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Perimetrium of uterus

The perimetrium is the outermost layer of the uterus, consisting of a thin serous membrane derived from the visceral peritoneum. It provides a smooth covering for the uterus and reduces friction between the uterus and surrounding pelvic organs. Together with the myometrium and endometrium, it forms one of the three main layers of the uterine wall. The perimetrium is important in gynecology, surgery, and radiology as it defines the external uterine surface and its relationships within the pelvis.

Synonyms

  • Serosa of uterus

  • Uterine serous coat

  • Uterine serosa

Location and Extent

  • Covers most of the fundus and body of the uterus

  • Laterally continuous with the broad ligament of the uterus

  • Does not cover the entire uterus: the anterior surface of the cervix and lateral aspects of the uterus may remain uncovered

  • Posteriorly, it reflects onto the rectum forming the rectouterine pouch (pouch of Douglas)

  • Anteriorly, it reflects onto the bladder forming the vesicouterine pouch

Relations

  • Anteriorly: Urinary bladder (via vesicouterine pouch)

  • Posteriorly: Rectum and sigmoid colon (via rectouterine pouch)

  • Laterally: Broad ligament of the uterus and adnexa (fallopian tubes and ovaries)

  • Superiorly: Abdominal peritoneal cavity

Function

  • Provides a protective serosal covering for the uterus

  • Reduces friction between the uterus and adjacent pelvic organs during movement, filling, and emptying

  • Acts as a barrier to local spread of infection or disease

  • Serves as a landmark in imaging and surgery for delineating uterine margins

Clinical Significance

  • Involved in peritoneal adhesions following pelvic infections, endometriosis, or surgery

  • In endometriosis, ectopic endometrial tissue can implant on the perimetrium causing pain and adhesions

  • Uterine serosal tumors (e.g., subserosal fibroids) project beneath the perimetrium and can distort its contour

  • Defines the outer boundary of the uterus in radiology, important for staging gynecological malignancies

MRI Appearance

T1-weighted images:

  • Perimetrium appears as a thin, low-signal intensity line outlining the uterus

  • Adjacent fat and pelvic peritoneal fluid enhance visibility

T2-weighted images:

  • Appears as a hypointense line covering the uterus

  • Adjacent fluid-filled spaces (bladder, rectouterine pouch) provide contrast

STIR (Short Tau Inversion Recovery):

  • Perimetrium remains low signal

  • Adjacent inflammatory changes or adhesions may appear bright

T1 Fat-Sat Post-Contrast:

  • Perimetrium shows thin, uniform enhancement

  • Pathological changes (inflammation, peritoneal deposits, tumor spread) show irregular or nodular enhancement

CT Appearance

Non-Contrast CT:

  • Perimetrium itself is not separately visible but contributes to the smooth outer contour of the uterus

  • Subserosal fibroids may distort this contour

Post-Contrast CT:

  • Outer uterine surface enhances slightly along with myometrium

  • Pathology (tumor invasion, peritoneal implants, inflammatory changes) may cause irregular thickening, nodularity, or enhancement of the perimetrium

MRI image

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

CT image

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