Diagnosis: Malignant Mesothelioma of the Pleura

Radiologic Findings

PA chest radiograph shows a moderate amount of left pleural effusion with diffuse pleural thickening.
Left decubitus view shows no significant free-shifting fluid, suggestive of loculated pleural effusion.
Contrast-enhanced CT scans show diffuse, nodular, circumferential pleural thickening in the left hemithorax with a moderate-sized pleural effusion. Note mild volume decrease of the involved hemithorax.

Brief Review

Diffuse malignant mesothelioma is an uncommon and fatal neoplasm of the serosal lining of the pleural cavity, peritoneum, or both. The risk of mesothelioma in any asbestos worker is approximately 10 % over his or her lifetime. A history of occupational exposure of asbestos is found in only 40-80 % of patients wit malignant pleural mesothelioma. Usually, a latency period of approximately 20 to 40 years occurs between exposure and detection of tumor (1). Of the various types of asbestos fibers, crocidolite, amosite and tremolite are highly carcinogenic (2). The amount of asbestos exposure needed to produce malignant pleural mesothelioma, or the dose-response relationship, is unknown (3).
Common radiographic findings include a moderate-to-large amount of pleural effusion with or without a pleural mass or diffuse pleural thickening with or without an effusion. Pleural effusion occurs in 30 % to 80 % of the patients with malignant mesothelioma.

Although mediastinal shift to the contralateral side is usually seen in association with massive pleural effusions, it is not a common finding in the patients with malignant mesothelioma. Instead, there may be evidence of volume loss on the affected side wit narrowing of the intercostal spaces, elevation of the hemidiaphragm, and ipsilateral shift of the mediastinum (3).

Diffuse, unilateral pleural thickening occurs in up to 60 % of patients. Sheet-like or lobulated pleural thickening may encase the lung, grow into the fissures, and create a pleural rind. Mesothelioma may also present as discrete pleural masses (3). Discrete pulmonary masses and hilar mass can also occur. Invasion of the chest wall occurs in far-advanced disease.

CT is helpful both in the detection of other underlying signs of asbestos exposure, such as pleural plaques, and in determining the extent of tumor. Differential diagnoses include benign asbestos pleurisy, infections, and metastases to the pleura, especially adenocarcinoma.

The prognosis is uniformly poor, and distant hematogenous metastases may occur.

References

1. McLoud TC. Conventional radiography in the diagnosis's of asbestos-related disease. Radiol Clin North Am 1992; 30:1177-1189
2. Wechsler RJ, Steiner RM, Conant EF. Occupationally induced neoplasms of the lung and pleura. Radio Clin North Am 1992; 30:1245-1268
3. Miller BH, Rosado-de-Christenson ML, Mason AC, Fleming MV, White CC, Krasna MJ. Malignant pleural mesothelioma: radiologic-pathologic correlation. RadioGraphics 1996; 16:613-644