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.

Female Reproductive Anatomy

🧩 Key Structures

🎞️ Imaging Planes & Modalities

📏 Landmarks & Normal Values

🔀 Anatomical Variants

🧠 Pathology Correlation

💡 Pitfalls & Mimics