Pleura & peritoneum

Peritoneum

Mesothelial hyperplasia



Last staff update: 8 February 2022

Copyright: 2021-2022, PathologyOutlines.com, Inc.

PubMed Search: Mesothelial hyperplasia of the peritoneum

Nazim Benzerdjeb, M.D., Ph.D.
Page views in 2021: 520
Page views in 2022 to date: 2,132
Cite this page: Benzerdjeb N. Mesothelial hyperplasia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/pleuraperitmesothelialhyper.html. Accessed July 6th, 2022.
Definition / general
  • Reactive proliferation of mesothelial cells with no or minimal cytologic atypia and without invasion
Essential features
  • Common response to inflammation occurring in any process that leads to irritation of peritoneal surface
  • Reactive proliferation of mesothelial cells with minor degrees of nuclear atypia
  • Without invasion, positive for mesothelial markers (CK5/6, calretinin and WT1)
  • BAP1 and MTAP retained
Terminology
  • Simple mesothelial hyperplasia
  • Florid mesothelial peritoneal hyperplasia
Epidemiology
  • Exact incidence is unknown but mesothelial cell hyperplasia is not an uncommon phenomenon
  • May occur at any age, whatever the sex (J Clin Pathol 2011;64:313)
Sites
  • May occur at any site of the peritoneum
Pathophysiology
  • Common response to inflammation occurring in any process that leads to irritation of peritoneal surface
Etiology
  • Chronic effusions (ascites)
  • Inflammatory processes
  • Endometriosis
  • Hernias
  • Neoplasms (e.g. ovarian tumor, colorectal tumor)
  • Reference: Int J Gynecol Pathol 2014;33:393
Diagnosis
  • Exploratory laparoscopy with tissue sampling
  • Often incidentally identified in peritoneal tissue obtained for other purposes
Radiology description
  • No gross evidence of disease on imaging
Case reports
Gross description
  • Not commonly visible upon gross examination (incidental findings on microscopic examination)
  • Occasionally observed as small nodules or flat plaques from the peritoneum (Int J Gynecol Pathol 2014;33:393)
Microscopic (histologic) description
  • Variety of architectural patterns (solid sheets, nests, discrete small papillary or tubulopapillary growths, gland-like structures, cord-like linear arrays or single cells) (Int J Gynecol Pathol 2014;33:393)
  • Minor degrees of nuclear atypia (small, regular, round or oval and exhibit central nucleoli) without invasion; more common to be uniform in appearance
  • Reactive changes may be present that are worrisome for malignancy (enlarged vesicular nuclei, multinucleation, conspicuous nucleoli and rare mitotic figures)
  • Usually accompanied with inflammatory cells
  • Sometimes florid mesothelial peritoneal hyperplasia or psammoma bodies may be seen (Int J Gynecol Pathol 1993;12:51)
  • Rare findings:
Microscopic (histologic) images

Contributed by Nazim Benzerdjeb, M.D., Ph.D.

Monomorphous mesothelial cells

Small papillary

Slightly atypical mesothelial cells

Cytology description
  • Usually mesothelial cells may be numerous or not, dispersed or present in small clusters
  • Binucleation, multinucleation, mitosis, prominent nucleolus can be present in benign proliferations (Cytojournal 2013;10:7)
  • 2 or more mesothelial cells are often separated by window or a narrow space (Cytopathology 2004;15:131)
  • Benign mesothelial cells usually have recognizable halo at outer rim of cell
  • Complex papillary or branching clusters should not be present (Cytojournal 2013;10:7)
Positive stains
Negative stains
Molecular / cytogenetics description
  • FISH for CDKN2A: intact
Sample pathology report
  • Peritoneal biopsy:
    • Mesothelial hyperplasia of the peritoneum (see comment)
    • Comment: There are small papillary structures containing myxoid stroma, which are lined by a single layer of uniform cuboidal mesothelial cells without any infiltrative cells or necrosis. Immunohistochemically, the mesothelial cells are positive for calretinin and WT1. BAP1 and MTAP are retained.
Differential diagnosis
Board review style question #1
Which of the following statements regarding mesothelial hyperplasia of the peritoneum is true?

  1. Approximately 10% of patients progress to malignant mesothelioma over 10 years
  2. BAP1 immunostain can be lost
  3. Common response to inflammation occurring in any process that leads to irritation of peritoneal surface
  4. Lesions harbor consistently mutation of TRAF7
  5. Psammoma bodies are never seen
Board review style answer #1
C. Common response to inflammation occurring in any process that leads to irritation of peritoneal surface

Comment Here

Reference: Mesothelial hyperplasia
Board review style question #2

A small focal nodule depicted in the above photomicrograph was found incidentally during a resection of an ovarian serous cystadenoma in a 26 year old woman. Lesional cells were positive for calretinin. Which of the following is true about the depicted entity?

  1. CDKN2A homozygous deletion is never seen
  2. Deciduoid morphology can be occasionally seen
  3. Immunohistochemical loss of BAP1 is seen in 10% of cases
  4. Lesions harbor consistently mutation of TRAF7
  5. Most cases are causally linked to asbestos exposure
Board review style answer #2
A. CDKN2A homozygous deletion is never seen. This is a peritoneal mesothelial hyperplasia.

Comment Here

Reference: Mesothelial hyperplasia
Back to top
Image 01 Image 02