The endometrium is the inner lining of the uterus, an organ that plays a central role in the female reproductive system. This specialized tissue prepares for a potential pregnancy each month by thickening and enriching with blood vessels. If fertilization does not occur, the functional layer of the endometrium is shed during menstruation, and the process begins anew in the next cycle.
What Endometrial Thickness Means
Endometrial thickness refers to the measurement of this uterine lining, assessed using a transvaginal ultrasound. This imaging technique uses a slender device to generate detailed images of the uterus, allowing precise measurement of the endometrial stripe. The thickness of the endometrium fluctuates throughout a woman’s life, varying with her menstrual cycle and menopausal status. During menstruation, the lining is thinnest, ranging from 2 to 4 millimeters.
As the cycle progresses into the early proliferative phase (around days 5-9), the endometrium begins to regenerate, reaching about 5 to 7 millimeters. By the late proliferative or pre-ovulatory phase (days 10-14), estrogen stimulates further growth, and the lining can thicken up to 11 millimeters. During the secretory phase (days 15-28), under the influence of progesterone, the endometrium becomes even thicker, ranging from 7 to 16 millimeters, preparing for potential embryo implantation. For postmenopausal women not on hormone replacement therapy (HRT), an endometrial thickness of 5 millimeters or less is considered normal. If a postmenopausal woman is on HRT, the acceptable thickness can be up to 8-11 millimeters, as estrogen in HRT can cause the endometrium to thicken.
Signs and Causes of Abnormal Thickness
Abnormal endometrial thickness often presents as abnormal vaginal bleeding, the most common indicator. This includes bleeding after menopause, unusually heavy or prolonged menstrual periods, or spotting between periods. Such bleeding patterns warrant medical evaluation, especially in postmenopausal women, as they may indicate underlying issues.
The causes of abnormal endometrial thickness vary, from benign conditions to serious concerns. Endometrial polyps, which are overgrowths of endometrial tissue, are a common benign cause of abnormal bleeding and thickened lining. Uterine fibroids, non-cancerous growths of the uterine muscle, also contribute to changes in endometrial appearance or symptoms. Endometrial hyperplasia, a non-cancerous overgrowth of the uterine lining, is another common cause, resulting from an imbalance of estrogen and progesterone. While most cases of endometrial hyperplasia are benign, one type, atypical hyperplasia, carries a higher risk of progressing to endometrial cancer. Abnormal endometrial thickness, particularly in postmenopausal women experiencing bleeding, may indicate endometrial cancer, with approximately 10% of women with postmenopausal bleeding being diagnosed with this condition.
Diagnosing Endometrial Changes
When abnormal endometrial thickness is suspected, a doctor will investigate the cause. The initial screening tool is a transvaginal ultrasound. It allows the doctor to visualize the uterus and measure the endometrial thickness. While highly sensitive in detecting a thickened lining, ultrasound alone cannot definitively diagnose cancer and cannot rule out malignancy, particularly in women on hormone replacement therapy.
If the ultrasound reveals a thickened endometrium or if symptoms persist, more definitive diagnostic procedures are recommended. Hysteroscopy involves inserting a thin, lighted telescope (hysteroscope) through the vagina and cervix into the uterus. This allows the physician to visualize the uterine cavity, identify any growths or abnormalities, and determine the precise area from which to take a tissue sample.
Often performed concurrently with hysteroscopy, an endometrial biopsy collects a tissue sample from the uterine lining for analysis. This can be done using a suction catheter or a curette, and the procedure is often performed in the doctor’s office. Although highly informative, an endometrial biopsy can sometimes miss precancerous or cancerous growths if the sample is taken from a random location.
Understanding Your Results
After an endometrial biopsy, the tissue sample is examined by a pathologist to interpret findings. The results will differentiate between benign conditions, precancerous changes, and endometrial cancer. If the biopsy indicates benign findings, it might reveal conditions such as endometrial polyps or simple hyperplasia, which are non-cancerous overgrowths. Simple hyperplasia without atypia has a low risk of progressing to cancer, estimated at less than 5% over 20 years, with many cases resolving spontaneously.
A more concerning finding is atypical hyperplasia, signifying abnormal cell changes and considered precancerous. The risk of atypical hyperplasia progressing to endometrial cancer ranges from 20% to 50%, depending on histopathology and genetic mutations. For women diagnosed with atypical hyperplasia, follow-up care is recommended, including regular endometrial biopsies every 3 to 6 months to monitor progression or recurrence.
Treatment for atypical hyperplasia involves hormonal therapy, particularly progestins, to stabilize the disease and reduce cancer risk. In cases where medical treatment fails, or for higher-risk patients, a hysterectomy (surgical removal of the uterus) may be considered to eliminate cancer risk. If the biopsy confirms endometrial cancer, further evaluation and treatment, typically involving surgery, will be discussed. Remember that a thickened endometrium does not always mean cancer, and the biopsy results provide the definitive diagnosis and guide management.