Certainly, the World does not need another pictorial essay of aortic arch variants. However, what the world does need, and badly, is a practical guide of how to go about catheterizing them. For example, what would you do when a chest X-ray of your acute stroke patient looks like this:
I suppose one answer is to look at this page, if you remember how to find it. Another way is to be prepared beforehand. Certainly, there will need to be lots of room for improvization. Nevertheless, one can generally do ok.
RIGHT SIDED AORTIC ARCH WITH A DIVERTICULUM OF KOMMERELL
That’s the image above. The heart is still on the left, but the arch is on the right.
The most important thing to keep in mind for successful catheterization is the order in which the great vessels come off the aorta. The schematic below shows this arch, with the numbers corresponding to the order in which the vessels originate proximal to distal — first comes the bicarotid trunk of right and left CCA (1), then right subclavian (2), and finally the Kommerell diverticulum / left subclavian (3).
Drawing: Backer CL, et al: Resection of Kommerell’s diverticulum and left subclavian artery: transfer for recurrent symptoms after vascular ring division. Eur J Cardiothorac Surg22:64, 2002 http://www.ncbi.nlm.nih.gov/pubmed/12103375
Thus, the diagnostic catheter will encounter these vessels in reverse order: 3,2,1. Once you know this, you understand that in order to get into the carotids one must pass both subclavians and come over the arch. The position of the catheter to engage the carotids will look something like this:
The standard 5F VERT (135 degree) catheter (orange arrow) is curved over the arch and is positioned in its proximal portion. Yellow arrow is right vert, purple is right subclavian, green is right CCA, pink is left CCA, red is diverticulum of Kommerell (left aortic arch remnant), and black is left subclavian.
The left subclavian is easy — it is the first vessel to be encountered. Notice how the unsupported catheter (orange) kicks back on injection within the arch.
The right subclavian is generally straighforward also — it will be pointing to the right from the upper arch. The carotids are a problem, because the ostium or ostia may point away from the direction of the catheter — akin to the left CCA in a bovine arch, except worse. It is essential that one have an understanding of the anatomy in this case if one were to use the Simmons! Otherwise, things can evolve from frustrating to dangerous rather quickly.
ABERRANT RIGHT SUBCLAVIAN ARTERY
A relatively common variant. The right subclavian is the most distal great vessel. Sometimes the wire will select the right subclavian first, and the operator needs to recognize this and probe for the arch to access the other great vessels. The right vertebral artery will often originate from the common carotid trunk in this variant. In fact, this suggests that embryonically the brachiocephalic strunk and the proximal subclavian artery can be regarded as a single unit, so that in the aberrant subclavian variant the very proximal common carotid trunk is in fact the brachiocephalic equivalent. The segment distal to the vertebral artery is the proper subclavian segment.
Views of the great vessels, in order of their takeoff from the arch, proximal to distal
Frontal and lateral views of the right common carotid trunk, demonstrating origin of the vertebral artery, and its intraforaminal course at C4 level and up
Another example of right vertebral artery origin from right common carotid trunk
Most often, this variant is associated with aberrant origin of the left subclavian artery. It is important to keep this in mind so as to not blindly stick the wire or catheter into the vert on the way up to the ICA. Below is one example of such a vert. Notice that this vertebral artery enters the vertebral foramina at C5 level — the extravertebral portion is green, and intravertebral is red. It is a consistent finding, reflecting embryology of the vertebral artery (a proatlantal spectrum variant, in fact)
Here is another example. Subclavian yellow, deep cervical pink, vert green, CCA red, extra-vertabral vert white, intra-vertebral black:
Lateral view of the same patient. Notice small radiculomedullary contribution to the anterior spinal (purple)
Direct origin vertebral artery — ~ 1% incidence. Usually, direct origin vert is not so difficult to engage with a 5F VER catheter (with notable exceptions). This stereo CTA pair demonstrates direct vert disposition in a patient with cervial vertebral fistula.
Direct origin vert is marked with red arrows. Notice also marked tortuosity of the both vertebral arteries (right vert is shown with yellow arrows). Bone fragment post-processing remnants demonstrate extra-foraminal location of the tortuous loops, which project medially with respect to the intraforaminal segments — and therefore are located within the neural foramina themselves (see vertebral artery page for more images). Premature opacification of the left perivertebral venous plexus (blue arows) and jugular vein reflects presence of an underlying cervical vertebral fistula.