes, the most common one being myasthenia gravis.

Thymomas are composed of lymphocytes and epithelial cells and are classified according to the predominant cell type. Those with epithelial predominance are associated with a poor prognosis, as are those accompanied by thymoma-associated syndrome. Most thymomas are well-encapsulated and benign and have a good prognosis. Management is by resection and postoperative radiotherapy as was carried out in the presented case.