Measuring Endometrial Thickness on Transvaginal Ultrasound
Correct Measurement Technique
- The American College of Radiology recommends performing a combined transabdominal and transvaginal approach whenever possible for complete assessment of pelvic structures 2
- To measure endometrial thickness, position the transvaginal probe to obtain a longitudinal (sagittal) view of the uterus, and identify the endometrium as the echogenic lining of the endometrial cavity 3
- Measure the double-layer thickness at the thickest portion of the endometrium, ensuring measurement is perpendicular to the endometrial-myometrial interface, and include both anterior and posterior layers of the endometrium in the measurement 1
Common Errors in Endometrial Measurement
- Measuring in an oblique plane rather than true sagittal plane falsely increases thickness, and including adjacent myometrium in the measurement is also an error 3
- Failing to identify the true endometrial-myometrial interface, measuring only a single layer of the endometrium, and not measuring at the thickest portion of the endometrium are common mistakes 2
- Normal endometrial thickness varies by menstrual cycle phase in premenopausal women, and the presence of intrauterine fluid should be measured and reported separately 4
Clinical Significance of Measurements
- In postmenopausal women, endometrial thickness ≤4 mm has a negative predictive value for endometrial cancer of nearly 100%, and thickness ≥5 mm generally requires endometrial tissue sampling 1
- In premenopausal women, there is no validated absolute upper limit cutoff for endometrial thickness as it varies with menstrual cycle phase, and abnormal echogenicity and texture of the endometrium correlate with significant underlying uterine pathology 2
Additional Imaging Considerations
- The American College of Radiology suggests using color Doppler to evaluate endometrial vascularity, which can help identify vessels within endometrial polyps or cancer 6
- Consider sonohysterography for further characterization if initial TVS demonstrates a focal endometrial abnormality, and be aware that fibroids or adenomyosis may limit visualization and accurate measurement 3