Diffuse malignant mesothelioma (DMM) is a rare malignancy with significant clinical implications because it is still an incurable disease with the majority of patients dying within months of diagnosis.
Although the frequency of DMM is leveling off or falling in affluent nations due to strong asbestos management, it is increasing in countries where asbestos control is lacking.
In some cases, benign, reactive mesothelial hyperplasias and organizing pleuritis can be difficult to distinguish from DMM, and the diversity of DMM’s histopathologic features leads to a long list of differential diagnoses with other malignancies, especially metastatic malignancies, which are more common in the pleura than primary malignancies.
These two difficulties are discussed in this study, as well as a brief presentation of a case of DMM that manifested in a 66-year-old man with recurrent right pleural effusions and for whom DMM was not suspected clinically, radiographically, surgically, grossly, or initially on frozen section.
A diagnosis of DMM could not be made until localized invasion into the skeletal muscle was observed on permanent sections.