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To Begin At The Beginning: Imaging
Features And Embryological Basis Of
Variants And Anomalies Of Cerebral
Circulation
eEdE-64
Komal Sharma MD , Betty Mathew MD , Thanuja
Jeyakumar MD , Nishant Gupta MD , Joshua Sapire MD
DISCLOSURE
Komal Sharma, MD
No Disclosures
Betty Mathew, MD
No Disclosures
Thanuja Jeyakumar, MD
No Disclosures
Nishant Gupta, MD
No Disclosures
Joshua Sapire, MD
No Disclosures
EMBRYOLOGY
Early development of vascular network
4 weeks
2-4 weeks: Initially the exposed neural plate and
groove and the open neural tube are simply fed
by diffusion from the amniotic fluid
5-8 weeks: After closure of the neural tube it is surrounded
by a dense connective tissue, the meninx primitiva which
contains meningeal vascular meshwork . Diffusion of
nutrients to the neural tissue reach by diffusion from the
peripheral meninx primitiva
Cephalic portion of the neural tube grows and forms 3 primary
brain vesicles, the meninx invaginates into the roofs of the
prosencephalic and rhombencephalic vesicles, forming the
primordia of the choroid plexuses
(5–7 weeks).
At this stage diffusion of nutrients to the neural tissue is both
peripheral from the meninx primitiva and ventricular from the
developing choroid plexuses
5-8 weeks
Meninx
primitiva
The brain arteries evolve from
the differentiation of specific
choroid feeders within the
meningeal vascular meshwork
Neurosurg Clin N Am 2010
EMBRYOLOGY
Early development of vascular network
5-8 weeks CONTD:
Meninx primitiva begins to undergo the dramatic changes forming calvarium, dura,
fluid-filled lepto-meninges, choroid plexuses and opening of the fourth ventricular
outlets.
Vascular meshwork follows this meningeal reorganization:
 The deeper vascular endothelium that covers the wall of the neural tube flattens
and takes the appearance of a capillary network.
 The superficial vascular layer takes the appearance of larger and more continuous
channels that form clear connections with the paired dorsal aorta and cardinal
veins, and will eventually become the major brain arteries and veins.
 The communications between superficial and deep layers become the branches of
the arteries and the tributaries of the veins
Neurosurg Clin N Am 2010
EMBRYOLOGY
Early development of vascular network
Stage 1: 4–5 mm, 28–29-day embryo: The forebrain as well as hind brain is
supplied by the primitive carotid artery through carotid-vertebro basilar
connections. The hind brain is supplied by longitudinal neural arteries(lna). The
connections are named after their accompanying nerves/location: craniocaudally
the trigeminal (tga), hypoglossal (hga) and pro-atlantal (paa) arteries.
The channels exist for a very short time of 4-8 days before vanishing at about
stage 3
Uncommonly they may persist and be functional
as anatomic variants as will be discussed later
in this presentation.
Neurosurg Clin N Am 2010
Contrib Embryol 1948
EMBRYOLOGY
Stages of morphogenesis of the brain arteries
Stage 2: The posterior communicating artery forms (5–6 mm, 29-day embryo).
The paired lna along either sides
of the hindbrain unite by fusion in
midline to form BA .
All brain arteries are plexular at
this stage
Simultaneously, the lna become
connected cranially to anterior
circulation via the PCOMs and
caudally with the forming VAs
The new blood supply results in
the regression of the trigeminal,
hypoglossal and proatlantal
arteries.
Neurosurg Clin N Am 2010
EMBRYOLOGY
Stages of morphogenesis of the brain arteries
Stage 3: The forebrain arteries can be
recognized; the basilar and vertebral arteries
are completed (7–12 mm, 32 days).
The vertebral artery (VA) forms as a
longitudinal paravertebral anastomosis
between the intersegmental cervical arteries
from C1 to C7
Developing choroid plexuses
Stage 4: The mature pattern becomes
apparent (12–14 mm, 35 days).
Stage 5: The choroid stage, the adult pattern has become
obvious (16–18 mm, 40-day embryo). The choroid
plexuses are large, well vascularized structures loaded with
glycogen and they strongly determine the prominence of
their feeding arteries: ACA, ACHA, PCHA, from which the
whole brain vasculature originates.
Neurosurg Clin N Am 2010
EMBRYOLOGY
Stages of morphogenesis of the brain arteries
Stages 6: (20–24 mm, 44 days) and stage 7 (40 mm, 52 days), the mature
pattern is completed with the circle of Willis and the capture by the posterior
hemispheres of the vertebro-basilar blood supply.
Neurosurg Clin N Am 2010
VARIATIONS
OF INTRACRANIAL ARTERIES
Persistent Vestigial Carotid-Vertebrobasilar Anastomoses
Persistent primitive trigeminal artery (PPTA)
Persistent primitive otic artery (PPOA)
Persistent primitive hypoglossal artery (PPHA)
Persistent primitive pro-atlantal intersegmental artery (PPIA)
Segmental agenesis/hypoplasia of the vertebro-basilar junction
Variations of the Leptomeningeal Segments of the Brain Arteries
Variations of circle of Willis
Variations of anterior cerebral artery
Variations of posterior cerebral artery
Variations of vertebrobasilar system
Variations of middle cerebral artery
PERSISTENT VESTIGIAL
CAROTIDVERTEBROBASILAR
ANASTOMOSES
PERSISTENT VESTIGIAL
CAROTID-VERTEBROBASILAR
ANASTOMOSES
Persistence of carotid and vertebral anastomosis is due to either a defect of the
inhibition processes, or a defect of induction of the normally later-appearing
vascular changes (eg, PCOM connection cranially and VA caudally).
Persistent primitive trigeminal artery (PPTA)
Persistent primitive otic artery (PPOA)
Persistent primitive hypoglossal artery (PPHA)
Persistent pro-atlantal intersegmental artery (PPIA)
PERSISTENT PRIMITIVE
TRIGEMINAL ARTERY (PPTA)
PPTA is the most common vestigial artery observed with a reported pre-valance of
0.1-0.6%
PPTA artery normally regresses at week 5, before stage 3
PPTA have been classified in different types depending on the territory they supply
 Saltzman type I is when it supplies the upper BA with the paired ASCAs and
PCAs; the proximal BA is typically hypoplastic and the ipsilateral PCOM is missing.
 Saltzman type II is when it supplies the BAs with the ASCAs only, both PCAs
being supplied by the ICAs through the PCOMs
Acta Radiol 1959
CTA
Raybaud, 2010
Axia
l
MIP
Persistent Trigeminal
Artery (TGA)
CTA
PERSISTENT PRIMITIVE
TRIGEMINAL ARTERY (PPTA)
Course:
A PPTA arises from the cavernous ICA near the posterior genu, and may follow either
a para- or an intra-sellar course.
Ohshiro et al. has classified this into two types:
 Medial type : PTA runs through the dorsum sellae and perforates the dura near the
clivus
 Lateral type : PTA 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
Clinical Importance:
May be injured in surgical procedures in the cavernous sinus or the posterior fossa.
The PTA are also associated with increased prevalence of other vascular
abnormalities such as aneurysms. Aneurysms are found in nearly 14% of all cases
Neurosurgery 1993
THE PERSISTENT PRIMITIVE
OTIC ARTERY (PPOA)
The persistent otic artery (POA) is exceedingly rare. It is existence is questioned by
many.
Only 8 cases are reported in literature none of which convincingly displayed typical
features.
In case you see one one day!! To be a real otic artery:
 Artery should arise from the lateral most portion of the petrous segment of the
ICA (proximal to the carotico-tympanic artery)
 Course internal auditory meatus
 Join the BAs at its caudal end.
THE PERSISTENT PRIMITIVE
HYPOGLOSSAL ARTERY (PPHA)
The persistent hypoglossal artery (PHA) is the second most common persistent
vestigial artery with prevalence of 0.1–0.25%.
Normally regresses before stage 2, in week 5.
Course:
The vessel leaves the ICA at the C1 to C3
level
Enters the skull through the anterior
condylar (hypoglossal) canal
Courses postero-medially to form the
terminal segment of the VA that gives off
the PICA and the BA.
Typically both VAs are absent
Radiographics 2009
or hypoplastic.
CT angiogram depicts a hypoglossal artery (arrowhead)
that arises from the proximal internal carotid artery
(arrow) at the C2 vertebral level and anastomoses with
the basilar artery.
Ann Anat
1995, Radiographics 2009
THE PERSISTENT PROATLANTAL INTERSEGMENTAL
ARTERY (PPIA)
The persistent pro-atlantal intersegmental artery (PPIA), corresponds to the first
spinal intersegmental artery.
The PPIA disappears at stage 3, in week 6, when the VA becomes functional.
Even in normal anatomy, it persists as the horizontal segment of the vertebral
artery that passes between the occipital bone and C1, and as portions of the
occipital artery.
Classifications
Type-1 proatlantal artery is a persistent primitive proatlantal artery. The type-1
proatlantal artery rises from the ICA or ECA and runs upward and dorsolaterally and
joins the fourth segment of the VA.
type-2 proatlantal artery is a persistent primitive first cervical intersegmental artery.
The type-2 proatlantal artery rises from the ECA and joins the third segment of the
VA below the first cervical vertebra
Stroke 1993
Figure A-C demonstrate The
type-2 pro-atlantal artery rises
from the ECA and joins the
third segment of the VA below
the first cervical vertebra
B. Axial MIP:
A. Sagittal MIP:
Note absence of V1
and V2 segments of
the ipsilateral vertebral
artery
C. 3D
D. Coronal MIP
SEGMENTAL
AGENESIS/HYPOPLASIA
OF THE VERTEBROBASILAR JUNCTION
SEGMENTAL
AGENESIS/HYPOPLASIA OF THE
VERTEBRO-BASILAR JUNCTION
May represent the reverse situation from
the persistent lower vestigial arteries.
Extremely common when it is unilateral, but
it is extremely rarely bilateral.
Hypoplastic VA may supply an ipsilateral
PICA only, and the missing segment is then
between the PICA and the BA. Correspond
to a failure to form the distal hypoglossal
artery.
Alternatively, VA is totally absent and the
PICA is supplied by the BA. It is speculated
due to failure to form the proatlantal/
intersegmental artery.
Hypoplastic right vertebral artery
terminating in PICA. Right superior
cerebellar and PCA supplied by BA
Neurosurg Clin N Am 2010
VARIATIONS OF THE
LEPTOMENINGEAL
SEGMENTS OF THE BRAIN
ARTERIES
CIRCLE OF WILLIS
VARIATIONS
 Variations of circle of willis are extremely common
 The variations are thought to reflect hemodynamic balance of an individual. This
balance may even change overtime and circle of wills may remodel accordingly
 Fenestrations reflect original plexiform arrangement and defined as division of the
arterial lumen into distinctly separate channels, each with its own endothelial and
muscularis layers, while the adventitia may be shared.
 Duplication is defined as two distinct arteries with separate origins and no distal
arterial convergence.
 Hypoplasia of any segment is common.
 Complete aplasia rare. Complete aplasia certainly may compromise collateral flow
in case of disease.
Pergamon Press; 1963
VARIATION OF MAJOR
ARTERIAL BRANCHES: ACA
Azygous ACA (ncidence of azygos ACA ranges from 0 to 5%) [9] : Midline fusion of
normally paired trunk
Bi-hemispheric ACA (2–7% of anatomic specimens) (10): Very common. A1 ACA
hypoplastic and contralateral ACA supplies via ACOM
Persistent primitive olfactory artery arises from the terminal portion of the ICA, runs
along the olfactory bulb, makes an abrupt posterior HAIR PIN LOOP, and finally
becomes the distal ACA. It is associated with the absence of ACoA and the recurrent
artery of Heubner
Azygous ACA
Persistent primitive olfactory artery
Eur radiol 2002
VARIATION OF MAJOR
ARTERIAL BRANCHES: ACA
Infra-optic origin of the ACA.
The ACA originates at the level of the
ophthalmic artery and runs under the optic
nerve to join its distal territory at the level of
the ACOM. If it ours together with a ‘‘normal’’
A1, then a ring forms around the optic nerve.
Raybond 2010
Fenestration of the anterior cerebral artery
The prevalence of fenestration of the A1 segment is
between 0% and 4% in anatomic imaging studies
 Fenestration
VARIATION OF MAJOR
ARTERIAL BRANCHES: MCA
 Duplicated MCA: Early origin of one MCA trunk from ICA
 Early vascular embryogenesis : Two forebrain arteries emerge from the ICA :the
ACA and the ACHA. Both the artery of Heubner and the MCA develop as basal
striatal branches of the primitive ACA. Typically, the cortical branches of the artery
of Heubner supply the frontobasal cortex adjacent to the medial striatum, and the
more proximal duplicate MCA supplies the temporal territory of the MCA
 Accessory MCA: MCA branch from ACA (also thought to be cortical extension of
recurrent artery of heubner). Higher chances of aneurysm at accessory MCA origin.
Radiographics 2009
VARIATION OF MAJOR ARTERIAL
BRANCHES: ANTERIOR
CHOROIDAL ARTERY (ACHA)
Hyperplastic ACHA
The anterior choroidal artery, usually a small ves sel,
arises from the supraclinoid internal carotid artery
just distal to the posterior communicating artery.
From there it subdivides into important branches
that supply the cerebral peduncle and optic tract.
The temporo-occipital branches of the posterior
cerebral artery may arise from the anterior choroidal
artery is described as hyperplastic ANTERIOR
CHOROIDAL ARTERY. The prevalence of hyperplastic anterior choroidal arteries reported to be
1.1%–2.3%
Hyperplastic anterior choroidal
artery (straight arrow),ipsilateral
posterior communicating artery
(arrow-head), and contralateral fetal
posterior cerebral artery (curved
arrow).
VARIATION OF MAJOR
ARTERIAL BRANCHES: PCA
 Most common variation of PCA.
 P2 segment of the PCA appears to be a continuation of large PCOM. Associated P1
PCA hypoplasia and in some cases A1 ACA hypoplasia.
 Embryologically, represents failure of the P comm (a remnant of the caudal
embryonic ICA) to regress with resulting hypoplasia or agenesis of the P1 PCA
segment that serves to connect the basilar artery to the PCA.
 Reported incidence of 22%.
Left fetal
PCA
Hypoplastic
ipsilateral A1
ACA
Right fetal PCA with
Hypoplastic P1 PCA
VARIATION OF MAJOR
ARTERIAL BRANCHES: PCA
Duplicate PCAs are cases in which the ACHA supplies the inferior temporal cortex and
the PCA supplies the medial temporo-occipital cortex
The ACHA branch is also referred by some as true ‘fetal PCA’
MRA, 3D reconstartuction: Small pink arrow
demonstrate the ACHA arising from distal ICA
and long pink arrow demonstrate the PCA
arising from the basilar artery.
Common trunk of the PCA and SCA :
Seen in 2–22% of cases.
VARIATION OF MAJOR
ARTERIAL BRANCHES: BASILAR
LONGITUDNAL NON FUSION:
• Fenestration
Duplication
AJNR: 2004
Small area of longitudnal non fusion
consistent with fenestration
MRA demonstrate the two separate
nonfused duplicated basilar arteries.
VARIATION OF MAJOR
ARTERIAL BRANCHES: BASILAR
AXIAL NON FUSION: The 3 segments that are constitutive of the BAs remain
discontinuous: CAUDAL ‘‘vertebral’’ segment that supplies the PICAs only;
INTERMEDIATE ‘‘trigeminal’’ segment that supplies the AICA, ASCA, and the pontine
perforators ; CRANIAL ‘‘carotid’’ segment that supplies the PCAs
Right VA injection DSA demonstrates that the
right vertebral artery terminates in the right
posterior inferior cerebellar artery.
Right ICA injection DSA, demonstrate the
separate midbasilar trunk segment supplying the
bilateral anterior inferior cerebellar arteries and
bilateral superior cerebellar arteries and supplied
via a persistent trigeminal remnant artery.
Left CCA injection DSA demonstrates the fetal
origin of left posterior cerebral artery.
AJNR 2004
DEVELOPMENT OF
INTRACRANIAL VENOUS
SYSTEM
 Before the intrinsic vasculature develops, the venous drainage is strictly
meningeal and choroidal; transient vein of Markowski.
 5 and 6 weeks : Vascular network is confined to the meninx primitiva. The
pericerebral meshwork divides into :
 Deep (future pial) layer over the brain surface which is simple capillary layer.
 Superficial (future dura) layer become continuous and connect with the cardinal
veins, to form early venous trunks.
 Connections between the superficial layer and the deep capillary layer early
form of bridging veins.
EMBRYOLOGY
Morphogenesis of the venous system
Week 6
ANTERIOR
PLEXUS
MIDDLE
PLEXUS
Week 7
POSTERIO
PLEXUS
PRIMARY HEAD
SINUS
Early venous drainage
system. Three venous
plexuses (ant, mid, post)
drain the neural tube into a
ventrolateral primary head
sinus
Growth of the otic capsule
induces collateralization
between the anterior and
middle plexuses
Collateralization
between the
anterior and
middle plexuses
Week 8
OTIC
CAPSULE
PRIMARY HEAD
SINUS
The dorsal collateralization
develops via a lateral
anastomosis. The primary
head sinus becomes the
jugular vein
OTIC
CAPSULE
Collateralization
between the
posterior and
middle plexuses
The choroid plexus develops
drained ventrally by diencephalic
vein (dv) and dorsally by vein of
Markowski (mpvm).
The growth of the otic vesicle
obliterates the primary head sinus
Collateral develop dorsal to the
otic vesicle between the middle
and the posterior plexuses
EMBRYOLOGY
Morphogenesis of the venous system
Month 3, early
Week 9
Month 3, late
SUPERIOR SAGITTAL SINUS
DORSAL
COLLATERAL
TENTORIAL
PLEXUS
SIGMOID SINUS
POSTERIOR
STEM
TRANSEVERSE
SINUS
Dorsal collateral with the
posterior stem forms the
complete sigmoid sinus.
The anastomosis between the
anterior and middle plexuses
forms the transverse sinus.
The consolidation of the dorsal
dural plexuses forms the superior
sagittal sinus .
More posteriorly, the tentorial
plexus is still primitive
Condensation of the
tentorial plexus forms torcular
The internal cerebral veins
are formed together with the
final vein of Galen and
straight sinus
DEVELOPMENTAL VENOUS
ANOMALY(DVA)
 Also known as cerebral venous angioma, DVA are common congenital
variants of cerebral venous drainage that are frequently identified in
imaging studies.
 They are most common cerebral vascular malformations , accounting for
~55% of all such lesions.
 Usually incidentally found with no consequence to the patient.
 The brain surrounding the DVA is nearly always normal, and histologically
the anomaly is limited to the venous structures, without involvement of
capillaries or arteries.
 Imaging appearance: Caput medusae sign. Veins draining into a single
larger collecting vein, which in turn drains into either dural sinus or into a
deep ependymal vein.
DEVELOPMENTAL VENOUS
ANAMOLY(DVA)
Subtle DVA identified on Post Contrast
T1W image
AJNR 2008
SWI and, Postcontrast T1-weighted image demostarting
DVA with draining vein (arrow) and medullary veins (arrow
head) : Caput medusa sign
VEIN OF GALEN ANEURYSM
Developmental Theory:
Raybaud proposes that vein of Galen aneurysms are not a result of dilatation of the
veins of Galen, but rather a consequence of dilatation of persistent median
prosencephalic veins. The evidence he cites supporting this statement includes the
following:
(a) The vein of Galen develops late and lacks connections to the choroidal branch of
the anterior cerebral artery, which is a primary feeder in most vein of Galen
aneurysms;
(b) The typical vein of Galen aneurysm directly drains both prosencephalic and
mesencephalic arteries in a pattern typical of the median prosencephalic vein,
but the normal mature vein of Galen does not.
(c) Anomalous venous drainage as described in previous sections probably
represents persistent fetal drainage that remains intact because it effectively
deals with the high-flow system. Such persistent fetal drainage may prevent the
development of the normal sinus system.
Neurosurg Clin N Am 2010
VEIN OF GALEN
ANEURYSM
Images from the case of a 3-month-old triplet with worsening congestive heart failure.
A. Volume-rendered MR
B, Carotid injection during
angiogram shows, from an arterial embolization
inferior prospective, the
procedure performed when
arterial feeders supplying
the patient was 6 months old
the lesion from the left
shows residual flow to the
side (arrows).
lesion from pericallosal and
Blaise V. Jones et al. AJNR Am J Neuroradiol
2002;23:1717-1724
posterior choroidal arteries
(arrowheads).
©2002 by American Society of Neuroradiology
C, Coronal view fast spinecho T2-weighted MR
image obtained 6 years
after embolization shows
continued patency of the
varix and mild
enlargement of extra-axial
fluid spaces.
REFERENCES
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System. Neurosurg Clin N Am 2010; 21: 399–42
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;1948: 212(32):205–271
3. Saltzman G. Patent primitive trigeminal artery studied by cerebral angiography. Acta Radiol
1959;51: 329–336
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an autopsy case. Neurosurgery 1993; 32:144–147
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Caro R de, Parenti A, Munari PF. The persistent primitive hypoglossal artery: a rare
anatomic variation with frequent clinical implications. Ann Anat 1995;177:193–198
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Dimmick S, Faulder K .Normal Variants of the Cerebral Circulation at Multidetector CT
Angiography RadioGraphics 2009; 29:1027–1043.
REFERENCES
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(proatlantal type 1) results in ‘‘top of the basilar” syndrome. Stroke 1993;24:2114–2117
8. Klosovskii BN. Fundamental facts concerning the stages and principles of development of
the brain and its response to noxious agents. London Pergamon Press 1963; 3–43.
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1991;18:277– 285
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Atypical Findings on Susceptibility-Weighted Imaging AJNR August 2008; 29: e56.