Ultrasound of the Endometrium: How to Measure and Report According to ISUOG 2026
What ISUOG 2026 Standardizes
The ISUOG 2026 consensus on sonographic assessment of the endometrium is not intended to replace clinical algorithms but to provide uniform descriptions. The main goal of the protocol is to ensure that another physician understands how the thickness was measured, whether there is a cavity, focal lesion, disruption of the endomyometrial junction, and pathological blood flow.
The document continues the logic of standardized IETA terminology: measurements, echostructure, cavity line, endomyometrial junction, fluid, intracavitary lesions, and Doppler signs are described separately. Numerical risk thresholds should not be mechanically transferred to every protocol: interpretation depends on menopausal status, bleeding, hormone therapy, tamoxifen, and technical confidence in the study.
Basic Scanning Technique
The optimal approach for most non-pregnant patients is transvaginal ultrasound. Transabdominal examination is applicable as an adjunct for a large uterus, high fundus, large fibroids, vaginal stenosis, or inability to access transvaginally.
The first mandatory step is to obtain the true mid-sagittal plane of the uterus: the cervical canal, uterine cavity, and fundus are visualized. If the uterus is markedly anteflexed or retroflexed, the probe is rotated so that the endometrium is visible along its entire length, not just in fragments. Measurement outside the mid-sagittal plane is a common cause of overestimation or underestimation of thickness.
How to Measure Endometrial Thickness
Thickness is measured at the point of maximum endometrial thickness, perpendicular to the longitudinal axis of the endometrial complex, from one endomyometrial boundary to the other. This is the double layer of the endometrium. The protocol should ideally specify the value in mm and technical confidence: measured reliably, limited, or unmeasurable.
In normal technique, the myometrium is not included in the measurement. If the boundary between the endometrium and myometrium is unclear, this is not concealed: the endomyometrial junction is described as irregular, interrupted, or not visualized. In cases of cavity deformation by a submucosal fibroid, synechiae, or large polyp, a simple thickness number may be less informative than a description of the lesion.
If There Is Fluid in the Cavity
If fluid is present, the overall anteroposterior size of the complex with fluid should not be measured as endometrial thickness. According to the ISUOG/IETA approach, the anterior and posterior single-layer endometrial sheets are measured separately and these two values are summed. The fluid is described separately: volumetrically or qualitatively, with echogenicity specified.
Fluid variants: anechoic, with low-level echoes, ground-glass type, mixed. It is important to note whether the fluid freely fills the cavity or is associated with a focal intracavitary component. In postmenopausal patients, fluid alone does not replace the assessment of endometrial sheets.
Echogenicity and Structure
The endometrium is described not only by number. Echogenicity relative to the myometrium is specified: hyperechoic, isoechoic, hypoechoic, or mixed. Homogeneity is then assessed: uniform or non-uniform structure. For reproductive age, it is essential to specify the day of the cycle or clinical phase if known, otherwise echogenicity assessment easily becomes falsely pathological.
The midline of the uterine cavity is described as linear, non-linear, irregular, or indeterminate. The endomyometrial junction is regular, irregular, interrupted, or indeterminate. These elements are especially important when suspecting an infiltrative process, adenomyosis, scar changes, and when preparing for hysteroscopy.
Focal Intracavitary Lesion
If there is a polypoid or other focal lesion, it should not be reduced to the phrase "endometrium thickened." Localization, maximum dimensions, contours, echogenicity, base, relation to the uterine wall, and presence of a vascular stalk or other vascular pattern should be described.
The size of the lesion is indicated in three mutually perpendicular dimensions if technically possible. In 3D ultrasound, coronal reconstruction of the cavity is additionally useful: it helps distinguish diffuse thickening from a local lesion, assess the extent of the base, and its connection with the uterine angles.
Color Doppler: Scale and Pattern
Doppler assessment is performed after optimizing the 2D image. The protocol records not only the presence of blood flow but also its intensity on a color scale of 1–4, as well as the architecture of the vessels. This increases the reproducibility of descriptions among specialists.
| Parameter | ISUOG/IETA Description Standard | What to Write in the Conclusion |
|---|---|---|
| Endometrial Thickness | Double layer at the thickest point | mm; plane and measurement reliability |
| Fluid in the Cavity | 2 single-layer sheets measured separately and summed | total thickness of sheets; fluid character separately |
| Focal Lesion | Local object described separately from diffuse endometrium | localization, 3 dimensions, contours, echogenicity, base |
| Color Score 1 | No blood flow detected | color score 1 |
| Color Score 2 | Minimal blood flow | color score 2 |
| Color Score 3 | Moderate blood flow | color score 3 |
| Color Score 4 | Marked blood flow | color score 4 |
The vascular pattern is described separately: single dominant vessel, branching vessel, multiple vessels, scattered blood flow, circular blood flow. For a polyp, a typical description may include a single feeding vessel, but the ultrasound formulation should not sound like a definitive histological diagnosis.
What to Include in a Standard Report
A practical protocol should be short but complete. The minimum set: access and quality of visualization; position and size of the uterus if necessary; endometrial thickness and measurement method; echogenicity and homogeneity; midline; endomyometrial junction; fluid; focal lesions; Doppler assessment; final category — diffuse changes, focal lesion, cavity without visible pathology, or limited study.
Clinical context is mandatory: premenopause or postmenopause, day of the cycle if available, abnormal uterine bleeding, postmenopausal bleeding, hormone replacement therapy, tamoxifen, intrauterine system, recent interventions. Without this data, the same image may have different clinical significance.
Example Protocol Formulation
Diffuse Assessment: transvaginal ultrasound, satisfactory visualization. Uterus in mid-sagittal plane. Endometrium measured as double layer at thickest point: __ mm. Structure __, echogenicity __. Midline __. Endomyometrial junction __. Fluid in cavity: none / present, character __; if fluid present, total thickness of 2 sheets __ mm.
Focal Assessment: focal lesion in uterine cavity determined / not determined. If present: localization __, dimensions __ × __ × __ mm, contours __, echogenicity __, base __. Color score __ out of 4, vascular pattern __. Conclusion: ultrasound signs __; recommend clinical-morphological verification as indicated.
Common Mistakes
- Measurement not in the true mid-sagittal plane.
- Including intracavitary fluid in endometrial thickness instead of separate measurement of 2 sheets.
- Replacing the description of a polypoid lesion with the phrase "endometrium thickened."
- Lack of assessment of the endomyometrial junction in suspicious heterogeneity.
- Doppler without indicating color score 1–4 and vascular pattern.
- Conclusion without clinical context: day of cycle, menopause, bleeding, hormone therapy.
How to Formulate the Conclusion
The conclusion should be descriptive and actionable: "diffuse thickening/heterogeneity of the endometrium," "focal intracavitary lesion," "fluid in the cavity with measured endometrial sheets," "assessment limited." If the signs are suspicious, it is more appropriate to write "ultrasound signs requiring morphological verification" rather than establishing a histological diagnosis.
The standardized protocol according to ISUOG 2026 makes the conclusion comparable between ultrasound rooms, gynecologists, and endoscopists: it is clear what was measured, what was described as a lesion, and what limitations of the study may affect further management.
Frequently asked questions
Should fluid in the uterine cavity be measured together with the endometrium?
No. If fluid is present, measure the two single-layer endometrial sheets separately and sum them; describe the fluid in a separate line.
What is more important in the protocol: endometrial thickness or description of structure?
Both components are needed. Thickness without echogenicity, homogeneity, midline, endomyometrial junction, and Doppler is insufficient for a standardized conclusion.
Is it necessary to write the color score for Doppler?
Yes. According to ISUOG/IETA, the intensity of blood flow is described on a scale of 1–4 and supplemented by the vascular pattern: single, branching, multiple, scattered, or circular blood flow.