Ultrasound Signs of Adenomyosis According to MUSA: Direct and Indirect

Why the MUSA Revision is Important in Ultrasound Protocols

The MUSA 2022 consensus standardized the morphological ultrasound signs of adenomyosis and divided them into two groups: direct and indirect. This is crucial for clinical conclusions: direct signs reflect the presence of ectopic endometrial tissue in the myometrium, while indirect signs indicate secondary changes in the myometrium and junctional zone.

The main practical implication: the diagnosis of adenomyosis on ultrasound should be based on the presence of at least one direct sign. If only indirect signs are visualized, it is more accurate to indicate suspicion of adenomyosis and describe the observed changes without substituting them with a definitive ultrasound diagnosis.

MUSA 2022 Classification of Signs

Direct Signs: What is Considered Sufficient

Direct MUSA signs indicate the pathological substrate itself — ectopic endometrial tissue in the myometrium. Therefore, they carry more diagnostic weight than changes in uterine shape, wall thickness, or acoustic artifacts.

Myometrial cysts are described as anechoic round structures within the myometrium. It is important to note their location in the protocol and not confuse them with vascular lacunae, the uterine cavity, dilated endometrial glands, or cystic degeneration of a fibroid nodule.

Hyperechoic islands are hyperechoic myometrial foci. They should not be interpreted in isolation as calcifications, scar changes, or artifacts without analyzing the entire picture.

Echogenic subendometrial lines and buds originate from the endometrium or junctional zone and extend into the myometrium. This sign is particularly important in internal, subendometrial types of involvement.

Indirect Signs: How Not to Overestimate the Finding

Indirect signs reflect the myometrial response: hypertrophy, fibrosis, changes in architecture, vascular pattern, and junctional zone. According to MUSA, they are not a standalone basis for a confident diagnosis of adenomyosis if direct signs are absent.

A globular uterus and wall asymmetry can occur in other conditions, including fibroids, congenital uterine shape variations, and postoperative changes. Fan-shaped shadowing requires differentiation from shadows from fibroid nodules, where there is often a clear boundary of the formation and peripheral vascular pattern.

Junctional Zone: Irregular and Interrupted

The junctional zone is a key area of assessment when suspecting adenomyosis. MUSA 2022 highlights irregular and interrupted junctional zones as indirect signs. They are best evaluated with good image quality; 3D reconstruction can enhance the reproducibility of the description but does not replace morphological criteria.

In conclusions, arbitrary numerical thresholds for junctional zone thickness should not be used unless they are part of a standardized rule in a specific protocol. The revised MUSA definitions emphasize morphological description and the division of signs into direct and indirect.

Doppler: Translesional Vascularity

Translesional vascularity is an indirect sign. In adenomyosis, vessels pass through the affected myometrial area. This differs from the typical fibroid pattern, where the vascular pattern is more often peripheral or encircling the nodule.

Doppler should not be used instead of grayscale assessment. Its role is to clarify the nature of the lesion, assist in differential diagnosis, and confirm that the area of change is not a typical fibroid nodule.

How to Formulate a Conclusion

The optimal protocol structure: first describe direct signs, then indirect, followed by the extent and location. For each sign, it is advisable to specify the uterine wall or section: anterior, posterior, lateral, fundus, subendometrial zone, outer myometrium.

If there is at least one direct sign, the conclusion may read: Ultrasound signs of adenomyosis according to MUSA: myometrial cysts and echogenic subendometrial lines detected; additionally — fan-shaped shadowing and irregular junctional zone.

If there are no direct signs but several indirect ones, a more accurate formulation is: Indirect ultrasound signs suspicious for adenomyosis: globular uterine shape, asymmetric thickening of the posterior wall, interrupted junctional zone. Direct MUSA signs are not visualized.

Differential Diagnosis with Fibroids

The main pitfall is mistaking adenomyosis for a fibroid nodule or vice versa. Fibroids are more characterized by a well-defined formation, capsular or pseudocapsular contour, peripheral vascularization, and shadows associated with the edges of the nodule. Adenomyosis is more typical of an indistinct area of involvement, translesional vessels, subendometrial lines and buds, myometrial cysts.

When both fibroids and adenomyosis are present, both processes should be described separately. The presence of a fibroid nodule does not negate the search for direct MUSA signs in the surrounding myometrium.

Practical Examination Algorithm

1. Assess the uterine body in sagittal and transverse planes: shape, wall symmetry, focal formations.
2. Specifically search for direct signs: cysts, hyperechoic islands, subendometrial lines and buds.
3. Then describe indirect signs: globularity, asymmetry, fan-shaped shadows, condition of the junctional zone.
4. Add color or power Doppler to assess translesional or peripheral vascularization.
5. In the conclusion, indicate whether there is a direct MUSA sign; this determines the confidence of the diagnosis.

Key Mistakes

• Diagnosing adenomyosis solely based on a globular uterine shape.
• Using indirect signs as equivalent to direct ones.
• Failing to specify which MUSA signs are identified.
• Not differentiating fan-shaped shadowing in adenomyosis from edge shadows in fibroids.
• Describing the junctional zone without assessing image quality.