Diffuse tumoural thickening of the pleura can be caused by malignant mesothelioma or by pleural metastasis. Both entities are usually indistinguishable with imaging. Diffuse malignant mesothelioma is a rare primary neoplasm and its development is strongly related to asbestos exposure. It presents on a chest radiograph as an irregular and nodular pleural thickening with or without associated pleural effusion. Tumour extension into the interlobular fissures, accompanying pleural effusion, and invasion into the chest wall are better appreciated with CT (Fig. 1).

FIGURE 1 ■ Malignant pleural thickening caused by metastatic disease. Malignant pleural thickening was caused by pleural metastases. Note the compression on the right hemidiaphragm and the extension of the tumour into the liver (arrows).

On CT, malignant mesothelioma presents as a nodular soft-tissue mass sometimes with hypodense areas corresponding with necrosis. Metastatic enlargement of hilar and mediastinal nodes is seen in up to 50% of patients. Malignant mesothelioma has a minimally increased signal on T1 and a moderately increased signal on T2. MRI may be superior to CT in determining extent of disease because it allows better evaluation of the relationship of the tumour to the structures of the chest wall, mediastinum and diaphragm. However, in most cases CT and MRI provide similar morphological information. Ultrasound may be a supplementary method for biopsy and surgery planning.18,24 Finally, in many institutions, FDG-PET CT is used as a staging tool for malignant mesothelioma, although it should be emphasised again that FDG uptake is not entirely tumour-specific19–21 (Fig. 2).

FIGURE 2 ■ Malignant mesothelioma. FDG-PET CT of a patient with malignant mesothelioma. CT (A), PET (B, C) and PET-CT fusion image (D) showing extent of the tumour.

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