Differences between proximal and distal endometrial monolayer thickness in women aged over 50 years undergoing saline infusion sonohysterography

Background: Saline infusion sonohysterography (SIS) is a procedure performed to evaluate the endometrium in women with postmenopausal bleeding. Purpose: To investigate differences in endometrial monolayer measurements in women aged >50 years undergoing SIS. Material and Methods: Retrospective study of women aged >50 undergoing SIS. Endometrial echo (EE) was measured according to the International Endometrial Tumor Analysis (IETA) guidelines. Monolayer thickness was compared between anterior and posterior uterine walls and between the monolayer that was proximal or distal to the ultrasound probe. Presence and location of focal thickening and polyps on each of the monolayers were assessed. Results: SIS was performed in 608 patients. Of them, 485 (79.8%) had anteverted, 85 (14%) retroverted, and 38 (6.2%) a midposition uterus. The mean posterior monolayer was thicker than the anterior monolayer (2.14 mm vs. 1.88 mm; P = 0.002). The distal monolayer was thicker than the proximal layer in both anteverted and retroverted uteri (2.18 mm vs. 1.84 mm; P < 0.0001). In 16% of women, the difference between distal and proximal monolayers was ≥1 mm. Focal thickening was seen 3.3 times more frequently in the distal endometrium. Among women with a double layer EE >4 mm, 18.8% had a proximal layer of <2 mm while only 4.6% had a distal EE <2 mm. Conclusion: Distal endometrium measures thicker than the proximal endometrium in most SIS cases and in one out of six women, the difference is >1 mm. The distal layer is three times more likely to contain focal thickening. Sonologists should be conscious of possible enhancement artifact when measuring the EE during SIS.