The primary benign mesotheliomas of the pleura usually originate from the visceral pleura. They grow slowly and solitary. Pleural effusion is found in only about 10 % of cases (Steinbeck 2005).
Primary malignant mesotheliomas mostly start in the parietal pleura and are also found in the visceral pleura leaf in the later stage (approx. 80 %). However, they can also occur in the area of the peritoneum, the pericardium and the testicular sheaths (Fisseler-Eckhoff 2015). Primary malignant mesotheliomas are a so-called "asbestos-related signal tumour" for an inhalative (mostly occupational) exposure to asbestos fibres. The term asbestos-related signal tumour was coined by Selikoff in 1965.
However, mesotheliomas are often only discovered in an advanced tumour stage.
Sonography
Malignant processes often involve a pleural effusion. Fluid-filled cavities in the tumour can also simulate an encapsulated effusion of the thoracic wall.
X-ray image
In malignant mesothelioma the thoracic view mostly shows a unilateral effusion with a pleural callosity (Siewert 2006).
Computer tomography
In malignant mesothelioma there is a nodular thickening of the parietal pleura which shows an increase in size from cranial to caudal (Siewert 2006). Computed tomography is the gold standard for mesothelioma, as it allows both the extension of the tumor and a possible lymph node involvement to be diagnosed.
Based on the density measurement, a suspected lipoma can be determined under certain circumstances (Köhler 2010).
Biopsies
A biopsy is performed under sonographic or CT control or with the help of a thoracoscopy.
With regard to biopsies, it should be noted that the malignant mesothelioma often shows an initially flat, invasive growth in its early phase and the biopsies should therefore be sufficiently deep and of sufficient size (Fisseler-Eckhoff 2015).
Cytology
The cytology only leads to the detection of a mesothelioma in 35 % - 50 %. In case of a possible asbestos contamination a histological clarification should therefore be performed. In this case, pleural plaques in X-rays or CT are indicative (Matthys 2008).