Optimal TVUS evaluation includes endometrial measurements in the sagittal plane, with the bilayer thickness measured from the proximal to distal myometrialendometrial junctions. In the coronal view, measurement should be from the cervix to the fundus. When intraluminal fluid is present, each endometrial thickness should be measured separately (in single layers), and the combined endometrial thickness should be expressed as the sum of the 2 layers.
Characterize the endometrium. Sonographic hallmarks increasingly are used to describe uterine pathology. These include endometrial thickness, morphology, endocavitary lesions, borders, and myometrial invasion. In addition, a number of practitioners have attempted to describe the sonographic texture of the endometrium in post-menopausal women to increase sensitivity in the detection of disease, improve diagnosis, and guide treatment.
The endometrium can be characterized as homogeneous, diffusely inhomogeneous, or associated with focally or diffusely increased echogenicity. Textural inhomogeneity is present in cases of endometrial cancer.2 A homogeneous endometrium less than 6 mm thick is commonly associated with tissue insufficient for diagnosis. If focal or diffuse increased echogenicity occurs with a thin endometrium, SIS or hysteroscopy is more sensitive than TVUS in identifying the endometrial abnormality.
We rely increasingly on descriptions of the echogenicity and heterogeneity of the entire endometrial echo, as well as on echo measurements, to define endometrial health. Most experts use an endometrial echo of 5 mm as the cutoff for significant endometrial disease. A number of investigators have noted that the endometrial thickness in hyperplasia often ranges from 8 mm to 15 mm in post-menopausal women, but the number of reported cases is too low to draw firm conclusions based on endometrial echo alone.3,4
A prospective evaluation of 200 postmenopausal women with endometrial echo ranging from 3 mm to 10 mm noted that homogeneity, thin endometrium, and sonographically demonstrable central endometrium with symmetry were associated with absence of pathology. In contrast, heterogeneity and high echogenicity were indicative of pathology.5
Endometrial echo measurement and morphology increase sensitivity in predicting endometrial disease and can point to the need for ancillary testing with SIS or hysteroscopy. For example, in the postmenopausal patient, an endometrial echo of less than 5 mm, in combination with a negative endometrial biopsy, might be the only evaluation the patient needs if she responds to medical therapy for endometrial atrophy. If symptoms persist, office hysteroscopy or SIS could be performed to rule out endometrial polyps and endometrial hyperplasia (which is less likely).
Saline-infusion sonography offers an exquisite view of the endomyometrial complex that cannot be obtained with transvaginal ultrasound alone.
A thickened endometrial echo (more than 5 mm) at the initial TVUS in the postmenopausal patient should be evaluated promptly with SIS. In most of these patients, polyps or fibroids are the cause of bleeding.
Perform imaging at optimal time. In postmenopausal women, the endometrial thickness remains constant unless the patient is taking hormone replacement therapy (HRT) or tamoxifen.6 Thus, it is easier to detect or predict endometrial pathology in this population.
In premenopausal women, TVUS is most likely to detect fibroids during the early follicular stage because the endometrium is thin, usually measuring 2 mm to 4 mm. Endometrial polyps and submucosal fibroids are best viewed when a trilayered midfollicular endometrium is present, while uterine synechiae are visualized most clearly during midcycle. Adhesions appear as hyperechoic irregular structures that vary in size from 2 mm to 6 mm. They interrupt the continuity of the endometrial layer and appear much different from polyps, which tend to be round, symmetrical, and uniform.7
Diagnosing endometrial hyperplasia among premenopausal women based on an absolute endometrial measurement is more difficult than it is in postmenopausal women because of the wide range in thickness associated with the menstrual cycle (TABLE 1). Although endometrial hyperplasia or cancer is more likely when the endometrial echo is thicker than anticipated based on age or menstrual phase, it can only be proven definitively with histologic sampling.
Sensitivity and specificity. Because of the monotonous nature of the endometrium in healthy postmenopausal women, TVUS has higher sensitivity in this age group than in reproductive-age women. In the postmenopausal population, the sensitivity for detecting uterine pathology is 87%, while specificity is 82%.
Office hysteroscopy offers immediate evaluation and direct visualization of the endometrium and endocervix.
In premenopausal women, polyps were the pathology most likely to be missed, according to one literature review.8 TVUS identified only 275 of 344 polyps in this population—a sensitivity of 80%. When submucosal fibroids were located near the endometrium, the diagnostic sensitivity rose to 94%. It was difficult to discern location (i.e., submucosal or intramural or polyps) with TVUS alone, however.