Adenomyosis is a condition where the tissue that normally lines the inside of the uterus, called the endometrial tissue, begins to grow into the muscular wall of the uterus, known as the myometrium. Ultrasound is a non-invasive imaging technique that allows medical professionals to visualize internal organs, including the uterus.
Understanding Adenomyosis and Ultrasound Basics
When endometrial tissue grows into the myometrium, it still responds to hormonal changes during the menstrual cycle. This misplaced tissue can bleed during menstruation, leading to symptoms such as pelvic pain and heavy bleeding. Ultrasound is frequently the initial diagnostic tool for uterine conditions due to its accessibility, non-invasive nature, and ability to provide real-time images of the uterus.
For a detailed examination of the uterus, a transvaginal ultrasound is often performed. This procedure involves inserting a small probe into the vagina, which allows for clear, close-up images of the uterus and surrounding structures.
Hallmark Ultrasound Signs of Adenomyosis
One of the most recognized signs is a thickened junctional zone (JZ), which is the inner layer of the myometrium. A JZ thickness greater than 12 mm is often considered a strong indicator of adenomyosis. This thickening occurs due to the infiltration of endometrial tissue and associated muscular hypertrophy.
Another common finding is a heterogeneous myometrial echotexture, meaning the uterine muscle appears non-uniform or “patchy” on the scan. This irregular appearance results from scattered endometrial glands and surrounding muscle changes. Small, dark areas within the myometrium, known as myometrial cysts or cystic spaces, are also frequently observed. These anechoic regions can represent dilated endometrial glands or tiny areas of hemorrhage.
Subendometrial linear striations or fan-shaped shadowing may also be visible, appearing as fine lines or dark, fan-like areas extending from the uterine lining into the myometrium. These shadows are caused by architectural disorganization from ectopic tissue and hypertrophic muscle fibers. Additionally, the uterus may show asymmetrical enlargement, where one wall appears significantly thicker than the other. The boundary between the uterine lining (endometrium) and the muscular wall (myometrium) might also appear poorly defined or indistinct. A diagnosis is typically made based on a combination of these ultrasound findings rather than relying on a single sign.
Different Presentations: Diffuse vs. Focal Adenomyosis
Diffuse adenomyosis is the more common manifestation, characterized by widespread infiltration of endometrial tissue throughout the myometrium. This leads to a generalized enlargement of the uterus and a more pervasive heterogeneous echotexture across the uterine muscle.
Conversely, focal adenomyosis, often termed an adenomyoma, presents as a localized collection of adenomyotic tissue that forms a mass-like lesion within the myometrium. While an adenomyoma might sometimes resemble a fibroid, it typically has less distinct margins and often blends into the surrounding myometrial tissue. Its internal echo pattern is usually more heterogeneous, and it may contain small cystic areas, distinguishing it from the more clearly defined appearance of a fibroid.
Distinguishing Adenomyosis from Similar Conditions
Ultrasound imaging is crucial for differentiating adenomyosis from other uterine conditions, particularly uterine fibroids, also known as leiomyomas. Fibroids typically appear as well-circumscribed masses with distinct margins on ultrasound, often showing a hypoechoic (darker) or heterogeneous internal structure. They can sometimes have calcifications or produce posterior shadowing.
In contrast, adenomyosis, especially focal adenomyomas, often has ill-defined borders that blend into the surrounding myometrial tissue, lacking the clear capsule seen with fibroids. While fibroids commonly exhibit peripheral vascularity, adenomyomas may show more diffuse internal blood flow when assessed with Doppler imaging. An experienced sonographer or radiologist evaluates these subtle differences in appearance, echotexture, and vascularity to make an accurate diagnosis.