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Arterial Anatomy

Last Updated: March 27, 2020

Aortic Arch and Proximal Great Vessels

Overview

Understanding of aortic arch anatomy is important in neuroangiography for complete radiographic evaluation of the craniocervical vasculature and in vessel selection during angiography procedures. In the majority of individuals, the thoracic aorta courses right to left and anterior to posterior in four segments: ascending aorta, aortic arch, aortic isthmus, and descending aorta. The aortic arch has three proximal great vessels, in the majority of cases (~80%), (from right to left): brachiocephalic artery (BCA), left common carotid artery (LCCA), left subclavian artery (LSCA).

Figure 1: CT Angiogram reconstruction of the aortic arch (left). DSA of the aortic arch and its large branch vessels (right).

Proximal great vessels

  • BCA (brachiocephalic artery or innominate artery)
    • First aortic arch branch, ascends anterior to trachea and bifurcates into right subclavian artery (RSCA) and right common carotid artery (RCCA)
    • RSCA
      • Right vertebral artery (VA)
      • Thyrocervical trunk
        • Inferior thyroid artery
        • Ascending cervical, laryngeal and pharyngeal branches
        • Suprascapular artery
      • Costocervical trunk

        • Gives off superior intercostal, deep cervical arteries
    • RCCA
      • Bifurcates into right internal and external carotid arteries (RICA, RECA)
  • LCCA
    • Arises from aortic arch (AA) distal to BCT, courses anteromedial to internal jugular vein
    • Bifurcates into internal and external carotid arteries (ICA, ECA)
  • LSCA
    • Arises from AA just distal to LCCA
    • Left vertebral artery
    • Left thyrocervical trunk
    • Left costocervical trunk

Important Variants and Anomalies of the Aortic Arch

  • Important to recognize for vessel selection during endovascular procedures
    • Common Variants:
      • Common origin of the (BCT), (LCCA) or (“Bovine Arch”) (10-25%)
      • LCCA origin from BCT in (5-7%)
      • Common origin of the LCCA and LSCA (1-2%)
      • Left vertebral artery (VA) origin from AA in (~1%)
    • Anomalies - Arch configurations with lower incidence (<1%)

      • Left AA with aberrant RSCA
        • Most common congenital arch anomaly (0.5-1%)
        • 70%: RCCA, LCCA, LSCA, RSCA
        • 25%: Common stem for RCCA/LCCA, LSCA, RSCA
        • 5%: Other variations with RSCA as last branch from AA
        • Aneurysmal dilation of RSCA - “ductus of Kommerell”
      • Right AA with mirror image branching

        • Left brachiocephalic trunk, RCCA, RSCA
        • High association with congenital heart anomalies
      • Right AA with aberrant LSCA

        • LCCA, RCCA, RSCA, LSCA
        • Lower association with congenital heart anomalies
      • Double AA and other anomalies (rare)

Imaging Pearls

  • Digital subtraction angiography: use Left anterior oblique (LAO) positioning for arch-vessel visualization (“opening” or “unfolding” the arch)

Intracranial Arteries

Overview

Internal Carotid Artery’s relationship to the dural rings:

The cervical segment of the ICA extends from the carotid bifurcation to skull base. It then courses anteromedially through the petrous temporal bone (petrous segment), and turns superiorly at the foramen lacerum. It passes under the petrolingual ligament, and enters the cavernous sinus, where it forms the carotid siphon. In the cavenous sinus, the artery is surrounded by venous plexus.

After the anterior turn (genu), the ICA leaves the cavernous sinus, passing through the dural cover of the sinus that is called the “proximal dural ring”. The ICA then passes through the transitional segment region, outside the cavernous sinus, but not yet within the subarachnoid. After this short transitional segment, the ICA goes through another dural ring, called the “distal dural ring”, and then becomes intradural (subarachnoid).This transition is critical, since aneurysms past the “distal dural ring” are located in the subarachnoid space, and their rupture leads to subarachnoid hemorrhage.

ICA Segmental Anatomy (origin to terminus):

Multiple classification schema with different nomenclature exist, the most widely accepted/utilized is the Bouthillier nomenclature (Bouthillier et al,1996):

  • C1 cervical
  • C2 petrous
  • C3 lacerum
  • C4 cavernous
  • C5 clinoid
  • C6 ophthalmic
  • C7 communicating

Figure 2: Segments of the right internal carotid artery on frontal (left) and lateral (right) views by DSA. Proximal anterior and middle cerebral artery branches more clearly visible on frontal (left) view.

ICA Branches by segment

  • C1 - cervical segment
    • Typically no branches
  • C2 - petrous segment

    • Normal course:
      • C2 and C3 segments of the internal carotid will traverse the vertical and horizontal segments of the carotid canal through the petrous bone
      • Caroticotympanic artery branch
        • The cochlear promontory will pick up arterial supply from the inferior tympanic artery via the inferior tympanic canaliculus and the caroticotympanic artery emerging from the carotid canal
      • Vidian artery (Artery of pterygoid/vidian canal)

        • Important anastomotic branch between the ICA and internal maxillary artery
        • The ascending pharyngeal artery can also collateralize with the vidian artery in the pterygopalatine fossa
      • Mandibular artery
    • Important variant: Aberrant internal carotid artery

      • C1 segment of the carotid artery arrests in development, resulting in an enlarged inferior tympanic artery that anastamoses with the embryologic hyoid artery.
      • The artery courses through the hypotympanum and inferior tympanic canaliculus entering the horizontal carotid canal through dehiscent bone, leaving the vertical portion of the canal absent
        • Symptomology:
          • Otalgia, tinnitus, hearing loss, and vertigo
          • Seen as retrotympanic pulsatile mass
        • Majority are right-sided and 90% are discovered in females

          • Very rare

Figure 3: Axial (top row) and sagittal (bottom row) CT angiography images of the head demonstrate an aberrant left internal carotid artery coursing through the temporal bone, superficial to the cochlear promontory. Patients with this variant anatomy occasionally present with pulsatile tinnitus. A pulsatile retrotympanic mass is commonly seen on otoscopy.

  • C3 - lacerum segment
    • Typically no branches
      • Note - the foramen lacerum, though largely filled with connective tissue, transmits small meningeal branches of the ascending pharyngeal artery and emissary veins from the cavernous sinus
  • C4 - cavernous segment

    • C4 segment within the cavernous sinus, where it forms the carotid siphon, surrounded by venous plexus. After the anterior turn (genu), the ICA leaves the cavernous sinus, passing through the dural cover of the sinus that is called the “proximal dural ring”
    • Meningohypophyseal Trunk a. (MHT)
      • Inconstant branch of the cavernous segment of the internal carotid artery
      • Classically, the meningohypophyseal artery itself has three named branches
        • Dorsal meningeal artery
        • Inferior hypophyseal artery (can originate from ICA)
        • Tentorial artery (artery of Bernasconi and Cassinari)
          • Tentorial basal branch (inconstant, variable origin)
          • Tentorial marginal branch (inconstant, variable origin)
    • Inferolateral trunk (ILT)

      • Originates as a single trunk (or a collection of smaller vessels) laterally
      • Supplies adjacent dura and cranial nerves
      • Extensive anastomoses with the extracranial circulation,
      • Important anasmotic branch collateralizing the ICA with the internal maxillary artery, middle meningeal artery, and ophthalmic artery
    • Artery of the foramen rotundum
    • Additional small regional branches including:

      • Meningeal branch - meninges of the anterior cranial fossa
      • Clival branches - supply the clivus
      • Capsular branches - supplies wall of cavernous sinus
      • Trigeminal ganglion branches - trigeminal ganglion
      • Small variable branches to CN III, IV, VI
  • C5 - clinoid segment

    • Typically no branches
  • C6 - ophthalmic segment

    • Ophthalmic artery
    • Superior hypophyseal artery
  • C7 - communicating segment

    • Posterior communicating artery (PCoA)
    • Anterior choroidal artery (AChA)
  • Carotid terminus

    • Terminal bifurcation into anterior cerebral artery (ACA) and middle cerebral artery (MCA).

Anterior Cerebral Artery (ACA)

3-5 Segments

  • A1 - precommunicating segment
    • Courses medially above optic chiasm, joined by Anterior Communicating Artery (ACoA) to join the contralateral A1
    • Important perforating arteries arise from A1 and ACoA
    • “Recurrent artery of Heubner”
      • A dominant medial lenticulostriate perforator arising from distal A1 or proximal A2 near the ACoA
  • A2 - postcommunicating segment

    • Courses superiorly within interhemispheric fissure, around the genu of the corpus callosum
  • A3 - pericallosal segment

    • Marginal to the corpus callosum genu, divides into pericallosal, callosomarginal arteries
  • A4/A5 - supracallosal/callosomarginal

    • variable terminal cortical branches
  • Cortical branches:

    • Orbitofrontal artery
      • Arises from proximal A2
      • Distributed over inferior surface of frontal lobe
  • Frontopolar artery

    • Arises from mid-A2
    • Extends anteriorly to frontal pole
  • Pericallosal artery

    • Arises from A2 near corpus callosum genu
    • Larger of two major distal ACA branches
    • Courses posterosuperiorly above corpus callosum, below cingulate gyrus
    • Gives off several callosal branches inferiorly
  • Callosomarginal artery

    • Courses posterosuperiorly in cingulate sulcus, above cingulate gyrus

Figure 4: Lateral view of the distal right internal carotid artery and its branches by DSA.

Normal Variants

  • Unilateral hypoplastic or absent A1
  • Bi-hemispheric ACA
    • Distal ACA supplies portions of contralateral hemisphere
  • Absent, fenestrated, or duplicated ACoA
  • Median artery of corpus callosum forms as branch from developing ACoA, then regresses (may persist, appear as a third A2 segment)

Anomalies

  • Azygous ACA
    • Associated with holoprosencephaly
    • Single ACA arises from junction of both A1s
  • Infraoptic ACA

    • A1 passes under (not over) optic nerve
    • Increased incidence of aneurysms

Territory supplied by ACA:

  • Corpus callosum (rostrum)
  • Caudate head
  • Anterior commissure
  • Anteromedial portions of the putamen
  • Globus pallidus
  • Anterior limb internal capsule (variable depending on recurrent artery of Heubner anatomy);
  • Cortical branches supply the gyrus recti and inferomedial frontal lobes, cingulate gyrus and anterior 2/3 of medial hemisphere surface.

Pearls:

  • ACA displacement from midline by mass effect secondary to tumor, hemorrhage, and edema on CT, MRI, and catheter angiography. Rotation of the head off midline can cause ACA to appear displaced on frontal projection DSA
  • May need to compress contralateral carotid artery during DSA to force contrast across ACoA
  • Lack of ACA filling on ipsilateral ICA injection usually indicates absent or hypoplastic A1; both ACA territories fill from the contralateral ICA

Middle Cerebral Artery (MCA)

4 Segments:

  • M1 - Horizontal segment
    • Courses laterally to Sylvian fissure below anterior perforated substance, bi- or trifurcates
    • Lenticulostriate perforators
    • Anterior temporal artery
    • Genu of MCA - posterosuperior turn towards the lateral cerebral (Sylvian) fissure
    • The M1 segment gives rise to the 2 or 3 main trunks of the M2 segment
      • Superior (frontal) division trunk
      • Inferior (temporal) division trunk
      • Intermediate trunk, variable
    • Variants

      • Duplication of the MCA at the internal carotid artery (ICA)
      • Accessory MCA which arises as a branch from the anterior cerebral artery
  • M2 - Insular segments

    • Course within lateral cerebral fissure
    • 6 to 8 small arterial branches usually arise from the M2 trunks, course within Sylvian fissure and supply the surface of the insula
  • M3 - Opercular segments

    • Begin at the top of insula, turn laterally in Sylvian fissure to supply the insular operculum (frontal, parietal, and temporal)
  • M4 - Cortical branches

    • Emerge from lateral cerebral fissure, course over the hemispheric surface

Figure 5: Frontal view of the distal right internal carotid artery and its branches by DSA.

Cortical branches:

  • Orbitofrontal (lateral frontobasal) artery and prefrontal arteries
  • Precentral (prerolandic) artery
    • Runs between precentral and central sulci
  • Central sulcus (rolandic) artery

    • Runs within central (rolandic) sulcus
  • Postcentral sulcus (anterior parietal) artery

    • Runs in postcentral, then intraparietal sulcus
  • Posterior parietal artery

    • Exits posterior end of Sylvian fissure
    • Runs posterosuperiorly along supramarginal gyrus
  • Angular artery

    • Most posterior branch exiting Sylvian fissure
    • Runs posterosuperiorly over transverse temporal gyrus
  • Temporooccipital artery

    • Runs posteroinferiorly in superior temporal sulcus
  • Posterior temporal, medial temporal arteries

    • Extend inferiorly from Sylvian fissure

Territory supplied:

  • Putamen
  • Globus pallidus
  • Superior aspect of the internal capsule
  • Caudate body
  • Portions of the deep white matter
  • Cortical branches (highly variable in territory of individual branches) majority of the lateral surface of cerebral hemispheres, temporal pole.

Normal Variants

  • High variability in branching patterns
  • MCA duplication seen in 1-3% of cases
    • Large branch arises from distal ICA just prior to terminal bifurcation
    • Parallel to main M1
  • Accessory MCA (rare)

    • Arises from anterior cerebral artery
    • High association with saccular aneurysm
  • True anomalies (hypoplasia, aplasia) rare

Vertebrobasilar System

Just before joining to form the basilar artery, each of the vertebral arteries give off a branch that will become the anterior spinal artery, which extend downward and medially to join in the midline with a corresponding branch from the other vertebral artery. The posterior spinal arteries can originate from the posterior inferior cerebellar arteries or from the intracranial portion of the vertebral arteries.

Figure 6: Reconstruction of CT Angiography demonstrating the Circle of Willis and its more distal branches (left). The distal cervical and intracranial posterior circulation by DSA (right).

Vertebral Arteries (VA)

4 Segments

  • V1 - Extraosseous segment
    • Origin from each subclavian artery coursing superiorly to enter the C6 transverse foramen (80-90%)
    • Variations
      • Origin of the left vertebral artery from the aortic arch between the left common carotid artery and left subclavian artery has been described in 2-6% of cases
        • Enters the C5 transverse foramen in majority of cases
      • Origins of the left vertebral artery from the left common carotid artery or external carotid artery (rare)
      • Origin of the right vertebral artery from the aorta, carotid arteries, or brachiocephalic arteries (rare)
    • Important branches

      • Segmental cervical muscular branches
  • V2 - Foraminal segment

    • Ascends from C6 to C2
    • Important branches
      • Anterior meningeal artery
  • V3 - Extradural segment

    • Exits top of atlas (C1) transverse foramen, makes a wide extracervical loop between C2 and C1, courses superior to C1, curves posteromedially around atlantooccipital joint, turns sharply anterosuperiorly to enter dura at foramen magnum
      • Prone to dissection/pseudoaneurysm
    • Variations

      • Persistent first intersegmental artery - vertebral artery courses below the C1 arch after exiting the transverse foramen of C2 and enters the spinal canal without passing through the C1 transverse foramen (3-4%)
    • Important branches

      • Posterior meningeal artery
        • Supplies the falx cerebelli and the medial dura of the occipital posterior fossa
  • V4 - Intradural segment

    • Enters the craniumvia the foramen magnum.
    • Important Branches:
      • Anterior spinal artery (1) and posterior spinal arteries (2) originate
      • Medullary perforators
      • Posterior Inferior Cerebellar Arteries (PICA)
        • Originate from this segment with variations
        • Variations
      • Non-dominant vertebral artery commonly terminates in the PICA (does not join to form basilar artery)

Figure 7: 3D Reconstruction of the Circle of Willis and its branches from MR Angiogram.

Basilar artery (BA)

The two vertebral arteries fuse to form the basilar artery, usually at the level of the pontomedullary junction within the prepontine cistern, ventral to the pons and midbrain. Variations are possible including right or left dominant vertebral artery supply. Occasionally, a vertebral artery will terminate in the PICA and not join to form the basilar artery.

  • Numerous pontine and midbrain perforators
  • Anterior Inferior Cerebellar Arteries (AICA)
    • Lies ventromedial to CN7 and 8
    • Can loops into internal auditory meatus
  • Superior Cerebellar Arteries (SCA)

    • Originates near the basilar terminus before the PCA takeoff
    • Courses below CN III
  • Posterior Cerebral Arteries (PCA) at terminal bifurcation

Territory supplied

  • VA: PICA territory, medulla, cervicomedullary junction, cervical spine, cerebellar tonsils, inferior vermis/cerebellar hemispheres
  • BA: PCA territory, most of the ventral pons, SCA and AICA territory including the superior cerebellum/vermis

Normal variants:

  • BA/VA:
    • R/L variation in size, dominance common and slightly more commonly on the left
    • Aortic arch origin 1-5%
    • AICA/PICA may share common trunk off the BA
    • Fenestrations, duplications

Posterior Cerebral Arteries (PCA)

  • Originate at the basilar tip, bifurcation
  • 4 segments
    • P1 - pre-communicating segment, interpeduncular cistern
      • Thalamoperforators
      • Artery of Percheron - rare variant with dominant unilateral P1 perforator, supplies bilateral midbrain, thalami
    • P2 - post-communicating segment, ambient cistern, curves and courses posteriorly, stays above tentorium
    • P3 - Quadrigeminal segment, quadrigeminal plate cistern
    • P4 - Cortical terminations, calcarine fissure

Cortical branches:

  • Anterior temporal artery
    • Arises from P2, courses anterolaterally under parahippocampal gyrus of inferior temporal lobe
  • Posterior temporal artery

    • Arises from P2, courses posteriorly
  • Distal PCA divides into two terminal trunks

    • Medial branches:
      • Medial occipital artery
      • Parietooccipital artery
      • Calcarine artery
      • Posterior splenial arteries
    • Lateral branches:

      • Lateral occipital artery

Territory supplied:

  • Diencephaphalon (thalamus, hypothalamus, portions of the midbrain)
  • Portions of the choroid plexus
  • Cortical branches: inferomedial temporal lobes, and occipital poles

Normal Variants

  • “Fetal PCA”
    • Large posterior communicating artery gives direct origin to PCA
    • P1 (precommunicating) PCA segment hypoplastic or absent

Vascular Territory:

  • Midbrain
  • Thalami
  • Posterior limb of internal capsule
  • Optic tract
  • Ventricular and choroidal branches:
    • Choroid plexus of third/lateral ventricles, parts of thalami, posterior commissure, cerebral peduncles. Splenial branches: Posterior body and splenium of corpus callosum.
  • Cortical branches:

    • Posterior 1/3 of medial hemisphere surface; most of inferior temporal lobe, most of occipital lobe (including primary visual cortex).

Pearls:

  • Absent PCA on vertebral angiogram usually due to hemodilution from “fetal” origin, not occlusion.
    • Injection of ipsilateral carotid artery confirms presence of “fetal” PCA

Circle of Willis

  • Central arterial anastomosis between the anterior and posterior circulation
  • Critical for providing cross-flow and collateral support in large vessel occlusions and arterial injuries
  • Located within the suprasellar cistern
  • Prototypical configuration
    • Bilateral ICAs
    • Bilateral A1 segments of the ACA
    • Single anterior communicating artery (ACoA)
    • Bilateral posterior communicating arteries (PCoA)
    • Basilar artery
    • Bilateral proximal or horizontal (P1) posterior cerebral artery (PCA) segments
  • Normal Variants, Anomalies

    • Absent/hypoplastic components (55-60%)
    • Hypoplastic/absent PCoA (25-30%)
    • Hypoplastic/absent A1 segment of ACA (10-20%)
    • Fetal origin of the PCA from ICA (15-25%)
      • PCoA is same diameter as ipsilateral P1 segment of PCA
      • P1 is hypoplastic or absent
    • Infundibulum at the origin of PCoA from ICA in 5-15%

      • Should be < 2 mm
      • PCoA arises from apex

Figure 8: On this lateral digital subtraction angiography image, the small infundibulum is clearly visible at the origin of the posterior communicating artery from the distal internal carotid artery (arrow), but even without the visible presence of the posterior communicating artery, small focal outpouching in this area implies an infundibulum rather than aneurysm.

Perfusion border zones (“watersheds”)

Cortical “watershed” zones are areas receiving dual supply at the distal confluences between the ACA, MCA, and PCA territories with variable subpial-leptomeningeal collateral support and are prone to hypoperfusion ischemia.

Internal “watershed” zone are areas receiving dual supply at the confluence of cortical deep penetrating branches and perforating branches from circle of Willis and lenticulostriates with variable subpial-leptomeningeal collateral support and are prone to hypoperfusion ischemia.

Persistent carotid-vertebrobasilar anastomoses

Embryologic anastomotic connections between the anterior and posterior circulations that fail to regress in-utero.

  • Persistent trigeminal artery (PTA)
    • Origin from proximal cavernous ICA
    • Most common persistent carotid-vertebrobasilar anastomosis
    • Saltzman classification
      • Type I- PTA supplies the distal vertebrobasilar arteries; absent ipsilateral PCoA
      • Type II- PTA supplies the SCA; PCAs are supplied via the PCoA (fetal origin of ipsilateral PCoA)
    • “Neptune's trident sign” on angiography

Figure 9: Axial CT angiography of the head (left) and lateral projection digital subtraction cerebral angiography (right) images demonstrate a persistent left trigeminal artery coursing from the cavernous left internal carotid artery to the left superior cerebellar artery.

  • Persistent otic artery
    • Controversial existence, very few confirmed cases in literature
    • Arises from petrous ICA within the internal acoustic meatus along with cranial nerves VII/VIII
  • Persistent hypoglossal artery (PHA)

    • Origin from cervical ICA at the level of C1-C2 or C2-C3, joins BA via the hypoglossal canal.
    • Parallels the hypoglossal nerve.
    • 2nd most common persistent carotid-vertebrobasilar anastomosis
  • Persistent proatlantal intersegmental artery

    • Most caudal of the persistent carotid-vertebrobasilar anastomosis
    • Types:
      • Type I - cervical ICA at C2-C3 level (most common) to vertebral artery coursing between arch of C1 and occiput
      • Type II - ECA origin (less common)
      • Other - CCA origin (very rare)
    • Vertebral arteries may be absent or hypoplastic
    • Proatlantal intersegmental artery may be dominant or only supply to BA

Contributors: Daniel Murph, MD; Jacob Eitel, MD; Andrew DeNardo, MD; John Scott, MD and Daniel Sahlein, MD

DOI: https://doi.org/10.18791/nsatlas.v2.03.03.02

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