The endometrial stripe is the measurement of the endometrium, the inner lining of the uterus, as seen on a pelvic ultrasound scan. This dynamic tissue changes thickness throughout a person’s life in response to hormonal signals. A thickened endometrial stripe is an observation, not a diagnosis, made by a radiologist or gynecologist. This finding commonly prompts further investigation, as the significance of the measurement depends entirely on the patient’s hormonal status.
Understanding the Measurement and Normal Limits
The endometrium is made of two layers: a deeper basal layer and a superficial functional layer that grows and sheds each month during the menstrual cycle. On a transvaginal ultrasound, the opposing walls of the lining appear as a single echogenic line, which is the stripe that is measured. The measurement is taken at the thickest point, from one basal layer across the cavity to the other basal layer.
The interpretation depends highly on whether a person is pre-menopausal or post-menopausal. For pre-menopausal individuals, the thickness fluctuates widely, ranging from 2 to 4 millimeters (mm) during menstruation up to 16 mm during the secretory phase. Since the lining is meant to thicken in preparation for potential pregnancy, there is no single upper limit defining “abnormal” outside of the menstrual cycle phase context.
The measurement is more specific for post-menopausal women, whose endometrium should be thin and stable due to low estrogen levels. If they are not experiencing vaginal bleeding, a measurement of 5 mm or less is considered normal. When a post-menopausal woman experiences bleeding, a thickened stripe is often defined as greater than 4 mm, which warrants immediate follow-up due to the risk of malignancy.
Common Conditions That Cause Thickening
Hormonal Effects and Medications
The causes of a thickened endometrial stripe range from benign hormonal effects to potentially precancerous or cancerous conditions. A common cause is the use of certain medications, such as Tamoxifen, which stimulates endometrial growth, or estrogen-only hormone replacement therapy (HRT) without counterbalancing progesterone. These hormonal influences cause a generalized, diffuse thickening of the entire lining.
Endometrial Polyps
Localized, non-cancerous growths called endometrial polyps are a frequent finding. These are overgrowths of endometrial tissue that attach to the inner uterine wall, making the stripe appear thicker in a specific area. Polyps are typically benign, though they can cause abnormal bleeding and occasionally harbor abnormal cells.
Hyperplasia and Carcinoma
A more concerning cause is endometrial hyperplasia, an excessive, disorganized proliferation of the endometrial glands. This results from prolonged exposure to estrogen without the counter-regulatory effect of progesterone, often seen in women with obesity or Polycystic Ovary Syndrome (PCOS). Hyperplasia is classified based on cell appearance, with the “atypical” form being a direct precursor to endometrial cancer. The most serious, though least common, cause is endometrial carcinoma, or cancer of the uterine lining.
While a thickened stripe is a sensitive screening tool for cancer, it is important to remember that the majority of thickened stripes are ultimately found to be benign, such as polyps or hormonal effects.
Clinical Procedures for Further Evaluation
Endometrial Biopsy
Once a thickened stripe is identified, the next step is determining the cellular cause. The first-line procedure is often an office-based endometrial biopsy, frequently performed using a small, flexible suction device called a Pipelle. This procedure is quick and minimally invasive, retrieving a sample of the lining for pathological analysis to check for hyperplasia or cancer.
Saline Infusion Sonography (SIS)
If the initial biopsy is insufficient or negative despite persistent symptoms, Saline Infusion Sonography (SIS), or sonohysterography, may be performed. SIS involves injecting sterile saline solution into the uterine cavity to gently distend it. This allows the ultrasound to better visualize the lining and distinguish focal lesions, like polyps, from diffuse, generalized thickening.
Hysteroscopy and Dilation and Curettage (D&C)
If SIS reveals a focal mass or if the initial biopsy is inadequate, the patient may undergo a hysteroscopy combined with a Dilation and Curettage (D&C). Hysteroscopy involves inserting a thin camera through the cervix to visually inspect the entire uterine cavity. This allows the physician to target and remove specific abnormal areas, while the D&C provides a larger tissue sample for definitive diagnosis.
Management Based on Diagnosis
Subsequent management is determined by the tissue analysis. Benign findings, such as simple hormonal thickening, may only require monitoring or hormonal therapy to resolve. Hyperplasia without atypia is often managed with progesterone treatment to induce shedding and thinning of the lining. Atypical hyperplasia or carcinoma typically requires surgical intervention, such as a hysterectomy.