Internal Iliac Artery
Both the left and right common iliac arteries, branches of the abdominal aorta, bifurcate at the level of the sacroiliac joint to form external and internal iliac arteries. The internal iliac artery supplies the peritoneum, gluteal region and the walls and viscera of the pelvis. This article will discuss the anatomical course, anatomical relations and branches of the internal iliac artery as well its differences in the fetus. This will be followed by any related clinical pathology.
The internal iliac artery begins at the common iliac bifurcation, which is anterior to the sacroiliac joint, at the level of the intervertebral disc between the L5 and S1 vertebrae. The artery is 4 cm long and traverses inferoposteriorly to the superior margin of the greater sciatic foramen. Here it bifurcates into two main trunks, referred to as the:
- Anterior trunk, which continues on the same trajectory as the main artery, towards the ischial spine .
- Posterior trunk, which passes towards the greater sciatic foramen.
Relationships of the internal iliac artery to other structures in the pelvic region can be important in clinical practice. The artery is located posterior to the ovaries and the uterine tubes in females, as well as the ureter in both sexes. The internal iliac artery is anterior to the sacroiliac joint, internal iliac vein and lumbosacral trunk. The parietal peritoneum and tributaries of the internal iliac vein are located medial to the artery, whilst the external iliac vein and obturator nerve are found on the lateral side of the artery.
In the fetus, the internal iliac arteries are a direct continuation of the common iliac arteries and travel anteriorly along the anterior abdominal wall to the umbilicus. Once entering the umbilicus, the arteries are now referred to as the umbilical arteries. These arteries conduct blood to the placenta in order to be replenished with oxygen and nutrients. At birth, the pelvic aspect of the internal iliac artery remains patent or functional, whilst the umbilical arteries become occluded and form fibrous medial umbilical ligaments.
The anterior trunk of the internal iliac artery gives off eight branches:
- Superior vesical artery: it is a large branch, which runs medial to the periosteum of the posterior aspect of the pubis. It supplies the bladder and the distal ureter in both sexes, as well as the proximal aspect of the vas deferens and the seminal vesicles in males.
- Inferior vesical artery (in males): it is sometimes present and arises with the middle rectal artery. It supplies the vas deferens, the bladder, seminal vesicles and the prostate gland.
- Middle rectal artery: it is a small artery, which sometimes arises close to the inferior vesical artery in males.
- Vaginal artery (in females): it usually replaces the inferior vesical artery in females and arises near the uterine artery.
- Obturator artery: it runs in an anteromedial direction from the anterior trunk on the lateral pelvic wall to the obturator foramen.
- Uterine artery (in females): it is a large artery, which runs inferomedially from the lateral pelvic wall to the broad ligament of the uterus. It is only present in females and arises below the obturator artery.
- Internal pudendal artery: it arises just inferior to the origin of the obturator artery and descends laterally towards the greater sciatic foramen. Within the pelvis, it crosses the piriformis muscle, the inferior gluteal artery and the sacral plexus. In the gluteal region, it curves around the ischial spine before entering the perineum through the lesser sciatic foramen. In the pelvic and gluteal regions, it gives off muscular branches which supply surrounding muscles and nerves.
- Inferior gluteal artery: it is the largest terminal branch of the anterior trunk, supplying both the buttock and the thigh. It travels inferoposteriorly before it passes between the anterior rami of S1 and S2, or S2 and S3, and then travels between the piriformis and ischiococcygeus muscles. It supplies branches to these muscles as well as to the iliococcygeus muscle. Like the internal pudendal artery, it enters the gluteal region through the greater sciatic foramen. It then descends between the greater trochanter and ischial tuberosity to supply the skin of the thigh.
The posterior trunk of the internal iliac artery gives off three branches:
- Iliolumbar artery: it runs anterolaterally towards the medial border of the psoas major muscle, where it divides into the lumbar and iliac branches. The lumbar branch supplies the psoas major and quadratus lumborum muscles, whilst the iliac branch supplies the iliacus muscle. Both of these branches anastomose with other arteries. The lumbar branch anastomoses with the fourth lumbar artery and the iliac branch anastomoses with iliac branches of the obturator artery.
- Lateral sacral artery or arteries: there are usually two lateral sacral arteries which branch off from the posterior trunk. If there is a single artery, it usually quickly divides into superior and inferior branches. The superior artery is larger and supplies the sacral vertebrae before exiting the sacrum through the dorsal foramen. It supplies the skin and muscles dorsal to the sacrum. The inferior artery crosses the piriformis and anterior spinal rami of the sacrum obliquely before descending laterally towards the sympathethic trunk. Here, it anastomoses with the superior counterpart and with the medial sacral artery.
- Superior gluteal artery: it is the largest branch of the internal iliac artery and essentially a continuation of the posterior trunk. It exits the pelvis by the greater sciatic foramen and divides into superficial and deep branches. Within the pelvic region, it supplies the piriformis and obturator internus muscles. The superficial branch supplies the gluteus maximus muscle and the skin over the sacrum. The deep branch supplies the gluteus medius and gluteus minimus muscles.
The superior gluteal artery, inferior gluteal artery and internal pudendal artery sometimes arise directly from the internal iliac artery.
Ligation of the internal iliac artery is an effective method in controlling pelvic haemorrhage. Due to numerous anastomoses, ligation will not prevent blood flow, but it will reduce blood pressure resulting in haemostasis.
Internal iliac artery aneurysms are a rare cause of intra-abdominal aneurysm and are difficult to diagnose. The aneurysm can compress on surrounding structures resulting in symptoms such as constipation and difficulty urinating. These aneurysms can also rupture into surrounding structures, such as the bladder and rectum, and the subsequent haemorrhage can lead to death. Therefore, early intervention is essential and involves surgery if symptomatic or interventional radiological techniques if asymptomatic.