Female pelvic organs

Uterus: parts and position

• Pear-shaped, about 7.5 × 5 × 2.5 cm and 60 g in the adult. Parts: fundus (above the tubes), body, cornua (where tubes enter), isthmus, cervix.
• Body to cervix ratio: 1:2 in a child (tubular uterus), 2:1 in the adult (oestrogen at puberty).
• Normal position: anteverted (cervix tilted forward on the vagina, about 90 degrees) and anteflexed (body bent forward on the cervix), lying on the bladder.
• Retroversion (about 1 in 5) is normal if mobile; fixed and tender suggests adhesions (endometriosis, PID). A retroverted gravid uterus usually rises by 12–14 weeks; rarely the fundus is trapped under the sacral promontory, pushing the cervix behind the symphysis and causing acute urinary retention.
• Relations: front, vesicouterine pouch and bladder; back, pouch of Douglas with ileum and sigmoid colon; sides, broad ligament, uterine vessels and ureter. A cannula perforating the posterior wall of a retroverted uterus can draw in sigmoid colon and ileal loops, so suction stops at once.
• Layers: endometrium, myometrium (three layers; the middle interlacing layer kinks vessels after delivery), and serosa. Myometrium has wide venous channels: during long hysteroscopic resection, distension fluid such as glycine is absorbed through opened myometrial veins, causing dilutional hyponatraemia.

Supports of the uterus

• In a grand multipara with the cervix at the introitus, the chief failure is the cardinal ligament (with levator ani damage); uterosacral weakness mainly gives posterior vault descent.

Blood supply and lymph drainage

• Uterine artery: anterior division of the internal iliac; runs medially in the cardinal ligament and crosses above the ureter about 1.5–2 cm lateral to the cervix, then ascends tortuously and anastomoses with the ovarian artery near the cornu.
• Ovarian artery: from the abdominal aorta at L2, just below the renal arteries, through the suspensory (infundibulopelvic) ligament. Right ovarian vein drains to the IVC, left to the left renal vein.
• The tube is supplied by an arcade of uterine and ovarian branches in the mesosalpinx. At salpingectomy the mesosalpinx is divided close to the tube to spare this arcade and the ovarian blood supply.

• Ovarian cancer spreads mainly transcoelomically: cells shed onto the peritoneum seed the omentum, diaphragm and pouch of Douglas and produce malignant ascites. Its first lymph nodes are para-aortic.
• Cervical cancer spreads into the fornices and parametrium and then to pelvic nodes; that is why radical hysterectomy removes the parametrium and upper vagina.

The isthmus and lower segment

• The isthmus lies between the anatomical internal os and the histological internal os (where endometrium changes to endocervical mucosa). A subtotal hysterectomy divides the uterus here, so the cervical stump remains and needs continued screening.
• It softens at 6–10 weeks, so bimanually the fingers almost meet between cervix and body (softening of the isthmus), and from about 12 weeks forms the lower uterine segment.
• Lower segment: thin, less muscular, fewer vessels, passive in labour, so a transverse incision bleeds less and ruptures far less than a classical scar.
• Obstructed labour: the upper segment retracts, the lower segment thins, the junction rises as a visible ridge, and rupture occurs in the lower segment.
• Fundal height: just palpable at 12 weeks, umbilicus at 20–22 weeks, xiphisternum at 36 weeks. At term in a primigravida the head engages and the fundus drops slightly (lightening): breathing eases but the bladder is pressed, so frequency increases. In multiparas the head may not engage until labour.
• The enlarging uterus displaces the caecum and appendix upwards, so appendicitis at 30 weeks is tender in the right flank.
• By about 12–16 weeks the decidua capsularis fuses with the decidua parietalis, obliterating the uterine cavity.

Cervix

• About 2.5 cm; supravaginal and vaginal parts. External os round in nulliparous women, a transverse slit after vaginal birth. Canal folds: plicae palmatae.
• Pregnancy changes: softening (more water, collagen remodelling), bluish discoloration of vagina and cervix (Chadwick sign, from pelvic venous congestion), and ectropion as oestrogen everts the endocervical columnar epithelium onto the ectocervix.
• Labour: in a primigravida the canal effaces first and then the external os dilates; in a multipara effacement and dilatation happen together.
• The bladder lies directly on the front of the supravaginal cervix with no peritoneum between, so advanced cervical cancer causes haematuria and vesicovaginal fistula.
• Parametrium: connective tissue beside the supravaginal cervix in the broad ligament base, holding the uterine vessels, lymphatics and the ureter.
• Cervical stroma is mostly collagen with little muscle, so it cannot contract to close vessels: evacuation of a cervical ectopic (barrel-shaped cervix, hourglass uterus) can bleed torrentially.
• Cervical stenosis after cone biopsy blocks outflow: amenorrhoea with cyclical pain and haematometra.
• Cervical incompetence is weakness at the internal os (painless mid-trimester loss). Dilatation can cause a vasovagal faint; moving the cervix stretches inflamed adnexa (cervical excitation).

Uterine tubes

• About 10 cm, in the upper border of the broad ligament (the mesosalpinx). Lined by ciliated simple columnar epithelium with secretory (peg) cells; cilia beat towards the uterus.

• Hysterosalpingography (HSG) injects contrast through the cervix to show the cavity and tubal patency. A tube that fills and dilates without spill is blocked at the fimbrial end; a proximal block leaves the tube unfilled. Spasm at the uterotubal junction can mimic block.
• Hydrosalpinx fluid flows back into the uterine cavity and harms implantation, so tubes are removed or clipped before IVF.
• The ovary is not inside the tube: the fimbriae capture the oocyte, and a remaining tube can collect an oocyte from the opposite ovary by transperitoneal migration.
• Blood from a ruptured tube irritates the diaphragm: shoulder tip pain (C4).

Ovaries

• About 3 × 2 × 1 cm; after menopause about 1.5 cm, so a palpable postmenopausal ovary needs investigation. Held by the mesovarium (posterior leaf of broad ligament), the ligament of the ovary and the suspensory ligament.
• Cortex holds the primordial follicles (harvested and frozen for fertility preservation); medulla holds vessels.
• Ovarian fossa: above, external iliac vessels; behind, ureter and internal iliac vessels; floor, obturator nerve (pain referred to the medial thigh). A prolapsed ovary in the pouch of Douglas causes deep dyspareunia and is felt through the posterior fornix.
• In young children the pelvis is small and the ovaries lie high, so a cyst presents as an abdominal mass. In pregnancy the growing uterus lifts the adnexa into the abdomen where they can twist, so torsion peaks at 10–17 weeks.
• A thin-walled simple cyst up to about 5 cm in a young woman that disappears after the next period is a follicular cyst; repeat the scan before operating. The corpus luteum of pregnancy supports the gestation until the placenta takes over at about 10 weeks.
• Visceral pain travels with the ovarian vessels to T10–T11 (periumbilical).

Vagina

• About 8 cm, running upwards and backwards; posterior wall (9 cm) longer than anterior (7.5 cm), so the posterior fornix is deepest. Adnexa are felt through the lateral fornices.

• Obstructed labour presses the bladder base and anterior vaginal wall against the pubic symphysis; pressure necrosis sloughs after 3–10 days, giving continuous leakage from a vesicovaginal fistula.
• Upper vagina: visceral nerves (stretch only); lower: pudendal, very sensitive.

Remember The isthmus becomes the lower segment: thin, quiet, and the place to cut at caesarean section.

Exam trap The ampulla is the commonest site of tubal ectopic, but the isthmus ruptures earliest; interstitial ectopic bleeds most.

Exam trap Cervical cancer reaches sacral nodes along the uterosacral ligaments; para-aortic nodes are reached later through pelvic nodes, whereas ovarian cancer goes straight to para-aortic nodes.

How FCPS asks about this

• Main support of the uterus, weak in prolapse: cardinal (transverse cervical) ligament, carrying the uterine vessels.
• Origin of ovarian artery and first nodes of ovarian cancer: aorta at L2; para-aortic nodes; ascites from transcoelomic spread.
• Carcinoma of the lower third of the vagina: superficial inguinal nodes.
• Epithelium of the uterine tube: ciliated simple columnar with peg cells.
• Retort-shaped tube on HSG with no spill: fimbrial (distal) block, usually after PID.
• Vesicovaginal fistula after obstructed labour: bladder base crushed against the pubic symphysis, sloughs days later.
• Effect of childbirth on the cervix: external os becomes a transverse slit.