Malignant mesothelioma (MM) is a rare tumor that is strongly linked to asbestos exposure and has a poor prognosis. The patient’s clinical history and radiologic findings are important in making a diagnosis of MM. The diagnosis of MM may be made from pleural effusion fluid, percutaneous pleural biopsy, or thoracoscopic pleural biopsy. MMs are classified as epithelioid, sarcomatoid, or mixed. Typically only the epithelioid and mixed type MMs are seen in cytologic specimens as the sarcomatoid type MM tends not to shed cells into the pleural space.
Treatment options for patients with MM include surgery (extrapleural pneumonectomy or pleural decortication), radiation therapy, and chemotherapy; however, the prognosis is generally poor despite therapy.
Radiographically, MM typically presents as a diffuse pleural thickening. Computed tomography is the preferred imaging modality.
On fine needle aspiration (FNA), epithelioid MM shows cellular smears with variably sized cellular fragments and some single cells (Fig. 9.1). The neoplastic cells are uniform with round nuclei and often prominent nucleoli. Binucleation is frequent and fine cytoplasmic lipid vacuoles are often present (Fig. 9.2). Although some fragments may show three-dimensional gland-like architecture, typical cellular pattern of MM on FNA is that of flat sheets. The latter feature may create diagnostic issues with peripherally located adenocarcinoma in situ (bronchioloalveolar carcinoma).