Malignant pleural disease usually heralds a poor prognosis, whether it represents a primary pleural malignancy or metastatic involvement.
Clinical presentation is variable. Patients may be asymptomatic or have pleuritic pain. If associated with a sizeable pleural effusion, then respiratory compromise may be evident. If a tumour is from the chest wall, then musculoskeletal pain or even a palpable mass may be present.
The pleura can be involved by malignancy by three main mechanisms:
- direct extension from an adjacent tumour, e.g. bronchogenic carcinoma
- a primary tumour, e.g. mesothelioma, primary pleural lymphoma
- pleural metastases
In each of these, the manifestation can be either solid disease or a malignant pleural effusion, or a combination of both. The relative aetiology is 1,6:
- metastatic carcinoma (e.g. primary lung): 58%
- mesothelioma: 28%
- non-Hodgkin lymphoma: 8%
- metastatic melanoma
- invasive thymoma
Conventional imaging is in general highly specific for the diagnosis of pleural malignancy but unfortunately lacks sensitivity 3.
Plain films in the setting of malignant pleural effusion are insensitive at distinguishing it from a benign effusion. See malignant vs benign pleural effusion
In cases where multiple nodular regions or pleural thickening are present the diagnosis may be evident, especially if a primary tumour or other metastatic deposits are visible.
CT is the work-horse of pleural imaging, able to achieve specificities of close to 100% 3. The portal-venous phase is optimal for demonstrating pleural enhancement, rather than arterial phase imaging used routine thoracic CT. A number of features are recognised, including 1,3:
- circumferential pleural thickening
- nodular pleural thickening
- parietal pleural thickening greater than 1 cm
- mediastinal pleural involvement
- pleural calcification generally suggests a benign process
FDG-PET is far more sensitive than conventional imaging in diagnosing malignant pleural disease and distinguishing them from benign processes 3. Hypermetabolism can be seen in either the pleura or pleural effusion. Although both benign and malignant processes, benign processes rarely increase the SUV over 2.0 3.
MRI findings of high signal intensity on T2 in relation to intercostal muscles and/or contrast-enhanced on T1 images together with CT morphology has a 100% and a specificity of 93% in the detection of pleural malignancy 5.
Treatment and prognosis
Both treatment and prognosis are dependent on the underlying type of malignancy. In the case of primary malignancies of the pleura (e.g. mesothelioma) resection may be a possibility in highly selected cases.
Thoracentesis of malignant pleural effusions has limited effect with reaccumulation occurring, on average, at four days.
In general, and certainly in the case of diffuse pleural metastatic disease, systemic therapies or radiotherapy are the only options. These are discussed separately as part of articles pertaining to individual malignancies:
Differential diagnosis depends on the predominant form the pleural disease takes:
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- 2. Kuhlman JE, Singha NK. Complex disease of the pleural space: radiographic and CT evaluation. Radiographics. 17 (1): 63-79. Radiographics (abstract) - Pubmed citation
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