Peritoneum, omentum and mesentery
Mesothelial lesions
Epithelioid mesothelioma

Senior Author: Raul S. Gonzalez, M.D.
Deputy Editor: Debra Zynger, M.D.

Topic Completed: 1 February 2018

Revised: 15 February 2019

Copyright: 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Peritoneum epithelioid mesothelioma
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Cite this page: Mubeen A, Gonzalez RS. Epithelioid mesothelioma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/peritoneummesothelioma.html. Accessed February 21st, 2019.
Definition / general
  • Mesothelioma is a neoplasm arising from mesothelial cells that line serous cavities, such as the pleura and peritoneum
  • Pleural mesothelioma is much more common than peritoneal mesothelioma
  • Epithelioid mesothelioma is the most frequent histologic type of malignant mesothelioma; sarcomatoid and biphasic subtypes are less common
  • 20 - 33% of malignant mesothelioma arises in the peritoneum (Semin Oncol 2002;29:51)
Essential features
  • Hallmark of epithelioid mesothelioma is the epithelioid cells which are polygonal cells with moderate to abundant eosinophilic cytoplasm, vesicular round nuclei and prominent nucleolus; often mimic nonneoplastic, reactive mesothelial cells (Arch Pathol Lab Med 2018;142:89)
  • The most common histologic patterns of epithelioid mesothelioma are tubulopapillary, adenomatoid, solid well differentiated, solid poorly differentiated and acinar (Arch Pathol Lab Med 2012;136:241)
  • Myxoid variant of peritoneal epithelioid mesothelioma is extremely rare with only 5 reported cases
Epidemiology
  • Often due to asbestos exposure, whether in the pleura, peritoneum and pericardium; cumulative asbestos exposure is directly proportional to risk of cancer (J Med Case Rep 2008;2:121)
Pathophysiology
  • Asbestos fibers lead to chronic inflammation, which causes the release of free radicals
  • Latent period between asbestos exposure and disease averages 20 - 30 years (Cancer Treat Rev 2012;38:605)
Clinical features
  • No distinctive symptoms, causing difficulties in diagnosis and treatment
  • When symptomatic, usually present with abdominal pain, ascites and abdominal distention
Radiology images

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CT with dilated loops of bowel

Prognostic factors
Case reports
Treatment
  • Systemic chemotherapy
  • Cytoreductive and palliative surgery
Clinical images

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Fig D: bilateral
intratubal masses

Gross description
  • Diffuse thickening or multiple nodules on the peritoneum
  • Myxoid variant is gelatinous
Microscopic (histologic) description
  • Epithelioid cells are arranged in different patterns (which form the basis of the different subtypes of epithelioid mesothelioma)
  • Form tubules and papillae with / without psammoma bodies (tubulopapillary variant), gland-like structures (acinar variant) and are in solid sheets, nests or cords (solid variant)
  • Myxoid variant:
    • Dyscohesive medium to large epithelioid cells with a moderate to abundant amount of eosinophilic cytoplasm dispersed in a myxoid background
    • Some cells can have intracytoplasmic clear vacuoles
    • Nuclei with coarse chromatin and prominent nucleoli
    • Mitotic figures are usually inconspicuous
    • Difficulty to differentiate from other myxoid lesions of the peritoneum (e.g. adenocarcinoma) thus panel of immunohistochemical markers is generally required
Microscopic (histologic) images

Contributed by Aysha Mubeen, M.D.

Epithelioid mesothelioma (pleural)


Myxoid variant of peritoneal mesothelioma

Calretinin

MOC31

Virtual slides

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Epithelioid mesothelioma: 70 year old man with pleural effusion

Cytology description
  • Clusters of epithelioid cells (morulae) with knobby contour
  • Abundant cytoplasm, round nuclei and prominent nucleoli
  • Mild atypia
Cytology images

Contributed by Aysha Mubeen, M.D.

Cell block, myxoid variant

ThinPrep, myxoid variant

DiffQuik, myxoid variant

Positive stains
Negative stains
Electron microscopy description
  • Very long, thin apical microvilli and the absence of glycocalyx (compared to adenocarcinoma, which has shorter villi)
Electron microscopy images

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Various images

Additional references
Board review question #1
Which of the following stains is positive in the myxoid variant of epithelioid mesothelioma and helps to differentiate it from mucinous adenocarcinoma?

  1. B72.3
  2. Claudin4
  3. D2-40
  4. MOC31
Board review answer #1
C. D2-40

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