The Bare Bones of Endometrial Osseous Metaplasia

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Video Description

In this video, we present the case of a healthy 39 year-old with a known history of endometriosis who presented with menstrual irregularities and chronic pelvic pain. An advanced transvaginal ultrasound demonstrated echogenic linearities predominantly within the uterine cavity with extension into the myometrium. Previous uterine instrumentation history includes two early pregnancies treated by D&C as well as two prior IUDs that were had been previously removed. Endometrial biopsy revealed sampling of normal endometrial tissue. Operative hysteroscopy was performed with findings of osseous trabecular tissue embedded within the myometrium This uncommon pathologic entity is important to recognize as a potential cause for chronic pelvic pain, menstrual irregularities and fertility issues. Appropriate detection with ultrasound first-line can help to increase suspicion of this phenomenon. Ultimate investigation via hysteroscopic removal of abnormal tissue with sampling of the underlying endomyometrium is necessary for diagnosis and treatment of symptoms.

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Mcmaster University

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Video Transcript: The Bare Bones of Endometrial Osseous Metaplasia

In this video, we are discussing a rare case of endometrial osseous metaplasia at a tertiary care center.

The objectives of this video include describing endometrial osseous metaplasia or EOM, including its proposed pathogenesis and prevalence, discussing the clinical symptoms and importance of this disease entity, identifying commonly used diagnostic tools for the identification of EOM, and highlighting an interesting clinical case involving surgical diagnosis and treatment of EOM, and outlining key takeaways.

We will do this by first discussing the prevalence in the pathophysiology of this rare phenomenon. We will then use a clinical case to highlight the workup and management options, concluding with key learnings in the case.

Endometrial osseous metaplasia, or EOM for short, involves the formation of mature or immature bone within the endometrium. First described by Virchow in 1884, its prevalence is difficult to estimate due to its rarity, though less than 100 cases have been reported in the literature thus far. 

The pathogenesis of EOM is still unclear, though there are two widely accepted theories. The first theory suggests that chronic inflammation from such conditions as repeated endometritis, as well as uterine instrumentation, insights pluripotent endometrial stromal cell transformation into osteoblasts, thereby creating bone. 

The second theory incorporates the association between past pregnancy and EOM. This theory suggests that previous pregnancy loss, or termination, and residual fetal tissue forms a graft in the uterus hardened by dystrophic calcification. This clinical case is a patient SC, who is a G2A2 with a background history of depression, anemia, and migraines. 

She’s previously had two D&Cs and a laparoscopic excision of endometriosis with the reception of uterosacral disease. Importantly, her obstetrical history includes two D&Cs, one for pregnancy loss and one for surgical abortion. Patient SC presented with a four-year history triggered after 2016, her most recent D&C. 

Her history was significant for irregular menstrual bleeding, with heavy flow and significant pain. Despite previous trials of four different OCPs, Lupron and Depo-Provera, as well as a surgical intervention for resection of endometriosis, her symptoms were persistent and significantly affected her quality of life. 

On finally starting Dienogest, her symptoms dramatically improved by achieving a state of amenorrhea. Though not experienced by this patient, fertility issues can also be a reason for seeking care in patients suffering from EOM. A workup for this patient included an ultrasound by an advanced, trained sinologist, including a transvaginal ultrasound as first-line imaging. 

On the left is a sagittal view of this patient’s uterus. There are hyperechoic granularities within the endometrium, giving the appearance of a possible intrauterine device, though the patient confirmed that she did not have an IUD in situ. A transverse view, as on the right, confirmed that the cavity was filled with these hyperechoic lesions. 

In this cine clip of a sonohysterogram view, we can see these hyperechoic granularities scattered throughout the uterine cavity. No Doppler vascularity is present. For a full diagnostic evaluation, and after a negative endometrium biopsy that showed normal endometrial cells but no other pathology, the patient has consented to diagnostic hysteroscopy resection of cavity lesions and an opportunistic endometrial resection ablation. 

This surgical video demonstrates an initial hysteroscopic view of the uterus, and the patient was prepped on Dienogest preoperatively. When exploring the cavity, we can see the sheets of bone arising from the fundal right and posterior walls. There were several sheets in a conglomerate, with more arising upon further dissection. 

In order to determine the density of the tissue, the loop electrode was deployed, and gentle probing elicited the breakage of some of the material. However, a significant portion of the material was still intact and did not simply disintegrate with pressure. Given the hardness and quantity of the lesions, we attempted curette and extract a specimen via polyp forceps. This yielded a significant amount of tissue, yet as demonstrated here, more still remained. 

With the looser pieces removed, there were several that were adhering to the wall of the uterus and needed probing with the loop to coax the tissue free from sites of attachment. Several passes were required in order to systematically remove the tissue, binding the tissue between the loop of the shaft of the scope. Some pieces appeared to be embedded within the myometrium layer of the uterus. 

Finally, an endometrial resection was performed globally for the treatment of the patient’s AUB. Despite this, on readying the cavity for endometrial ablation, more osseous tissue appeared within the wall of the uterus. And further extraction was required. Once this was complete, a global rollerball endometrial ablation was performed. 

The patient’s clinical symptoms were improved post operatively while she remained on Dienogest to control her AUB symptoms. Final pathology confirmed that the pieces of yellow, firm, lattice-like structures were, in fact, osseous tissue, and myometrial tissue with areas of metaplastic ossification, suggesting infiltration into the myometrial layer. 

Fortunately, the underlying endometrium was also negative for hyperplasia and malignancy. Several key takeaways from this case include incorporating endometrial osseous metaplasia on a differential for chronic pelvic pain, menstrual irregularities, and fertility issues. Also, ultrasound can be an important first-line non-invasive tool for diagnosis.

Suspicion should heighten when the endometrial cavity includes hyperechoic lesions similar in appearance to an IUD. Ultimately hysteroscopy is needed for sampling and pathologic diagnosis. Preneoplastic, and even malignant conditions, have been associated with this rare entity.

Thank you for your time and attention to this video. As well, thank you to our clinical and research team at McMaster University.