Osseous Metaplasia of the Endometrium: A Rare but Striking Ultrasound Finding

 

Osseous metaplasia of the endometrium is an uncommon yet unforgettable diagnosis on pelvic ultrasound. Although rare, recognizing it is important because it is a treatable cause of secondary infertility and is frequently misinterpreted as retained products of conception (RPOC) or chronic endometritis.

What Is Endometrial Osseous Metaplasia?

A condition where bone tissue forms within the endometrium, usually after a prior pregnancy loss.
The proposed mechanisms include:

• Metaplastic transformation of endometrial stromal cells

• Chronic inflammation stimulating osteoblastic activity

• Retained fetal bone fragments (less common)

Typical Ultrasound Appearance

Ultrasound is often diagnostic due to its characteristic features:

On grayscale USG:

• Highly echogenic linear or plate-like foci within the endometrial cavity

• Posterior acoustic shadowing — often dense

• Fragmented, irregular calcific elements

• Endometrial thickening may be present

On Doppler:

• Minimal to no internal vascularity
  (This helps differentiate it from vascular retained products)

On 3D USG or saline infusion sonography (if performed):

• Better delineation of the calcified plaques projecting into the cavity

This pattern is distinct and often pathognomonic, making USG the first-line modality.

❗ Why It’s Often Confused With RPOC

Both conditions may occur after miscarriage.
However, key differences:

Feature	Osseous Metaplasia	RPOC
Echogenicity	Very bright, shadowing calcification	Mixed echogenicity, soft tissue
Vascularity	Absent	Variable, often present
Chronicity	Months–years later	Days–weeks after pregnancy
Response to curettage	Often incomplete	Effective

Mislabeling it as calcified RPOC leads to repeated curettage, which risks adhesions without resolving the problem.

Clinical Significance

• Secondary infertility

• Irregular bleeding

• Pelvic discomfort

• Sometimes asymptomatic — detected incidentally

Removal of osseous tissue dramatically improves fertility outcomes.

Management

• Hysteroscopic removal is the gold standard

• Under ultrasound guidance if needed

• Complete removal is usually curative

• Pathology confirms mature bone fragments

Key Takeaway

Osseous metaplasia is rare but easily recognizable.
If you see bright echogenic linear foci with posterior shadowing in the endometrium, think beyond RPOC. Correct identification prevents unnecessary curettage and restores reproductive potential for many patients.

Radiology isn't just about diagnosing lesions — sometimes, it’s about identifying the one thing standing between a patient and their long-awaited pregnancy.

Happy Learning,

-Dr. Upasana Y