Tutorial 28: how to remember the branches of the internal iliac artery

September 23, 2014

 

Internal Iliac Arteries - MJW 2011

Here’s a thing I put together to help my students understand the many branches of the internal iliac artery in humans. In the image above, we’re looking in superomedial view into the right half of the sacrum and pelvis. Bones are white, ligaments blue, the piriformis muscle sort of meat-colored, and arteries red (for a tour of the pelvis identifying all of this stuff, see my pelvic foramina slideshow). At the top is a big inverted Y-shape: the common iliac arteries branching from the abdominal aorta, which continues on, much reduced, as the median sacral artery. The right common iliac artery is shown bifurcating into the external iliac artery, which continues on out of the pelvis to become the femoral artery, and the internal iliac artery, source of much fear and doubt.

The first thing to understand is that any particular branching pattern of the internal iliac arteries, whether in an anatomical altas, a lecture, revealed in a dream, or even in your own body, will probably have no bearing whatsoever on the branching pattern in the next person you encounter, alive or dead. Furthermore, the variation between right and left in a single person can be as great as that among different people. The branches to pelvic viscera are particularly fiendish; they sometimes travel far into the pelvis as a common trunk and then “starburst” near their target organs, making identification almost impossible. Do not waste your time trying to memorize any particular branching sequence. Instead, concentrate on matching the arteries to their targets; you will discover the identities of the branches by seeing where they are going, not the order in which they branch.

There are typically 10 named branches of the internal iliac artery. Authorities quibble on the details, as we’ll see in a moment, but if you know these 10, you’ll be fine for almost any conceivable purpose. A simple scheme of my own devising for remembering them is 2-4-4:

TWO to the back body wall:

  1. iliolumbar A—may arise from external or common iliac AA; sometimes double
  2. lateral sacral A—note branches to anterior sacral foramina and anastomoses with median sacral A

FOUR leaving the pelvis entirely:

  1. obturator A—often arises from the external iliac A instead, exits pelvis through obturator canal
  2. superior gluteal A—exits pelvis through suprapiriform foramen
  3. inferior gluteal A—exits pelvis through infrapiriform foramen, with internal pudendal A
  4. internal pudendal A—exits pelvis through infrapiriform foramen, with inferior gluteal A

FOUR to pelvic viscera:

  1. superior vesical A—usually the dominant artery of the anterior trunk, this is the patent part of the obliterated umbilical artery, which survives as the medial umbilical ligament
  2. inferior vesical A (males) / vaginal A (females)—may branch off uterine A (females) or superior vesical A (both)
  3. uterine A (females)—major artery to uterus, approaches laterally within the broad ligament
    A to ductus deferens (males)—extremely small and difficult to trace
  4. middle rectal A—usually the most inferior branch of the entire internal iliac tree (at least inside the pelvis)

My way to explain those last four is to extend my index finger and say, “Everybody has to pee, so up front we have superior vesical.” Then extend my pinky and say, “And everyone has to poop, so in back we have middle rectal.” Then extend digits three and four and explain that the identity of the middle two arteries varies between the sexes (but that the inferior vesical artery of males and the vaginal artery of females are basically the same vessel).

There is a LOT of variation in the descriptions of the internal iliac artery branches among different sources — almost as much variation as there is in the arteries themselves.

  • ​The Thieme Atlas of Anatomy, 2nd Ed (Gilroy et al. 2009), Table 19.1 on p. 254, includes the inferior vesical artery for both sexes. The artery to ductus deferens is listed as a branch of the superior vesical artery, and the uterine and vaginal arteries are listed separately, bringing the total for females to 11.
  • Clinically Oriented Anatomy, 7th Ed (Moore et al. 2013), Table 3.4 and pp. 350-355, lists the 10 branches I went through above. Moore et al. explicitly say that the vaginal artery is the female homolog of the inferior vesical artery (p. 351).
  • Gray’s Anatomy, 40th Ed (Standring et al. 2008), pp. 1085-1089, splits the difference. The artery to ductus deferens is not listed; instead, the ductus deferens is said to be supplied by the inferior vesical A (in contrast to Thieme, which has it is supplied by the superior vesical A). Both the vaginal and inferior vesical arteries are listed, but the vaginal artery is said to frequently replace the inferior vesical artery.

The upshot is that pretty much all of these sources agree on how the blood is getting distributed, there are just some minor differences over what we call certain vessels. I have never personally seen a dissection detailed enough to allow an interior vesical artery to be recognized separately from the vaginal artery — the vagina lies so close behind the bladder that whatever you call the artery that runs lateral to them, it could easily be supplying both structures, and probably does. As far as I’m concerned, the inferior vesical artery in males and the vaginal artery in females are the same artery, in that they both supply the inferior portion of the bladder. I think it’s just a historical hiccup that we call them by different names, possibly perpetrated by smelly, lonely, vagina-obsessed men of centuries past.

A final note, added in revision: some sources refer to two trunks or divisions of the internal iliac artery: a posterior trunk that gives rise to the iliolumbar, lateral sacral, and superior gluteal arteries, and an anterior trunk that gives rise to everything else. If that’s what your professor tells you, smile and nod and keep your heretical thoughts to yourself. Personally, I regard the notion of trunks of the internal iliac artery alongside phlogiston, luminiferous aether, and snorkeling sauropods, as romantic nonsense at best. I have seen an obturator artery arise from a superior gluteal artery and a pudendal artery arise from a superior vesical artery. In a world where variants like those can and do turn up frequently, the stability and reason implied by regular trunks is illusory.

References

  • Gilroy, A., MacPherson, B., and Ross, L. (eds.) 2009. Atlas of Anatomy, 2nd ed. Thieme, Stuttgart.
  • Moore, K.L., Dalley, A.F., and Agur, A.M. 2013. Clincially Oriented Anatomy, 7th ed. Lippincott Williams & Wilkins, Philadelphia.
  • Standring, S. 2008. Gray’s Anatomy, 40 ed. Churchill Livingstone, London.
Advertisements

8 Responses to “Tutorial 28: how to remember the branches of the internal iliac artery”

  1. Mike Harris Says:

    I am trying to determine what the interior wall of the iliac artery looks like and what is it composed of. Is it influenced by age , diet and or nicoteen use?

  2. Matt Wedel Says:

    As far as I know, the interior walls of the iliac arteries are made of the same stuff as every other artery: a lining of endothelium, an internal elastic lamina under that, and belts of smooth muscle under that (and eventually an external elastic lamina, and then an outermost tunic of connective tissue). I also assume that it’s influenced by the same factors as other arteries in terms of health and disease. I have certainly seen some crunchy arteries in cadavers, where plaque had built up to the point that the arteries were rigid and even brittle. But I haven’t seen that in the iliac arteries any more or less than in any of the other large arteries.

    If anyone knows differently, please let me know!


  3. […] Tutorial 28: how to remember the branches of the … – Here’s a thing I put together to help my students understand the many branches of the internal iliac artery in humans. In the image above, we’re looking in … […]


  4. Reblogged this on jari m and commented:
    “A final note, added in revision: some sources refer to two trunks or divisions of the internal iliac artery: a posterior trunk that gives rise to the iliolumbar, lateral sacral, and superior gluteal arteries, and an anterior trunk that gives rise to everything else. If that’s what your professor tells you, smile and nod and keep your heretical thoughts to yourself. Personally, I regard the notion of trunks of the internal iliac artery alongside phlogiston, luminiferous aether, and snorkeling sauropods, as romantic nonsense at best.” HAHA! True!

  5. Mike Taylor Says:

    How can such a fundamental fact of anatomy be controversial? Surely it can be easily established by dissection?


  6. Anatomy books describe the most common pattern. The division into an anterior trunk and a posterior trunk of the internal iliac artery, as in Moore’s (p. 350, 7th ed.), is a highly variable pattern (which the source in-text already clarifies). In my experience in dissection class, there have been more cadavers displaying the exceptions than the rule (e.g. the three branches of the posterior trunk shoot off directly from the internal iliac artery, etc.), so I found the quoted text both relatable and amusing.

    Thanks for dropping by!

  7. Bleank Says:

    Interesting delivery. Just what i needed, thanks.
    Little observation: you said the idea of an anterior and posterior division was essentially nonsensical in a very colorful manner yet when you described the superior vesical artery you said it is “usually the dominant artery of the anterior trunk”

  8. Matt Wedel Says:

    Fair point. I should have said that (1) there is always an arterial trunk running forward, culminating in the medial umbilical ligament and superior vesical artery – we might call this ‘the anterior trunk’ no matter what else is present; (2) the posterior-most branches may or may not arise from a common trunk that could be called ‘the posterior trunk’; and (3) the concept of a regular division into those two trunks that has any predictive value for branching pattern is IME a deeply misleading fiction.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: