What is the normal thickness of the endometrium in a premenopausal woman?
In premenopausal women, the appearance of the endometrium changes depending on the phase of the menstrual cycle. On US, during menstruation the endometrium is identified as a thin, echogenic line measuring 1 to 4 mm, sometimes with blood products or sloughed endometrial lining seen in the uterine cavity. During the proliferative phase, the endometrium is thicker, with a trilaminar appearance typically measuring 5 to 7 mm, composed of a thin echogenic central line, a hypoechoic functional layer, and a surrounding outer echogenic basal layer. During the secretory phase, the endometrium reaches its maximum thickness (up to about 16 mm) and is homogenously echogenic.
On MRI, the endometrium is typically homogenous, is high in signal intensity on T2-weighted images and low in signal intensity on T1-weighted images, and can vary in thickness depending on the phase of the menstrual cycle. On CT, the measurement of endometrial thickness should be performed on sagittal reconstructed images and can be accurate and reproducible compared with that obtained from transvaginal US.