Background: Endometrial osseous metaplasia (EOM), also known as endometrial ossification or heterotopic intrauterine bone, is a rare benign condition characterized by the presence of mature or immature bone in the endometrium. While rare, it is an under-recognized, reversible cause of secondary infertility and abnormal uterine bleeding, and sonographic appearance is easily confused with a copper intrauterine device (IUD).
Objective: To present a complete review of the terminology, the first description, the biological background, epidemiology, pathogenesis, clinical presentation, diagnostic evaluation, differential diagnosis, and treatment of EOM with a particular focus on the frequent clinical mistake of transvaginal sonography misdiagnosing intracavitary bone as a copper intrauterine device, thus delaying definitive treatment for the woman's infertility.
Methods: Review of published literature (case reports, case series, histopathological and molecular analysis, and previous reviews on endometrial ossification and osseous metaplasia).
Findings: EOM is primarily a disease of women of reproductive age, with most women having a previous pregnancy loss or uterine instrumentation. There are two main and possibly separate mechanisms suggested: (1) fetal skeletal tissue persisting after an abortion and (2) the actual transformation of maternal endometrial stromal cells to osteoblasts due to chronic inflammation and repeated injury. The intracavitary bone acts as an endogenous foreign body, causing mechanical and inflammatory (prostaglandin-mediated) implantation problems just like an IUD. The diagnosis is confirmed by transvaginal ultrasonography (which usually shows hyperechoic, shadowing endometrial foci that strongly resemble a copper IUD), the reference standard for diagnosis, and the definitive treatment is hysteroscopy; histopathology is useful to exclude malignant heterologous elements. Rapid symptom clearance and often spontaneous reversion to fertility are seen with complete hysteroscopic removal.
Conclusion: An echogenic focus within the cavity of the uterus should alert the clinician to the possibility of EOM in any woman of reproductive age who has secondary infertility or abnormal uterine bleeding, especially in women who have not had an IUD inserted. High index of suspicion, hysteroscopic diagnosis, and complete surgical removal under direct vision have a very good prognosis.