Answer: Hyaline pleural plaque

Histology:

Discussion: Sections show portion of parietal pleura with a hyalinized pleural fibrosis (plaque). Focal chronic inflammation is present. Hyaline pleural plaques (HPP) are important because they are good indicator of occupational-level dust exposure including asbestos. They can also mimic mesothelial neoplasms and metastasis to the pleura. HPP-s have also been linked to asbestos exposure although the plaques themselves do not contain asbestos bodies (those are usually seen in underlying lung parenchyma) . Unilateral plaques can be seen in association with any kind of pleural injury, whereas bilateral plaques are typically seen in association with asbestos exposure. In the latter case the plaques are typically in the lower lungs and involve the parietal pleura.

Histologically, these are hypocellular bundles of dense collagen often showing a “basket-weave” appearance with no or minimal chronic inflammation. There is no cytologic atypia that separates it from desmoplastic malignant mesothelioma.