Pleura & peritoneum

Pleura mesothelial tumors

Atypical mesothelial hyperplasia

Last author update: 1 July 2013
Last staff update: 29 October 2020

Copyright: 2003-2024,, Inc.

PubMed Search: Atypical mesothelial hyperplasia pleural

Vaidehi Avadhani, M.D.
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Cite this page: Avadhani V. Atypical mesothelial hyperplasia. website. Accessed February 26th, 2024.
Definition / general
  • Worrisome proliferations of mesothelial cells that are not unequivocally malignant are termed atypical mesothelial proliferation or atypical mesothelial hyperplasia
  • Pseudoneoplastic lesion of the pleural surface
  • Are actually reactive mesothelial proliferations, associated with both benign and malignant conditions
  • Any mesothelial surface, including pleura, peritoneum, tunica, etc.
  • Associated with anemia, bronchogenic carcinoma, cirrhosis, connective tissue diseases, pneumothorax (recurrent), viral infections
Clinical features
  • History of pleural effusion or ascites, fluid may be hemorrhagic
Radiology description
  • Description of pleura on imaging or pleuroscopy helps differentiate benign and malignant mesothelial proliferations
  • Circumferential pleural thickening and nodular pleural thickening are highly suggestive of malignancy (Arch Pathol Lab Med 2012;136:1217)
Case reports
Microscopic (histologic) description
  • Identification of neoplastic invasion is definitive criteria for diagnosis of malignant mesothelioma
  • Finding of mesothelial cells in fat makes the proliferation malignant
  • Challenges and controversies in diagnosis of mesothelioma discussed at J Clin Pathol 2013;66:847
Microscopic (histologic) images

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Pleural patches - no invasion

Various immunostains - no invasion

Cytology description
  • Criteria are defined for malignant mesothelioma (high specificity - 99% when all criteria are fulfilled); refer to malignant mesothelioma
  • Cytology of atypical mesothelial cells:
    • Mesothelial cells in large groups
    • Cell groups with scalloped borders
    • Nuclear hyperchromasia
    • High N:C ratio
    • Coarse chromatin
    • Prominent nucleoli
    • Diagnostic problems in serous effusions discussed at Diagn Cytopathol 1998;19:131
Positive stains
  • All active mesothelial proliferations, benign or malignant, are pankeratin+
  • EMA, GLUT1 and IMP3 can be positive in both benign and malignant mesothelial proliferation so cannot be used to differentiate reliably
  • Homozygous deletion of p16 / CDKN2A demonstrated by FISH may be specific for malignant proliferations
  • p16 FISH staining usually negative in benign proliferations, 59% sensitive for malignant mesothelioma (Am J Clin Pathol 2011;135:619)
Negative stains
Differential diagnosis
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