Anterior Choroidal Artery

Anterior Choroidal Artery
 
Embryology (abbreviated)
For a fuller but still limited version of A Chor embryology see dedicated neuroembryology section.  For a masterful description, consult Lasjaunias and Berenstein’s work “Surgical Neuroembryology”, either 1st edition volume 3 or 2nd edition volume 1.
 
The anterior choroidal artery is almost as old as hills.  Phylogenetically, its homologs (recorded under various confusing names in archaic dissections of “lower” species) are already well developed in fishes and continue into amphibians and mammals.  In these species, it supplies the ever enlarging posterior hemispheres, in effect vascularising the territory of the posterior cerebral artery in the human.  This is because the posterior circulation does not begin to supply “supratentorial brain” until late in evolution when growing volume of the brain places increasing demand on additional vascular supply sources.  As the posterior cerebral artery is annexed by the vertebrobasilar system in relatively advanced mamals, the role of the anterior choroidal artery in hemispheric suppy diminishes.  Embryologically, in the human, the anterior choroidal is quite prominent at the “choroidal” stage of development (roughly 5 weeks or so) when the vertebrobasular system has not yet come to be and the carotid artery supplies almost the entire brain, including upper brainstem.  As the hemispheres grow, the volume of brain supplied by the anterior choroidal diminishes in favor of the posterior cerebral artery.  This expains why in some individuals the anterior choroidal artery can be quite prominent, in which cases it captures cortical territory of the PCA, usually involving temporal lobe regons.  This has led to numerous erroneous reports of “duplicated PCA” based on apperanec of two large vessels coming off the terminal ICA in the lateral angiographic projection.  However, even in its “normal” relatively small state, the anterior choroidal enjoys importance far out of proportion to its size.
 
Cross-sectional Imaging
The A. Chor. ostium is usually seen on 1.5T MRA, but the rest of the vessel is seldom visualized unless significant pathology exists to enlarge it.  In contrast, both cisternal and choroidal portions of normal-size anterior choroidal arteries are nearly always on 3T MRA.  All of these studies have to be of high quality.
3-Tesla MRA of normal anterior choroidal arteries (red)
1) Ostium of the A Choroidal artery lateral and distal to the PCOM (blue)
2) Cisteral portion of the A Chor
3) Lateral course in the perimesencephalic cistern at level of PCOM / PCA confluence.  Even medial choroidal artery (orange) can be seen on a 3-T
4) Entrance into the choroidal fissure
5) In the choroidal fissure, in plane of scan
6) Branching to feed choroid plexus
 
In contrast to 3T, this 1.5T MRA only shows an ostium of what is in fact a very prominent anterior choroidal artery (red), as seen on angio of the same patient.  Poor visualization is to some extent related to direction of Anterior Chorodial flow, which can be close to plane of MRA slab.
However, we do not stop there. Here’s what 7T can produce.  Pretty stunning.  I’d say there is diminishing marginal returns going from 3T to 7T as compared to 1.5T to 3T — nevertheless as of 2014, 7T is by far the top noninvasive imaging modality for the arteries.  Now lets see what happens 2024…  The Anterior Choroidal (light blue) can be traced perfectly well towards the choroid plexus (dark red).  Gadolinium contrast was administered prior to the scan, which explains some venous structures in there (not labeled).  Notice amazing views of the lateral lenticulostriates (black), thalamogeniculate (dark blue double-sided arrow), as well as posterior choroidal (white), poserior inferior temporal (green) and middle inferior temporal (pink).  The tentorium cerebelli enhancement (yellow) is also very helpful, as best seen in stereo
http://neuroangio.org/wp-content/uploads/ACh/Ach_7T_MRA.png
The same image in stereo.   Notice the graceful fall of the tentorium cerebelli, separating branches of the PCA and the SCA.  Can you see the junction of the medial septal and thalamostriate veins?
http://neuroangio.org/wp-content/uploads/ACh/Ach_7T_MRA_stereo.png
Anterior Choroidal Artery Anatomy and Landmarks
The course of anterior choroidal artery cisternal segment in the paramesencephalic cistern (around the cerebral peduncles) is superimposed angiographically upon the middle segment of the basal vein of Rosenthal. This can be demonstred on a single image by selecting the arterial phase of the injection to be the “mask” of a later venous phase (not all angio units allow for this maneuver, but similar images may be generated by post-processing superimposition/blending.) 
In the stereo projections above, where “mask” arteries appear white, a prominent Ant. Chor. artery is superimposed upon the basal vein.  The patient suffers from NFII with multiple meningiomas. Notice many tiny branches (red arrows) coursing superiorly from the Anterior Choroidal artery (best seen in the “normal” image below marked with red arrows).  No tentorial leaf meningiomas were visualized on cross-sectional imaging.
 
 
Anterior Choroidal perforatos 2
Another illustration of anterior choroidal perforators (purple) coming off the main trunk (red) prior to the plexal point (light blue).  A perforator distal to the plexal point may be present also (pink).  The PCOM is orange (with a large thalamic branch of its own). MHT (dark blue) and ILT (green) branches are also visible.
 
 
 
Typical appearance of an anterior choroidal artery in stereo.
Typical appareance of the anterior choroidal artery (red).  The red arrow marks the plexal point where the artery enters the choroidal fissure.  A small artery distal to the anterior choroidal is present also (orange)  These arteries ascend thru the perforator substance and may supply areas of hypothalamus or optic tract – these are the arteries which hypertrophy in the moya-moya condition.  An MHT branch is also present (blue)
 
Anterior Choroidal Projection — RAO projection (about 60 degrees RAO) of the RIGHT Anterior choroidal artery.  Angling the lateral into the anterior oblique position can help show the vessel to better advantage.
Red=A. Chor; Purple=plexal point; Yellow=choroidal segment
 
Anterior Choroidal-PCOM confusion
One of the more embarassing and potentially hemiparetic misidentifications is to mistake the anterior choroidal for a PCOM.  This is especially critical in surgical cases, where a PCOM aneurysm may be treated by sacrifice of the PCOM (unless it turns out to be the anterior choroidal).
The anterior choroidal is labeled in red, whereas a small PCOM, arising more proximally, is marked with orange arrows.  On the AP, you can see the hemispheric portion of the A Chor in red, and the choroidal portion in purple.
 
 
Prominent Anterior Choroidal Artery capturing PCA cortical territory.
Red=PCOM/PCA; Yellow=Anterior Choroidal Artery
 
 
Absent MCA — anterior choroidal and Heubner visualization is aided in this patient by absence of the MCA secondary to remote hemispherectomy for intractable epilepsy.  A duplicated anterior choroidal artery is labeled in orange, and its course is well seen in distinction to the PCA (purple).  This anterior choroidal also supplies portions of the posterior temporal and occipital lobes.  A Heubner is also well seen (red) with its parenchymal blush in the region of the basal ganglia (red, on lateral)
 
 
 Anterior Choroidal origin proximal to PCOM
According to theory, anterior choroidal artery can never be proximal to the PCOM — the latter being the caudal ramus of the internal carotid artery (see neuroembryology).  Although a lot of these “proximal” anterior choroidal cases are “fakeouts” of visual perception, on occasion the A. Chor. just seems to come off proximal to the posterior communicating artery, as below.  I have no explanation for this — a fakeout again, maybe, or some kind of superior hypophyseal artery which captured the choroidal territory.  Don’t know.  If you do, please let me know.
Proximal Anterior Choroidal=red; Choroidal segment of Ant. Chor = white; Parenchymal Ant. Chor. branches = yellow; PCOM=orange
 
 
Large Anterior Choroidal mimiking a duplicated PCOM
Stereo injections of the left common carotid artery in an NFII patient with a large frontal falx meningioma.  Notice mass effect on the anterior cerebral artery (MRI below).  The anterior choroidal artery (blue) is prominent, an anatomical variant whereby the vessel retains much of its embryonic cortical territory.  Notice how its origin is inseparable on these projections from the PCOM (green) leading to erroneous descriptions of “duplicated PCOM” in older literature.  In fact, a duplicated PCOM is extremely rare.  The anterior frontal meningeal branch (red) of the ophthalmic artery can be seen in stereo to course laterally along the convexity and not in the midline, where without stereo it may be mistaken for a posterior ethmoidal artery of the falx.  The falxine artery (purple) participates in supply of the meningiomas, as expected.  Notice prominent contribution from a falxine branch (orange) of the anterior cerebral artery.  An enlarged posterior clival branch of the MHT is labeled in purple.
 
 
Anterior Choroidal AVM supply
Vascular malformations involving the lateral ventricle are often supplied by the Anterior Choroidal Artery, demonstrating the anatomy of the vessel and adjacent structures.
 Stereo projections of a large hemispheric AVM extending to the ventricular trigone, with minor anterior choroidal contribution.  The plexal point is labeled in red.  The PCOM is shown in orange.
 
AVM Anterior Choroidal II
AP and Lateral views (Stereo pair on top) of a temporal lobe avm with deep anterior choroidal supply component.
 
Anterior Choroidal – Posterior Lateral Choroidal anastomosis — the anterior choroidal beyond the plexal point supplies the plexus of the temporal horn, where it is in balance with the posterolateral choroidal going to the atrium region.  This is elegantly shown in the following case of left choroidal plexus AVM, supplied by both vessels with beautiful illustration of draining veins.
Red=anterior choroidal; yellow = posterolateral choroidal; pink=choroidal vein; light blue=inernal cerebral vein; brown=basal vein to sylvian veins; dark blue = atrial vein; white = superior petrosal sinus; green = midbasilar agenesis