ACR Codes: 66.3254
Although a chest radiograph may detect a diffuse pleural abnormality, the most critical information about the nature of a pleural disease process is best evaluated by CT. Both benign and malignant pleural processes have been found to have some characteristic CT features, although many of these are shared. Benign pleural disease, for instance, is most often smooth and uninterrupted, extending over about one quarter of the chest wall or more. Presentation frequently includes pleural effusion and calcification generally signals benignity. This definition is not without controversy. Malignant disease is more often nodular and irregular. It best distinguishes itself when there is involvement of the mediastinal pleural or focal fissural thickening. Enhancement on CT imaging is usually easily seen. Calcification is uncommon, but can be seen in up to 20% of cases of mesothelioma.
Diffuse mesothelioma is an uncommon but dire diagnosis . Two to three thousand cases are seen in the US each year. Mean survival is 11 months. Up to 80% of cases are associated with exposure to asbestos (most often crocidolite) after an average latency period of 35 years. The much less common focal form, sometimes known as a pleural fibroma, is not associated with asbestos exposure. Patients with diffuse mesothelioma frequently present with cough, weight loss, dyspnea and chest pain. The most common radiographic finding is pleural effusion Further study is best performed with CT. The most consistent CT radiographic finding is pleural thickening (92%). Additional findings include thickening of the interlobar fissures (86%) and pleural effusion (74%). Nodular, enhancing pleura – particularly at the interlobar fissures and mediastinum – is highly suggestive of malignant pleural disease. . The tumor arises from the parietal pleural.
Until thoracocentesis or pleural biopsy is performed, mesothelioma or metastatic disease cannot be distinguished. CT commonly demonstrates lymph node involvement (50%) but may underestimate the degree of chest wall and diaphragmatic involvement. Computed tomography’s utility lies in assessing the extent of disease and aiding in determining resectability. For diagnostic accuracy in staging it is nearly equivalent to MRI, but it is considered the standard imaging choice due to its lower cost. MRI is superior to CT in demonstrating diaphragmatic or chest wall involvement not seen on CT.
Reference(s): 1. Groskin SA. Heitzman’s The Lung. Radiogic-Pathologic Correlations. 3rd ed. St. Louis: Mosby, 1993;609-613.
2. Heelan RT, et al. Staging of Malignant Pleural Mesothelioma: Comparison of CT and MR Imaging. AJR 1999;172:1039-1047.
3. Miller BH et al. Malignant Pleural Mesothelioma: Radiographic-Pathologic Correlation. RadioGraphics 1996;16:613-644.
4. Muller NL. State of the Art: Imaging of the Pleura. Radiology 1993; 186(2):297-309.
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