FINDINGS
    Enhanced chest CT scans, obtained on Sep. 1996, show a well defined mass in the superior mediastinum, which extends into the pericardial space forming infiltrative mass. The main and right pulmonary arteries are encased and compressed by the mass. Large amount of pericardial effusion is present. Follow-up CT scans, performed Apr. 1998, show slight decrease in size of the superior mediastinal mass with heterogeneous internal attenuation meaning necrosis or cystic degeneration. The mass of intrapericardial portion increases in extent with more severe mass effect on pulmonary artery. But there is no further pericardial effusion. Bilateral pleural effusion is developed.
 

DISCUSSION
    Thymomas are neoplasms of thymic epithelium that can behave in either a benign or malignant fashion. Thymoma is the second most common primary neoplasm (about 11.5%, after lymphoma) to affect the mediastinum. Most tumors are discovered in middle-aged adults and occur rarely in individuals under 20 years of age. The vast majority of thymomas arise in the upper portion of the anterior mediastinum, corresponding to the position of the normal thymus gland. Rarely, they are discovered in an unusual location such as the posterior mediastinum, perihilar tissues, neck, or lung parenchyma. Infiltration of adjacent structures, particularly the pleura and lung and less commonly the pericardium, chest wall, diaphragm, and mediastinal vessels, occurs in 10 to 15% of cases. These tumors are routinely asymptomatic for prolonged periods of time. The most common presentation is discovery on routine chest x-ray. Symptomatic pericardial tamponade as initial manifestation due to a thymoma with a massive pericardial effusion is uncommon.
    Although malignant pericardial effusion is a common complication of malignancy, it is rarely the initial manifestation. Cardiac tamponade due to malignant effusion, though rarely the initial manifestation of malignancy, is usually secondary to adenocarcinoma of the lung. Even in the absence of a pulmonary mass, lung carcinoma may be the likely primary in patients with malignant pericardial effusions. Lung carcinoma leads as the most common malignancy involved, followed by carcinoma of the stomach, pancreas, kidney and ovary, mediastinal rhabdomyosarcoma, malignant lymphoma and leukemia. According to one report, the lung was the site of the primary tumor in 58% of the cases and irrespective of the sites of the primary tumor, mediastinal involvement or intrapulmonary metastases or both were documented in 88% of the cases.
    Several cases of thymoma and mesothelioma were reported as benign tumors of pericardial involvement with pericardial tamponade.

References
1. Woldow A, Kotler M, Goldstein S, Milcu M. Thymoma with pericardial tamponade. Clin Cardiol 1995;18:484-485
2. Fincher RM. Case report: malignant pericardial effusion as the initial manifestation of malignancy. Am J Med Sci 1993;305:106-110
3. Almagro UA, Caya JG, Remeniuk E. Cardiac tamponade due to malignant pericardial effusion in breast cancer: a case report. Cancer 1982;49:1929-1933
4. Nishimura T, Kondo M, Miyazaki S, Mochizuki T, Umadome H, Shimono Y. Two-dimensional echocardiographic findings of cardiovascular involvement by invasive thymoma. Chest 1982;81:752-754
5. Almagro UA, Remeniuk E. Non-Hodgkin's lymphoma presenting as malignant pericardial effusion and cardiac tamponade. Hum Pathol 1985;16:315-317