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Reproductive

Female Reproductive Anatomy

The female pelvic organs—uterus, ovaries, fallopian tubes, and vagina—sit within the peritoneal-lined pelvis and are best characterized by ultrasound and multiparametric MRI, which resolve the zonal anatomy of the uterus and follicular architecture of the ovaries. Appearances change dynamically with the menstrual cycle, hormonal status, and pregnancy. Precise anatomic and zonal knowledge underpins the evaluation of bleeding, masses, infertility, and gynecologic malignancy.

Key Structures

  • Uterus: fundus, body, and cervix; MRI shows three zones—high-T2 endometrium, low-T2 junctional zone (inner myometrium), and intermediate outer myometrium
  • Endometrium: cyclical thickening; measured as a bilayer on ultrasound (thin postmenstrual, thicker secretory)
  • Ovaries: cortex containing follicles and a corpus luteum, with a more vascular medulla; follicles are simple anechoic cysts
  • Fallopian tubes: interstitial, isthmic, ampullary, and infundibular segments—normally not visualized unless fluid-filled
  • Vagina and cervix: cervical stroma is low signal on T2; fibromuscular vaginal wall in H-shape on axial imaging
  • Ligaments and spaces: broad ligament, round and uterosacral ligaments; pouch of Douglas (rectouterine) is the most dependent recess
  • Ovarian/gonadal vessels: ovarian arteries from the aorta, right ovarian vein to the IVC, left to the left renal vein

Imaging Planes & Modalities

  • Transvaginal ultrasound is first-line for the endometrium, ovaries, and early pregnancy; transabdominal views assess large masses and the whole pelvis; Doppler evaluates ovarian torsion and vascularity
  • Multiparametric MRI (T2 for zonal anatomy, T1 with/without fat-sat for hemorrhage/fat, DWI, dynamic contrast) characterizes masses and stages endometrial, cervical, and ovarian cancer
  • Sagittal and axial oblique T2 planes aligned to the uterine and cervical axes optimize junctional-zone and cervical staging
  • Sonohysterography (saline infusion) delineates intracavitary polyps and submucosal fibroids
  • Hysterosalpingography assesses tubal patency in infertility
  • CT is used for staging spread and complications but is inferior for zonal soft-tissue detail

Landmarks & Normal Values

  • Endometrial thickness: postmenopausal <4-5 mm reassuring for bleeding; premenopausal varies with cycle phase
  • Junctional zone <12 mm on MRI; diffuse thickening >12 mm suggests adenomyosis
  • Normal premenopausal ovarian volume ~5-15 mL; dominant follicle up to ~2.5 cm; postmenopausal ovaries small and follicle-poor
  • A simple ovarian follicle/cyst up to 3 cm is physiologic; corpus luteum shows a crenulated, vascular ring
  • The pouch of Douglas is the dependent site for free fluid, hemoperitoneum, and endometriotic/peritoneal deposits

Anatomical Variants

  • Müllerian duct anomalies: septate, bicornuate, unicornuate, and didelphys uterus—distinguished by the external fundal contour on MRI
  • Retroverted/retroflexed uterus and normal positional variation
  • Arcuate uterus (mild fundal indentation) as a normal variant versus a septate uterus
  • Paraovarian/paratubal cysts and hydrosalpinx-mimicking cystic structures
  • Ovarian position variation and pelvic/undescended ovaries
  • Nabothian cysts of the cervix—benign retention cysts

Pathology Correlation

  • Leiomyoma (fibroid): well-defined low-T2 myometrial mass; location (submucosal, intramural, subserosal) guides symptoms and treatment
  • Adenomyosis: junctional-zone thickening with myometrial T2 hyperintense foci
  • Endometrial carcinoma staged by depth of myometrial invasion and cervical involvement on dynamic MRI/DWI
  • Cervical carcinoma: disruption of the low-T2 cervical stroma and parametrial invasion determine stage and treatment
  • Adnexal masses characterized by O-RADS/ADNEX features—solid components, papillary projections, and vascularity raise malignancy risk; endometrioma shows T1 hyperintense shading
  • Ovarian torsion: enlarged ovary with peripheral follicles, twisted vascular pedicle, and absent/reduced Doppler flow; ectopic pregnancy in the tube with an adnexal ring

Pitfalls & Mimics

  • A hemorrhagic corpus luteum or endometrioma can mimic a complex neoplasm—correlate with cycle timing and T1 signal
  • Do not overcall a physiologic follicle or corpus luteum cyst as pathology
  • Adenomyosis is frequently missed—look for junctional-zone thickening and myometrial cysts, not just a discrete mass
  • Pedunculated subserosal fibroids and broad-ligament fibroids can mimic adnexal masses; trace the vascular pedicle
  • Doppler flow may still be present in early or intermittent ovarian torsion—do not exclude torsion on flow alone
  • Distinguish an arcuate from a septate uterus and correctly classify Müllerian anomalies, as management differs

References

  • Hricak H, et al. Diagnostic Imaging: Gynecology. Elsevier
  • ACR O-RADS US and MRI risk stratification systems (ACR guidance)
  • Doubilet PM, Benson CB. Atlas of Ultrasound in Obstetrics and Gynecology. Wolters Kluwer
  • Reznek RH, et al. Imaging in Oncology / gynecologic staging (ESUR guidelines)

⚕️ Educational reference — correlate with clinical context and confirm with a qualified radiologist.