Download Embryology and variations of cerebral arteries - a

Embryology and variations of cerebral arteries - a pictorial
review
Poster No.:
C-2520
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
B. A. Feldman; Warsaw/PL
Keywords:
Neuroradiology brain, Arteries / Aorta, Interventional vascular, CTAngiography, MR-Angiography, Catheter arteriography, Computer
Applications-3D, Aneurysms, Hemorrhage, Ischemia / Infarction
DOI:
10.1594/ecr2013/C-2520
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Learning objectives
To provide brief overview of the development of cranial arterial anatomy. To obtain a
better understanding of some arterial anomalies. To point out commonly encountered
anatomial variatons that may have clinical significance.
Background
In the embryonic period severeal developmental anomalies of the cerebral arteries can
occur. During embryogenesis the brain vascular system continuously adapts the supply of
oxygen and other nutrients to the needs of the parenchyma. These changes often deviate
from normal pathway and produce various anatomic variations. Discussion of cerebral
arterial development begins with the formation of the six pairs of primitive brachial arch
arteries that either regress or are subject to modifications. The aortic arches arise from
the aortic sac, course through the branchial arches, and terminate in ipsilateral dorsal
aorta.
Brief overview of the development of cranial arterial anatomy
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Fig. 1: Overview of cerebral arteries development. This is only a schematic animation.
ICA-Internal Carotid Artery, MCA-Middle Cerebral Artery, ACA-Anterior Cerebral
Artery, AcomA-Anterior Communicating Artery, PCA-Posterior Cerebral Artery, PcomAPosterior Communicating Artery, LNA-longitudinal neural arteries, BA-Basilar Artery,
VA-Vertebral Artery.
References: Beata Feldman, Warsaw / Poland 2013
Internal carotid artery (ICA)
ICA is composed from seven segments. The first - C1 (cervical) segments derive from the
fetal third aortic arches. Other segments C2-C7 (petrous to communicating) represent
cranial extensions of the embryonic dorsal aorta.
Anterior cerebral artery (ACA)
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In emryo the last portion of ICA divides into cranial and caudal branches. Cranial division
of the ICA forms the primitive olfactory artery (POA), and this artery branches off the
anterior choroidal artery and middle cerebral artery (MCA). The POA has two branches,
the one going to the nasal fossa, and the secondary one - future continuation of the ACA
- going more medially. The latter artery joins with its fellow of the opposite side by the
plexiform anastomosis that constitutes the future anterior communicating artery (ACoA).
There is no branch except the POA in the horizontal part of the ACA, it is postulated that
the medial striate artery and the recurrent artery of Heubner derive from the anastomosis
between the POA and ACA. A small embryonic branch known as the median artery of
the corpus callosum arises from the ACoA. This vessel normally involutes.
Middle cerebral artery (MCA)
MCA branches from the primitive ICA proximal to the ACA. MCA becomes more
prominent and gives branches that spread over the cerebral hemisphere. The MCA
development is related to development of the sylvian fissure and insula.
Posterior cerebral artery (PCA)
When cranial and caudal divisions of the ICA are established, the caudal divisions
anastomose with the cranial ends of the longitudinal neural arteries (LNA). The caudal
divisions then regress and become posterior communicating arteries (PComAs). The
caudal divisions also supply the stems of the posterior cerebral arteries. The PComAs
should regress in caliber as the vertebrobasilar system develops.
Presegmental Arteries and Carotid-basilar anastomoses:
Anterior cerebral circulation becomes established as the primitive ICAs reach the
developing forebrain. The paired longitudinal neural arteries (LNA), precursors of the
basilar artery (BA) and partly of vertebral arteries (VAs) form on the medial edges
of bilateral vascular networks on the ventral surface of the hindbrain. Small branches
arise from the ICA to deliver blood to the LNA while the vertebrobasilar system is under
construction. These branches include three transient presegmental arteries (named
after the 5th, 8th, 12th cranial nerves with which they course: trigeminal, otic and
hypoglossal arteries), one permanent presegemental artery (future PcomA), and the first
intersegmental artery (termed Proatlantic Artery). These arteries also contribute to the
formation of the LNA by anastomosis. After formation of the posterior communication
artery from the caudal branch of the ICA, the presegmental arteries normally regress,
starting with the otic artery, followed by the hypoglossal and trigeminal arteries.
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Images for this section:
Fig. 1: Overview of cerebral arteries development. This is only a schematic animation.
ICA-Internal Carotid Artery, MCA-Middle Cerebral Artery, ACA-Anterior Cerebral
Artery, AcomA-Anterior Communicating Artery, PCA-Posterior Cerebral Artery, PcomAPosterior Communicating Artery, LNA-longitudinal neural arteries, BA-Basilar Artery, VAVertebral Artery.
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Fig. 7: Bilateral fetal posterior cerebral arteries (arrows) on CT angiogram. Both P1
segments are hipoplastic.
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Fig. 11: MR angiogram demonstrates lateral persistent trigeminal artery Saltzman type
1 (arrows). Note the hypoplastic vertebral artery (arrowhead).
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Fig. 8: Basilar artery fenestration. CT angiogram shows fenestration at the origin of the
basilar artery.
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Imaging findings OR Procedure details
Schematic animations, illustrations, CT angiograms and MRI aniograms are used to
illustrate development, anatomy and variants of cerebral arteries. Normal variations
include fenestrations, duplications, variants of the circle of Willis, persistent carotidbasilar anastomoses, and other vascular anomalies in the skull base.
When assessing CT or MRI angiograms, it is important to think about normal variants,
their prevalence, and their clinical relevance, particularly with respect to the risk of
aneurysm formation or surgical complications.
Imaging of variations:
There are some anomalies which can be depicted in several arteries and they should
be described at the beginning of the review - these include fenestrations, duplications
and infundibulum.
Fenestration is defined as a division of the arterial lumen into separate channels.
Various mechanisms have been proposed for development of different fenestrations.
Fenestrations of intracranial arteries are generally asymptomatic but similar to arterial
bifurcations, they have a tendency to develop aneurysms.
Duplication is defined as two arteries with separate origins and no distal arterial
convergence.
Infundibulum it is funnel-shaped region of dilatation at the origin of the artery, it must be
distinguished from aneurysm.
Below these and other variations of circle of Willis arteries.
Anterior cerebral artery (ACA)
•
Fenestration:
Description: it is postulated that this anomaly is the remnant of the plexiform
anastomosis between the two converging ACAs.
Clinical significance might be mistaken for aneurysm on MRA.
•
Median artery of corpus callosum (medial ACA, median callosal artery,
superior callosal artery, third A2 artery, triplicated ACA, ACA trifurcation,
accesory ACA)
Description: branch of the AcoA, runs parallel to and behind the normal
pericallosal artery; it is postulated that this variant results from persistence of
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embryonic MACC or marked development of MACC because of hypoplastic
ACA.
Clinical significance: frequently encountered as one of the draining arteries of
the ACoA aneurysm, it can be difficult to identify such aneurysms, depending
on their orientation, and it is easy to damage them during surgery.
•
A1 Segment Absence or Hypoplasia
Description: absent or hypoplasia of A1 segment, contralateral anterior
cerebral artery may supply part or all of the territory of the normal anterior
cerebral artery via anterior communicating artery.
Clinical significance: in the event of thromboembolic disease, these conditions
result in a diminished collateral supply and therefore an increased risk of
infarction.
•
Azygos (undivided, unpaired) ACA:
Description: single midline vessel arising from the confluence of the A1
segment of ACAs, represents persistence of the embryonic median artery of
the corpus callosum.
Clinical significance: no direct evidence of any increased incidence of stroke
associated with azygous ACA but occlusion can cause ischemic infarction in
both cerebral hemispheres and the corpus callosum. An azygous ACA can
be associated with midline central nervous system malformations, such as
agenesis of corpus callosum, holoprosencephaly, intracranial arteriovenous
malformation, and aneurysm.
•
Bi-hemispheric ACA
Description: two ACAs exist but only one is dominant.
Clinical significance: the same as the azygos ACA.
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Fig. 2: Fenestrations of the anterior cerebral artery. CT angiogram shows dual
channels arising from the origin of the A2 segment (arrow).
References: - Warsaw/PL
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Fig. 3: Trifurcation of the anterior cerebral artery. MR angiogram shows three A2
segments (arrow).
References: - Warsaw/PL
Fig. 4: Absence of an A1 segment of the anterior cerebral artery (arrow). CT
angiogram shows also trifurcation of the anterior cerebral artery (arrowhead).
References: - Warsaw/PL
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Anterior Communicating Artery (AcomA)
•
•
•
Fenestration,
Description: it is postulated that this anomaly is the remnant of the plexiform
anastomosis between the two converging ACAs , ACOM is one of the most
common sites of fenestration,
Clinical significance might be mistaken for ACoA aneurysm on MRA.
Duplication,
Description: each vessel originating separately from an anterior cerebral
artery.
Absence
Description: the AcomA often is not depicted at angiography, but this does not
necessarily mean that the artery is absent.
Middle Cerebral Artery (MCA)
•
•
•
•
Duplication
Description: two vessels originating from the distal end of the ICA. The
duplicate vessel parallels the main MCA and supplies the anterior temporal
lobe; it is postulated that this anomaly iderives from persistent anastomoses
between the ACA and MCA.
Clinical significance: reports of aneurysms formation at the origin of a duplicate
middle cerebral artery.
Accessory MCA,
Description: anomalous vessel originating from ACA, which courses parallel
to the M1 segment of the middle cerebral artery, supplying the anterior-inferior
region of the frontal lobe, it is postulated that this anomaly derives from
persistent anastomoses between the ACA and MCA.
Clinical significance: aneurysm formation.
Early branching
Description: Early division of the M1 segment close to its origin at the internal
carotid artery.
Clinical significance: not associated with an increased risk of aneurysm
formation.
Fenestrations
Description: Early branching temporopolar artery may participate in the
formation of MCA fenestration.
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Fig. 5: Early branching of the middle cerebral artery. CT angiogram shows a unilateral
early bifurcation of the right middle cerebral artery (arrow).
References: - Warsaw/PL
Posterior Cerebral Artery (PCA)
•
•
•
Fetal PCA,
Description: failing in regression of embryonic PCoA, ipsilateral P1 segment
may hipoplastic or absent.
Clinical significance: while treating the ICA-PCoA aneurysm, fetal PCA should
not be occluded to avoid infarction of the PCA territory.
Fenestration
Description: origin not clear.
Common Posterior Cerebral and Superior Cerebellar Artery Trunk
Description: common trunk of the superior cerebellar artery and P1 segment
of the posterior cerebral artery.
Clinical significance: important in the surgery and endovascular treatment of
the BA aneurysm.
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Fig. 6: MR angiogram shows A1 segment absence (arrow) and bilateral fetal posterior
cerebral arteries (arrowheads).
References: - Warsaw/PL
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Fig. 7: Bilateral fetal posterior cerebral arteries (arrows) on CT angiogram. Both P1
segments are hipoplastic.
References: - Warsaw/PL
Posterior Communicating Artery (PcomA)
•
•
Duplications
Description: very rare
Fenestration
Description: very rare
Vertebral Artery (VA)
•
Fenestration,
Description: extracranial fenestrations are probably caused by the persistence
of cervical intersegmental arteries, the intracranial components may arise from
persistent basivertebral anastomoses or passage of a solid structure (such as
the hypoglossal nerve).
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•
Clinical significance: often associated with anomalies of the brain, spinal cord,
and spine, and with other vascular anomalies, also reported an increased
prevalence of aneurysms and vascular malformations.
Duplication
Description: very rare
Basilar Artery (BA)
•
Fenestration
Description: caused by incomplete fusion of parallel arterial segments of two
longitudinal neural arteries (LNA)
Clinical significance: high incidence of aneurysm
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Fig. 8: Basilar artery fenestration. CT angiogram shows fenestration at the origin of the
basilar artery.
References: - Warsaw/PL
Hyperplastic Anterior Choroidal Artery
Description: usually a small vessel, arises from the supraclinoid ICA just distal to the
PcomA. Anterior choroidal artery is described as hyperplastic when the temporo-occipital
branches of the PCA arise from this vessel.
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Fig. 9: CT angiogram shows hyperplastic anterior choroidal artery (white arrow),
ipsilateral fetal posterior cerebral artery (red arrow), note also the trifurcation of the
anterior cerebral artery (arrowhead).
References: - Warsaw/PL
Persistent primitive olfactory artery
Description: arises from the terminal portion of the ICA, runs along the olfactory bulb,
makes an posterior turn behind the olfactory bulb, and finally becomes the distal ACA.
Usually involutes to a remnant known as the recurrent artery of Heubner. Persistance is
associated with the absence of AComA and the recurrent artery of Heubner.
Clinical significance: high incidence of cerebral aneurysms.
Persistent Dorsal Ophthalmic Artery
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Description: two primitive ophthalmic arteries are present: The ventral ophthalmic artery,
which normally persists, and the dorsal ophthalmic artery, which normally regresses. In
some instances, the opposite situation occurs, and the dorsal ophthalmic artery persists.
This variant artery arises from the dorsal aspect of the supraclinoid portion of the ICA
and enters the orbit by way of the superior orbital fissure instead of the optic canal.
Presegmental Arteries and Carotid-basilar anastomoses:
Description: among all persistent carotidbasilar anastomoses, persistent trigeminal artery
(PTA) is the most common and most cephalic in location.
Clinical significance: persistent anastomoses may be associated with various vascular
anomalies, these include carotid-cavernous fistula, aneurysms, Sturge-Weber syndrome,
hemangioma of the head and neck, cerebral arteriovenous malformations, etc.
Persistance may be responsible for neuralgia or paralysis of associated cranial nerves.
Recognition of these variants also warrant appropriate modifications of interventional
neuroradiology or endovascular procedures.
For example recognition of the PTA can be important in surgical procedures in the
cavernous sinus or the posterior fossa, and may prevent injury or disruption of the
PTA. Endovascular procedures should be modified accordingly to avoid ischemia to the
brainstem and the cerebellum.
•
Persistent primitive trigeminal artery (PTA)
th
Description: artery named for its association with 5 nerve, PTA arises from
posterior genu of cavernous (C4) segment of ICA and joins the cephalic end of
the basilar artery adjacent to the clivus - may follow either a parasellar (lateral
to the dorsum) or intrasellar course.
PTA is classified into two types according to its course: a medial type in which
the artery runs through the dorsum sellae and perforates the dura mater near
the clivus, and a lateral type in which the artery runs between the sensory root
of the trigeminal nerve and the lateral side of the sellae and penetrates the
dura mater medial to Meckel's cave.
PTA is also classified according to configuration of other arteries into three
types of patterns:
Saltzman type I - PTA joins basilar artery between the superior cerebellar
arteries and anterior inferior cerebellar arteries. The basilar artery proximal to
the junction is usually hypoplastic and the posterior communicating arteries
are absent or poorly opacified;
Saltzman type II - PTA joins the basilar artery between superior
cerebellar arteries and anterior inferior cerebellar arteries, but the posterior
communicating arteries are present and supply the posterior cerebral arteries;
Saltzman type III - PTA directly joins to the cerebellar artery.
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•
Persistent primitive hypoglossal artery (HA)
th
Description: artery named for its association with 12 nerve, second most
common after PTA, persistent vessel arises from ICA at C1 to C3 segments,
enters the skull through anterior condylar or hypoglossal canal (not through
the foramen magnum) and courses posteromedially to continue as terminal
segment of the VA and BA. The contralateral VA, if present, generally
terminates in the posterior inferior cerebellar artery.
•
Persistent Otic Artery
th
Description: artery named for its association with 8 nerve, existance of
persristent OA in human is controvertial. True otic artery must originate from
lateral-most portion of the petrous segment of the ICA and then traverse
through the internal auditory meatus before joining the caudal end of basilar
artery.
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Fig. 10: MR angiogram demonstrates lateral persistent trigeminal artery Saltzman type
1 (arrow). Note the hypoplastic vertebral artery (arrowhead).
References: - Warsaw/PL
Page 22 of 33
Fig. 11: MR angiogram demonstrates lateral persistent trigeminal artery Saltzman type
1 (arrows). Note the hypoplastic vertebral artery (arrowhead).
References: - Warsaw/PL
Internal Carotid Artery (ICA)
•
Agenesis and hypoplasia
Description: improper developments of one of 7 different emryologic segments
that form the ICA; may be congenital or acquired due to occlusion or stenosis
respectively (key finding is the absence of petrous bony carotid canal in ICA
agenesis and smaller size of the canal in ICA hypoplasia).
Clinical significance: unilateral absence generally asymtomatic, in the
presence of insufficuent collaterals may occur symptoms related to
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uncompensated blood flow, intracranial aneurysms because of hemodynamic
changes in collateral vessels has been described. Congenital agenesis or
hypoplasia of the internal carotid artery may be associated with anencephaly
and basal telangiectasia.
•
•
Aberrant Internal Carotid Artery
An aberrant intratympanic ICA
Description: enters the floor of middle ear space (through an enlarged inferior
tympanic canal that lies posterior to the normal carotid canal) instead of staying
anterior to this space before entering the foramen lacerum and middle cranial
fossa. The normal vertical portion of the carotid is absent or hypoplastic and
can be confused with dissection.
Pathology: due to agenesis or hypoplasia of ICA, the inferior tympanic
artery does not regress, instead hypertrophies and anastomoses with the
caroticotympanic artery to supply carotid siphon.
Clinical significance: asymptomatic or nonspecific symptoms such as
conductive hearing loss, pulsatile tinnitus, ear fullness, otalgia, vertigo; middle
ear vascular mass comon - danger of iatrogenic ear bleeding - if suspected it
is crucial to inform clinician.
An abberant lateral pharyngeal ICA
Description: ICA extends to or near the midline posterior pharyngeal wall.
Pathology: ICA uncoils as the dorsal aortic root descends into the chest and
finally assumes a stright course in the neck.
Clinical significance: recognition is crucial in preoperative diagnosis
(before oropharyngeal tumor resection, tonsillectomy, adenoidectomy,
palatopharyngoplasty.
Fenestration
Persistent Stapedial Artery
Description: The stapedial artery is a normally transient anastomosis between the
branches of the future external carotid artery and internal carotid artery. The stapedial
artery arises from the vertical part of the petrous internal carotid artery, passes through
the obturator foramen of the stapes, and terminates as the middle meningeal artery.
Clinical significance: pulsatile tinnitus, presence may complicate tympanotomy,
stapedectomy, and cholesteatoma resection and prevent cochlear implantation.
Images for this section:
Page 24 of 33
Fig. 1: Overview of cerebral arteries development. This is only a schematic animation.
ICA-Internal Carotid Artery, MCA-Middle Cerebral Artery, ACA-Anterior Cerebral
Artery, AcomA-Anterior Communicating Artery, PCA-Posterior Cerebral Artery, PcomAPosterior Communicating Artery, LNA-longitudinal neural arteries, BA-Basilar Artery, VAVertebral Artery.
Page 25 of 33
Fig. 11: MR angiogram demonstrates lateral persistent trigeminal artery Saltzman type
1 (arrows). Note the hypoplastic vertebral artery (arrowhead).
Page 26 of 33
Fig. 5: Early branching of the middle cerebral artery. CT angiogram shows a unilateral
early bifurcation of the right middle cerebral artery (arrow).
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Fig. 8: Basilar artery fenestration. CT angiogram shows fenestration at the origin of the
basilar artery.
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Fig. 7: Bilateral fetal posterior cerebral arteries (arrows) on CT angiogram. Both P1
segments are hipoplastic.
Page 29 of 33
Fig. 6: MR angiogram shows A1 segment absence (arrow) and bilateral fetal posterior
cerebral arteries (arrowheads).
Page 30 of 33
Fig. 4: Absence of an A1 segment of the anterior cerebral artery (arrow). CT angiogram
shows also trifurcation of the anterior cerebral artery (arrowhead).
Page 31 of 33
Fig. 2: Fenestrations of the anterior cerebral artery. CT angiogram shows dual channels
arising from the origin of the A2 segment (arrow).
Page 32 of 33
Conclusion
Understanding of cerebral arterial embryology is fundamental for anyone seriously
involved in any field where neural vasculature plays a role.
Knowledge of the presence and clinical relevance of normal variants plays a great role
in surgical planning or assesing the risk of aneurysm formation.
References
1. Padget DH, The development of the cranial arteries in the human
embryo, Contr Embryol 12:205-261, 1948.
2. Raybaud C, Normal and abnormal embryology and development of the intracranial
vascular system, Neurosurg Clin N Am. 2010 Jul;21(3):399-426. doi: 10.1016/
j.nec.2010.03.011.
3. Kathuria S, Gregg L, Chen J, Gandhi D, Normal Cerebral Arterial Development
and Variations, Semin Ultrasound CT MR. 2011 Jun;32(3):242-51. doi: 10.1053/
j.sult.2011.02.002.
4. Okahara M, Kiyosue H, Mori H, Tanoue S, Sainou M, Nagatomi H, Anatomic variations
of the cerebral arteries and their embryology: a pictorial review, Eur Radiol. 2002
Oct;12(10):2548-61. Epub 2002 Mar 21.
5. Dimmick SJ, Faulder KC, Normal variants of the cerebral circulation at multidetector CT
angiography, Radiographics 2009 Jul-Aug;29(4):1027-43. doi: 10.1148/rg.294085730.
Personal Information
Beata A. Feldman, M.D. / Miedzyleski Specialistic Hospital in Warsaw, AVI Diagnostic
Imaging / Warsaw, Poland.
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