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Rectouterine pouch (pouch of Douglas)

The rectouterine pouch, also called the pouch of Douglas or posterior cul-de-sac, is the deepest peritoneal recess in the female pelvis. It is formed by the peritoneal reflection between the rectum and the posterior wall of the uterus. Because it is the most dependent portion of the peritoneal cavity in the upright female, it is the most common site for free fluid accumulation. It is clinically important in gynecology, obstetrics, surgery, and radiology.

Synonyms

  • Pouch of Douglas

  • Rectouterine recess

  • Posterior cul-de-sac

Location and Boundaries

  • Superiorly: Uterine body and posterior uterine wall covered by peritoneum

  • Inferiorly: Rectum and upper posterior vaginal wall

  • Anteriorly: Posterior surface of uterus and cervix

  • Posteriorly: Anterior surface of rectum

Relations

  • Lies between the uterus (anteriorly) and rectum (posteriorly)

  • Superiorly related to the body and fundus of the uterus

  • Inferiorly related to posterior fornix of vagina and anterior rectum

  • In direct continuity with peritoneal cavity above

Function

  • Acts as a potential peritoneal space between uterus and rectum

  • Serves as the most dependent pelvic recess, often collecting free fluid (blood, pus, ascites)

  • Provides a surgical access route (culdocentesis, transvaginal procedures)

  • Important landmark in gynecologic and pelvic imaging

Clinical Significance

  • Endometriosis: Common site for peritoneal implants and adhesions

  • Pelvic inflammatory disease: May collect pus or exudate

  • Trauma: Frequent site of free blood accumulation

  • Tumors: May contain malignant peritoneal deposits

  • Surgical importance: Accessed in culdocentesis or transvaginal drainage procedures

MRI Appearance

T1-weighted images:

  • No fluid: Pouch appears as a thin dark peritoneal line

  • Simple fluid: Dark (low signal intensity)

  • Fat: Bright signal surrounding uterus and rectum

  • Blood/proteinaceous fluid: Bright signal intensity

T2-weighted images:

  • No fluid: Pouch not well visualized, thin dark peritoneal lining only

  • Simple fluid: Bright signal intensity

  • Fat: Intermediate to bright signal outlining pelvic structures

  • Endometriosis/fibrosis: Dark foci or plaques within the pouch

STIR (Short Tau Inversion Recovery):

  • No fluid: Pouch not visualized, normal pelvic tissues suppressed

  • Fluid: Bright hyperintense signal

  • Fat: Suppressed, appears dark

  • Inflammatory changes/implants: Bright signal intensity

T1 Fat-Sat Post-Contrast:

  • No fluid: Pouch seen as thin peritoneal lining, no significant enhancement

  • Simple fluid: No enhancement

  • Fat: Suppressed and dark

  • Pathology (endometriosis, tumor, infection): Focal, nodular, or rim enhancement

CT Appearance

Non-Contrast CT:

  • No fluid: Pouch indistinct, visible only as a potential space between uterus and rectum

  • Simple fluid: Low-attenuation collection between uterus and rectum

  • Fat: Low-density tissue surrounding pelvic organs

  • Blood/pus: Higher attenuation than simple fluid

Post-Contrast CT:

  • No fluid: Peritoneal lining may enhance faintly, pouch remains collapsed

  • Fluid: Persists as low attenuation; rim enhancement if inflammatory

  • Fat: Remains low attenuation; stranding may appear in inflammation

  • Pathology: Enhancing nodules, thickening, or soft tissue masses indicate tumor deposits or endometriotic lesions

MRI image

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MRI image

rectouterine pouch MRI sagittal anatomy image-img-00000-00000_00001

CT image

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CT image

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