Other nonneoplastic lesions


Editorial Board Members: Gulisa Turashvili, M.D., Ph.D., Stephanie L. Skala, M.D.
Lisa Han, M.D.
Carlos Parra-Herran, M.D.

Last author update: 8 November 2023
Last staff update: 8 November 2023

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PubMed Search: Ovarian endometriosis

Lisa Han, M.D.
Carlos Parra-Herran, M.D.
Page views in 2023 to date: 65,344
Cite this page: Han L, Garcia R, Busca A, Parra-Herran C. Endometriosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/ovarynontumorendometriosis.html. Accessed November 28th, 2023.
Definition / general
  • Presence of endometrial tissue outside of endometrium and myometrium, consisting of both endometrial glands and stroma
Essential features
  • Ectopically located endometrial tissue consisting of at least 2 of the following: endometrial type glands, endometrial type stroma or evidence of chronic hemorrhage
  • Endometriosis is associated with ovarian clear cell carcinoma and endometrioid carcinoma and shares similar molecular alterations
  • Endometriosis in patients without cancer harbors oncogenic mutations in ARID1A, PIK3CA, KRAS and PPP2R1A, suggesting a neoplastic nature in some cases (N Engl J Med 2017;376:1835)
  • CD10 immunohistochemistry can be used to confirm the presence of endometrial stroma
  • Endometriotic cyst / endometrioma: cystic form of endometriosis
  • Atypical endometriosis: endometriosis with cytologic atypia or crowded glands lined by atypical epithelium resembling endometrial atypical hyperplasia (Adv Anat Pathol 2007;14:241)
ICD coding
  • ICD-10: N80 - endometriosis of uterus
    • N80.0 - endometriosis of uterus
    • N80.1 - endometriosis of ovary
    • N80.2 - endometriosis of fallopian tube
    • N80.3 - endometriosis of pelvic peritoneum
    • N80.4 - endometriosis of rectovaginal septum and vagina
    • N80.5 - endometriosis of intestine
    • N80.6 - endometriosis in cutaneous scar
    • N80.8 - other endometriosis
    • N80.9 - endometriosis, unspecified
  • Affects 5 - 15% women of reproductive age
  • Peak incidence: 30 - 45 years of age
  • Estrogen dependent; can rarely affect individuals assigned male at birth taking large doses of estrogen (Fertil Steril 2012;98:511)
  • Retrograde menstruation hypothesis: endometrial lining cells travel backwards through fallopian tubes during menses to reach peritoneal cavity, proliferate and cause chronic inflammation with formation of adhesions (Nat Rev Endocrinol 2014;10:261)
  • Coelomic metaplasia hypothesis: metaplastic transformation of coelomic cells lining the pelvic peritoneum (J Lab Physicians 2010;2:1)
  • Induction hypothesis: a combination of the first 2 theories (N Engl J Med 1993;328:1759)
  • Development of malignant neoplasm occurs in < 1% of cases; 75% of malignant neoplasms arise in ovarian endometriosis (J Lab Physicians 2010;2:1)
Clinical features
  • Pelvic pain (Arch Gynecol Obstet 2015;292:1295)
  • Dyspareunia
  • Dysmenorrhea
  • Infertility
  • Rarely, infection or rupture of an endometriotic cyst with ascites or hemoperitoneum
  • Laparoscopy required for definitive diagnosis, although ~50% laparoscopic biopsy specimens contain microscopic endometriosis (Am J Obstet Gynecol 2001;184:1407)
  • Endometriosis in pelvis categorized as superficial peritoneal, ovarian and deeply infiltrating
Radiology description
  • Ultrasound is mostly used for ovarian endometriotic cysts
  • Typically multilocular cysts with septations and hyperechoic mural nodules (Radiology 1999;210:739)
Prognostic factors
  • Risk of development of malignant neoplasm is estimated at 1% for premenopausal women and up to 2.5% for postmenopausal women
  • ~75% neoplasms complicating endometriosis arise within the ovary; most common extraovarian site is rectovaginal septum
    • Increased risk of endometrioid carcinoma followed by clear cell carcinoma (Clin Chim Acta 2019;493:63)
    • Other associated neoplasms include seromucinous neoplasms (mainly borderline), endometrioid adenofibromas and borderline neoplasms, adenosarcomas and endometrial stromal sarcomas (Histopathology 2020;76:76)
  • Women with carcinoma arising in endometriosis tend to be premenopausal, obese and with history of unopposed estrogens (Gynecol Oncol 2000;79:18)
  • Endometriosis associated carcinomas (other than clear cell) tend to be lower grade and stage than similar ovarian carcinoma without associated endometriosis (Gynecol Oncol 2001;83:100)
Case reports
Gross description
Gross images

Contributed by University of Washington Medical Center and AFIP
Uterus with shaggy hemorrhagic adhesions

Uterus with shaggy hemorrhagic adhesions

External surfaces of the ovarian wedges show red, blue and brown areas, some associated with fibrotic puckering External surfaces of the ovarian wedges show red, blue and brown areas, some associated with fibrotic puckering

External surfaces of the ovarian wedges

Cyst contains chocolate colored fluid

Cyst contains chocolate colored fluid

Cyst has dark brown discoloration

Cyst has dark brown discoloration

Images hosted on other servers:
Small foci resembling powder burns Small foci resembling powder burns

Small foci resembling powder burns

"Chocolate" cyst

Chocolate cyst

Frozen section description
  • Presence of endometrial glands or endometrial stroma (Taiwan J Obstet Gynecol 2019;58:328)
    • Sometimes only macrophages and hemosiderin are present (diagnose as consistent with clinical impression of endometriosis, as other causes are possible)
  • Can be associated with fibrous adhesions
  • Negative for neoplastic features such as glandular complexity
Frozen section images

Contributed by University of Washington Medical Center
Endometriosis involving omental nodule

Endometriosis involving omental nodule

Endometriosis in peritoneal nodule

Endometriosis in peritoneal nodule

Microscopic (histologic) description
  • At least 2 of the following 3 features
    • Endometrial type glands
      • Müllerian type epithelium (can be atrophic to cycling endometrium)
      • Can show degenerative atypia (enlarged smudgy nuclei) or metaplasia
    • Endometrial type stroma
      • Often contains fine capillary network
      • May undergo smooth muscle metaplasia, fibrosis (longstanding), decidual change
      • May be myxoid (particularly in pregnancy)
      • Stroma may be the only identifiable component (stromal endometriosis)
    • Evidence of chronic hemorrhage (hemosiderin laden or foamy macrophages)
  • Other rare findings
    • Necrotic pseudoxanthomatous nodules: central necrosis surrounded by histiocytes and outer fibrous zone
    • Liesegang rings: eosinophilic acellular rings within necrotic tissue (Histopathology 2020;76:76)
    • Burnt out endometriosis: this term has been proposed for changes suggestive of endometriosis, such as central necrosis with surrounding fibrosis and pseudoxanthoma cells but lacking confirmatory features as listed above
    • Atypical endometriosis: this has been reported in 1.7 - 4.4% of endometriotic lesions and is considered the precursor lesion for endometriosis associated carcinomas (clear cell or endometrioid); may be in continuity with these tumors
Microscopic (histologic) images

Contributed by University of Washington Medical Center and Aurelia Busca, M.D., Ph.D.
Uterine serosa with endometriosis

Uterine serosa with endometriosis

Endometriosis, partially denuded

Endometriosis, partially denuded

Endometriosis with hemosiderin

Endometriosis with hemosiderin

Endometriosis involving appendix

Endometriosis involving appendix

Denuded hemorrhagic cyst

Denuded hemorrhagic cyst

Endometriotic cyst Endometriotic cyst

Endometriotic cyst

CD10 CD10




Virtual slides

Images hosted on other servers:
Ovarian endometriotic cyst

Ovarian endometriotic cyst

Cytology description
  • Reported in peritoneal fluid and fine needle aspiration of scar tissue following gynecologic procedure (e.g., Caesarean section) (J Cytol 2017;34:61)
  • Variably sized, 3 dimensional spherules with periphery of polygonal endometrial cells with larger, hyperchromatic nuclei and moderate amount of cytoplasm, often with a center of stromal cells with hyperchromatic nuclei, scant cytoplasm and indistinct cytoplasmic borders (Cancer Cytopathol 2013;121:582)
  • May have admixed hemosiderin laden macrophages
Cytology images

Contributed by Carmen Luz, M.D.
FNA from abdominal wall

FNA from abdominal wall

Positive stains
Molecular / cytogenetics description
  • Endometriosis and synchronous carcinoma share similar genetic alterations including ARID1A, PTEN and PIK3CA
  • Mutations in ARID1A, a tumor suppressor gene, identified in up to 57% of ovarian endometrioid carcinoma and up to 30% of clear cell carcinoma
    • Multiple studies suggest ARID1A mutation occurs at early stage of canceration of endometriosis (Oncol Rep 2016;35:607)
    • Endometriosis occurring distant from ARID1A deficient carcinomas are more likely to retain ARID1A expression
  • Other associated genetic alterations include loss of BAF250a, ER and PR and upregulation of hepatocyte nuclear factor - beta and SKP2
  • In one study, loss of DNA mismatch repair protein expression was found in 10% of patients with endometriosis associated ovarian carcinoma (Int J Gynecol Pathol 2012;31:524)

Causes, symptoms, diagnosis, treatment, pathology

Histopathology - ovary

Sample pathology report
  • Uterus, hysterectomy:
    • Proliferative endometrium negative for hyperplasia or malignancy
    • Unremarkable cervix
    • Myometrium with leiomyomata
    • Uterine serosa with multifocal endometriosis

  • Right ureterosacral peritoneum, excision:
    • Fibrous tissue with focal endometrial type stroma and hemorrhage, suggestive of endometriosis
Differential diagnosis
  • Endocervicosis:
    • Glandular component is endocervical mucinous type, no endometrial stroma, no hemorrhage
  • Endosalpingiosis:
    • Glandular component is tubal (ciliated with peg / intercalated) cells, no endometrial stroma, no hemorrhage
  • Adenomyosis:
    • Endometrial glands and stroma in myometrium
  • Endometrioid adenocarcinoma:
    • Complex glandular growth and cytologic atypia
  • Metastatic carcinoma:
    • Morphology varies by site of origin; however, no endometrial stroma
    • Other features of neoplasm present, including crowded irregular glands, nuclear atypia or elevated mitotic activity
Board review style question #1

A 39 year old woman presents with pelvic pain and menorrhagia. Hysterectomy was performed and the histologic findings shown in this photomicrograph were present on the serosal surface and right ovary. What malignant neoplasm is most associated with the lesion?

  1. Clear cell sarcoma
  2. Endometrial stromal sarcoma
  3. High grade serous carcinoma
  4. Immature teratoma
  5. Ovarian endometrioid carcinoma
Board review style answer #1
E. Ovarian endometrioid carcinoma. Endometriosis can be associated with endometrioid and clear cell carcinoma, with the greatest association identified in the former neoplasm. Rare endometrial stromal sarcomas and adenosarcomas have also been reported to arise in association with endometriosis. Answer D is incorrect because there is no reported association between germ cell tumors and endometriosis. Answer C is incorrect because there is no reported association between high grade serous carcinoma and endometriosis. Answer A is incorrect because there is no reported association between clear cell sarcoma and endometriosis. Answer B is incorrect because even though some cases of adenosarcomas have been reported to arise in association with endometriosis, the association is less frequent than endometrioid carcinoma.

Comment Here

Reference: Endometriosis
Board review style question #2
Which of the following genes is most commonly altered in endometriosis associated carcinomas?

  1. ARID1A
  2. BRAF
  3. CDKN2A (p16)
  4. PTEN
  5. TP53
Board review style answer #2
A. ARID1A. Of the 5 genes listed, mutations in tumor suppressor gene ARID1A are most commonly identified in endometriosis and endometriosis associated carcinomas. Many studies suggest that loss of ARID1A expression is an early driver mutation. Other common molecular alterations include mutations in PTEN, PIK3CA, KRAS and to a lesser extent, microsatellite instability with MMR protein loss. Answer D is incorrect because PTEN mutations are less frequent. Answers E and C are incorrect because TP53 and CDKN2A mutations are rare. Answer B is incorrect because BRAF mutations are not associated with endometriosis.

Comment Here

Reference: Endometriosis
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