There are three distinct histological subtypes of mesothelioma: epitheloid mesothelioma, sarcomatoid mesothelioma and biphasic mesothelioma. The subtype of the disease is determined by the type of cells involved: epitheloid mesothelioma arises in epithelial cells, which line inner and outer surfaces of the body, while sarcomatoid mesothelioma arises from cells in certain connective tissues. Biphasic mesothelioma presents as a mixture of these cell types, but is categorized as its own distinct form. Determination of the histological type of the disease is an important factor in determining a patient’s prognosis. The epithelial subtype presents with the best prognosis and is the type most amenable to the available treatments for mesothelioma. Sarcomatous mesothelioma has the worst prognosis, while the biphasic form presents between these two extremes, with a prognosis dependent on the distribution of the individual cell types involved. Thus, the determination of the cell type involved is nearly as important as the diagnosis of mesothelioma itself.

Computed tomography (CT) scans are the most common imaging technique used in the diagnosis of pleural mesothelioma, itself the most common form of the disease. Although magnetic resonance imaging (MRI) and positron emission tomography (PET) offer certain benefits over traditional CT scans, as a first-line diagnostic tool, CT remains the tool-of-choice in most cases. The radiographic findings that CT returns are especially good at imaging pleural thickening and pleural effusions, which are two of the common symptoms of pleural mesothelioma. If it were possible to correlate specific CT findings with histological subtype, treatment strategies could potentially be developed earlier in the patient’s presentation, which could have major benefits for his or her prognosis.

Researchers from Canada have recently released the results of a study they conducted that looked at just this question.

Overview of the Study

The researchers conducted a retrospective analysis of 92 cases of proven pleural mesothelioma that occurred between 1997 and 2006. They gathered each of the patients’ CT scans and histology specimens and had the samples independently analyzed by lung pathologists (for the slides) and chest radiologists (for the scans).

Histologically, there were 72 cases of epitheloid mesothelioma, 15 cases of the sarcomatous subtype and 5 of the mixed form. All of the patients showed some form of pleural thickening on their scans. 87% (80 of 95) of patients presented with pleural effusions, with large effusions found in 19 (21%) of them. 42 patients demonstrated ipsilateral volume loss. A number of atypical presentations were recorded but none of these rose to the level of statistical significance. As regards tumor staging, the majority of the patients presented at stage 3 (50%) or stage 4 (35%).

During analysis, the researchers determined that two correlations achieved statistical significance: large pleural effusions were seen only in epithelial mesothelioma, while ipsilateral volume loss was highly correlated with sarcomatous or mixed mesothelioma. No other correlations were found significant.

Conclusion

The determination of the actual histological subtype of the disease is an important step in any diagnostic process, but there may be times when biopsy isn’t possible or the results returned were not conclusive or were contaminated. In these cases, CT correlations may be the best method to begin moving forward. If so, CT findings of ipsilateral volume may suggest a sarcomatous subtype of the disease, while the presence of a large pleural effusion may indicate a case of epithelial pleural mesothelioma. Study after study has shown that earlier diagnosis and subsequent treatment is one of the most important factors for patients with mesothelioma, so the confirmation of the findings as presented in this study could have a real benefit to newly-diagnosed patients everywhere.

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