Diagnostics · Ultrasound
Abstract
Please reference the attached page which provides direct top to bottom comparisons using an illustration of endometrial "anatomy" composed of histological and physiologic information with a row of corresponding ultrasound images and then a description of related endometrium sonographic signs.
One of the most basic ultrasound physics concepts from the original use of ultrasound including now is the requirement to transmit sound waves as perpendicular to critical reflective interfaces as much as possible. Careful and fastidious detail to optimally angled scanning techniques is highly important to monitor progressive changes. The estrogen controlled hypoechoic proliferative endometrium glands with smooth, linear walls parallel to the incident sound beam convert to progesterone controlled hyperechoic secretory endometrium walls that are irregular, saccular, tortuous, and therefore provide many more reflective interfaces 90 degrees perpendicular to the incident sound beam.
In addition to endometrial assessment, the triple-line or tri-laminar appearance and posterior acoustical enhancement is also very dependent on the use of optimally angled scanning techniques.
Proliferative endometrium progressively thickens under the influence of increasing Estrogen levels. Slow or lack of progression may point to an estrogen receptor issue. The most definitive characteristic is a triple-line or tri-laminar appearance. The central line is produced by the central uterine endometrial canal where the anterior and posterior wall endometrium meet. The two outer lines represent the basal layer and the change of impedance interface between the endometrium and myometrium. The hypoechoic layers between the triple lines represent the functional endometrium. The glands orientation and smooth walls provide few reflective interfaces at 90 degrees to the sound beam in this stage. Within 24 hrs. evidence of progesterone conversion is obvious.
Secretory endometrium appearance and adequate thickness levels are directly related to adequate, successful development of late proliferative endometrium.
As graphically demonstrated in the attachment, the columnar shaped, smooth wall surface has now been converted from its non-echo producing appearance to a gland with a very irregular saccular, tortuous, vascular configuration with many interfaces now available for the 90 degree incident angle reflection to occur and producing very bright hyperechoic secretory endometrium. 90 degrees beam angle to interfaces is again crucial.
Another defining characteristic of secretory endometrium is the posterior acoustic enhancement. This enhancement along with acoustic shadowing forms the "bedrock" for determining if masses are solid (tissue filled) or cystic (fluid filled). The sound waves go through fluid full force since it contains no reflective interfaces. The increased fluid and resulting appearance is due to a greater tissue thickness that has increased storage of mucous and glycogen plus supporting neovascularity which all ads up to that cystic characteristic demonstrated by the posterior acoustic enhancement. Attention to the 90 degree rule is critical with complete as possible visualization of the endometrial cavity centering on the exact midline. In the Ultrasound secretory endometrium example, the myometrium beneath the endometrial canal is much brighter than the myometrium above the canal. This is due to the cystic posterior enhancement of the secretory endometrium.
One final observation is a hypoechoic "halo" which has been correlated histologically with the vascular network in the myometrium surrounding the endometrial layers. Before today's level of ultrasound resolution, this halo was difficult to differentiate. In the ultrasound secretory endometrium image in the attachment this halo is nicely demonstrated. The 90 degree rule and exact midline centering is crucial to get the optimal myometrium/endometrium interface differentiation. Since excellent vasculature development is so critical for a successful pregnancy, this observation may have some positive predictive value.
Technical Absolutes: 1) Absolutely empty bladder, quick transabdominal look to verify if possible. 2) Empty bladder enhances adherence to the 90 degree rule as related for all of the previously described reasons 3) FOCUS additional time on exact mid endometrial cavity evaluation 4) FULL scanner contact with no shadowing
