Pelvic blood supply
Blood supply of the pelvic organs: internal iliac, uterine and ovarian arteries; ligation and embolisation in haemorrhage
The uterus is fed from two directions, the uterine artery from the internal iliac below and the ovarian artery from the aorta above, joined by an arcade along the side of the uterus. At term this bed carries up to 750 mL of blood a minute, which is why PPH can kill in minutes and why surgeons and radiologists need to know exactly which branch to tie, embolise or avoid.
Internal iliac artery
- Arises at the common iliac bifurcation in front of the sacroiliac joint (L5–S1), runs down about 4 cm to the upper border of the greater sciatic foramen and divides into anterior and posterior divisions.
- Relations: ureter in front (crossing near its origin), internal iliac vein behind, ovary in the ovarian fossa in front and medially. Dissecting an adherent ovary from the fossa can tear it.
| Division | Branches | Territory |
|---|---|---|
| Posterior | Iliolumbar, lateral sacral, superior gluteal (largest, leaves above piriformis) | Body wall and buttock (gluteus medius and minimus) |
| Anterior | Umbilical (gives superior vesical; distal part becomes medial umbilical ligament), obturator, uterine, vaginal (female; replaces the inferior vesical), middle rectal, internal pudendal, inferior gluteal | Pelvic viscera and perineum |
- The middle rectal (rectal arteries: superior from inferior mesenteric, middle from internal iliac, inferior from internal pudendal) stays inside the true pelvis. In women the vaginal arteries supply the bladder base and neck; a separate inferior vesical is usually absent.
Uterine artery
- Branch of the anterior division; runs medially in the base of the broad ligament (cardinal ligament) and crosses above and in front of the ureter about 1.5–2 cm lateral to the cervix, at the level of the internal os. This is the commonest site of ureteric injury at hysterectomy.
- At the side of the uterus it divides: a tortuous ascending branch runs up between the layers of the broad ligament to the cornu, where it anastomoses with the ovarian artery; a descending (cervicovaginal) branch runs down the side of the cervix at 3 and 9 o'clock (stay sutures there reduce bleeding at cone biopsy).
- Inside the myometrium: arcuate, then radial, then spiral (functionalis) and straight (basalis) arteries.
- Uterine blood flow rises from about 50 mL/min to 500–750 mL/min at term as the spiral arteries become wide channels without muscle. Haemostasis after delivery depends on myometrial contraction, so a soft atonic uterus can lose 1.5 L in minutes.
- A lateral tear of the lower segment at caesarean section opens uterine artery branches, and blood tracks between the layers of the broad ligament.
- Injury at caesarean section can leave a pseudoaneurysm: heavy secondary bleeding weeks later.
Ovarian artery and veins
- Arises from the aorta at L2, below the renal arteries, crosses in front of the ureter and the external iliac vessels at the pelvic brim, and enters the infundibulopelvic ligament to reach the ovary through the mesovarium.
- Its tubal branches and the uterine artery form an arcade in the mesosalpinx; a tubal ligation or salpingectomy bleeds from this arcade, so the mesosalpinx is cut close to the tube.
- A slipped tie on the infundibulopelvic ligament causes a retroperitoneal haematoma tracking up towards the kidney.
| Vein | Drains into | Clinical point |
|---|---|---|
| Right ovarian | IVC directly | Postpartum ovarian vein thrombosis is commoner on the right; risk of pulmonary embolism |
| Left ovarian | Left renal vein at a right angle | Reflux causes pelvic congestion (dull ache worse on standing) |
Ligation for PPH
- Internal iliac ligation: tie the anterior division, or the trunk 2.5–3 cm beyond its origin (distal to the posterior division, sparing the buttock). Retract the ureter; pass the clamp lateral to medial to avoid the internal iliac vein behind.
- It does not stop uterine flow; it cuts the distal pulse pressure sharply, so arterial bleeding behaves like venous bleeding and clots. Pelvic organs survive, and fertility is preserved.
| Collateral after ligation | Joins |
|---|---|
| Lumbar arteries (aorta) | Iliolumbar |
| Median sacral (aorta) | Lateral sacral |
| Superior rectal (inferior mesenteric) | Middle rectal |
| Ovarian (aorta) | Uterine |
- The rectum stays perfused mainly by the superior rectal artery.
Embolisation
- Uterine artery embolisation (fibroids, PPH): the catheter passes from the femoral artery into the anterior division of the internal iliac and selects the uterine artery. The uterus survives on ovarian collaterals. Particles reaching the ovary through utero-ovarian anastomoses can cause ovarian insufficiency (high FSH), more often after 45.
- Coiling the main trunk instead occludes the superior gluteal artery, causing buttock ischaemia and claudication.
Other vessels at risk
- Internal pudendal artery: perineal and vulval haematoma below the levator (after episiotomy). Bleeding above the levator (paravaginal) comes from uterine or vaginal branches.
- Median sacral artery and the presacral venous plexus over the promontory bleed during sacrocolpopexy.
- An aberrant obturator artery from the inferior epigastric crosses the superior pubic ramus near the iliopectineal ligament and can bleed at colposuspension.
- Vasopressin injected around a fibroid constricts vessels through V1 receptors (Gq, calcium rise).
Remember Uterine artery from below, ovarian artery from above, meeting at the cornu: tie one and the other keeps the uterus alive.
Exam trap Internal iliac ligation lowers pulse pressure rather than stopping flow; tie beyond the posterior division to protect the buttock.
Exam trap The ureter passes under the uterine artery near the internal os, and in front of the internal iliac artery at the brim.
Test yourself on this topic
5 of the 30 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
Three hours after a spontaneous vaginal delivery with a right mediolateral episiotomy, a woman has severe perineal pain and a tense, purple swelling of the right labium majus. Branches of which artery are most likely bleeding?
Answer: Branches of the internal pudendal artery
A vulval haematoma lies below the levator ani, in the superficial tissues of the perineum and labia. These tissues are supplied by the perineal and labial branches of the internal pudendal artery, which enters the perineum through the lesser sciatic foramen and pudendal canal. Haematomas above the levator ani, in the paravaginal tissues, come from descending branches of the uterine artery and the vaginal artery. The ovarian and obturator arteries do not supply the vulva.
Puerperal haematomas
- Vulval: below levator, internal pudendal
- Vaginal: above levator, uterine or vaginal arteries
- Tense purple labial swelling
- Severe perineal pain after delivery
Remember Below the levator, think internal pudendal.
Exam trap Do not confuse a vulval haematoma (internal pudendal) with a paravaginal one above the levator (uterine and vaginal branches).
Why the other options are wrong
- Vaginal branches of the uterine artery Bleed into the paravaginal space above the levator ani.
- Ovarian artery in the suspensory ligament Supplies the ovary and tube from the aorta.
- Obturator artery on the pelvic wall Supplies the medial thigh.
- Inferior epigastric artery in the wall Lies in the anterior abdominal wall.
At laparotomy, an endometrioma stuck to the left lateral pelvic wall is dissected out of the ovarian fossa. Sudden arterial bleeding wells up from the posterior boundary of the fossa, beside the ureter. Which vessel is most likely injured?
Answer: Internal iliac artery
The ovarian fossa is a shallow depression on the lateral pelvic wall. Its posterior boundary is formed by the ureter and the internal iliac vessels, its upper (anterior) boundary by the external iliac vessels, and its anterior limit by the obliterated umbilical artery. The obturator nerve and vessels lie in its floor. An ovary densely adherent in the fossa therefore places the internal iliac artery and ureter at risk when it is freed from behind.
Ovarian fossa
- Posterior: ureter and internal iliac vessels
- Above: external iliac vessels
- Floor: obturator nerve and vessels
- Front: obliterated umbilical artery
Remember Behind the ovary: ureter and internal iliac artery.
Exam trap The external iliac vessels bound the fossa above; the vessel directly behind it is the internal iliac.
Why the other options are wrong
- External iliac artery Forms the upper boundary, not the posterior one.
- Obturator artery Lies in the floor of the fossa, not its posterior border.
- Ovarian artery Enters the ovary from above in the suspensory ligament.
- Superior vesical artery Arises from the umbilical artery near the anterior limit.
Three months after bilateral uterine artery embolisation for fibroids, a 44-year-old woman has amenorrhoea and hot flushes, and her FSH is 70 IU/L. What is the most likely mechanism?
Answer: Particles passing to the ovary via utero-ovarian anastomoses
The ascending uterine artery anastomoses with the ovarian artery near the cornu and in the mesovarium. During embolisation, particles can pass along these channels into the ovarian circulation and cut off follicular blood supply, causing ovarian insufficiency with a high FSH; women in their mid-forties with low ovarian reserve are most at risk. Whole-uterus necrosis is rare and would not raise FSH. Fluoroscopy doses are far below those that destroy follicles, and pain does not suppress the pituitary in this way.
Utero-ovarian anastomosis
- Uterine and ovarian arteries anastomose
- Particles can reach the ovary
- Result: ovarian insufficiency, high FSH
- Higher risk after 45
Remember High FSH after fibroid embolisation: particles reached the ovary.
Exam trap The same utero-ovarian anastomosis that keeps the uterus alive can carry particles to the ovary.
Why the other options are wrong
- Necrosis of the whole uterus including the endometrium Rare; and uterine necrosis would not raise FSH.
- Radiation from fluoroscopy destroying the follicles Fluoroscopy dose is too small to ablate follicles.
- Reflux of particles into the internal pudendal artery Would affect the perineum, not the ovary.
- Pituitary suppression from post-procedure pain Pain does not cause a high-FSH ovarian failure.
A 34-year-old para 4 has a dull pelvic ache that is worse on standing and after intercourse. Venography shows reflux down a dilated left ovarian vein into tortuous pelvic veins; the right ovarian vein is normal. Which anatomical feature best explains why reflux is commoner on the left?
Answer: It joins the left renal vein at a right angle
The left ovarian vein ascends on psoas and drains at a right angle into the left renal vein, whereas the right ovarian vein drains obliquely into the inferior vena cava. The longer left vein, its right-angled entry into a vein with higher pressure, and frequently absent or incompetent valves make the left side the usual site of ovarian vein reflux, which dilates the pelvic venous plexuses (pelvic congestion syndrome). Compression of the left renal vein between the aorta and superior mesenteric artery can worsen this.
Ovarian veins
- Left ovarian into left renal vein
- Right ovarian into IVC
- Left enters at a right angle
- Reflux causes pelvic congestion
Remember Left gonadal vein to the left renal vein, as in the male.
Exam trap Only the right ovarian vein drains directly into the IVC.
Why the other options are wrong
- It runs a shorter course than the right vein The left vein is longer, not shorter, than the right.
- It drains obliquely into the inferior vena cava This describes the right ovarian vein, which refluxes less.
- It is compressed by the right common iliac artery That artery compresses the left common iliac vein (May–Thurner), not the ovarian vein.
- It receives the inferior mesenteric vein The inferior mesenteric vein joins the splenic vein.
To control bleeding from a deep cervical tear extending into the vaginal vault, the anterior division of the right internal iliac artery is tied. Which of the following arteries still receives direct flow from the right internal iliac?
Answer: Iliolumbar artery
The internal iliac artery divides into anterior and posterior divisions at the upper border of the greater sciatic foramen. The posterior division gives the iliolumbar, lateral sacral and superior gluteal arteries, all to the body wall and buttock. The anterior division gives the visceral branches (umbilical with superior vesical, uterine, vaginal, middle rectal) and the obturator, internal pudendal and inferior gluteal arteries. Tying the anterior division therefore leaves the iliolumbar artery supplied.
Internal iliac divisions
- Posterior: iliolumbar, lateral sacral, superior gluteal
- Anterior: visceral branches
- Anterior: obturator, internal pudendal, inferior gluteal
- Ligate the anterior division for pelvic bleeding
Remember Posterior division goes to the wall and buttock; anterior to the viscera.
Exam trap The iliolumbar and lateral sacral arteries are posterior division branches, not anterior.
Why the other options are wrong
- Uterine artery Visceral branch of the anterior division.
- Obturator artery Anterior division branch to the thigh.
- Internal pudendal artery Anterior division branch to the perineum.
- Middle rectal artery Anterior division visceral branch.
Where this sits in the CPSP syllabus
- Obstetrics & Gynaecology, Paper 2: Pelvic organs, vessels and nerves, Blood supply of pelvic organs: internal iliac, uterine and ovarian arteries; ligation in haemorrhage