Pleura & peritoneum

Pleura mesothelial tumors

Benign mesothelial proliferations

Last author update: 1 August 2013
Last staff update: 28 February 2023

Copyright: 2003-2024,, Inc.

PubMed Search: Benign mesothelial proliferations pleural

Vaidehi Avadhani, M.D.
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Cite this page: Avadhani V. Benign mesothelial proliferations. website. Accessed April 14th, 2024.
  • Also called simple mesothelial hyperplasia
  • Normal mesothelial surface has single layer of flat cuboidal epithelium
  • Irritation of pleural surface causes simple hyperplasia of mesothelium
  • Due to asbestos, benign pleural effusion, benign pleural plaque, collagen infections, drug reactions, pneumothorax, pulmonary infarct, trauma, vascular disease
Uses by pathologists
  • If malignancy cannot be excluded, use diagnosis of "atypical mesothelial hyperplasia" and recommend rebiopsy if clinically suspicious (Arch Pathol Lab Med 2012;136:1217)
Case reports
Microscopic (histologic) description
  • Mesothelial cells form conspicuous layer of regularly spaced, bland cuboidal cells along pleural surface; normally, mesotheial cells present only along surface and not in underlying tissue
  • Distinct nucleoli may be present
  • Likely benign if papillary excrescences with tufts of cells with bland tubule-like nonbranching structures, no fibrovascular cores
  • Capillaries are parallel to each other and perpendicular to pleural surface (in malignancy, the capillaries are haphazard)
  • Necrosis may be seen but usually accompanied with inflammatory cells and debris (Arch Pathol Lab Med 2005;129:1421)
Microscopic (histologic) images

Images hosted on other servers:

Exfoliated reactive mesothelium

Reactive mesothelial hyperplasia

Organizing pleuritis

Chronic fibrous pleuritis

Cytology description
  • Usually mesothelial cells will be numerous, dispersed or present in small clusters
  • Clusters of > 12 cells is unusual in simple hyperplasia
  • Binucleation, multinucleation, mitosis, prominent nucleolus can be seen in benign proliferations
  • Two or more mesothelial cells are often separated by "window" or a narrow space
  • Benign mesothelial cells usually have characteristic "skirt" or "halo" at pale outer rim of cell
Cytology images

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Normal mesothelium in pelvic washings

Reactive mesothelium

Positive stains
  • Immunostains do not differentiate benign and malignant mesothelial cells as both are positive for keratin
  • However, immunostains can demonstrate invasion into underlying tissues
Additional references
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