Malignant Thymoma

malignant thymoma

This 66 year-old male presented with a history of known thymoma. The chest x-ray shows evidence of previous median sternotomy, and unilateral increased density of the right hemithorax. This was due to extensive pleural metastatic disease.

The causes of unilateral increased density of a hemithorax include: consolidation; pleural effusion; pleural malignancy including mesothelioma; pulmonary collapse; status post pneumonectomy; lymphangitis carcinomatosa; and pulmonary agenesis / hypoplasia. Ninety percent of unilateral diffuse lung opacities are accounted for by just five conditions: pneumonia; aspiration; pulmonary oedema; lymphangitis; and radiation pneumonitis.2

Thymoma is the most common primary neoplasm of the anterior superior mediastinum. The majority occur between the ages of 40-60. Thymoma is associated with parathymic syndromes in 40%, including: myasthenia gravis; pure red cell aplasia; and hypogammaglobulinaemia. Histologically thymomas are usually biphasic, with both epithelial and lymphocytic components. One or the other component may predominate. 30-35% of thymomas are malignant, and spread is often by contiguous pleural reflections (as in this case). Unilateral pleural involvement is common. Pleural effusions are uncommon.1

1. Dahnert W. Radiology Review Manual. 5th edition. Lippincott Williams & Wilkins 2003.
2. Chapman S & Nakielny R. Aids to Radiological Differential Diagnosis. 4th edition. Saunders 2003.

Credit: Dr Laughlin Dawes