External Iliac Artery
The external iliac artery is the larger terminal branch of the common iliac artery. Both the left and right common iliac arteries bifurcate into the external and internal iliac arteries at the level of the sacroiliac joints on either side. The external iliac artery is the main blood supply to the lower limb as it continues down into the thigh as the femoral artery at the level of the inguinal ligament.
After the external iliac artery has branched from the common iliac artery, it travels down and runs laterally along the medial border of the psoas major muscle. It then runs between the pubic symphysis and the anterior superior iliac spine before passing posteriorly to the inguinal ligament to enter the thigh.
Before the external iliac artery passes under the inguinal ligament, it gives off two major branches which play an important role in the blood supply of the inferior portion of the anterolateral abdominal wall. The two branches are the inferior epigastric artery and the deep circumflex iliac artery. The external iliac artery also has very small branches that help supply the psoas major muscle and the nearby lymph nodes.
Inferior Epigastric Artery
The inferior epigastric artery branches from the external iliac artery just posterior to the inguinal ligament. It then turns forwards in the anterior extraperitoneal tissue before it runs obliquely along the medial margin of the deep inguinal ring.
Here, it continues to ascend superiorly in the transversalis fascia before entering the rectus sheath, lying deep to the rectus abdominis muscle. The terminal branches of the inferior epigastric artery then anastomose with the superior epigastric artery, a blood vessel that is a continuation of the internal thoracic artery.
Deep Circumflex Iliac Artery
The deep circumflex iliac artery is a lateral branch of the external iliac artery which bifurcates almost opposite to the origin of the inferior epigastric artery. It runs posterior to the inguinal ligament in the sheath formed by the iliac and transversalis fasciae, running laterally to the anterior superior iliac spine of the iliac bone. Here it anastomoses with the ascending branch of the lateral circumflex femoral artery.
The deep circumflex iliac artery then continues medially along the internal lip of the iliac crest where halfway along the iliac crest it pierces through the transversus abdominis muscle. It continues to run between the transversus abdominis muscle and internal oblique muscle to anastomose with the superior gluteal artery and iliolumbar artery, branches of the internal iliac artery.
Finally, the deep circumflex iliac artery gives off a branch at the anterior superior iliac spine, which ascends between the internal oblique muscle and transversus abdominis muscle, supplying both muscles. This branch also anastomoses with the lumbar artery and inferior epigastric artery.