How to accurately measure endometrium (endometrial lining) on Transvaginal Ultrasound (TVS) and what are common mistakes to avoid?

Proper Technique for Measuring Endometrial Thickness on Transvaginal Ultrasound

The correct technique for measuring endometrial thickness on transvaginal ultrasound (TVS) requires measuring the double-layer thickness of the endometrium in the sagittal plane at its thickest point, perpendicular to the endometrial-myometrial interface. 1

Correct Measurement Technique

• Perform a combined transabdominal and transvaginal approach whenever possible for complete assessment of pelvic structures 2
• Position the transvaginal probe to obtain a longitudinal (sagittal) view of the uterus 1
• Identify the endometrium as the echogenic lining of the endometrial cavity 2
• Measure the double-layer thickness at the thickest portion of the endometrium 1
• Ensure measurement is perpendicular to the endometrial-myometrial interface 1
• Include both anterior and posterior layers of the endometrium in the measurement 1
• Do not include surrounding hypoechoic myometrium or intracavitary fluid in the measurement 1

Common Errors in Endometrial Measurement

• Measuring in an oblique plane rather than true sagittal plane, which falsely increases thickness 1
• Including adjacent myometrium in the measurement 2
• Failing to identify the true endometrial-myometrial interface 2
• Measuring only a single layer of the endometrium instead of the double layer 1
• Not measuring at the thickest portion of the endometrium 1
• Failing to recognize that normal endometrial thickness varies by menstrual cycle phase in premenopausal women 2
• Not accounting for the presence of intrauterine fluid, which should be measured and reported separately 2

Clinical Significance of Measurements

• In postmenopausal women, endometrial thickness ≤4 mm has a negative predictive value for endometrial cancer of nearly 100% 1
• In postmenopausal women, endometrial 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 2
• Abnormal echogenicity and texture of the endometrium correlate with significant underlying uterine pathology even when thickness is normal 2

Additional Imaging Considerations

• Use color Doppler to evaluate endometrial vascularity, which can help identify vessels within endometrial polyps or cancer 2
• Consider sonohysterography for further characterization if initial TVS demonstrates a focal endometrial abnormality 2
• When measuring endometrial thickness in the presence of fibroids or adenomyosis, be aware that these conditions may limit visualization and accurate measurement 2
• For enlarged uteri where the limited field of view of TVS cannot image all portions, combine with transabdominal ultrasound 2

By following these guidelines for proper endometrial measurement, clinicians can avoid common pitfalls and ensure accurate assessment for clinical decision-making regarding abnormal uterine bleeding and other gynecologic conditions.