In postmenopausal patients with bleeding, the normal width of the endometrium in longitudinal view should measure less than or equal to 4 mm and appear linear, with no focal irregularities. Some authors report that a measurement less than 5 mm is normal; hence there is disagreement as to whether the upper limit of normal should be 4 or 5 mm; however, the American College of Obstetrics and Gynecology states less than or equal to 4 mm is normal. It is important to evaluate the endometrium in its entirety. If part of the endometrium is obscured by fibroids, polyps, or adenomyosis or if the margins are indistinct, saline infusion sonohysterography can be used for further evaluation. There is no accepted normative data for the width of the endometrium in nonbleeding postmenopausal patients. The sonographic appearance of the endometrial echo and color flow are important factors in detecting the presence of endometrial disease.

Tamoxifen is a selective estrogen receptor modulator used in the treatment and prevention of breast cancer. The estrogen receptor agonist activity in the uterus caused by Tamoxifen has been associated with an increased risk of endometrial polyps, hyperplasia, and cancer when used in postmenopausal women. In addition, patients on Tamoxifen can have a very indistinct endometrial/myometrial border that often results in the overestimation of the endometrial echo width. This is often caused by microcystic formation in the subendometrial region, which results in an irregular endometrial-myometrial junction. These microcysts are glandular cystic atrophy. Sonohysterography is very useful to delineate the true appearance of the endometrial surface itself.