Content Reviewers:Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.), Viviana Popa, MD, Ghassan Tranesh, MD, MSC FCAP
The pelvis contains numerous structures, all supplied by the neurovascular structures of the pelvis, including nerves, arteries, veins, and lymph nodes. These structures are found on the posterolateral walls of the pelvic cavity.
Lymph nodes are usually clustered around the veins, and lymph vessels that come off these nodes ascend parallel to the veins. Let's focus our attention on the arteries and veins of the pelvis.
Now, the arteries of the pelvis originate from the abdominal aorta, which is the continuation of the thoracic aorta below the aortic hiatus in the diaphragm. The abdominal aorta gives branches to various organs in the abdomen, then divides at the level of the fourth lumbar vertebra into the right and left common iliac arteries.
Each artery runs inferolaterally, and ends at the level of the intervertebral disc between L5 and S1 by dividing into the internal and external iliac arteries. Let’s talk about each of those branches. First are the external iliac arteries, which descend on the medial border of a muscle called the psoas major.
After running for a short distance, each external iliac artery gives two branches, called the inferior epigastric and deep circumflex iliac arteries. These branches supply the anterolateral aspect of the abdominal wall. Then, each external iliac artery passes underneath the inguinal ligament to become the femoral artery, which is the main artery that supplies the lower limbs.
Next are the internal iliac arteries, which are the main arteries of the pelvis, and also supply parts of the gluteal region, medial thigh, and perineum. The branching pattern of the internal iliac arteries is one of the most variable in the body, so in order to identify each branch we must think about the structures they are nourishing.
Each internal iliac artery runs posteromedially to reach the upper border of the greater sciatic foramen. Then, each internal iliac artery divides into anterior and posterior divisions or trunks. These trunks give smaller branches that are either visceral or parietal. Visceral branches supply organs, like the bladder and the rectum, and parietal branches supply muscles and skin that form the walls of the pelvic cavity.
Let’s zoom in on the branches of the anterior division of the internal iliac artery. There are nine branches coming off the anterior division of the internal iliac artery: the umbilical, superior vesical, inferior vesical, obturator, uterine, middle rectal, internal pudendal, and the inferior gluteal arteries. And in biologically female individuals, there are also vaginal arteries.
To make things a bit easier to remember, these branches are grouped into three categories, each with three branches. The first group includes the branches that supply the urinary organs, which are the umbilical, superior vesical, and inferior vesical arteries.
The next group has three branches that supply the organs of the pelvis, which are the uterine, vaginal, and middle rectal arteries. Finally, three branches supply the walls of the pelvis, and these are the obturator, internal pudendal, and inferior gluteal arteries.
Remember that these branches also supply structures of the genitourinary tracts, so they’ll have variations depending on whether you are born biologically male or female. So let’s start off with the umbilical arteries, which run antero-inferiorly along the lateral wall of the pelvis, and ascend towards the umbilical ring.
Before birth, the umbilical arteries are the main continuation of the internal iliac arteries and pass through the umbilical ring and travel through the umbilical cord to deliver nutrient and oxygen poor blood from the fetus to the placenta.
Here, the blood becomes replenished with nutrients and oxygen, and is sent back to the fetus by the umbilical vein. After birth, the umbilical cord is cut and the umbilical arteries obliterate distally. The obliterated parts of the umbilical arteries persist as fibrous cords called the medial umbilical ligaments, and they’re covered by folds of peritoneum, called the medial umbilical folds.
In an adult, these folds are seen on the inside of the anterior abdominal wall, and they sit lateral to the median umbilical fold which contains the urachus, another fibrous remnant of an embryonic structure called the allantois. Finally, lateral to the medial umbilical folds, there are the lateral umbilical folds, which is peritoneum covering the inferior epigastric artery and vein.
So to quickly summarize, remember the single median umbilical fold sits on the median line of the body. The paired medial umbilical folds are on either side of the median umbilical fold. And finally, the lateral umbilical folds are most lateral!
Ok, now, each umbilical artery gives multiple superior vesical artery branches proximal to the medial umbilical folds in adults. The superior vesical arteries supply the superior aspect of the urinary bladder. In males, the superior vesical arteries may also give a branch to the ductus deferens, or vas deferens, which facilitates the transport of sperm from the scrotum.
There’s also an inferior vesical artery that is only found in males, whereas in females, it’s replaced by the vaginal artery which has inferior vesical branches. In males, the inferior vesical arteries supply the inferior aspect of the urinary bladder, the prostate gland, seminal glands, and pelvic parts of the ureters. Finally, the branch to the ductus deferens may arise from the inferior vesical arteries, instead of arising from the superior vesical arteries.
Next are the obturator arteries, which pass antero-inferiorly on the obturator fascia that covers the obturator foramen. Interestingly, in 20% of the population, an accessory or aberrant obturator artery arises from the inferior epigastric artery.
Before leaving the pelvis, each obturator artery gives off multiple branches. First are muscular branches, which supply the muscles of the pelvis. Then, it gives a nutrient artery that supplies part of the ilium.
Finally, it gives a branch called the pubic branch, which ascends on the internal surface of the pubis. Each pubic branch anastomoses with the pubic branch of the opposite side. Finally, the obturator artery passes through the obturator canal to enter the lower limb and supply the medial compartment of the thigh.
Next are the uterine arteries, which are the female counterpart to the artery of ductus deferens in males. These arteries most often arise from the anterior division of the internal iliac artery, but may arise from the umbilical artery.
Now, the uterine arteries descend on the lateral walls of the pelvis, crossing superior to the ureters on each side, and then turn medially to reach the junction between the cervix and the vagina. You can think about the uterine arteries as a bridge over a river, where the bridge is the uterine artery, and the river is the urine passing through the ureters to the urinary bladder.
At the junction of the cervix and the vagina, each uterine artery divides into two branches: a small descending branch called the vaginal branch -which supplies parts of the vagina and the cervix - and a larger ascending branch, which runs superiorly along the lateral margins of the uterus supplying it.
And now, an important point. Besides the vaginal branch of the uterine artery, in females, there’s also a vaginal artery per se. The vaginal artery gives two branches: the vaginal branch, which gives multiple branches for the anterior and posterior aspects of the vagina, and the inferior vesical branch, which nourishes the inferior aspect and the fundus of the urinary bladder.
The vaginal artery anastomoses with the vaginal branch of the uterine artery, and the inferior vesical branches anastomose with the superior vesical branches of the umbilical artery.
Next is the middle rectal artery, which can have a variable origin from the anterior division of the internal iliac artery, and descends into the pelvis to supply the inferior parts of the rectum, the prostate, and seminal gland in males, as well as parts of the vagina in females. The middle rectal artery anastomoses with the superior and inferior rectal arteries to supply the whole rectum.
There is also the internal pudendal artery, which descends and runs anterior to the piriformis muscle and the sacral plexus. Then, it leaves the pelvis by going through the greater sciatic foramen inferior to the piriformis muscles. Finally, the internal pudendal artery loops around the ischial spine, along with the internal pudendal vein and the pudendal nerve, to enter the ischioanal fossa via the pudendal canal.
Then, it passes through the lesser sciatic foramen to supply structures in the perineum. Anteriorly and anterolaterally, the perineum is bounded by the symphysis pubis and the ischiopubic rami. Posteriorly, the perineum is bounded by the lower part of the sacrum and the coccyx.
Finally, there’s the inferior gluteal artery, which is the largest terminal branch of the anterior division of the internal iliac artery. However, it may also originate from the posterior division in some individuals. Remember when we said there is a lot of variability in this area? Well, we hate to say, we told you so!
The inferior gluteal artery passes posteriorly, usually between the second and the third sacral spinal nerves (S2-S3). Then, it leaves the pelvis next to the internal pudendal artery, inferior to the piriformis muscle.
The name of this artery gives a clue about the structures it supplies: namely, the gluteus maximus, which is the largest muscle in the human body. This artery also supplies muscles of the pelvic diaphragm, quadratus femoris and piriformis muscles. Finally, it supplies the sciatic nerve, which is the largest nerve in the human body.
Okay, so let’s switch gears and talk about branches of the posterior division of the internal iliac artery. These branches can be remembered with the mnemonic PILLS G. P means that this mnemonic is used to remember branches off the posterior division. IL is for the iliolumbar artery, L is for the lateral sacral artery, and SG is for the superior gluteal artery.
Let’s start with the iliolumbar artery. Its course is a bit different from other arteries, meaning it runs in the opposite direction of its origin. Instead of running inferiorly, -like the posterior division- it runs superolaterally, reaching the iliac fossa.
In the fossa, the iliolumbar artery gives two branches, called the iliac and lumbar branches. The iliac branch supplies the ilium and the muscle covering the iliac fossa, called the iliacus, while the lumbar branch supplies the psoas major and quadratus lumborum muscles.
Next are the superior and inferior lateral sacral arteries, which may arise independently from the posterior division, or arise as a common trunk. The lateral sacral arteries both pass medially and descend anterior to the ventral rami of sacral nerves.
These arteries give off the sacral branches, which pass through the anterior sacral foramina to supply the meninges surrounding the roots of sacral nerves. Also, some branches of lateral sacral arteries pass through the posterior sacral foramina to supply a group of back muscles called the erector spinae muscles.
The last branch of the posterior division is the superior gluteal artery, which is the largest branch of the posterior division. This artery exits the pelvis through the greater sciatic foramen, directly above the piriformis muscle.