Black Spots of the Parietal Pleura: Morphology and Formal Pathogenesis

Abstract

Background: Dark incorporations (black spots) have been described in various organs. ‘Black spots’ seen as flat-to-nodular lesions of the parietal pleura are common findings in former miners. They represent areas of coal dust accumulation. An increased incorporation of asbestos fibres has been described in these areas, causing them to be seen as potential starting points for malignant mesotheliomas. Objectives: The aim of our examinations was to describe the morphology of black spots in order to understand their formal pathogenesis and discuss their role in the development of malignant mesotheliomas. Materials: We report the results of the morphological and energy dispersive X-ray analysis of 12 black spots (4 surgical and 8 autopsy specimens) located in the parietal pleura. Results: Black spots of the pleura develop in close correlation to lymphatic channels and blood vessels. Their formal pathogenesis is characterized by a mild fibrosis and an inflammatory reaction to the incorporated foreign particles. The proliferation of connective tissue may result in the formation of hyaline granulomas. Aluminum, silicone and sometimes fibres are also found in such areas. Mesothelial cells may be irritated. Conclusion: Although there are hints for an increased proliferation of mesothelial cells in some areas with black spots, our findings do not support the classification of black spots as an obligate early lesion in the development of malignant mesotheliomas.