Other nonneoplastic

Epithelial inclusion cyst

Topic Completed: 1 September 2017

Minor changes: 27 July 2021

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PubMed Search: Epithelial inclusion cysts [title]

Aurelia Busca, M.D., Ph.D.
Carlos Parra-Herran, M.D.
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Cite this page: Busca A, Parra-Herran C. Epithelial inclusion cyst. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/ovarynontumorinclusioncyst.html. Accessed October 25th, 2021.
Definition / general
  • Invaginations of the ovarian surface epithelium into the ovarian cortex
Essential features
  • Two types based on morphology and pathophysiology:
    • Peritoneal inclusion cyst: lined by flat epithelium invaginated from ovarian surface epithelium; these express a peritoneal phenotype (calretinin, WT1 and D2-40 positive, PAX8 and BerEP4 negative)
    • Müllerian inclusion cyst: lined by ciliated tubal epithelium as a result of implantation of tubal epithelium in the ovarian parenchyma, presumably at the time of ovulation when the ovarian surface epithelium is disrupted; these express a tubal Müllerian phenotype (PAX8, BerEP4 and WT1 positive, calretinin and D2-40 negative)
  • Size is less than 1 cm; if more than 1 cm, by convention the lesion is designated as cystadenoma or cystadenofibroma
  • Cortical inclusion cyst
  • Can occur at any age but more common postmenopausal
Clinical features
  • Incidental findings, usually asymptomatic
Prognostic factors
  • Benign entities
  • Presence of inclusion cyst in postmenopausal women does not increase the risk of ovarian or other hormone driven cancers (breast and endometrial cancers, BJOG 2012;119:207)
  • Traditionally thought to represent a precursor lesion of ovarian carcinoma, but most ovarian serous carcinomas are now considered as tubal in origin with serous tubal intraepithelial carcinoma (STIC) as precursor lesion
  • For a subset of ovarian serous carcinomas in which STIC or tubal involvement is not identified, a potential origin in epithelial inclusion cyst of Müllerian (tubal) phenotype has been postulated (Gynecol Oncol 2013;130:246, Mod Pathol 2011;24:1488, Int J Gynecol Pathol 2015;34:3)
  • Use of oral contraceptives for more than 5 years was shown to reduce the number of Müllerian type inclusion cysts (PAX8 positive), supporting the hypothesis that this subtype constitutes a precursor lesion of ovarian serous carcinoma (Diagn Pathol 2016;11:30)
Gross description
  • Most are not apparent grossly unless very superficial in the cortex
  • When visible, they appear as small cysts bulging at the ovarian surface
Microscopic (histologic) description
  • Small cysts ( < 1 cm)
  • Peritoneal inclusion cyst: lined by simple flat epithelium devoid of cilia or mucinous cytoplasm
  • Müllerian inclusion cyst: lined by simple cuboidal to columnar epithelium with ciliated cells, sometimes admixed with nonciliated (secretory, peg) cells
  • Can have psammoma bodies in adjacent stroma
Microscopic (histologic) images

Images hosted on other servers:

Figure 1:

Figure 2:
ovarian surface

Figure 3:
OEIs with double
PAX8 and
calretinin staining

Figure 4:
secretory cell

images of the tumor

Differential diagnosis
  • Endometriosis: presence of endometrial stroma or hemosiderin laden macrophages
Board review style question #1
Which of the following immunohistochemical markers is NOT useful in determining the phenotype of an ovarian epithelial inclusion cyst?

  1. BerEP4
  2. Calretinin
  3. D2-40
  4. ER
  5. PAX8
Board review style answer #1
D. BerEP4 and PAX8 are positive in Müllerian type cysts, while D2-40 and calretinin are positive in peritoneal type inclusion cysts.

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Reference: Epithelial inclusion cyst
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