Should the myometrium be homogeneous?

From the Guidelines

The myometrium should typically appear homogeneous on imaging studies to ensure optimal uterine health and minimize the risk of complications associated with heterogeneous myometrium, such as fibroids, adenomyosis, or malignancy. In a normal uterus, the myometrium should have a uniform, consistent texture and echogenicity on ultrasound or signal intensity on MRI 1. However, it's essential to note that some variations can occur naturally with age, hormonal status, and during different phases of the menstrual cycle. During pregnancy, the myometrium undergoes significant changes and may appear less homogeneous. Heterogeneity in the myometrium outside of these normal variations could indicate pathological conditions, and further evaluation with additional imaging or possibly biopsy may be warranted to determine the cause 1.

Key Considerations

• The myometrium's homogeneity is crucial for maintaining uterine health and preventing complications associated with fibroids, adenomyosis, or malignancy.
• Imaging studies, such as ultrasound or MRI, can help assess the myometrium's texture and echogenicity.
• Variations in the myometrium's appearance can occur naturally, but heterogeneity outside of these normal variations may indicate underlying pathological conditions.
• Further evaluation and monitoring are necessary to determine the cause of heterogeneity and prevent potential complications.

Diagnostic Approaches

• Pelvic ultrasound (US) or MRI can be used to diagnose and characterize fibroids, adenomyosis, or other uterine pathologies 1.
• Saline infusion sonohysterography (SIS) and three-dimensional transvaginal ultrasound (TVUS) can provide additional information on submucosal fibroids and endometrial pathologies 1.
• Diffusion-weighted imaging with apparent diffusion coefficient (ADC) can help distinguish between fibroids and sarcomas, a critical distinction for surgical planning and optimizing outcomes 1.

From the Research

Myometrium Homogeneity

The question of whether the myometrium should be homogeneous is complex and multifaceted. Research suggests that the myometrium is not always homogeneous, with different zones and layers exhibiting distinct characteristics and functions.

• The junctional zone, a distinct layer of the myometrium, has been identified as having different structural and functional properties compared to the outer myometrium 2.
• Studies have shown that the myometrium undergoes significant changes in thickness during labor and immediately postpartum, with significant thinning during active labor and thickening during the second stage of labor 3.
• The expression of gonadotropin-releasing hormone 2 (GnRH2) and its receptor (GnRHR2) has been found in both human myometrium and leiomyomas, suggesting a potential autocrine loop 4.
• The role of calcium in the contraction and relaxation of the myometrium has been highlighted as crucial in understanding the mechanisms of uterine contractility 5.

Heterogeneity of the Myometrium

The myometrium is composed of different cell types and layers, which can exhibit heterogeneous properties and functions. For example:

• The subendometrial myometrium or junctional zone has been found to be structurally and functionally different from the outer myometrium 2.
• The myometrium has been shown to undergo significant changes in thickness and contractility during different phases of labor and postpartum 3.
• The expression of GnRH2 and GnRHR2 in both myometrium and leiomyomas suggests a potential role in the regulation of uterine function 4.

Implications of Myometrium Heterogeneity

The heterogeneity of the myometrium has important implications for our understanding of uterine function and dysfunction. For example:

• The identification of distinct zones and layers within the myometrium can inform the development of new diagnostic and therapeutic strategies for uterine-related disorders 2.
• The changes in myometrial thickness and contractility during labor and postpartum can inform the management of labor and delivery 3.
• The expression of GnRH2 and GnRHR2 in myometrium and leiomyomas can inform the development of new treatments for uterine fibroids and other disorders 4.