Thursday, November 1, 2012

The Two Branches of the External Iliac Artery

Unlike the internal iliac artery, with its multiple branches to supply the muscles and organs of the pelvis, the external iliac artery is more or less a straight shot through the pelvis to supply the lower extremity.

More or less... there are actually two branches off the external iliac right near the inguinal ring -- one more recognized, and the other... less so.

First... before enumerating the branches... a quick review. What actually demarcates the external iliac artery?  Well... the origin is obvious. It begins at the branch point of the common iliac arteries into the internal and external arteries. But where's the end point?  As soon as the external iliac passes beneath the inguinal ligament, through the femoral canal, it becomes the femoral artery... But in the angiography suite, the inguinal ligament is not likely to be visible during a DSA run, so the branches near the inguinal ring act as a surrogate marker for the transition.

So... these two branches:

1. The inferior epigastric artery 
2. The deep iliac circumflex artery

An internal view of the distal external iliac artery as it leaves the pelvis.  The inferior epigastric artery (IEA) and deep iliac circumflex artery (DICA) branch off right before the external iliac artery enters the femoral canal (and becomes the femoral artery). The red oval highlights the small anastomosis between a branch of the IEA and a branch of the obturator artery, which can become an important collateral pathway in internal or external iliac occlusion.

1. The inferior epigastric artery

This is the more well-known branch of the external iliac artery. It originates medially from the external iliac artery (right), and then extends superiorly and medially, eventually reaching the region of the umbilicus, where it anastomoses with the superior epigastric artery -- an end branch of the internal thoracic artery.  This collateral pathway can become useful in aorto-iliac stenosis in order to provide arterial supply to the pelvis and lower extremities (say, for instance, in mid-aortic syndrome). The inferior epigastric also anastomoses with lower intercostal (a potential pathway in aorto-iliac stenosis) and the obturator arteries (a potential pathway in internal or external iliac stenosis, pic above).

Modified from ref 3

2. The deep iliac circumflex artery

The second branch off the external iliac artery is not quite as well known as the first.  It arises on the opposite side to the inferior epigastric artery and travels in the other direction (laterally) toward the anterior superior iliac spine (ASIS).  Here it anastomoses with the lateral femoral circumflex artery. At that point it turns ventrally and moves between the transversalis fascia and the internal oblique muscles, acting as their arterial supply.

Some texts claim that the superficial iliac circumflex artery is another branch of the external iliac, and some that it's a first branch of the femoral artery. For our purposes, we'll assume that the superficial iliac circumflex is a branch of the femoral artery.

Modified from ref 3

The deep iliac circumflex artery (DICA) can act as a collateral to the internal iliac artery or lumbar arteries, which can prove useful in common iliac artery and internal iliac artery stenosis

(internal iliac artery --> iliac circumflex artery --> ipsilateral common femoral artery) 
(lumbar arteries --> iliac cirumflex artery --> ipsilateral common femoral artery)

The other DICA claim to medical fame is as part of a bone flap for reconstructive surgery.

1. "Vascular and Interventional Radiology: The Requisites" Kaufman and Lee. 1st ed. (2004)
2. "Diagnostic Angiography" Kadir S. (1986)
3. Katz MD, Sugay SB, Walker DK, et al. "Beyond Hemostasis: Spectrum of Gynecologic and Obstetric Indications for Transcatheter Embolization" October 2012 RadioGraphics, 32, 1713-1731.
4. Taylor GI, Townsend P, Corlett R. Superiority of the deep circumflex iliac vessels as the supply for free groin flaps. Experimental work. Plast Reconstr Surg 64:595, 1979.