cystic adenomatoid tumor

Localization

- anterior mediastinum

Synopsis

- homogeneous cut surface with numerous cystic structures that varied from 0.5 to 1.5 cm in greatest diameter
- numerous cystic spaces lined by flattened or cuboidal epithelial cells
- proliferation of small canalicular structures lined by round to polygonal epithelioid cells with vacuolated eosinophilic cytoplasm in the walls of the cysts

Immunohistochemical studies

- strong positivity of the epithelioid cells

  • AE1/AE3 cytokeratin
  • CK5/CK6
  • calretinin

- negative stains

  • CK7
  • CK20
  • alpha-fetoprotein
  • CD31
  • carcinoembryonic antigen
  • MOC 31
  • chromogranin

Electron microscopic examination

- numerous long microvilli on the cell surface
- abundant tonofilaments/desmosomal plaques in the tumor cells, characteristic of mesothelial cells

Differential diagnosis

- anterior mediastinal masses

References

- Plaza JA, Dominguez F, Suster S. Cystic adenomatoid tumor of the mediastinum. Am J Surg Pathol. 2004 Jan;28(1):132-8. PMID: 14707875

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