The term “endometrial complex” refers to the uterine lining, or endometrium, as seen in medical imaging. On an ultrasound, this tissue appears as a stripe. The appearance of this complex, particularly its thickness and texture, provides information about a person’s gynecological health. Its characteristics are monitored as they can indicate normal hormonal fluctuations or point toward underlying health conditions.
The Endometrial Complex and the Menstrual Cycle
The endometrial complex undergoes predictable, hormone-driven changes throughout the menstrual cycle. After menstruation, the proliferative phase begins, where the hormone estrogen stimulates the endometrium, causing it to regrow and thicken. This initial rebuilding phase prepares the uterus for a potential pregnancy.
Following ovulation, the cycle transitions to the secretory phase. Under the influence of progesterone, the endometrium stops thickening and begins to mature. Its structure changes to become more receptive to a fertilized egg by developing the glands and blood supply needed to support an embryo.
If pregnancy does not occur, falling estrogen and progesterone levels trigger the breakdown of the endometrial lining. This leads to menstruation, where the tissue is shed, marking the end of one cycle and the beginning of the next.
Measuring Endometrial Thickness
The primary method for measuring the endometrial complex is a transvaginal ultrasound. This technique uses a slender transducer placed in the vagina to create detailed images of the uterine lining. This approach provides a clearer and more accurate measurement compared to an ultrasound performed over the abdomen.
For premenopausal individuals, the expected thickness changes with the menstrual cycle. During and immediately after menstruation, the lining is at its thinnest, measuring between 2 and 4 millimeters. In the proliferative phase, it thickens to between 5 and 11 millimeters, reaching a maximum thickness of up to 16 millimeters during the secretory phase.
After menopause, the measurement is a more direct health indicator since cyclical changes stop. A postmenopausal endometrium is expected to be thin, and a measurement under 5 millimeters is considered normal. A thickness greater than this 5-millimeter threshold prompts further investigation. For those not experiencing bleeding, a slightly higher threshold may be used, but a thickened lining still requires follow-up.
Causes of an Abnormal Endometrial Complex
An abnormally thick endometrial complex can result from several conditions, ranging from benign to malignant. One of the most frequent causes is endometrial hyperplasia, a condition where the lining of the uterus becomes too thick due to an imbalance between estrogen and progesterone. Some forms of hyperplasia have a higher likelihood of progressing to cancer if left untreated.
Benign growths are another primary reason for a thickened endometrium. Endometrial polyps (tissue growths on the uterine wall) and submucosal fibroids (noncancerous tumors under the lining) can distort the cavity and increase the measurement.
The most serious cause is endometrial cancer. This is a concern, particularly in postmenopausal women who present with uterine bleeding and a thickened lining.
Conversely, an unusually thin endometrium can also be a sign of an underlying issue. Conditions such as endometrial atrophy, a thinning of the lining common after menopause, or Asherman’s syndrome, which involves scar tissue from previous surgeries, can prevent the endometrium from growing properly.
Diagnostic Procedures and Follow-Up
If an ultrasound reveals an abnormal endometrial complex, further diagnostic tests are needed to determine the cause. A sonohysterogram, or saline-infusion sonogram, offers a more detailed view than a standard ultrasound. During this procedure, sterile saline is infused into the uterine cavity, separating the walls to better visualize abnormalities like polyps or fibroids.
For a definitive diagnosis, a tissue sample is often necessary. An endometrial biopsy is a common office-based procedure where a thin, flexible tube is passed through the cervix into the uterus to collect a small piece of endometrial tissue using suction. The collected tissue is then sent to a laboratory to be examined under a microscope.
In some cases, a more comprehensive evaluation is needed. A hysteroscopy allows a doctor to look directly inside the uterus using a thin, lighted instrument to visually inspect the lining and take targeted biopsies. This procedure may be combined with a dilation and curettage (D&C), where an instrument is used to scrape tissue from the uterine lining for examination.