Anterior Cerebral Artery |

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24/07/13 8:54 AMAnterior Cerebral Artery | neuroangio.org

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azygous configuration, the same patterns are seen in thehuman, whose classic ACOM is but one of many possiblearrangements. Some variations of the ACA relate to its earlysupply to the orbit via the ventral ophthalmic artery (see examplbelow) for example, the infraoptic course of the ACA is

persistence of the ventral ophthalmic in setting of true A1hypoplasia.It used to be, that the most common search string leading to this website hitwas the Azygous ACA or some variant of anterior cerebral artery. I am notsure why that was, since there is very little on this site on the subject, and Imust say (since I have nothing to sell you) that the subject is not all that excitinfor me. I cant help saying at the outset that the debate on ACA nomenclatureis very silly, to put it mildly. Its really quite simple: there are usually two antericerebral arteries, from A1 to A2 to A3 segments. Sometimes, however, there ionly one A2 segment, with no ACOM. Call it what you like; I prefer to say thatthe A2 segment is unpaired to the level of! and leave it at that. Call itAzygous if you like (the Lasjaunias and Berenstein definition of an AzygousACA is one that is unpared for its entire length from A1 confluence to thevery end, supplying both hemispheres with individual branches arising from acommon trunk), but it will invariably confuse some people who have a differentnotion of what Azygous ACA is. The same goes for the triplicated ACA there is really no such thing. It only looks triplicated the third branch is eithea frontopolar or an early division into pericalossal and calossomarginal

branches immediately near the ACOM, or a Heubner with hypoplasic A1, etc.These types of nomenclature are bound to generate more problems than theywere well-meaningly meant to solve. Enough of this however to thepictures!Duplicated A1 segment this is not an uncommon incidental finding. It hasvery low increased association with presence of berry aneurysms. On very raroccasion, the optic nerve can go through the fenestration, which implies a verydifferent embryologic pattern from the more common supraoptic fenestration.

The fenestration must obviously be kept in mind if surgical dissection iscontemplated.
http://neuroangio.org/anatomy-and-variants/ophthalmic-artery/


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Another patient with a fenestrated A1, stereo pair from CT angiogram


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Unpaired (Azygous) Anterior Cerebral ArteryA single ACA A2 segment distal to the A1 confluence that neverbifurcatesagain is sometimes called an Azygous ACA, but I think it adds more clarity andsimplicity to call it unpaired to the level of whatever (pericalossal, calossumgenu, etc). There is no ACOM, by definition. The incidence is about ~0.1-1%,depending on the author. Embryologically, its significance is unclear.Phylogenetically, it is the normal disposition in some monkeys and other

mammals. There is a resemblance to the vertebrobasilar arrangement, but itmay just be a resemblance only. You may think of it as an ACOM gone berserbut thats probably wrong also. This disposition carries a strong associationwith aneurysm formation at the terminal end of the unpaired segment, or atthe calossomarginal takeoff region, as illustrated below.


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Images of the aneurysm courtesy of Dr. J.A. Bello and Dr. A. Brook, MontefiorMedical Center, The Bronx, NYConfusion can arise when this unpaired A2 segment is associated with earlytakeoff of the frontopolar branch of the ACA or a hypertrophied Heubner. Thisbranch originates from the A1 segment proximal to A1 fusion into the unpairedA2 segment. The resulting apperance makes it seem as though there is anACOM in fact it is NOT an ACOM but A1 segment distal to the frontopolar

origin but proximal to the contralateral A1 fusion. Recognition of the correctanatomy is very important for surgical planning

Unpaired ACA angiogram and hydrocephalus

Unpaired configuration on the angiogram (red) with bifurcation above the gen(orange). Because a bifurcation is present, the artery cannot be called

Azygous according to Lasjaunias and Berenstein. A small A1 fenestration isalso present (blue). Notice uplifting of the distal pericalossal ACA portion,reflectin h droce halus ellow . The atient suffered from ru ture of a


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thalamic AVM (see posterior choroidal artery)Triplicated ACA Another potential source of costly error is establishedwhen a classical normal appearance of the bilateral A1 and A2 segments isassociated with early takeoff of the the frontopolar branch from the AnteriorCommunicating Artery. The resulting apperance (see below) can be

erroneously interpreted as three A2 segments with 2 Anterior Communicatingarteries. Indeed, there are three vessels arising at the ACOM, but one of themis a frontopolar branch, not an A2. Should an aneurysm arise in this region it icritical to understand this anatomy; otherwise the surgeon, coming upon whatappears to be the contralateral A2 without realising that the true A2 is yetdeeper into the surgical field, may think that the ACOM has been fully exploredIn fact, if the aneurysm arises from the ACOM segment distal to the frontopolabranch, the surgeon will not see it and may back off before reaching the trueA2.

MRA MIP images demonstrating the so-called ACA triplication which is in faca normal disposition with two A2 segments (red) and a smaller frontopolarbranch (green) arising from the ACOM (purple and orange). This can beerroneously interpreted as having two ACOMS when there is truly one. Alsopresent is an inferior branch (blue) going toward the region of the optic chiasm.ACOM origin of frontopolar artery
http://neuroangio.org/anatomy-and-variants/posterior-choroidal-arteries/


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Stereo view of frontopolar artery (yellow) origin from ACOM (red)Triplicated ACA angiographic pitfalls. Angiography of the ACOM regioncan be challenging, for many reasons. This is one of them. A cursory view ofthe left and right CCA injections below (top row) may lead one to believe that anormal disposition of two A2 segments exists with a robust anteriorcommunicating artery. A stronger right CCA injection however shows that infact 3 vessels emerge from the ACOM region, not two! Since all three vessels

are difficult to opacify from a unilateral injection, one may arrive at an erroneouconclusion as to the ACOM region anatomy. Right CCA injection on the bottoleft and MRA on bottom right of the same patient, in fact, show an earlybifurcation of the right ACA into calossomarginal (purple) and pericalossal (redbranches. on the left, a single A2 (yellow) is present, thereby giving a falseapperance of triplication. The true ACOM is shown in dark blue, whereas thefalse ACOM (a projectional illusion since the right calossomarginal arises frothe ACOM region) is marked in light blue. The left A1 reflux is marked in pink.


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The same patient in lateral with early calossomarginal takeoff (purple) and

pericalossal in red. The same MRA image as above.Asymmetric A1 there is often asymmetry, with dominant A1 segment onone side and a hypoplastic one on the other side. Usually this leads toasymmetry in the size of the carotid artery as well, which sometimes generateconfusion as regads potential dissection or long segment stenosis.


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Notice that the right ICA (purple) is larger than the left (yellow) since the left sidalso supplies both ACA territories thru a dominant left A1 (red).

Infraoptic course of the ACA


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aspects which also concern the ophthalmic artery. In early embryonicdevelopment, orbital structures are supplied by two vessels, both of which donot originate from the adult location of the ophthalmic. Instead, a dorsalophthalmic artery arises from the region of future ILT, and second ventralophthalmic artery extends from the anterior cerebral artery (ACOM region),underneath the optic nerve, and through the optic canal into the orbit.Occasionally, the dorsal ophthalmic artery persists, with several examplesshown in the ophthalmic artery and ILT sections. Extremely rarely, the ventralophthalmic artery can persist as well. More commonly, however, the ventralophthalmic artery conduit perists as the A1 segment of the ACA, as in thiscase, and takes an infraoptic course. It appears as though the ICA bifurcatedearly at the ophthalmic segment such that everything distal to the earlyICA bifurcation may be percieved as the MCA implying that both PCOM andA. Choroidal arise from this M1 segment. This, of course, is an incorrectinterpretation in fact, the classical A1 segment is developmentally

hypoplastic, and is compensated by its collateral ventral ophthalmic conduit,which functions as the A1 segment, such that both PCOM and A. Chor. ariseexactly as they should, and the M1 segment is defined as the vessel distal tothe choroidal.


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Angiographic and MRI images demonstrating a giant, partially thrombosedcavernous segment aneurysm in association with early takeoff and infraopticcourse of the left ACA (yellow). MCA is red. A second aneurysmal dilatation(pink) at the trifurcation of the ICA, ACA, and ophthalmic artery (purple) ispresent also. Frontal projection of contralateral right ICA injection showsredundant course of the right A1 segment (white arrow), which should berecognised as a distinct anatomical variant in bilateral A1 segmentdevelopment, correlating with the more obvious issues on the left side.


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Stereo pair of rotational volumetric dataset in the same patient. Notice normallocation of the anterior choroidal artery, once it is understood that the vesseldistal to ACA takeoff and proximal to the choroidal is still the ICA, not an M1segment.


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Top row lateral DSA immediately post Pipeline embolization of the cavernous segment aneurysm. Bottom

row 4 months post embolization shows cure of cavernous aneurysm. The anterior choroidal artery is well

seen.

Recurrent Artery of HeubnerFamous artery. Usually comes off the A1 or on occasion A2 or ACOM.Recurrent because it goes back laterally along the A1 segment towards theterminal ICA, so it often looks like a small artery running alongside and abovethe much bigger A1. It is simply one of the larger medial perforator arteriesarising from A1 and M1 segments to head towards the basal ganglia. Ithappens to be usually conspicuous and therefore has proportionally largersurgical and endovascular implications to preserve it. It is also instructive in

terms of MCA embryology cases of MCA duplication are often not MCAduplication but a particularly large Heubner which supplies much of the basalganglia and sometimes cortical territory, and therefore looks like another ICA.


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Going back to amphibians and fishes, where an MCA-like vessel is firstrecognized, it turns out that MCA develops from coalescence of multiple smallperforator-type vessels which assume prominence with phylogeneticenlargement of the brain volume to capture cortical surface territory. It is notdifficult to conceptualize that on occasion instead of a single MCA trunk, two

vessels may develop to split the MCA territory, thereby earning the name ofduplicated MCA. The other MCA is usually another perforator-like vessel,i.e. Heubner. As with any vasuclar arrangement, the size of the Heubner willvary depending on development of collateral vessels to the same area it willbe small when other medial perforators are well-developed, and vice versa.

MRA, catheter angiogram, and 3-D DSA stereo pair demonstrating the sameartery of Heubner.Heuber and M1 perforatorsAgain, 3-T MRA is very nice for small arteries like Heubner. This is a very cleademonstration that Heubner and medial perforators off the MCA serve the samfunction. In this patient, a large Heubner on the left serves the same function


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the medial M1 perforators on the right, supplying the putamen, caudate, andparts of the anterior limb of the internal capsule.

Red=Heubner; Yellow=lateral perforatorsRight MCA, same patient


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Yellow=lateral perforators; Red=medial perforatorsHeubner in patient with no MCA the anterior choroidal artery and Heubnerartery are well seen in this patient, whose MCA was surgically removed in

context of a left hemispherectomy for intractible seizures. The anteriorchoroidal, which appears duplicated, captures some of the posteriortem roal/occi ital territor . The heubner and its basal an lia arench mal


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blush are well seen.

Red = Heubner; Orange = Anterior Choroidal; Purple = PCA; Blue = distalsuperior cerebellar artery visualized through reflux into the basilar.

RAH pseudoaneuyrsm a case of parenchymal hemorrhage from a RAH. ThCTA demonstrates a spot sign (red) which, within a hematoma, is stronglysuggestive of source of bleeding (active or pseudoaneurysm). No delayedimages were acquired, unfortunately. Angio (middle) demonstrates theaneurysm. Intraoperative angiogram (right) following aneurysm surgery.


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Stereo pairs of same case 1 week (top) and two weeks (bottom) followinghemorrhage, demonstrating interval aneurysm growth in fact showing anenlarging pseudoaneurysm in face of resolving hemorrohage. The patient wasoperated on after the second angiogram.


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Cortical branches and variationsNaming scheme for cortical ACA branches no educational endeavor iscomplete without a silly diagram like this. Extreme variability is the rule. Aslong as there is understanding of where the artery is going to, naming is amatter of semantics. Naming classifications are variable, this one is as

reasonable as any other.


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Examples of variability are given below.No calossomarginal artery medial hemispheric branches originating fromdominant pericalossal


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Dominant Calossomarginal Artery same patient as with nocalossomarginal, contralateral side


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Dominant Calossomarginal Artery another example of variability in thepericalossal-calossomarginal balance.


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Trifurcation of post-genu segment; (plus superior hypophyseal artery)


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Early calossomarginal takeoff at ACOM level (same case as above triplicatedaca)


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Lateral projection angiogram with early calossomarginal takeoff (purple) andpericalossal in red. Corresponding MRA image with left A2 shown in yellow anACOM in dark blue. This is the appearance of a triplicated ACA which isdiscussed above; it is a misleading term since not 3, but 2 ACA arteries arepresent. It is the A2 segment on the right thats absent because of earlybifurcation into calossomarginal and pericalossal.

Trifurcation, on a mini scale a small frontopolar artery (red) is seen tooriginate from the ACOM complex in this stereo view.

ACA territory collateral circulationPCA (particularly posterior pericalossal / splenial branches can effectively


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reconstitute distal pericalossal ACA territory. Embryologically this corresponds

to a PCA/ACA anastomosis which exists in some mammals and possibly in thehuman embryonic stage.Carotid Occlusion PCA reconstitution of the ACA territory.

The right ICA is occluded at the origin. Notice how effectively posteriorpericalossal branches of the PCA (red) can reconstitute the pericalossal territoof the ACA (yellow), with runoffi into the anterior frontal branch (purple)

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