Ultrastructural diagnosis of pleural tumors

Pleural mesothelioma: an approach to diagnostic problems

In the 1960s, a close relationship between heavy exposures to crocidolite asbestos and mesothelioma was established. The debate on the diagnosis of mesothelioma became complicated because of the possibility of litigation. Well differentiated mesothelioma cells are mucicarmine negative but alcian blue and periodic acid-Schiff (PAS) positive, which are removed by hyaluronidase and diastase digestion. By electron microscopy (EM), they show bush-like elongated, slender, and branching microvilli. By immunohistochemistry they express both keratin and vimentin but not carcinoembryonic antigenicity (CEA), B72.3, Ber-EP4, and Leu-M1. In poorly differentiated mesotheliomas, chromosomal and molecular biological alterations are common and complex but these alterations also overlap with that of poorly differentiated tumours of the lung and other organs. A poorly differentiated pleural tumour is most likely metastatic and needs good team work to locate the primary site. The diagnosis of a mesothelioma and asbestosis should be established separately. Future studies will be focused less on the phenotypic differences but more on the broad molecular and multi-phasic mechanisms of carcinogenesis, irrespective of the aetiological agents, in poorly differentiated tumours.

Diagnostic criteria for human diffuse malignant mesothelioma

Diffuse malignant mesothelioma is a rare tumor in the general population, yet is unique in that it is caused almost exclusively by exposure to asbestos with long-term latency (15 years and over). Pathologists are required to provide a reliable diagnosis of the tumor for clinicians who are responsible for the treatment of affected patients. Pathological diagnosis of diffuse malignant mesothelioma is not always easy; however, it has improved over the last few decades. Currently, comprehensive analysis, including gross appearance, histology, histochemistry, immunocytochemistry and electron microscopy is recommended as the best approach to an accurate diagnosis of diffuse malignant mesothelioma.

Diagnostic value of some matrix components

Although most diagnostic markers lie within the cell, a few are found in the matrix. Well-known examples of these are amyloid filaments and fibrous long-spacing collagen (Luse body). Perhaps not so well-known are the diagnostic values of anchoring fibrils and microvillus-matrix associations. The latter two form the subject of this paper.

Malignant epithelioid pleural mesothelioma versus peripheral pulmonary adenocarcinoma: a histochemical, ultrastructural, and immunohistologic study of 103 cases

The distinction between malignant epithelioid pleural mesothelioma (MEPM) and peripheral adenocarcinoma of the lung with pleural invasion (PAL) continues to represent a diagnostic challenge in selected cases. In order to provide comparative data on histologic, histochemical, and immunohistochemical features of these neoplasms, we analyzed 51 ultrastructurally categorized MEPMs and 52 PALs with the periodic acid-Schiff-diastase (PAS-D), mucicarmine, and colloidal iron stains, and a panel of immunohistologic reagents. Antibodies to cytokeratin, vimentin, epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), Leu M1, the B72.3 antigen, blood group isoantigens (BGI), placental alkaline phosphatase, amylase, S100 protein, and Clara cell antigen were used, as applied to paraffin sections with the avidin-biotin-peroxidase complex technique. Ultrastructural studies revealed long, branching microvilli in MEPM cells in all cases, with length-to-diameter ratios (LDR) of 10:1 or more. In contrast, PAL manifested short, nonbranching microvilli with LDR of 8:1 or less. Reactivity with PAS-D and mucicarmine stains was strictly confined to PAL, and hyaluronidase-sensitive colloidal iron-positivity was restricted to MEPM. However, only 63% and 41% of these respective neoplasms demonstrated such histochemical reactivity. Immunohistologic results correlated well with electron microscopic classification. All MEPMs and PALs were reactive for cytokeratin; in addition, the majority of tumors in each group expressed EMA, and a minority were reactive for vimentin. In adenocarcinomas of the lung, Leu M1 was observed in all cases, CEA was apparent in 96%, B72.3 labeled 84%, and BGI were present in 67%; all PALs expressed at least two of these determinants, but none was seen in any mesothelioma. The other markers included in this study also were observed in some PAL cases, but not in MEPM. These findings suggest that immunohistology parallels electron microscopy in efficacy in the diagnostic separation of MEPM and PAL. Using antibodies to Leu M1, CEA, and the B72.3 antigen, reactivity for at least two of these three markers appears to exclude a diagnosis of pleural mesothelioma. The other glycoproteinaceous, oncoplacentofetal, and cytoplasmic antigens we studied can be used to reinforce such a determination, since their distribution is confined to adenocarcinomas.

Pleural mesothelioma of epithelial type and pulmonary adenocarcinoma: an ultrastructural and cytochemical comparison

Twelve diffuse pleural mesotheliomas of epithelial type have been compared with 20 intrapulmonary adenocarcinomas. All mesotheliomas were negative for epithelial mucin by diastase periodic acid Schiff staining and for carcinoembryonic antigen by immunoperoxidase staining, whereas 17/20 carcinomas stained for epithelial mucin and 15/20 for carcinoembryonic antigen. Hyaluronidase-sensitive alcian blue positive material was present in 6/10 mesotheliomas and 0/20 carcinomas. Previously described electron microscopic differences were validated, including one which has so far received insufficient emphasis: microvilli making direct contact through basement membrane deficiencies with collagen fibres on the abluminal side of tumour cells were identified in 10/12 mesotheliomas and in 0/20 carcinomas.

Diffuse epithelial mesothelioma: a review of the ultrastructural spectrum

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.

Diagnosis of pleural malignant mesothelioma in life--a practical approach

This review documents a practical approach to the pathological diagnosis of pleural malignant mesothelioma based on the closed needle biopsy and effusion cytology, thus avoiding the need to resort to open surgery. Tissue diagnosis is often difficult, and the pathologist's opinion may be influenced by a consideration of three factors: the clinical setting; the adequacy and availability of specimens; and the criteria for assessment and interpretation of these. The level of confidence with which a tissue diagnosis of mesothelioma can be established using limited material depends on there being an appropriate clinical background including a history of asbestos exposure. Without this, the diagnosis should be a qualified or tentative one. For an adequate tissue sample to be obtained, the closed needle biopsy procedure is best performed by an experienced operator. All aspirated pleural effusions should be forwarded for cytological evaluation. In addition to conventional morphological studies, adequate samples permit ancillary tests to be carried out. A combined interpretive approach utilizing both histopathology and cytology is recommended in order to increase the accuracy of the diagnosis.