Differential CT Features between Malignant Mesothelioma and Pleural Metastasis from Lung Cancer or Extrathoracic Primary Tumor Mimicking Malignant Mesothelioma

PURPOSE: To evaluate the differential CT features found among malignant mesothelioma and pleural metastasis from lung cancer and from extrathoracic primary tumor which on CT mimic malignant mesothelioma. MATERIALS AND METHODS: Forty-four patients who on chest CT cans showed pleural thickening suggesting malignant pleural disease and in whom this condition was pathologically confirmed were included in this study. On the basis of their pathologically proven primary disease [malignant mesothelioma (n=14), pleural metastasis of lung cancer (n=18), extrathoracic primary tumor (n=12)]. they were divided into three groups. Cases of lung which on CT showed a primary lung nodule or endobronchial mass with pleural lesion, or manifested only pleural effusion, were excluded. The following eight CT features were retrospectively analyzed: 1) configuration of pleural lesion (type I, single or multiple separate nodules, type II, localized flat pleural thickening, type III, diffuse flat pleural thickening; type IV, type III with pleural nodules superimposed; type V, mass filling the hemithorax), 2) the presence of pleural effusion, 3) chest wall or rib invasion, 4) the involvement of a major fissure, 5) extrapleural fat proliferation, 6) calcified plaque, 7) metastatic lymph nodes, 8) metastatic lung nodules. RESULTS: In malignant mesothelioma, type IV (8/14) or II (4/14) pleural thickening was relatively frequent. Pleural metastasis of lung cancer favored type IV (8/18) or I (6/18) pleural thickening, while pleural metastasis from extrathoracic primary tumor showed a variable thickening configuration, except type V. Pleural metastasis from lung cancer and extrapleural primary tumor more frequently showed type I configuration than did malignant mesothelioma, and there were significant differences among the three groups. Fissural involvement, on the other hand, was significantly more frequent in malignant mesothelioma than in pleural metastasis from lung cancer or extrapleural primary tumor . Metastatic lymph nodes and metastatic lung nodules were significantly more frequent in pleural metastasis from lung cancer and extrapleural primary tumor than in malignant mesothelioma. CONCLUSION: Malignant mesothelioma showed significantly frequent fissural involvement and the frequency with which pleural metastasis from both lung cancer and extrathoracic primary tumor showed type I pleural lesion, metastatic lymph nodes or metastatic lung nodules, was significantly frequent. Even though no CT features for differentiating between pleural metastasis from lung cancer and from extrathoracic primary tumor were found, the CT features stated above would help differentiate malignant mesothelioma from the other two groups.

CT Findings of Pleural Dissemination in Primary Lung Cancer

PURPOSE: To evaluate the CT findings of pleural dissemination in primary lung cancer and the limitations of CT scanning in detecting pleural dissemination in primary lung cancer. MATERIALS AND METHODS: Primary lung cancer with pleural dissemination was diagnosed in 68 patients and confirmed by pleural biopsy, cytology and surgery, and these cases were the subject of this study. Adenocarcinoma accounted for 49, squamous cell carcinoma for 13 and small cell carcinoma for six. Eight CT features, namely the amount of pleural effusion, the contour, extent andlocation of pleural thickening, the shortest distance between pleura and mass, pleural calcification, pleural tailsign and the extent of extrapleural fat proliferation, were evaluated. RESULTS: Pleural effusion was noted in 51 of 68 patients(75%), though in most cases(70%), the amount of this was small. Among 42 patients(62%) in whom thickened pleura, were noted, pleural thickening was thin and irregular in 22(52%), thick and irregular in 16(38%), and thin and regular in 4(10%). The extent of pleural thickening was multifocal in 22 patients(52%),diffuse in 16(38%), and circumferential and single in two(5%). Pleural thickening was more frequently noted at theposterior than the anterior pleura. Pleural abutting was seen in 53 patients(78%). In ten patients(15%), chest CTscans revealed no perceptible pleural abnormalities. CONCLUSION: If in primary lung cancer, the primary lung masscontacts the pleura, and if pleural thickening, even when slight, shows marginal irregularity, pleuraldissemination should be considered. Although CT scanning is very useful for the detection of pleural disseminationin primary lung cancer, about 15% of patients showed no perceptible pleural abnormalities. Other diagnosticmodalities such as thoracoscopy are mandatory for the correct diagnosis of pleural dissemination in primary lung cancer.

Malignant and Benign Diffuse Pleural Disease: Utility of FDG PET in Differential Diagnosis and Comparison with CT

PURPOSE: To assess the utility of 2-[18F] fluoro-2-deoxy-D-glucose (FDG) PET in differentiating malignant and benign diffuse pleural disease, and to compare it with CT. MATERIALS AND METHODS: Both FDG PET and CT scans were performed in 20 consecutive patients with diffuse pleural disease (13 malignant and seven benign cases). In FDG PET, peak standardized uptake value (SUV) as well as visual assessment of abnormally increased uptake in the pleura was evaluated. The results were compared with CT findings. RESULTS: With only visual assessment of PET images, sensitivity, specificity, and accuracy for malignancy were 92%, 43%, and 75%, respectively. With peak SUV of 4.8 or more, the corresponding figures were 100%, 57%, and 85%, respectively, and on CT interpretation, were100%, 57%, and 85%, respectively. Tuberculous empyema simulated malignant pleural disease both on FDG PET (3/6 patients with peak SUV more than 4.8) and CT (3/6 patients). CONCLUSION: For the differentiation of malignant and benign diffuse pleural disease, FDG PET and CT are equally accurate. Combined visual and quantitative assessments of PET images enhance discriminatory ability. Tuberculous empyema simulates malignant pleural disease both on FDG PET and CT.