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.
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.
References:
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
