Adenomyosis is a common gynecological condition where the tissue that normally lines the inside of the uterus, the endometrium, begins to grow into the muscular wall of the uterus, known as the myometrium. This misplaced tissue remains functional, causing the muscle layer to thicken and enlarge as it responds to hormonal signals by bleeding during the menstrual cycle. To non-invasively detect this condition, transvaginal ultrasound (TVUS) is the primary imaging modality, offering a high degree of accuracy comparable to more expensive techniques like Magnetic Resonance Imaging (MRI). The visual signs of adenomyosis on an ultrasound scan are distinct, reflecting the diffuse nature of the disease as it infiltrates the uterine muscle.
Key Internal Sonographic Markers
The most frequently observed sign of adenomyosis on ultrasound is a heterogeneous, or mottled, appearance of the myometrium. Instead of the uniform, smooth texture of healthy muscle, the myometrium appears speckled and non-uniform due to the scattered islands of endometrial tissue and the surrounding muscle reaction. This disrupted texture is highly sensitive for the diagnosis of adenomyosis and represents the infiltration of the inner uterine lining into the muscle.
Another specific sign is the presence of subendometrial echogenic linear striations, which appear as bright streaks radiating outward from the endometrial lining into the muscle layer. These striations are sometimes accompanied by “venetian blind shadowing,” characterized by thin acoustic shadows caused by distorted muscle fibers. The misplaced endometrial glands may also accumulate fluid, forming small, round pockets called myometrial cysts or anechoic lacunae.
These cysts range from one to five millimeters in diameter. The ectopic endometrial tissue itself can also appear as hyperechoic islands, presenting as brighter spots within the abnormal myometrium. These internal markers provide a visual representation of the glandular invasion and the resulting structural disorganization within the uterine wall.
Changes to Uterine Size and Shape
Beyond the internal texture, adenomyosis causes significant changes to the overall geometry and size of the uterus. A healthy uterus is typically pear-shaped, but adenomyosis frequently causes the uterus to become enlarged and take on a globular or spherical shape. This diffuse enlargement affects the entire organ, making the uterus appear bulkier than normal.
The infiltration of endometrial tissue often causes an asymmetrical thickening of the myometrial walls. This means one wall, such as the posterior wall, may be visibly thicker than the opposing anterior wall, a measurable criterion used in diagnosis.
A defining area of change is the junctional zone (JZ). In adenomyosis, this zone becomes ill-defined or blurred, making it difficult to distinguish the inner endometrial lining from the outer myometrium. The junctional zone is often thickened, with a measurement greater than 12 millimeters being a strong indicator of the condition.
In more advanced or focal cases, the extent of muscle distortion may contribute to the uterus adopting a specific curvature known as the “question mark sign.” This overall change in shape, size, and wall symmetry distinguishes the condition from a normal or a fibroid-affected uterus.
Distinguishing Adenomyosis from Uterine Fibroids
Adenomyosis must be carefully distinguished from uterine fibroids, or leiomyomas, because the two conditions frequently coexist and can cause similar symptoms. The primary difference on ultrasound lies in their structural organization: adenomyosis is a diffuse, infiltrating disease, while a fibroid is a focal, solid tumor.
Fibroids appear on ultrasound as well-defined, round or oval masses, often with a clear boundary or pseudo-capsule separating them from the surrounding healthy myometrium. In contrast, adenomyosis lesions lack a true capsule and instead blend gradually into the adjacent muscle tissue, making their borders indistinct. Even when adenomyosis presents as a focal mass, called an adenomyoma, the borders remain ill-defined.
Color Doppler ultrasound provides another method of differentiation by assessing the vascularity, or blood flow, within the lesions. Fibroids typically show blood vessels that run around the periphery of the mass, creating a distinct peripheral flow pattern. Adenomyosis, however, often exhibits a pattern of diffuse, penetrating vessels that are scattered or run throughout the affected myometrium.
While TVUS is effective, the presence of multiple fibroids can sometimes obscure or mimic the subtle signs of adenomyosis, making the diagnosis challenging. In these complex cases, Magnetic Resonance Imaging (MRI) may be used as a secondary tool to provide more detailed tissue characterization and separate the two pathologies. Understanding these visual distinctions is paramount for accurate diagnosis and management.