Embryology of the Internal Iliac Artery
In fetal life, the internal iliac artery is a direct continuation of the common iliac artery and is twice the size of the external iliac artery. The internal iliac artery runs superiorly alongside the urinary bladder to the umbilicus to meet its partner from the other side, and the two arteries become the umbilical arteries within the umbilical cord.
The umbilical arteries coil around the umbilical vein and finally branch out within the placenta. At birth, the part of the umbilical arteries within the pelvis persists as the superior vesical arteries in adults, while the rest form the medial umbilical ligament. The medial umbilical ligament (or cord of umbilical artery) is a paired structure found on the deep surface of the anterior abdominal wall, and is covered by the medial umbilical folds (plicae umbilicales mediales).
Arterial Supply to the Pelvis
The abdominal aorta branches into the two large common iliac arteries at the level of the L4 vertebra. The common iliac arteries end at the sacroiliac articulation by bifurcating into the paired external and internal iliac arteries. The arteries entering the pelvis are:
- Paired: internal iliac, ovarian and testicular arteries
- Unpaired: medial sacral, superior rectal.
Internal Iliac Artery
The internal iliac artery begins anterior to the sacroiliac joint, at the common iliac artery bifurcation, and then runs inferiorly to the superior border of the sciatic foramen where it divides into two divisions: the anterior and the posterior division.
The internal iliac artery is the primary supplier of oxygenated blood to the medial compartment of the thigh, the buttocks, urinary system, the walls and the organs within the pelvic cavity. In adults, the internal iliac artery is a 3-4 cm thick vessel, and is smaller than the external iliac artery.
Relations of the internal iliac artery with clinical significance
During its course, the internal iliac artery is
- Anterior to the sacroiliac articulation, the piriformis muscle, internal iliac vein, the lumbosacral trunk.
- Posterior to the ureters in males and females; posterior to the ovaries and fallopian tubes in females.
- Medial to the external iliac vein.
- Lateral to the parietal peritoneum and internal iliac vein tributaries.
- Superior to the obturator nerve.
Classification of the Internal Iliac Artery
The internal iliac artery is of clinical significance to surgeons, obstetricians – gynecologists, orthopedic surgeons, urologists, as well as radiologists. All these medical professionals have to be able to identify the variations and branching pattern of the internal iliac artery to prevent inadvertent injury during surgery. Several classifications have been proposed over the years.
- Based on the terminal course of the artery (Herbert, 1825): branches in the pelvic wall, the pelvic viscera and the extra pelvic branches.
- Based on the terminal course (Power, 1862): internal and external branches.
- Based on the size of the artery (Jastschinski, 1891):
- Large caliber: superior gluteal, inferior gluteal, internal pudendal
- Medium caliber: obturator artery
- Small caliber: iliolumbar, lateral sacral arteries.
- Based on anatomical branching pattern (Carter, 1867; Sharpey et al, 1867; Wilson, 1868): anterior and posterior trunks.
- Adachi classification (1928):
- Type I: the superior gluteal arises independently while the inferior gluteal and the internal pudendal arteries arise from a common trunk and divide either inside or outside the pelvis.
- Type II: the superior gluteal and the internal pudendal arteries arise from a common trunk, while the inferior gluteal arises independently.
- Type III: all three arteries, the superior gluteal, inferior gluteal and the internal pudendal, arise independently.
- Type IV: all three arteries arise from a common trunk.
- Type V: the inferior gluteal arises separately, while the superior gluteal and the internal pudendal arise from a common trunk.
Branches of the Internal Iliac Artery
As aforementioned, the branches of the internal iliac artery are variable. Occasionally, the branches arise from other named branches instead of from the internal iliac artery.
The internal iliac artery has two main divisions: the anterior and the posterior division. In addition, it gives off several visceral and parietal branches. The anterior division gives off eight branches, while the posterior division gives off three branches, as listed below:
- Anterior division
- Superior vesical
- Inferior vesical/vaginal
- Artery to the ductus deferens
- Branches to the prostate
- Vaginal branch
- Internal pudendal
- Middle rectal
- Inferior gluteal
- Posterior division
- Lateral sacral
- Superior gluteal
Testes in males is supplied by the testicular artery (also called the internal spermatic artery), which is a branch of the abdominal aorta. Each testicular artery runs inferiorly, in the retroperitoneum, to the scrotum through the inguinal canal encased within the spermatic cord.
On the right side, the testicular artery lies anterior to the inferior vena cava and posterior to the middle and ileocolic arteries and the terminal ileum. On the left, the testicular artery lies posterior to the sigmoid and left colic arteries and the iliac colon.
In females, the ovarian artery, a direct branch from the abdominal aorta, travels inferiorly through the suspensory ligament of the ovary to enter the mesovarium and then supplies oxygenated blood to the ovary and uterus.
The ovarian arteries are the female counterparts of the testicular arteries in males. Their origin and course is identical to the internal spermatic arteries in the first part, but, at the pelvic brim, the ovarian arteries travel medially through the layers of the ovarian-pelvic ligament and the broad ligament of the uterus to supply the ovary.
The testicular arteries follow a different course as the testes are located in the scrotum. The ovarian arteries are also shorter as compared to the testicular arteries and, during pregnancy, become engorged to provide for the increased requirements of the uterus.
The arterial supply to the rectum is from the following arteries:
- The superior rectal, which is a terminal branch of the inferior mesenteric artery, supplies the proximal part of the rectum.
- The middle rectal branch of the internal iliac artery supplies the middle and inferior parts of the rectum.
- The inferior rectal artery, which is a branch of the internal pudendal artery, which in turn is a branch of the internal iliac artery, supplies the anorectal junction and the anal canal.
Clinical Relevance of the Internal Iliac Artery
- Branching pattern of the internal iliac artery: Knowing the variability of the internal iliac branching pattern is extremely important for endovascular radiologists, surgeons, obstetricians – gynecologists, orthopedic surgeons and urologists. The organization of the branching pattern can be studied with pelvic embolization. This can avoid unnecessary embolization, embolectomy or ligation, and iatrogenic injury to the internal iliac artery can be prevented if the branching pattern is known.
- Internal iliac ligation: is required for hemostasis in cases of severe pelvic hemorrhage e.g. severe postpartum hemorrhage or open book pelvic fractures. As there are extensive anastomoses, collateral circulation develops soon after ligation.
- Aneurysms of the internal iliac artery: These are rare but are not easy to diagnose. The aneurysm causes obstructive symptoms by compressing the ureters or rectum leading to constipation or difficulty passing urine. Rupture of the aneurysm can be fatal due to severe hemorrhagic shock. Treatment is endovascular stenting in asymptomatic aneurysms, or surgical ligation in symptomatic aneurysms.