|IX. Pleural Lesions|
|A. Effusions and pleuritis:|| Cytologic examination of pleural fluid can be extremely helpful. Inflammation can be characterized and malignancy looked for. Culture is also invaluable.|
|B. Pneumothorax, hemothorax and chylothorax:||Cytologic examination and cultures need to be done.|
|C. Mesothelial plaques:||These are fibrous plaques and nodules on pleura associated with asbestos exposure. Their presence, by itself, does not predispose to malignant mesothelioma or asbestos-related lung disease.|
|D. Solitary, fibrous tumor:||Previously known as localized pleural mesothelioma, solitary fibrous tumor of the pleura is a sessile or pedunculated mass, ranging in size from 1 to 36 cm. Microscopically, these are composed of bundles of bland spindle cells with elongated nuclei. The histogenesis of SFTs is controversial. Immunocytochemical and ultrastructural studies favour fibroblastic differentiation. Approximately 30% of SFTs are malignant with local invasion, recurrence and distant metastases.|
|E. Malignant mesothelioma: ||Almost all cases are related to asbestos exposure. There are three major histologic patterns which may blend into one another.
Immunohistochemistry (Keratin, vimentin and epithelial membrane antigen are positive) and electron microscopy (numerous long microvilli and no secretory granules) are very helpful in diagnosis.
- Epithelioid mesotheliomas (60-65%): There are epithelial cells arranged in cords, nests, acini, cell balls and papillary formations. Individual malignant cells are mostly polygonal with abundant eosinophilic cytoplasma and bland nuclei.
- Sarcomatoid mesotheliomas (10-15%): They have a fibrosarcoma like appearance and are composed of cells with elongated cytoplasm, arranged in parallel bundles. There is greater pleomorphism, more mitoses and worse prognosis than epithelioid mesothelioma.
- Biphasic mesotheliomas (25-30%): Their prognosis is the same as sarcomatoid mesothelioma i.e., worse than the epithelioid type. They are composed of various mixtures of epithelioid and sarcomatoid cells.