Ultrasound Diagnosis of Adenomyosis According to MUSA Criteria: Direct and Indirect Signs, Differentiation from Fibroids
Basics of MUSA Systematization
The MUSA statement (Morphological Uterus Sonographic Assessment) is a consensus on terms, definitions, and measurements for describing and reporting ultrasound features of the myometrium in grayscale sonography, color/power Doppler, and three-dimensional ultrasound examination (MUSA group, 2015). The revised definitions of adenomyosis features (Harmsen et al., 2022) divide the signs into direct and indirect for consistent identification, description, and classification of adenomyosis.
Direct Signs of Adenomyosis
Direct signs represent ectopic endometrial glands and stroma beyond the subendometrial layer (Harmsen et al., 2022). Direct signs include:
| Sign | Meaning |
|---|---|
| Myometrial cysts | Indicate more specifically ectopic endometrial tissue in the myometrium |
| Hyperechoic islands | Similarly, a marker of ectopic tissue |
| Echogenic subendometrial lines and 'buds' | Similarly, a marker of ectopic tissue |
Indirect Signs
Indirect signs may be present in the absence of direct signs; in this case, the diagnosis is uncertain (Harmsen et al., 2022). Indirect signs include: a globular uterus, asymmetric myometrial thickening, fan-shaped shadowing, translesional vascularization, as well as irregular or discontinuous characteristics of the junctional zone.
Differentiation from Fibroids
Adenomyosis presents a different sonographic challenge compared to fibroids. Unlike fibroids, which form a discrete encapsulated mass, adenomyosis typically reflects ectopic endometrial tissue within the myometrium and a secondary myometrial response (Holland, 2026). This is why the direct MUSA signs (cysts, hyperechoic islands, subendometrial lines/'buds') specifically indicate endometrial ectopia, whereas the absence of a discrete encapsulated nodule distinguishes adenomyosis from fibroids.
Reproducibility of Signs and Training
According to Rasmussen et al., inter-expert and intra-expert agreement on MUSA terms for well-defined lesions was good, but several signs showed poor reproducibility: serosal contour, asymmetry, hyperechoic rim, and fan-shaped shadowing. In certain series, the assessment of lesion echogenicity and border characteristics also proved less reproducible. This reflects the need for appropriate training in the use of MUSA terms and definitions (Ultrasound Obstet Gynecol, 2024).
Frequently asked questions
What MUSA signs are considered direct?
Myometrial cysts, hyperechoic islands, echogenic subendometrial lines and 'buds'. They more specifically indicate ectopic endometrial tissue in the myometrium (Harmsen et al., 2022).
What signs are considered indirect?
Globular uterus, asymmetric myometrial thickening, fan-shaped shadowing, translesional vascularization, irregular or discontinuous junctional zone (Holland, 2026).
What does the presence of only indirect signs without direct ones mean?
Indirect signs may be present in the absence of direct ones; in this case, the diagnosis of adenomyosis is considered uncertain (Harmsen et al., 2022).
How does adenomyosis differ from fibroids on ultrasound?
Fibroids form a discrete encapsulated mass, whereas adenomyosis typically reflects ectopic endometrial tissue in the myometrium and a secondary myometrial response, without a discrete nodule (Holland, 2026).
Which MUSA signs have poor reproducibility?
Serosal contour, asymmetry, hyperechoic rim, and fan-shaped shadowing; in some series, the assessment of echogenicity and lesion borders (Ultrasound Obstet Gynecol, 2024).