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CT is superior to radiography for the identification of early abnormalities in patients with MPM. Very small effusions can be detected, and the lung and pleural surface that are obscured by large effusions can be visualized. The spread of the tumor into fissures, mediastinum, and chest wall can also be detected; thus the extent and morphology of the disease can be assessed better (50).
CT scans commonly depict pleural thickening (92%) and thickening of the interlobar fissures (86%) in patients with MPM (Figure 17) (50). CT allows visualization of the rindlike thickening, nodular thickening, fissural involvement, and focal pleural masses, which are not as readily distinguished on chest radiographs (Figure 18).
Unilateral pleural effusion is a common CT finding in patients with MPM (Figure 19a). In the study by Kawashima and Libshitz (53) of 50 patients with MPM, CT showed associated pleural effusions in 37 patients (74%). Of these 37 patients, 50% had effusions that filled one-third or less of the hemithorax, 40% had opacification of two-thirds of a hemithorax, and 10% had more than two-thirds of a hemithorax obscured by pleural fluid (Figure 19b). Also, contraction of the affected hemithorax was present in 42% of patients and was associated with ipsilateral mediastinal shift, narrowed intercostal spaces, and elevation of the ipsilateral hemidiaphragm (Figure 20). Only 14% of patients had contralateral mediastinal shift (53).
Calcified pleural plaques are found at CT in approximately 20% of patients with MPM. Plaques may become engulfed by the primary tumor and may mimic calcified MPMs (Figure 21) (54).
CT is of value in determining the extent of disease at initial staging. However, although invasion of the chest wall and mediastinal structures can be shown, early chest wall and diaphragmatic invasion may be underestimated (55). Use of the axial scanning plane is probably responsible for the inability to detect subtle contour abnormalities of the inferior surface of the diaphragm. Chest wall invasion may manifest as obscured fat planes, invasion of intercostal muscles, infiltration or separation of ribs by tumor, or bone destruction (Figure 22); however, irregularity of the interface between the chest wall and the tumor is not a reliable indicator of chest wall invasion (56). MPM also can extend out of the chest cavity into the chest wall through needle biopsy tracks, surgical scars, and chest tube tracts and create chest wall masses.
Invasion of vital structures, including the heart, great vessels, esophagus, and trachea, can manifest as obliteration of surrounding fat planes or as direct invasion of a mediastinal structure (Figure 23). The presence of tumor that surrounds more than 50% of the circumference of a vascular structure is strong evidence of invasion (56). Pericardial invasion may manifest as nodular pericardial thickening and may be accompanied by a pericardial effusion (Figure 24). Although lymph node groups are better appreciated with CT, the tumor mass itself may obscure adjacent nodal enlargement (Figure 25) (53).
The ability of CT to show lung that is obscured by pleural masses and effusions on chest radiographs is a major advantage. CT may allow identification of pulmonary fibrosis in the lung bases secondary to asbestosis. This fibrosis produces the "shaggy heart" seen in asbestosis. Hematogenous spread of MPM manifesting as multiple parenchymal nodules or masses and, rarely, as diffuse, miliary nodules can also be identified and differentiated from pleural changes (Figure 26). Lymphangitic spread of tumor manifests as a focal or diffuse prominence of interstitial markings and is rarely seen.
CT scans of the chest can show extrathoracic spread of MPM, such as direct hepatic invasion, retroperitoneal extension, and retrocrural adenopathy, each of which occurs in less than 10% of patients with MPM (Figure 27) (53). Rusch et al (57) stated that CT findings may lead to underestimating the extent of disease in the initial examination of MPM patients with early chest wall involvement, small tumor-containing mediastinal lymph nodes, transdiaphragmatic tumor extension, peritoneal studding, and abdominal solid organ metastases smaller than 2 mm. Although it is not perfect, CT is still the most accurate radiologic method for determining the initial stage of the disease and for following up patients with MPM.
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