Pleural neoplasm

may be benign or malignant and produce either a focal pleural mass or diffuse pleural thickening. There may be an associated pleural effusion. Focal pleural masses are usually produced by localized fibrous tumours of the pleura (see localized fibrous neoplasm pleura and thoracic lipoma). Local invasion from a bronchogenic carcinoma and metastatic spread from thymoma may also produce a focal pleural mass. Mesothelioma, pulmonary adenocarcinoma and lymphoma usually produce more extensive pleural involvement. Very rarely melanoma and certain sarcomas (leiomyosarcoma, liposarcoma, rhabdosarcoma and fibrous histiocytoma) may cause focal pleural masses (see sarcoma thoracic).

For focal pleural masses the chest radiograph typically shows an extrapulmonary opacity with a well-defined medial margin which fades out laterally as the lesion contacts the chest wall, with which it forms an obtuse angle (Fig.1). The appearances are often quite different on the frontal and lateral radiographs. It is usually impossible to differentiate pleural and chest wall tumours unless there is evidence of rib destruction or deformity. With more extensive pleural involvement such as in Mesothelioma, there is hazy, veil-like increased density of the affected hemithorax with peripheral pleural thickening which may have a nodular or lobulated outline. The tumour may form a circumferential sheet of tissue which encases the lung, extending into fissures and reducing the volume of the ipsilateral hemithorax.

CT is useful in determining the precise location and extent of pleural disease and in distinguishing it from parenchymal disease. CT also enables the detection of pleural neoplasms in patients in whom there is a coexistent pleural effusion, and of recurrent pleural tumour. CT of a focal pleural neoplasm demonstrates a well marginated lesion based on a pleural surface with which it usually makes obtuse angles. Large lesions may cause compression of adjacent pulmonary parenchyma and displacement of bronchi and pulmonary vessels around the mass. An associated pleural effusion may also be seen. Localized fibrous tumours of the pleura may be pedunculated. Most neoplasms are of soft tissue density with some larger lesions having areas of low attenuation due to necrosis. Benign lipomas are readily diagnosed by their uniform fat density.

Diffuse pleural thickening is particularly well seen on CT. Malignant tumours typically cause irregular or nodular thickening which often extends into the mediastinal aspect, into the fissures and across the diaphragm. Occasionally there is invasion of the chest wall. Ipsilateral volume loss is common as in an associated pleural effusion.

The differentiation of benign pleural fibrosis from malignant pleural thickening is often difficult even with histological analysis of samples obtained at thoracotomy and CT can be very useful in helping to make this differentiation; circumferential thickening, nodularity, thickening of greater than 1 cm and involvement of the mediastinal pleura are strongly predictive of a malignant aetiology (Fig.2). Extensive calcification favours previous tuberculosis,empyema or haemothorax. Bilateral pleural thickening  is most commonly found following asbestos exposure.

HRCT will show any associated pulmonary disease, such as the interstitial fibrosis of asbestosis or an underlying malignancy and is superior to conventional CT in the detection of pleural plaques and minor degrees of pleural thickening.

The findings on MRI of focal pleural neoplasms are similar to those on CT with lesions having similar signal intensity to soft tissue and enhancement after administration of gadolinium. The multiplanar compatibility of MRI is useful in the assessment of diffuse pleural thickening and the coronal plane is especially useful in assessing the lung apex and the relationship of tumour to the diaphragm and mediastinum. Disruption by tumour of the normal extrapleural fat plane is usually well demonstrated and suggests local invasion.

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CF-HM

CF - HM