Endometrial cancer is a malignancy arising from the endometrium, the inner lining of the uterus. When symptoms occur, such as unexpected vaginal bleeding after menopause, medical evaluation begins with an imaging test to assess the uterine structure. This initial investigation determines if the lining has become thicker than expected, which can be an early indicator of potential issues. Ultrasound provides a non-invasive way to gather structural information about the endometrium.
The Specific Role of Transvaginal Ultrasound
The preferred tool for this initial assessment is the transvaginal ultrasound (TVUS), due to its ability to provide high-resolution images of the pelvic organs. During the procedure, a slender probe called a transducer is gently inserted into the vagina, positioning it close to the uterus. This proximity allows the ultrasound device to emit high-frequency sound waves that travel through the tissue. The transducer captures the returning echoes and converts them into a detailed, cross-sectional image on a screen.
The primary function of the TVUS is to measure the thickness of the endometrial stripe, which is the central echo complex representing the uterine lining. The high resolution of this technique allows for a precise measurement, helping to triage patients for further diagnostic steps. The measurement is taken at the thickest part of the lining to determine if the tissue is within a normal range. A thickened endometrium is the most common sonographic finding associated with endometrial cancer.
Interpreting Endometrial Thickness Measurements
The clinical significance of the endometrial thickness measurement (ET) depends heavily on the patient’s menopausal status, as hormonal influences cause significant variation. For postmenopausal women experiencing vaginal bleeding, a measurement of 4 millimeters or less is considered highly reassuring. This thin measurement has a negative predictive value of nearly 100%, meaning it is extremely effective at ruling out endometrial cancer. If the measurement is 5 millimeters or greater in a symptomatic postmenopausal woman, the risk of malignancy rises, requiring further investigation.
Interpretation becomes more complex for women taking hormone replacement therapy (HRT) or in the premenopausal stage. Postmenopausal women on HRT may have a higher acceptable threshold, sometimes up to 8 to 11 millimeters, before a thickened lining is considered concerning. In premenopausal women, the endometrium naturally varies throughout the menstrual cycle, ranging from 2 to 4 millimeters during menstruation to as much as 16 millimeters during the secretory phase. Therefore, any measurement must be correlated with the specific phase of her cycle to be meaningful.
Population-specific studies suggest that the standard thresholds of 4 or 5 millimeters may not be reliable for all groups. Research indicates that Black women, in particular, may have a higher risk of false-negative results at these traditional cutoff points. Clinicians must consider a patient’s individual risk factors and clinical presentation alongside the numerical measurement.
Why Ultrasound Cannot Provide a Definitive Diagnosis
While ultrasound is an excellent screening and risk stratification tool, it cannot provide a final diagnosis of cancer. This limitation exists because ultrasound technology assesses the physical structure and density of tissues, but it cannot analyze cellular composition. A thick endometrium only indicates an increased amount of tissue, not the type of cells making up that tissue.
Structural thickening observed on a scan can be caused by several benign, non-cancerous conditions that appear similar to malignancy. For instance, endometrial polyps, submucosal fibroids, or simple hyperplasia can all lead to a thickened endometrial stripe. These conditions result from overgrowth or structural changes that increase the overall volume of the lining. Since ultrasound cannot distinguish between a benign cell overgrowth and a malignant tumor, the imaging is considered an indicator of risk, not a diagnostic confirmation.
Diagnostic Procedures Following Abnormal Ultrasound
When a transvaginal ultrasound reveals an abnormal endometrial thickness or other concerning structural findings, the next step is to obtain a tissue sample. Tissue sampling is the sole method for achieving a definitive diagnosis, as it allows a pathologist to examine the cells under a microscope. The most common first-line procedure is an office endometrial biopsy, often performed using a small suction device called a Pipelle. This device collects a small, random sample of tissue from the uterine lining for histological analysis.
If the initial biopsy is non-diagnostic, or if the ultrasound shows a focal abnormality, a more targeted procedure may be required. Hysteroscopy involves inserting a thin, lighted telescope through the cervix to visually inspect the uterine cavity. This allows the physician to directly view the lining and perform a directed biopsy on any suspicious areas. Only the pathological examination of the collected tissue can confirm or rule out endometrial cancer.