A 38-year-old woman in Nairobi had been trying to conceive for eight years. Her periods were regular and painless. She had no chronic illnesses. Her husband, 40, was healthy and had none either. Nothing in the history pointed anywhere.
Then a pelvic ultrasound found a two-centimeter streak of calcification sitting inside her uterine cavity. Her ovaries and adnexa looked normal. When gynecologists went in with a hysteroscope, they saw a white plaque the report describes as coral-like, sitting in the lining of her uterus.
It was bone.
Surgeons removed it as a day-case procedure with no complications. She conceived spontaneously in her next menstrual cycle and delivered a healthy boy weighing 3.6 kilograms, by cesarean section at 41 weeks after an induction failed to progress.
The case was published Aug. 26 by obstetrician-gynecologists at Aga Khan University in Nairobi in the Journal of Medical Case Reports. It is a peer-reviewed, accepted manuscript posted ahead of final editing, and the published version of record has not yet appeared, so minor details may change.
Bone Where Bone Does Not Belong
The condition is called endometrial osseous metaplasia, and it means exactly what it sounds like: mature or immature bone forming in the lining of the uterus. It is benign, and it is genuinely rare. A multicenter study across fourteen institutions in eight countries identified 63 cases among 419,673 women who underwent hysteroscopy over 25 years, a rate of 0.015%.
Nobody is certain how the bone forms. The leading explanation holds that stromal cells in the uterine lining, ordinarily fibroblasts, transform into osteoblasts and start laying down bone during healing after inflammation. Competing theories point to retained fetal bone from a lost pregnancy, calcification of dead tissue, prolonged estrogen exposure, and metabolic disorders.
Most theories share a trigger: something damaged the uterine lining first, and the bone appeared during repair. The case report's title captures the idea, framing the condition as healing that turns into an obstacle.
Why This Patient Breaks the Usual Pattern
Here is what makes the Nairobi case unusual. Endometrial osseous metaplasia is overwhelmingly a post-pregnancy phenomenon, and more than 80% of reported cases follow a pregnancy. A systematic review of 293 patients drawn from 155 published reports found that roughly 88% had undergone at least one prior surgical uterine evacuation related to a pregnancy termination or loss. In the multicenter study, 86.9% had been pregnant at least once.
This woman had primary infertility. She had never been pregnant. There was no miscarriage, no procedure, no obvious insult to explain what happened.
Her pathology offered a partial answer. The resected fragments showed endometrial tissue with bone in the stroma alongside features of chronic endometritis, a low-grade, persistent inflammation of the uterine lining that often produces no symptoms at all. The authors conclude that while post-miscarriage instrumentation is the most common cause, some cases arise on their own.
How Bone Blocks a Pregnancy
Two mechanisms have been proposed. The bone may act as a foreign body, functionally similar to an intrauterine device, physically preventing conception. Or it may drive a reactive inflammation in the lining that interferes with an embryo trying to implant.
Neither has been proven, and the two are not mutually exclusive. In this patient, chronic endometritis in the same specimen supports the inflammatory explanation, though a single pathology report cannot establish which mechanism was at work or which came first.
Either way, the fix is mechanical. Hysteroscopic resection is the preferred treatment, letting surgeons see the tissue and remove it under direct vision while confirming the cavity is empty at the end. Dilation and curettage has also been used, though unlike hysteroscopy, it is performed without direct visualization of the cavity. In this case, the surgical team documented an empty cavity at the close of the procedure, and the speed of the subsequent conception suggests the lining was not left significantly damaged.
Reported outcomes are encouraging. In the 293-patient review, 124 of 188 women attempting pregnancy after treatment conceived, and the large majority did so spontaneously. Other case reports similarly find that hysteroscopic resection restores fertility in most patients. Those numbers come with real limits. They are pooled from case reports, which favor publication of successes, and miscarriage rates afterward remained elevated at around 43%.
What This Does and Does Not Mean
One case does not establish that removing uterine bone restores fertility, and it says nothing about how many women with unexplained infertility have this condition. Almost certainly very few do.
The more useful point is diagnostic. A standard pelvic ultrasound picked this up. The bone produces a distinctive bright echo pattern, and ultrasound is cheap and widely available. The condition can be mistaken for a retained contraceptive device, which a patient history usually settles, or for endometrial tuberculosis, which also causes calcification and is much harder to distinguish. Signs pointing toward tuberculosis include a history of pulmonary disease, complex adnexal cysts, and fluid in the pelvis.
Women facing long-standing unexplained infertility should discuss imaging findings with a reproductive specialist rather than pursuing any specific test based on a case report. But the case makes an argument worth hearing: a rare, treatable structural cause can hide behind a normal-looking history, and eight years is a long time to spend not looking for it.
Key Questions Answered
What is endometrial osseous metaplasia?
A rare benign condition in which bone tissue forms inside the lining of the uterus. It can cause infertility, irregular bleeding, or pelvic pain, and in some cases produces no symptoms.
How rare is it?
A multicenter study found 63 cases among 419,673 women who underwent hysteroscopy, a rate of 0.015%. Other estimates place it near 3 in 10,000 women.
What usually causes it?
Most cases follow a pregnancy loss or termination involving a uterine procedure. Roughly 88% of published cases had a prior surgical uterine evacuation. This patient had never been pregnant, which is unusual.
How is it diagnosed?
Pelvic ultrasound typically shows a distinctive bright echo pattern in the uterine cavity. Hysteroscopy confirms the diagnosis and allows removal in the same procedure.
Does removing it restore fertility?
Published outcomes are favorable, with most treated women attempting pregnancy going on to conceive, usually without assistance. Those figures come from pooled case reports and may overstate success.
