What are the MUSA (Morphological Uterus Sonographic Assessment) criteria for diagnosing adenomyosis in a premenopausal woman?

MUSA Criteria for Adenomyosis

The MUSA (Morphological Uterus Sonographic Assessment) criteria are standardized sonographic features divided into direct signs (indicating ectopic endometrial tissue in myometrium) and indirect signs (reflecting secondary myometrial changes) used to diagnose adenomyosis on transvaginal ultrasound. 1

Direct Features of Adenomyosis

These features indicate the presence of ectopic endometrial tissue within the myometrium:

• Myometrial cysts: Small anechoic or hypoechoic round areas within the myometrium, representing dilated endometrial glands containing fluid 1, 2

• Hyperechogenic islands: Echogenic nodular areas within the myometrium representing ectopic endometrial glands and stroma 1, 3

• Echogenic subendometrial lines and buds: Linear or nodular echogenic structures radiating from the endometrium into the myometrium, representing ectopic glands extending from the endometrial-myometrial junction 1, 3

Indirect Features of Adenomyosis

These features reflect secondary changes in the myometrium due to the presence of adenomyosis:

• Globular uterus: Diffuse uterine enlargement with a rounded configuration rather than the normal pear shape 1, 3

• Asymmetrical myometrial thickening: Unequal thickness of the anterior and posterior myometrial walls, with one wall significantly thicker than the other 1, 2

• Fan-shaped shadowing: Thin "venetian blind" acoustic shadows extending from the myometrium, caused by muscular hyperplasia and hypertrophy 1, 3

• Translesional vascularity: Penetrating vessels coursing through affected myometrium on color Doppler imaging, reflecting increased uterine vascularity 1, 3

• Irregular junctional zone: Loss of the normal smooth interface between endometrium and myometrium, with blurring or irregularity of this border 1, 2

• Interrupted junctional zone: Focal breaks or discontinuity in the junctional zone 1

Diagnostic Approach

• Perform transvaginal ultrasound during the early proliferative phase (days 4-6) of the menstrual cycle when the endometrium is thinnest, allowing optimal visualization of myometrial features and the junctional zone 4

• Use three-dimensional (3D) ultrasound when available to optimize visualization of the junctional zone and assess the full extent of disease 1

• Combine both transabdominal and transvaginal approaches to fully assess pelvic structures and ensure adequate visualization of the endometrium and myometrium 4

• Obtain cine clips and coronal reformatted images to survey the entire endometrial-myometrial border comprehensively 3

Diagnostic Performance

• Transvaginal ultrasound using MUSA criteria demonstrates pooled sensitivity of 82.5% and specificity of 84.6% for adenomyosis diagnosis, making it the first-line imaging modality 4

• Diagnosis requires at least one direct sonographic feature to confirm the presence of adenomyosis 5

• Sensitivity drops significantly (from 97.8% to 33.3%) when coexisting fibroids are present, as leiomyomas can obscure adenomyotic features 4

Critical Pitfalls to Avoid

• Do not accept imaging performed during the secretory phase or menstruation as optimal for adenomyosis diagnosis, since endometrial thickening during these phases obscures myometrial detail 4

• Approximately 16% of symptomatic patients may not demonstrate direct ultrasound signs despite clinical adenomyosis, requiring integration of clinical context with imaging findings 4

• Standard pelvic ultrasound protocols do not routinely include the detailed assessment needed to identify adenomyosis features, so specifically evaluate for MUSA criteria 4

• Consider MRI when ultrasound is inconclusive or when adenomyosis obscures endometrial visualization, as MRI demonstrates 78-88% sensitivity and 67-93% specificity 4

Distinguishing Adenomyosis from Mimics

• Leiomyomas typically appear as well-defined masses with peripheral vascularity, unlike the diffuse heterogeneous appearance of adenomyosis 3

• Uterine contractions are transient and resolve on repeat imaging, whereas adenomyotic features persist 3

• Heterogeneous myometrium with blurring of the endometrial border is the hallmark combination that results from the presence of ectopic glands and muscular hyperplasia in adenomyosis 3, 6