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Myometrium of uterus

The myometrium is the thick, muscular middle layer of the uterine wall, situated between the endometrium and perimetrium. Composed primarily of smooth muscle fibers interlaced with connective tissue, it undergoes significant changes during the menstrual cycle, pregnancy, and labor. Its contractile properties are critical for menstruation, implantation, and childbirth.

Synonyms

  • Muscular layer of uterus

  • Uterine muscle layer

  • Smooth muscle coat of uterus

Structure and Layers

  • Outer longitudinal layer: Oriented mainly longitudinally, continuous with the muscular layers of the fallopian tubes, vagina, and ligaments

  • Middle vascular (intermediate) layer: Rich in blood vessels; also called the stratum vasculare

  • Inner circular layer: Surrounds the uterine cavity and cervix; involved in regulating menstrual flow and contractions during labor

Relations

  • Internal: Endometrium (uterine mucosa)

  • External: Serosa (perimetrium) and peritoneal reflections

  • Lateral: Broad ligaments of uterus and uterine vessels

  • Inferior: Cervix and vaginal fornices

  • Superior: Fundus and connection with fallopian tubes

Function

  • Provides contractility for expulsion of menstrual blood during menstruation

  • Supports implantation of fertilized ovum and growth of embryo

  • Contracts during labor to facilitate delivery

  • Contracts postpartum to control bleeding and restore uterine size

  • Provides vascular support to the endometrium and fetus during pregnancy

Clinical Significance

  • Site of common pathologies such as uterine fibroids (leiomyomas), adenomyosis, and uterine sarcomas

  • Abnormal myometrial contractility contributes to dysmenorrhea, infertility, and obstetric complications

  • Evaluation of the myometrium is essential in pelvic ultrasound, MRI, and CT to diagnose gynecological disorders

  • Junctional zone (seen on MRI) alterations are significant in adenomyosis and endometriosis

MRI Appearance

T1-weighted images:

  • Myometrium shows intermediate signal intensity

  • Hemorrhagic lesions or fibroids with degeneration may appear as bright foci

T2-weighted images:

  • Outer myometrium shows intermediate to high signal intensity

  • Junctional zone appears as low signal intensity band (thickness >12 mm suggests adenomyosis)

  • Fibroids appear as well-defined low-signal masses

STIR (Short Tau Inversion Recovery):

  • Normal myometrium shows low-to-intermediate signal

  • Pathology such as adenomyosis or inflammation appears with bright signal intensity

T1 Fat-Sat Post-Contrast:

  • Normal myometrium enhances homogeneously and progressively

  • Fibroids enhance variably (depending on vascularity/degeneration)

  • Malignancy or adenomyosis may show heterogeneous enhancement

CT Appearance

Non-Contrast CT:

  • Myometrium appears as soft tissue density

  • Fibroids or calcifications may be visualized as focal high-density areas

  • Limited sensitivity compared to MRI

Post-Contrast CT:

  • Myometrium enhances homogeneously in normal conditions

  • Leiomyomas enhance variably depending on degeneration and vascularity

  • Malignant lesions may show irregular or heterogeneous enhancement

MRI image

Myometrium of uterus MRI sagittal image anatomy image-img-00000-00000

CT image

Myometrium of uterus CT sagittal image anatomy image-img-00000-00000