Malignant Pleural Mesothelioma

Radiologic-Pathologic Correlation

Abstract Introduction Etiology and Epidemiology of MPM Clinical Features Microscopic Features Characterization of MPM with Histochemistry, Immunochemistry, and Electron Microscopy

Gross Pathologic Characteristics Radiographic Features CT Features MR Imaging Findings Differential Diagnosis

Diagnostic Methods Staging and Resectability Treatment Prognosis Source Information References

Microscopic Features

Malignant mesotheliomas are generally divided into three histologic categories: epithelioid, sarcomatoid, and biphasic. Within each category, several subtypes exist, and many malignant mesotheliomas exhibit multiple histologic patterns.

Epithelioid mesotheliomas constitute approximately 55%-65% of malignant mesotheliomas. Architecturally, the tubopapillary pattern is most commonly identified, although histiocytoid, glandular, clear cell, and cribriform patterns are also seen. Histologically, epithelioid malignant mesothelioma is characterized by relatively uniform cuboidal or polyhedral cells with a moderate amount of eosinophilic cytoplasm, central nuclei, and distinct nucleoli (Figure 6) (35). Epithelioid mesothelioma may be difficult to distinguish from peripheral adenocarcinoma of the lung with pleural invasion, or adenocarcinoma metastatic to the pleura (36). The similarities between peripheral adenocarcinoma and mesothelioma are so striking that the term pseudomesotheliomatous adenocarcinoma is sometimes used (36). Although they bear the hallmarks of malignancy, mesotheliomas often tend to exhibit a lesser degree of nuclear atypia than is commonly seen in adenocarcinoma. Glycogen and hyaluronic acid within the tumor may mimic mucin and may cause further difficulty in differentiating epithelioid mesothelioma from adenocarcinoma.

The sarcomatoid variant, which constitutes approximately 10%-15% of malignant mesotheliomas, also has several architectural patterns. Storiform, hemangiopericytomatous, pleomorphic, and desmoplastic patterns may be seen, in addition to the common fibrosarcomatous pattern of interlacing fascicles of spindle cells (Figure 7). Histologically, variable degrees of nuclear atypia may be encountered, from the bland characteristics of desmoplastic mesothelioma to the marked anaplasia of the pleomorphic variety. Mitoses are sometimes sighted. The sarcomatoid variant must be differentiated from a true sarcoma, such as osteosarcoma or chondrosarcoma, and this differentiation may be complicated by the presence of foci of osseous or cartilaginous metaplasia sometimes seen in mesotheliomas.

The remaining mesotheliomas (20%-35%) fall into the biphasic category, which evinces features of both epithelioid and sarcomatoid mesotheliomas, either in contiguous areas or intimately intermixed (Figure 8). Transitional areas intermediate between the two cell subtypes are often present.

Abstract Introduction Etiology and Epidemiology of MPM Clinical Features Microscopic Features Characterization of MPM with Histochemistry, Immunochemistry, and Electron Microscopy

Gross Pathologic Characteristics Radiographic Features CT Features MR Imaging Findings Differential Diagnosis

Diagnostic Methods Staging and Resectability Treatment Prognosis Source Information References