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Non-neoplastic cysts / other

Ectopic decidual reaction

Reviewer: Mohiedean Ghofrani, M.D. (see Reviewers page)
Revised: 9 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● A decidual reaction abnormally located in the ovarian stroma


● Typically occurs during pregnancy
● May occur as early as gestational week 9 and is found in almost all ovaries at term (Am J Anat 1978;152:7)


● May be an isolated finding or part of a more widespread decidual transformation of the subperitoneal pelvic mesenchyme


● Response of stromal cells to high levels (systemic or local) of estrogen or progesterone, usually during pregnancy
● Less commonly associated with trophoblastic disease, pelvic radiation (increased sensitivity of ovarian stromal cells to hormones), other causes of increased estrogen / progesterone, or idiopathic

Gross description

● Uncommonly is visible, grossly as tan to hemorrhagic nodules, or patches on ovarian surface

Micro description

● Cells similar to those seen in ectopic decidua appear singly, as small nodules or confluent sheets within superficial cortical stroma or ovarian surface within periovarian adhesions
● Smooth muscle cells (from submesothelial fibroblasts or ovarian stroma), distended capillaries and lymphocytes may also be present
● Focal nuclear pleomorphism and hemorrhagic necrosis are not necessarily evidence of malignancy

Negative stains

● Keratin

Differential Diagnosis

● Some cells may resemble signet ring cells due to cytoplasmic vacuoles (Mod Pathol 2005;18 Suppl 2:S113) but nuclei are bland, no mitotic activity, negative PAS stain, and concurrent pregnancy

End of Ovary-nontumor > Non-neoplastic cysts / other > Ectopic decidual reaction

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