Introduction
Mesothelial cells are a specialised type of epithelium which make up the mesothelium which lines all serosal surfaces.
They have microvilli on their luminal surface and the proteins and serosal fluid trapped by these provide a frictionless surface for internal organs to slide past one another. Their high fibrinolytic activity protects against the formation of adhesions.
They are very fragile cells which are frequently seen in smears following centesis or pleural cavities. However they regenerate very quickly.
Mesothelial cellular proliferation
Inflammatory response
Mesothelial cells may proliferate in response to irritation or an inflammatory disease at the mucosal surface. This may be due to fluid-accumulation in the peritoneal cavity following an effusion or due to a space-occupying mass like a tumour or intestinal enlargement.
Cytologically, these cells have typical morphological features of round, mononuclear to binuclear cells present individually or in small cohesive clusters.
Marked mesothelial cellular hyperplasia may have marked cellular pleomorphism and multiple strong nuclear criteria for malignancy. It may be impossible to distinguish reactive mesothelial cells from a neoplastic process. This is why the mesothelial cell population should always be considered in relation to the other types of cell in the sample. If the process is predominantly inflammatory, criteria for malignancy may be tolerated. However if the inflammation is minor and there are many mesothelial cells, one should strongly consider a malignant process.
Ancillary diagnostics such as imaging and biopsy of the lesion should always be considered.
Neoplasm
Mesotheliomas are malignant neoplasms which can arise from the pericardial, thoracic or abdominal pleural surfaces in all domestic animals.
References
Morrison, W. (2002) Cancer in dogs and cats Teton NewMedia
Meuten, D. (2002) Tumors in domestic animals Wiley-Blackwell
Slatter, D. (2002) Textbook of small animal surgery Elsevier Health Sciences
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