Uterus Anatomy: Position, Supports, and Clinical Correlations

Overview

The uterus is a hollow, pear-shaped, thick-walled muscular organ in the female pelvis, located between the bladder (anteriorly) and rectum (posteriorly). It is essential for menstruation, implantation, pregnancy, and labor.

Anatomical Position

Normal position: Anteverted and anteflexed
- Anteversion: angle between cervix and vagina (~90°, opening anteriorly)
- Anteflexion: angle between cervix and body of uterus (~170°)
Position variations: Retroverted uterus occurs in ~20-30% of women (usually asymptomatic)

Anatomical Regions

Fundus: Dome-shaped superior portion above the entry of the uterine tubes
Body (corpus): Main central portion
Isthmus: Narrowed transition between body and cervix (~1 cm long)
Cervix: Inferior cylindrical portion projecting into the vagina

Layers of the Uterine Wall

Perimetrium: Outer serous layer (peritoneum)
Myometrium: Thick smooth muscle layer; the layer that contracts during labor and menstruation
Endometrium: Inner mucosal layer that sloughs during menstruation and proliferates during the cycle
- Functional layer: Sloughs during menstruation
- Basal layer: Retained, regenerates the functional layer each cycle

Ligamentous Supports

Primary Supports

Transverse cervical (cardinal) ligaments: Most important support; contain the uterine vessels; extend from cervix to pelvic side walls
Uterosacral ligaments: From cervix to sacrum; resist posterior displacement

Secondary Supports

Round ligaments: Maintain anteflexion; pass through the inguinal canal to the labia majora (homologue of gubernaculum testis)
Broad ligaments: Double folds of peritoneum extending from uterus to lateral pelvic walls; contain the uterine tubes, ovaries (via mesovarium), round ligaments, and uterine vessels
Pubocervical fascia: Supports anteriorly; prevents cystocele
Uterovesical and rectovaginal fascia: Additional pelvic support

Blood Supply

Uterine artery (branch of internal iliac): Main supply
Ovarian artery (from abdominal aorta): Anastomoses with uterine artery; supplies the fundus and tubes

Clinical pearl: The ureter passes UNDER the uterine artery ("water under the bridge") at the lateral fornix — a critical relationship during hysterectomy to avoid iatrogenic ureteral injury.

Lymphatic Drainage

Fundus and upper body: Para-aortic nodes (along ovarian vessels)
Lower body: External iliac nodes
Cervix: External iliac, internal iliac (hypogastric), and obturator nodes
Clinical relevance: Cervical cancer staging requires sentinel node biopsy mapping

Clinical Correlations

Fibroids (Leiomyomas)

Benign smooth muscle tumors; most common pelvic tumor in women
Classified by location:
- Submucosal: Project into the uterine cavity (cause menorrhagia)
- Intramural: Within the myometrium (most common)
- Subserosal: Project outward (may compress bladder or ureter)

Uterine Prolapse

Descent of the uterus into the vagina due to weakened pelvic floor supports
Risk factors: Multiparity, vaginal delivery, obesity, age, chronic constipation
Staging (Pelvic Organ Prolapse Quantification, POP-Q):
- Stage 0: No prolapse
- Stage I: Cervix descends but remains in vagina
- Stage II: Cervix reaches introitus
- Stage III: Cervix protrudes beyond introitus
- Stage IV: Complete prolapse (procidentia)

Endometriosis

Functional endometrial tissue outside the uterine cavity
Common sites: Ovaries (chocolate cysts), uterosacral ligaments, rectovaginal septum, peritoneal surfaces
Symptoms: Dysmenorrhea, dyspareunia, dyschezia, infertility

Adenomyosis

Endometrial glands within the myometrium
Causes heavy painful periods and enlarged, boggy, tender uterus
Diagnosed definitively only on histology after hysterectomy

Endometrial Cancer

Most common gynecologic malignancy in developed countries
Type I (estrogen-driven, endometrioid): Associated with unopposed estrogen, obesity, PCOS, late menopause; better prognosis
Type II (serous, clear cell): Aggressive, p53 mutations, poor prognosis
Postmenopausal bleeding is the cardinal symptom

Key Takeaway

The uterus's anteverted/anteflexed position, layered muscular wall, and dual blood supply make it uniquely suited for pregnancy. Remember: uterine artery OVER ureter ("bridge over water"), cardinal and uterosacral ligaments as primary supports, and the clinical triad of fibroids/prolapse/endometriosis for exam questions.