Scanning electron microscopic distinction of pleural mesotheliomas from adenocarcinomas

Cases of mesothelioma and adenocarcinoma involving pleura were examined by light and scanning electron microscopy utilizing H & E stained slides of paraffin-embedded material. Areas of interest were identified and isolated, and the coverslips were removed. The slide fragments were mounted on scanning electron microscopy stubs and coated with gold for 45 sec. Cases were examined in a blinded manner. Microvilli were readily identified by scanning electron microscopy with preservation of morphologic detail through the processing and staining steps required for light microscopy. The length and diameter of 20 microvilli were measured from each tumor. The mean length:diameter ratio for the mesotheliomas (n = 7) was 19.7:1 (range 13.7-23.5:1), and for the adenocarcinomas (n = 7), 2.5:1 (range 1.3-4.1) (P < 0.0005). Correlative transmission electron microscopy was performed on "scanned" specimens, and length:diameter ratios were generated. This technique has utility in distinguishing mesothelioma from adenocarcinoma. It is especially useful when glutaraldehyde-fixed, plastic-embedded tissue is not available for transmission electron microscopy. Additionally, scanning electron microscopy allows more extensive examination than transmission electron microscopy and is far less limited by section thickness and tangential sectioning artifact.