A

irregular thickening and enhancement of the parietal pleura (arrow), including the mediastinal pleura. The lymph nodes in the paradi-aphragmatic fat are enlarged (curved arrow).

figure 29.8. A 70-year-old man with malignant mesothelioma. (A) Initial chest radiograph shows an asymmetric right pleural effusion that extends into the minor fissure (arrow). (B) CT scan shows irregular thickening and enhancement of the parietal pleura (arrow), including the mediastinal pleura. The lymph nodes in the paradi-aphragmatic fat are enlarged (curved arrow).

like extension tumor on the pleura in 70% of the 99 patients they imaged with MPM.80 Other findings suggesting MPM were multiple nodules encasing the lung, pleural thickening with an irregular pleuropulmonary margin, and pleural thickening with superimposed separate nodules. However, these findings were also seen with metastatic pleural disease, which was frequently indistinguishable. Rindlike thickening and thickness greater than 1 cm strongly suggested MPM, but other sources for pleural malignancy should be considered.

Knuuttila et al. reported that MR imaging was superior to CT in evaluating MPM. They found that MR imaging improved the detection of tumor involvement in the interlo-

bar fissures, diaphragm, peritoneum, and bony structures (Figure 29.9). The two modalities were equal, however, in detecting invasion of the chest wall, mediastinum, and adjacent lung.81 In a separate report, Knuutila et al. found that contrast-enhanced T1 fat-suppression was the most useful sequence for displaying invasion of adjacent anatomic structures, including the diaphragm, lung, mediastinum, pericardium, chest wall, and skeleton by mesothelioma, as well as pleural metastases.82

Heelan et al. also found MR imaging superior to CT in displaying tumor involvement in the diaphragm and chest wall (as extension through endothoracic fascia or solitary

figure 29.9. A 52-year-old man with malignant mesothelioma. (A) Chest radiograph shows loculated pleural effusion in left pleural space with compression of the left lung medially. (B) CT scan of the thorax with intravenous contrast shows large soft tissue mass in the pleural space that involves the pleura along the mediastinum (arrow) and fissure (curved arrow). (C) Tj-weighted MR image with fat satu-

ration following gadolinium administration shows no evidence for chest wall invasion, although mediastinal fat planes are obliterated (arrowheads). (D) Sagittal image of same sequence shows diffuse pleural tumor that involves the pleura (arrow). The mass displaces the diaphragm inferiorly without invasion (curved arrow).

figure 29.9. A 52-year-old man with malignant mesothelioma. (A) Chest radiograph shows loculated pleural effusion in left pleural space with compression of the left lung medially. (B) CT scan of the thorax with intravenous contrast shows large soft tissue mass in the pleural space that involves the pleura along the mediastinum (arrow) and fissure (curved arrow). (C) Tj-weighted MR image with fat satu-

ration following gadolinium administration shows no evidence for chest wall invasion, although mediastinal fat planes are obliterated (arrowheads). (D) Sagittal image of same sequence shows diffuse pleural tumor that involves the pleura (arrow). The mass displaces the diaphragm inferiorly without invasion (curved arrow).

chest wall foci).83 The difference between CT and MR imaging in detecting visceral pleural tumor, invasion of lung, and mediastinal and pericardial involvement was not statistically significant. Therefore, CT is recommended as the standard diagnostic choice and MR imaging as an additional study in patients for whom diaphragmatic and chest wall invasion is highly probable.

As with most malignant diseases in the thorax, FDG-PET has shown improved sensitivity in detecting MPM; however, limitations arise with the false detection of tumor in patients with benign inflammatory pleural disease and infection.84,85 Sensitivity in the detection of tumor as areas of increased uptake in pleural thickening and nodules identified on CT ranges from 91% to 100%. Although PET is sensitive in detecting tumor, Flores et al. found PET limited in specific tumor and local nodal staging; sensitivities were 19% and 11%, respectively.86 However, they concluded, as did Ger-baudo et al., that FDG-PET is very helpful in detecting distant metastases in supraclavicular lymph nodes and abdomen that were not identified with CT.85,86

Metastatic Disease to the Thorax

Pulmonary Metastases

Radiologic applications for imaging of metastases are useful in initial staging as well as assessment of a patient's response to neoadjuvant therapy for restaging before planned definitive surgical treatment and follow-up imaging for tumor recurrence. CT has evolved as the routine choice in staging, restag-ing, and detection of recurrence. Its superior anatomic resolution, combined with widespread availability and applications, contributes to its popularity. CT is superior to chest radiography for the detection of pulmonary metastases, although with limitations. Because of its excellent spatial resolution, CT demonstrates small lesions that mimic metastatic foci but are frequently benign. Limitations come into play especially in the initial diagnosis of patients with extrathoracic malignancies and no prior radiographic studies to document preexisting parenchymal disease.87 For instance, although Chalmers and Best found pulmonary nodules on CT in 20% of patients with extrathoracic malignancies and normal chest radiographs, 80% of these nodules were benign.88 Similar results were found by Kronawitter et al., who found, in routine preoperative workup for liver metasta-tectomy in patients with colon cancer, that the majority of nodules seen on chest CT images were benign.89 Only 5% of patients had true metastases. Povoski et al. reported that CT demonstrated pulmonary metastases in 4 of 100 patients with colon cancer whose results on chest radiographs before hepa-tectomy were normal.90 Picci et al. reported that, in 51 children with osteosarcoma, CT was sensitive but not specific in detecting pulmonary metastases.91 They found, however, that the likelihood of metastases increased with the number of nodules detected. Four of 13 patients with a single nodule had a true metastasis. All patients with more than seven nodules had metastases.

Other reports have demonstrated that the stage of an extrathoracic malignancy should be considered when determining whether CT should be included in the workup.92-94 Lim and Carter found that the detection of metastases from renal cell carcinoma with CT was low, especially with small primary tumors.93 With increasing tumor stage or with the demonstration of a nodule on a radiograph, however, they found CT more useful in detecting pulmonary metastases. Similarly, Heaston et al. reported that CT improved the detection of metastases in patients with locally advanced melanoma, as well as helping to identify extrapulmonary metastases.95 Reiner et al. found that routine chest CT was essential in the management of newly diagnosed squamous cell carcinoma of the head and neck.96 In 66 of 189 patients, CT demonstrated significant abnormalities, whereas only 23% were detected on chest radiographs. Thirty-six patients had 41 tumors, of which 13 were additional primaries and 28 were metastases. Conventional radiographs showed only 12 (29%) of these tumors. Reiner and colleagues therefore recommended routine thoracic CT before treatment for this patient population, which has a significant cigarette-smoking history and risk for bronchogenic carcinoma.

In the follow-up management of patients who have been treated for cancer and who undergo surveillance for recurrence, CT is very useful for detecting new pulmonary metas-tases.89 Follow-up CT imaging to detect early metastases can improve survival rates for patients with certain malignancies, such as sarcomas and colon cancer.91,97,98

Most pulmonary metastases reach the lungs through the pulmonary arterial system.99-101 The most common manifestation of pulmonary metastases is multiple nodules.99,100,102,103 Association of a nodule with a pulmonary vessel, the "mass-vessel sign" on high-resolution CT (HRCT), has been correlated with a hematogeneous origin.101 Although pulmonary metastases are generally multiple, a few tumors can manifest with a single pulmonary metastasis.95,104 Metastatic nodules can range from miliary to several centimeters in size. Miliary nodules are more likely to occur in association with tumors, such as thyroid carcinoma, renal cell carcinoma, and melanoma.105,106 Their distribution with respect to the interstitial compartments is typically random.107,108 Larger nodules are more likely to be seen with sarcomas and tumors from the colon and kidney. Metastases can be characterized not only by size but also by density and composition. For instance, metastases may have a solid, ground-glass, or mixed solid and ground-glass appearance. Others can calcify or cavitate.

Ground-glass nodules or nodules with surrounding ground-glass opacities are consistent with either hemorrhage or airspace disease into the adjacent lung (Figure 29.10). Metastatic nodules with surrounding hemorrhage have been described with choriocarcinoma, melanoma, renal cell carcinoma, angiosarcoma, and Kaposi's sarcoma.109-111 Bronchi-oloalveolar cell carcinoma nodules may have a ground-glass appearance or may have a surrounding ground-glass pattern.112 This pattern has been attributed to lining of adjacent airspaces by tumor through a lepidic growth pattern or to filling of airspaces with mucinous material.113 Nonmalig-nant processes with similar patterns may mimic metastases and should be included in the differential diagnosis. Infections, such as viral pneumonias, tuberculosis, fungal infections including invasive aspergillosis, arteriovenous malformations, and Wegener granulomatosis with local hemorrhage, can be very similar in appearance.109,112

The diagnosis of calcified metastases is straightforward when new nodules develop in a patient with osteosarcoma (Figure 29.11) or chondrosarcoma. However, in the absence of

figure 29.10. A 72-year-old man with history of metastatic melanoma involving the lungs. (A) CT scan image in lung windows at 5-mm slice thickness shows one of multiple ground-glass foci in

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