Pelvic Vein Anatomy Made Simple: Ovarian, Iliac and Left Renal Veins

Understanding ovarian vein anatomy, and how the other pelvic veins connect, makes pelvic vein conditions much easier to follow. The pelvis drains through a small number of main veins, and the left side is built differently from the right. That difference explains why pelvic congestion, nutcracker and May-Thurner syndromes so often affect the left. This guide gives a simple, step-by-step tour, without the medical-school detail.

The big picture: two ways out

Blood from the womb, ovaries, bladder, bowel and pelvic floor collects in networks of thin-walled veins called plexuses. From there it has two main routes back to the heart:

1. Upwards, through the two ovarian veins, which run up the back of the abdomen towards the kidneys.
2. Sideways and back, through the two internal iliac veins, which join the leg veins to form the common iliac veins.

Both routes end in the inferior vena cava (IVC), the large vein running up the right side of the spine to the heart. Most pelvic blood normally leaves through the internal iliac route.

A simple map of the pelvic veins

Here is the layout as a list, starting at the pelvis and working upwards:

• Womb and ovaries
• Uterine and parametrial plexus (veins beside the womb) and ovarian plexus (veins beside each ovary)
  • → Right ovarian vein → straight into the IVC
  • → Left ovarian vein → into the left renal vein → crosses between the aorta and the superior mesenteric artery → IVC
  • → Uterine veins → internal iliac veins (left and right)
• Pelvic floor, vulva, buttocks
• Internal pudendal, gluteal and obturator veins → internal iliac veins
• Legs
• Leg veins → external iliac veins in the groin
• Joining up
• Internal iliac + external iliac → common iliac vein on each side
• Left common iliac vein passes behind the right common iliac artery
• Left and right common iliac veins → IVC → heart

The ovarian veins: where each one drains

Each ovarian vein starts as a web of small veins beside the ovary, in the broad ligament that supports the womb. These merge into one or two channels that run upwards behind the bowel, alongside the ureter (the tube from the kidney to the bladder).

The two sides end differently:

• The right ovarian vein drains into the IVC directly, joining it at a gentle, slanting angle.
• The left ovarian vein drains into the left renal vein, joining it at close to a right angle. It is also a little longer than the right.

Small one-way valves, mostly in the lower part of each ovarian vein, normally stop blood falling back down. In a small minority of people the valves are missing, and this is more common on the left. “Gonadal vein” is simply the umbrella term: in men, the testicular veins follow the same pattern, which is why varicoceles are mostly left-sided.

The left renal vein

The left renal vein carries blood from the left kidney to the IVC. Because the IVC sits on the right, the left renal vein is longer than the right one and has to cross the midline. On the way it usually passes through a narrow gap between the aorta behind and the superior mesenteric artery in front.

As well as the left ovarian vein, it collects blood from the left adrenal gland and some veins of the back wall of the abdomen. If it is squeezed in that gap, pressure backs up into all of these branches, especially the left ovarian vein. When this causes symptoms, it is called nutcracker syndrome. In some people the vein runs behind the aorta instead, or splits around it, which can be squeezed in a different way.

The internal and common iliac veins

The internal iliac vein on each side collects blood from the pelvic organs, the pelvic floor, the vulva and perineum (via the internal pudendal veins), the buttocks (via the gluteal veins) and the inner thigh (via the obturator veins). These veins usually have few or no valves.

In the lower abdomen, the internal and external iliac veins join to form the common iliac vein. The two common iliac veins meet in front of the lower spine to form the IVC.

The left common iliac vein crosses behind the right common iliac artery, which can press it against the spine. When this narrowing causes symptoms, it is called May-Thurner syndrome. It can cause left leg swelling and clots, and it can also push blood back into the pelvic veins.

Escape points: how pelvic veins reach the vulva and thigh

The pelvic veins connect with veins outside the pelvis through a few small openings in the pelvic floor and groin. Specialists call them escape points or leak points. When pelvic veins are overfilled and refluxing, blood can leak out through them:

• Perineal (pudendal) point. The most common. Causes varicose veins on the vulva, perineum and upper inner thigh.
• Inguinal (round ligament) point. In the groin. Can cause veins in the groin, vulva and front of the thigh, and is sometimes mistaken for a hernia.
• Obturator point. Can feed veins on the inner thigh and perineum.
• Gluteal points. Can feed veins on the buttock and back of the thigh.

This is why some women have vulval varicose veins or unusual leg veins that come back after treatment. See leg varicose veins of pelvic origin.

Why the left side is more often affected

Put the pieces together and the left side has several extra weak spots:

• A longer left ovarian vein that meets the kidney vein at a near right angle
• Valves that are more often missing on the left
• A left renal vein that can be squeezed between two arteries
• A left common iliac vein that can be squeezed by an artery against the spine

Any of these can raise pressure in the left pelvic veins. That is why reflux in the left ovarian vein is the most common finding in pelvic congestion syndrome, although both sides and the internal iliac veins are often involved.

How this explains the symptoms

• A heavy, dragging ache that builds through the day. When you stand, gravity adds to the pressure in the pelvic veins, which have few working valves. Lying down lets them drain.
• Pain during or after sex, or around periods. The veins beside the womb and ovaries are stretched and swell further at these times.
• Visible veins on the vulva, buttock or thigh. Blood leaks out through the escape points.
• Blood in the urine with left flank pain. Points to the left renal vein being squeezed.
• Left leg swelling. Can point to the left common iliac vein.

For a full list, see pelvic congestion syndrome symptoms. A Singapore vascular surgeon’s overview of pelvic congestion syndrome also describes how these veins are involved.

When to see a doctor

Normal anatomy varies, and finding a wide vein on a scan does not always mean it is causing symptoms. See a doctor if you have a pelvic ache that has lasted months, pain that affects sex or daily life, new varicose veins on the vulva or upper thigh, or blood in your urine. Our pelvic symptom check can help you prepare.

Get urgent medical help for sudden severe pelvic or tummy pain, a suddenly swollen, painful leg, sudden breathlessness or chest pain, heavy bleeding, or fever with pelvic pain. In Singapore, call 995 in an emergency.

This article is general information, not personal medical advice. Please speak to a doctor about your own symptoms. How we create our content.