Diffuse Epithelial Mesothelioma: A Review of the Ultrastructural Spectrum

Abstract

Traditionally, diffuse epithelial mesotheliomas are mainly identified at the ultrastructural level by the numerous, long, wavy-appearing surface microvilli. By electron microscopy of a series of diffuse mesotheliomas of varying subtype (epithelial, biphasic, sarcomatous, and poorly differentiated), it can be demonstrated that the differentiation of this specialized surface organelle is quite variable even in well-differentiated lesions. The presence of only a few, scattered, short microvilli does not exclude a diagnosis of epithelial mesothelioma, particularly if historical, surgical, and radiologic findings support this diagnostic conclusion. Indeed, even the complete absence of surface microvilli is compatible with a diagnosis of diffuse epithelial mesothelioma. It is important to become aware of the spectrum of tumor cell differentiation in serosal tumors, as all of the fine structural diagnostic criteria in mesotheliomas are expressed to varying degrees in individual cases.

The diagnostic utility of immunohistochemistry and electron microscopy in distinguishing between peritoneal mesotheliomas and serous carcinomas: a comparative study

“…Additionally, the cell membranes in the serous carcinomas were intimately apposed, while, in the mesotheliomas, intercellular gaps that often exhibited microvilli were a common finding. Similar to previous ultrastructural studies, large collections of intermediate filaments arranged in tonofibrillar bundles and intracytoplasmic lumens covered by microvilli were common findings in mesotheliomas, [65][66][67] but not in serous carcinomas. [68][69][70] No intracytoplasmic lumens were identified in any of the serous carcinomas investigated, and only rare small bundles of intermediate filaments were found in a few cases.…”

Ectopic Expression of PA2.26 Antigen in Epidermal Keratinocytes Leads to Destabilization of Adherens Junctions and Malignant Progression

“…4 and 5; Table 1). Tumors exhibited an undifferentiated phenotype, although some areas showed a glandular differentiation pattern resembling malignant mesotheliomas, as demonstrated at the ultrastructural level by the presence of numerous wavy-appearing surface microvilli (Dardick et al, 1987;Oury et al, 1998). Interestingly, PA2.26 antigen was concentrated at these microvillous surfaces (Fig.…”

Guidelines for Pathologic Diagnosis of Malignant Mesothelioma: 2012 Update of the Consensus Statement from the International Mesothelioma Interest Group

“…Sarcomatous mesotheliomas for the most part do not show specific ultrastructural features, and tumors that are poorly differentiated by light microscopy and do not demonstrate a typical pattern of immunohistochemical staining usually lack specific features by electron microscopy as well. 98,99 Occasionally, electron microscopy is useful in establishing the correct diagnosis when the immunohistochemical results are equivocal or further support of a diagnosis of either MM or serous carcinoma is needed. 65 Formalin-fixed material retrieved from a paraffin block may be satisfactory, since microvilli and tonofilament bundles tend to be preserved.…”