21.2 Endometrium: Cyclic Changes, Hyperplasia & Cancer

Measuring and Interpreting the Endometrium

The endometrium is the mucosal lining of the uterine cavity and the structure that changes most dramatically over the menstrual cycle. Measure it in the midline sagittal plane at the thickest point near the fundus as a double-layer (anterior plus posterior) AP measurement, caliper to caliper on the echogenic basal layers. Exclude intracavitary fluid from the measurement — if fluid is present, measure each layer separately and add them.

Thickness and Appearance by Phase

The trilaminar pattern reflects a functionalis layer prepared for implantation under estrogen; after ovulation, progesterone makes the glands secretory and tortuous, and the endometrium becomes uniformly echogenic. The periovulatory trilaminar appearance is the pattern assessed in fertility workups.

Postmenopausal thresholds are high-yield exam material. In a woman not on hormone replacement therapy (HRT), an endometrial thickness of 4-5 mm or less has a very high negative predictive value for cancer. In a postmenopausal patient with bleeding, a thickness greater than about 4-5 mm warrants endometrial sampling. Patients on sequential HRT normally thicken and shed cyclically, so timing matters when interpreting their scans.

Endometrial Hyperplasia and Carcinoma

Endometrial hyperplasia is abnormal glandular proliferation driven by unopposed estrogen — chronic anovulation, polycystic ovary syndrome, obesity (peripheral conversion of androgens to estrogen), estrogen-only therapy, and estrogen-producing ovarian tumors. On ultrasound it appears as a diffusely thickened, usually homogeneous echogenic endometrium and cannot be reliably distinguished from early carcinoma by imaging alone; biopsy is required. Hyperplasia with atypia is the premalignant form.

Endometrial adenocarcinoma is the most common gynecologic malignancy and typically presents as postmenopausal bleeding — a symptom that must always be investigated. Sonographic features include:

• Thickened, heterogeneous endometrium with irregular margins
• An irregular or disrupted endomyometrial junction suggesting myometrial invasion
• Increased, disorganized internal vascularity on color Doppler
• Intracavitary fluid or hematometra if the tumor obstructs the cervix

Assessing the depth of myometrial invasion matters for staging (for example, invasion of less than versus more than half the myometrial thickness changes the stage and surgical plan). Transvaginal ultrasound can estimate invasion, but MRI is generally preferred for preoperative staging.

Tamoxifen, a selective estrogen receptor modulator used in breast cancer, has an estrogen-agonist effect on the endometrium. It increases the risk of polyps, hyperplasia, and carcinoma and characteristically produces subendometrial cystic changes — a thick endometrial complex with tiny cystic spaces at the endomyometrial junction. Any tamoxifen patient with bleeding deserves careful evaluation.

Endometrial Polyps

A polyp is a focal, benign overgrowth of endometrial glands and stroma. On ultrasound it appears as a focal echogenic mass within the cavity, sometimes containing tiny cystic spaces, and a single feeding vessel (pedicle artery sign) on color Doppler strongly supports the diagnosis. Polyps are a common cause of both premenopausal irregular bleeding and postmenopausal bleeding.

Saline infusion sonohysterography (SIS) — instilling sterile saline into the cavity during transvaginal scanning — distends the cavity and beautifully outlines focal lesions. It is the best ultrasound tool for distinguishing a focal process (polyp, submucosal fibroid) from diffuse endometrial thickening (hyperplasia) and for counting and localizing polyps before hysteroscopic removal.

Intrauterine Fluid, Synechiae, IUDs, and RPOC

A small amount of intracavitary fluid is normal during menses and around ovulation. In a postmenopausal patient, more than a trace of fluid suggests cervical stenosis and raises concern for an obstructing endometrial or cervical lesion; a large, echogenic, painful collection suggests hematometra or pyometra.

Asherman syndrome is intrauterine synechiae (adhesions), usually caused by traumatic dilation and curettage (especially postpartum curettage) or infection. The echogenic bands crossing the cavity are often invisible on standard ultrasound unless the cavity is distended — they are best demonstrated with SIS. Clinically the patient may have hypomenorrhea, infertility, or recurrent pregnancy loss.

Intrauterine devices (IUDs) are easy to assess sonographically and this is a common exam topic:

• A properly positioned IUD is a highly echogenic, shadowing linear structure (often with characteristic posterior shadowing or reverberation) seated in the endometrial cavity at the fundus
• A device sitting low in the body or cervical canal is malpositioned and less effective
• 3D coronal imaging is excellent for confirming the type and position of the device within the cavity
• If no IUD is seen on ultrasound and the strings are missing, the device may have been expelled or may have perforated the uterus — obtain an abdominal radiograph to locate it

Retained products of conception (RPOC) after delivery, miscarriage, or termination appear as an echogenic intrauterine mass, sometimes with calcification. The key discriminator is Doppler: RPOC typically shows internal vascularity, whereas a simple intracavitary blood clot is avascular and may change shape or resolve on follow-up. RPOC is clinically important because it causes continued bleeding and infection risk and may require evacuation.