The Uterus - Complete Anatomy

1. FEATURES

1. Perimetrium - outer peritoneal/serous coat
2. Myometrium - thick smooth muscle (1.5-2.5 cm thick); three sublayers - outer longitudinal (continuous with round ligament and tubal fibers), middle oblique/circular (carries blood vessels and nerves), inner longitudinal
3. Endometrium - inner mucosa; undergoes cyclical change under hormonal influence

2. BLOOD SUPPLY

Arterial Supply

• Courses medially and anteriorly in the base of the broad ligament
• Crosses OVER the ureter at ~2 cm lateral to the cervix ("water under the bridge" - ureter is the "water")
• Passes superiorly to the lateral vaginal fornix
• Reaches the cervix, then ascends along the lateral wall of the uterus in a tortuous course
• At the fundus, curves laterally and anastomoses with the ovarian artery
• Gives off: ascending main branch, descending vaginal artery (A4), tubal branch, and ovarian branch at the fundus

• Ovarian artery (from abdominal aorta) - anastomoses with uterine artery at the fundus; enlarges significantly in pregnancy; travels in the suspensory ligament of the ovary (infundibulopelvic ligament)

Clinical pearl: During hysterectomy, the uterine artery must be ligated without damaging the adjacent ureter. Failure to identify the ureter is the most common cause of ureteric injury in pelvic surgery.

Venous Drainage

• A network of valveless veins forms the uterine (venous) plexus around the body and cervix (in the parametrium)
• Drains via uterine veins → internal iliac veins
• Also connects with vaginal and ovarian plexuses

3. NERVE SUPPLY

Autonomic (the main innervation of the uterus)

• Via the inferior hypogastric plexus (pelvic plexus) and pelvic splanchnic nerves (S2-S4)
• These form a plexus lateral to the cervix with large ganglion cells - the uterovaginal plexus (Frankenhauser ganglion / Lee-Frankenhauser plexus)

• Causes uterine contraction and vasoconstriction

• Causes uterine relaxation (in non-pregnant state) and vasodilation

Sensory (Pain) Fibers

• Pain from the body and fundus travels with sympathetic fibers → T10-T12, L1 (referred to umbilical and inguinal regions - explains labour pain felt in lower back and groin)
• Pain from the cervix travels with parasympathetic fibers → S2-S4 (referred to perineum, thighs, lower back)

Clinical: In spinal cord injuries below T10-T12, patients have an intact uterine nerve supply and experience labour pains; injuries above T10 abolish uterine pain sensation.

4. SUPPORT OF THE UTERUS ⭐ (Most Asked)

ACTIVE SUPPORT (Most Important)

PASSIVE SUPPORT - Ligaments

A. CARDINAL LIGAMENT (Mackenrodt's Ligament / Transverse Cervical Ligament) ⭐ Most Important Clinical Ligament

• A condensation of connective tissue running from the cervix and upper vagina → lateral pelvic wall
• Contains the uterine artery and ureter
• Most important ligament for preventing uterine prolapse
• Weakness → cervical descent and uterovaginal prolapse

B. UTEROSACRAL LIGAMENTS (Rectouterine Ligaments / Sacrouterine Ligaments) ⭐ Most Important

• Dense subperitoneal connective tissue running from the posterior cervix → posterolateral pelvic wall / sacrum (S2-S4)
• Bound the rectouterine pouch (Pouch of Douglas)
• Maintain anteversion of the uterus by pulling the cervix posteriorly
• Carry autonomic nerve fibers (inferior hypogastric plexus)
• Palpable on per rectum examination in endometriosis (feel like nodular cords)

C. BROAD LIGAMENT

• A double fold of peritoneum extending from the lateral margin of the uterus to the lateral pelvic wall
• Not a true ligament - primarily contains vessels, nerves, and connective tissue
• Has subdivisions: mesometrium (covers uterus body), mesosalpinx (covers uterine tube), mesovarium (covers ovary)
• Provides lateral support; does not prevent prolapse

D. ROUND LIGAMENT OF THE UTERUS

• Arises from the uterine cornu (just anterior and below the uterine tube insertion)
• Passes through the inguinal canal → ends in labia majora
• Contains smooth muscle cells
• Maintains anteversion of the uterus
• Homologous to the gubernaculum testis in the male
• Carries the ilioinguinal nerve nearby
• Lymphatics from the fundus can follow this ligament → superficial inguinal nodes

E. PUBOCERVICAL LIGAMENT (Anterior Support)

• Condensation from cervix → posterior aspect of pubic symphysis
• Supports the bladder neck and anterior vaginal wall

F. OVARIAN LIGAMENT (Ligament of the Ovary)

• Connects the ovary to the uterine cornu; not a support ligament for the uterus per se

Summary Table: Support of the Uterus

Applied: When the cardinal and uterosacral ligaments weaken (multiparity, menopause, chronic straining), the uterus descends - uterovaginal prolapse. The operation to repair this (Manchester repair / Fothergill's operation or pelvic floor repair) involves plication of these ligaments.

5. LYMPHATIC DRAINAGE ⭐ (Most Asked)

Region-by-Region Drainage

All nodes ultimately drain to:

Key Clinical Points - Lymphatic Spread

Endometrial (uterine body) cancer: Spreads to external iliac, internal iliac, and obturator nodes first; then para-aortic nodes (especially for fundal tumors which drain with ovarian vessels)

Cervical cancer: Spreads to obturator and external iliac nodes first (the "primary" nodes). Sentinel node concept is used in staging. Posterior spread is to sacral nodes via uterosacral ligaments.

Round ligament route (fundus → inguinal nodes): Explains rare inguinal node involvement in endometrial cancer and why fundal tumors can spread to inguinal nodes.

6. APPLIED ANATOMY ⭐

A. Uterine Artery & Ureter Relationship

• The uterine artery crosses over the ureter ("water under the bridge") about 1.5-2 cm lateral to the cervix at the base of the broad ligament
• Critical in hysterectomy: Ureter is at risk when ligating the uterine artery
• Ureter can also be injured when clamping the cardinal ligament

B. Uterine Artery Embolization (UAE)

• An interventional radiology procedure where small particles are injected into both uterine arteries via the femoral approach
• Blocks blood supply to fibroids and adenomyosis, causing infarction and shrinkage
• Also used in postpartum hemorrhage

C. Hysterectomy Types

• Total abdominal hysterectomy (TAH): Removes body, fundus, and cervix
• TAH + bilateral salpingo-oophorectomy (BSO): Also removes tubes and ovaries
• Subtotal/supracervical: Cervix left in situ (rare)
• Performed via Pfannenstiel (transverse suprapubic) incision

D. Uterine Prolapse

• Caused by weakening of the cardinal and uterosacral ligaments and pelvic floor
• Degrees:
  • 1st degree - cervix descends into vagina
  • 2nd degree - cervix at vaginal introitus
  • 3rd degree (procidentia) - entire uterus outside the vagina
• Risk factors: multiparity, prolonged labour, obesity, chronic straining, menopause (estrogen loss)
• Treatment: pelvic floor exercises, pessary, surgical repair (Manchester operation, pelvic floor repair, or vaginal hysterectomy)

E. Referred Pain in Dysmenorrhoea / Labour

• Uterine body pain transmitted via T10-L1 sympathetic fibers → referred to lower back, umbilical region, and inner thighs
• Cervical pain via S2-S4 → referred to perineum, inner thighs, lower sacrum

F. Ectopic / Abnormal Implantation

• Normal implantation is in the body of the uterus (upper posterior wall preferred)
• Placenta praevia: implantation in the lower uterine segment / isthmus (over the internal os)
• Ectopic pregnancy: implantation outside uterus (most commonly ampulla of the tube)

G. Uterine Malignancy and Lymph Node Dissection

• Cervical cancer surgery (Wertheim's radical hysterectomy) removes the uterus + parametrium + upper vagina + pelvic lymph nodes (external iliac, internal iliac, obturator)
• Para-aortic node sampling is done for advanced disease or fundal tumors

• "Water under the bridge" = Ureter (water) passes UNDER the uterine artery (bridge) at the lateral cervix
• Ligament importance order: Cardinal > Uterosacral > Round > Broad (for prolapse prevention)
• Lymphatics by region: Fundus → para-aortic; Body → external iliac; Cervix → external iliac + internal iliac + sacral nodes; Fundus (minor) → inguinal (via round ligament)
• Nerve supply levels: Body/fundus pain → T10-L1 (labour pain felt in back); Cervical pain → S2-S4