CT angiography and DSA are used for evaluating the extracraneal and intracranial circulation. Normal variants and anomalies of the supra-aortic trunks and Circle of Willis,
are common images findings 1
Its knowledge and recognition is important in a radiological report,
in order to make a correct diagnosis,
management and aid in surgical planning. For example,
the detection of trigeminal artery that frequently connects the internal carotid with the basilar artery,
has a functional consequence,
it creates a reversed in the vertebral system and may cause trigeminal neuralgia and/or subarachnoidal hemorrhage. This simple finding helps to plan a surgery or endovascular treatment 1,2,3,4.
The aim of this pictographic review is to illustrate normal variants and anomalies by anatomic distribution of arterial branches.
1.
VARIANTS OF SUPRA-AORTIC TRUNKS:
- Common Brachiocephalic Trunk
- Aberrant Right Subclavian or Brachiocephalic Artery
- Variant Branching Sequence
- Variants of Common Carotid Arteries
- Variant Origin of Vertebral Arteries
1.1.
Common Brachiocephalic Trunk:
Common brachiocephalic trunk,
consists in both common carotid arteries and the right subclavian artery arise from a single trunk.
It is the most frequent normal variant of aortic arch branching.
Fig. 1: Common brachiocephalic trunk: Both common carotid arteries and the right subclavian artery arise from a single trunk.
1.2.
Aberrant Right Subclavian or Brachiocephalic Artery:
The right subclavian artery is the last branch of the aortic arch in l% of individuals.
It courses to the right behind the esophagus in most of these cases. The aberrant right brachiocephalic artery is uncommon 5.
Fig. 2: Aberrant Right Subclavian Artery: It courses to the right behind the esophagus in most of these cases.
1.3.
Other Variant Branching Sequence:
Variations in the sequence of branching,
occur rarely,
like the left subclavian artery may be the second branch (before the left common carotid),
or the internal and external carotid arteries may originate independently from the aortic arch 6.
Fig. 3: Variations in the sequence of branching
1.4.
Variants of Common Carotid Arteries 6:
- Absence of the right common carotid.
- Common trunk for both carotids.
- A higher or lower bifurcation of the common carotids.
- External and internal carotids arising directly from the arch of the aorta.
- Common carotid may provide one or more of the branches usually derived from the external carotid (vertebral,
inferior thyroid,
or ascending laryngeal)
Fig. 4: • Common trunk for both carotids.
1.5.
Variant Origin of Vertebral Arteries:
It will be explained with the vertebrobasilar system (see below)
2.
VARIANTS AND ANOMALIES OF THE INTERNAL CAROTID ARTERY: .
We can study the variations and anomalies following the division of the artery segments.
2.1 C1 Anomalies:
- Absence,
hypoplasia,
duplication,
fenestration.
- Hypoglossal Artery persistent or proatlantoidea intersegmental artery.
(Carotid-basilar anastomosis: are fetal anastomosis usually regress to develop posterior communicating arteries).
Fig. 5: Hypoplasia of the Internal carotid Artery
Fig. 6: Hypoglosal artery:
A.Angio-CT, axial view.
B.VR reconstruction.
Fig. 7: Hypoglosal artery. Sagital view
2.2 C2 Anomalies:
- Aberrant petrous ICA.
- Persistent stapedial artery.
Fig. 8: Aberrant internal carotid artery.A(right). B(left)
2.3 C3 or Lacerum Segment: No variations or anomalies.
2.4 C4 Segment:
- Variant: Internal carotid arteries paramedian "kissing carotid arteries".
Importance in hypofisial surgery.
- Anomalies:
- Persistent trigeminal artery: Carotid-basilar embryonic anastomosis most cranial and most frequent (0.02 to 0.6%).
In 25% is associated with vascular anomalies,
particularly aneurysms.
- Anastomosis intracavernosal-rare,
is associated with an ICA aplasia failure and the circle of Willis.
Fig. 9: DSA. Persistent trigeminal artery
Fig. 10: DSA. Persistent trigeminal artery
2.5 C5 Segment: No branches arise from C5.
2.6 C6 or ophthalmic segment:
- Variants: Middle meningeal artery originated in the ophthalmic artery.
- Anomalies: Ophthalmic artery originating from the middle meningeal artery.
2.7 C7Segment :
- Variants:
- Posterior communicating artery: high variability in size.
If P1 is hypoplastic or absent,
posterior cerebral artery has a provision fetal and vascularized ACoPost its territory.
- Anterior choroidal artery: hemodynamic equilibrium with posteromedial and posterolateral choroidal arteries (VB system),
so their size and territory are variables.
- Anomalies:
- Rare.
Hypo or hyperplastic anterior choroidal artery.
- Origin of the anterior choroidal artery proximal to the origin of the posterior communicating artery.
3.
VARIANTS AND ANOMALIES OF THE CIRCLE OF WILLIS 1,2,3,7,8:
Normal variants include fenestrations and duplications.
A normal circle of Willis to be one in which there is a complete anastomotic polygon,
which may show considerable variability not only of its components but also its branches.
The so-called normal or textbook description holds true in about 34.5% of cases.
3.1 Anterior Cerebral Artery (ACA):
- Variants: A1 hypoplasia (10-25%).
The vascularized contralateral ACA vascular territory of both hemispheres through ACoAnt
Fig. 11: Fenestration of the anterior cerebral artery
Fig. 12: Fenestration of the comunicante anterior artery and hypoplasia A1.
Fig. 13: Hypoplasia A1
- Anomalies:
- Bihemispheric ACA (2-7%).
A2 segment hypoplasia,
the contralateral gives branches to both hemispheres.
- Azygos ACA (0.2-4%).
Persistence of embryonic half artery of the corpus callosum.
A single ACA vascularized both hemispheres,
may be associated with holoprosencephaly,
neuronal migration abnormalities and aneurysms.
- Multiple ACA.
(2-13%).
Over two A2 segment.
- Anomalous origin of the ACA.
In the internal carotid artery at the level of the ophthalmic artery.
Rare,
is associated with other abnormalities such as aneurysms and carotid agenesis.
3.2 Medial Cerebral Artery:
- Variants: Bifurcation,
trifurcation,
division early.
- Anomalies:
- Duplication.
(1-3%) arises from the internal carotid artery and travels parallel to M1.
- Accessory middle cerebral artery.
(2.7%) arises from the ACA and travels parallel to M1.
It is associated with aneurysms.
Fig. 14: cerebral media accesory
Fig. 15: MCA.
A. Duplication
B. Accesory
3.3 Posterior Cerebral Artery:
- Variants: Hypoplasia P1 (20%).
The distal posterior cerebral artery is opacified mainly through the internal carotid artery by posterior communicating artery route.
Fig. 16: Hypoplasia P1
- Anomaly: Carotid-basilar anastomosis
3.4 Vertebral-basilar system:
- Anomalies:
- Vertebral artery origin in the aortic arch (5%)
- Anomalous origin of the Posterior-inferior cerebellar artery (PICA).
It is associated with higher prevalence of aneurysms.
- Duplication and fenestration of the vertebral artery.
Represents a persistence of embryonic plexiform ducts.
It is associated with higher prevalence of aneurysms and vascular malformations.
- Duplication or fenestration of the basilar artery (1.3%),
associated with increased incidence of aneurysms
- Carotid-basilar anastomosis
- Anomalous origin of cerebellar arteries.
Fig. 17: Fenestration of the basilar artery
- Variants:
- Anterior-inferior cerebellar artery (AICA)-PICA common Trunk
- Accessory AICA
- Multiple anterior cerebellar artery.