anatomic variations of the cerebral arteries - avaliação por imagem

Anatomic Variations of the Cerebral Arteries

Dr. Emanuel R. Dantas Médico Radiologista – Membro Titular C.B.R.

Artéria cerebral anterior -‐‑ Variantes

Dr. Emanuel R. Dantas

Agenesis/hypogenesis of ICA

•  Agenesis of ICA is rare, with an estimated prevalence of 0.01%.

•  Agenesis of ICA is usually unilateral. •  Agenesis can be distinguished from acquired ICA

occlusion by examination of the skull base. •  In cases of true agenesis, the bony carotid canal is

absent or hypoplastic. •  Clinically, there is an increased prevalence of

associated abnormalities, such as intracranial aneurysms, in these cases.


Hypogenesis of internal carotid artery. a On coronal view of MR angiography (MRA) right internal carotid artery is not seen. b, c High-‐‑resolution CT scan through the skull base shows a very small right carotid canal (arrows in c). Compare with the normal-‐‑sized left carotid canal (arrows in b)


Aberrant ICA •  Aberrant intratympanic ICA and lateral pharyngeal

ICA are recognized as aberrant ICA; the former is the anomaly that occurs when the ICA takes an aberrant course in the temporal bone and passes through the middle ear.

•  It is associated with the absence of the bone plate between the carotid canal and tympanic cavity.

•  Most often the condition presents as a hypervascular mass within the tympanic cavity on otoscopic inspection.


Aberrant ICA •  The lateral pharyngeal ICA is the anomalous vessel

that exhibits extreme, medial tortuosity in which the carotid artery extended to or near the midline posterior pharyngeal wall.

•  Clinically, the lateral pharyngeal ICA poses a risk during both major oropharyngeal tumor resections and less extensive procedures such as tonsillectomy, adenoidectomy, and palatopharyngoplasty; therefore, recognition of this anomaly and preoperative diagnosis is important.


Aberrant intratympanic internal carotid artery. Highresolution a CT scan through the skull base and b coronal reconstruction image show left aberrant internal carotid artery in the middle ear (arrows). c Frontal view of left carotid angiography demonstrates that the left internal carotid artery lies abnormally far laterally (arrowhead)


Azygos ACA (unpaired ACA)

•  The unpaired arterial arrangement represents a singletrunk arrangement that supplies both hemispheres.

•  In this anomaly, a single trunk throughout the ACA course is called the azygos artery.

•  The conventional type is a short or long common trunk (fused).

•  The statistical incidence of azygos ACA ranges from 0 to 5%.


Azygos ACA (unpaired ACA)

•  Azygos ACA may be observed as a finding with little clinical significance.

•  Azygos ACAs have also been reported in association with holoprosencephaly and an increased risk of aneurysm at its bifurcation.

•  The clinical importance of a correct diagnosis of azygos ACA arises from the presence of a single trunk, which supplies blood to both hemispheres


Unpaired anterior cerebral artery. a Magnetic resonance angiography demonstrates a single trunk (azygos artery) originates from the confluence of both A1 tracts. b In another case, frontal view of right carotid angiography and c 3D reconstruction image demonstrate unpaired anterior cerebral artery with small aneurysms (arrows). D Representation of Azygos artery


Bi-‐‑hemispheric ACA •  The bi-hemispheric pattern is constituted by a

pericallosal artery supplying the medial portions of both hemispheres.

•  The opposite ACA is hypoplastic and supplies only the callosomarginal group of branches.

•  This variation is found in 2–7% of anatomic specimens.

•  Clinical significance is the same as the azygos ACA.


Bi-‐‑hemispheric anterior cerebral artery. Representation of Bi-‐‑hemispheric anterior cerebral artery


Fenestration of ACA and ACoA

•  In previous reports, the incidence of fenestration of the ACA was 0.1–7.2% in autopsies.

•  In many cases fenestration occurred at the horizontal segment of ACA, and it has been reported that the incidence of fenestration of the ACoA was 7.5–40% in autopsies.

•  Clinically, a fenestration ofACoA and a small fenestration of ACA might be mistaken for ACoA aneurysm on MRA.

•  Diagnosis of those cases is difficult or impossible using conventional DSA


Fenestration of anterior cerebral artery. a Representation of the fenestration of the anterior cerebral artery and anterior communicating artery. b Magnetic resonance angiography demonstrates fenestration (arrows) in the horizontal segment of anterior cerebral artery


Fenestration of anterior communicating artery (ACoA). a Three-‐‑dimensional digital subtraction angiography (DSA) image of the left carotid angiography demonstrate fenestration (arrows) in ACoA. b In another case, 3D DSA image of the left carotid angiography shows fenestration (arrowheads) of ACoA with an aneurysm (arrow)


Persistent primitive olfactory artery

•  The persistent primitive olfactory artery (PPOA) is characteristic in that it arises from the terminal portion of the ICA, runs along the olfactory bulb, makes an abrupt posterior turn behind the olfactory bulb, and finally becomes the distal ACA.

•  It is associated with the absence of ACoA and the recurrent artery of Heubner.


Persistent primitive olfactory artery. a Oblique view of MRA shows the anomalous artery (arrow) originating at the bifurcation of the left ICA. It courses anteromedially and makes a hairpin turn to the posteriorly. b Axial T2-‐‑weighted MRI shows anomalous flow void originating left ICA and running anteromedially (arrowheads). c Representation of the persistent primitive olfactory artery


Artéria cerebral Média -‐‑ variantes


Duplicated and accessory MCA

•  The term “duplication of MCA” is used to characterized the two vessels originating from the distal end of the ICA, and the

•  The term “accessory MCA” is used to describe the anomalous vessel originating from ACA, that branch supplying the cortex in the distribution of the MCA.


Duplication of middle cerebral artery. a Representation of the accessory and duplicated middle cerebral artery. b Magnetic resonance angiography demonstrates left duplicated middle cerebral artery (arrows), which originates from left ICA


Accessory middle cerebral artery. a Magnetic resonance angiography and b frontal view of left carotid angiography demonstrate left accessory MCA, which originates from the proximal portion of the left anterior cerebral artery. The accessory MCA has perforating artery


Duplicated and accessory MCA

•  Komiyama has reported that duplication of the MCA supplies the anterior temporal lobe, and that the accessory MCA supplies the anterior frontal lobe.

•  The incidence of accessory MCA in autopsies is reported to be 0.3–2.7%, and that of duplicated MCA 0.7–2.9%


SISTEMA CAROTÍDEO E VÉRTEBRO -‐‑ BASILAR

variantes


Persistent Trigeminal Artery

•  Persistent trigeminal artery is the most common persistent carotid-basilar anastomosis.

•  It is located between precavernous ICA and basilar artery.

•  The caudad portion of the basilar artery is usually hypoplastic.

•  It is commonly associated with aneurysms due to abnormal flow dynamics

•  This variant may be identified by the presence of the Tau sign.


Persistent trigeminal artery. (A) Axial CTA, (B) MIP MRA, (C) Axial MRA, (D-‐‑F) MIP MRA, and (G-‐‑H) lateral projection cerebral angiogram. Persistent trigeminal artery is identified (red arrows) starting at the distal ICA canal. Tau sign (blue arrow, lower left in H only).


Persistent trigeminal artery. (A) Axial CTA, (B) MIP MRA, (C) Axial MRA, (D-‐‑F) MIP MRA, and (G-‐‑H) lateral projection cerebral angiogram. Persistent trigeminal artery is identified (red arrows) starting at the distal ICA canal. Tau sign (blue arrow, lower left in H only). Dr. Emanuel R. Dantas

Persistent trigeminal artery. (A) Axial CTA, (B) MIP MRA, (C) Axial MRA, (D-‐‑F) MIP MRA, and (G-‐‑H) lateral projection cerebral angiogram. Persistent trigeminal artery is identified (red arrows) starting at the distal ICA canal. Tau sign (blue arrow, lower left in H only).


Persistent Hypoglossal Artery

•  Persistent hypoglossal artery is the second most common persistent carotid-basilar anastomosis after persistent trigeminal artery.

•  It connects the cervical ICA to the basilar artery. •  It enters through the hypoglossal canal, not the

foramen magnum, and usually parallels the course of the hypoglossal nerve.

•  Often it is associated with vertebral artery aplasia or hypoplasia, aneurysms, and subarachnoid bleeds.

•  Typically no posterior communicating arteries are present.


Persistent hypoglossal artery. (A, B) 3D reconstruction CTA, (C) lateral projection cerebral angiogram, (D) CTA axial, and (E) MIP MRA. Abnormal bifurcating internal carotid artery (red arrows, A, B and E) giving off persistent hypoglossal artery, which enters the hypoglossal canal (gold arrow, D).


Persistent Stapedial Artery

•  Persistent stapedial artery is a persistent fetal branch of the hyoid artery.

•  It gives rise to the middle meningeal artery; thus, the normal foramen spinosum is absent.

•  It presents as a soft-tissue mass along the horizontal portion of the tympanic facial nerve.

•  It coexists with aberrant ICA in 60% of cases. •  Typically, they are asymptomatic and rarely can

present with tinnitus and pulsatile retro tympanic mass


Persistent stapedial artery. (A) Axial temporal bone CT, (B) coned-‐‑down axial temporal bone CT, (C) lateral projection cerebral angiogram, and (D) coned-‐‑down lateral projection cerebral angiogram


Fenestration or duplication of vertebral artery

•  The vertebral artery (VA) fenestration is found in 0.23–2.0 % of autopsies or angiographic studies.

•  Angiographically shown duplications of the origin of the VA are very rare.

•  The VA fenestration is often associated with other anomalies of the brain, spinal cord, and spine; these include fused vertebrae, other vascular anomalies, and an increased prevalence of aneurysms and vascular malformations


Fenestration of vertebral artery. Frontal view of right vertebral angiography demonstrates fenestration in the right vertebral artery (arrows)


Fenestration of basilar artery

•  Basilar artery fenestration is reported in 1–5% of autopsies and in 0.1–1.9% of angiographic series.

•  It can occur anywhere along the course of the BA but is most frequent in the proximal basilar trunk, close to the vertebral arteries.

•  The high incidence of aneurysm in association with BA fenestration has been reported.


Fenestration of basilar artery. A 3D reconstruction image demonstrates fenestration in proximal basilar artery (arrows). An aneurysm of the basilar tip is also noted (arrowhead)


Artéria vertebral posterior -‐‑ variantes


Fetal PCA (Persistent fetal origin from the ICA)

•  If the embryonic PCoA fails to regress, the dominant blood supply to the occipital lobes comes from the ICA via the fetal PCA instead of from the vertebrobasilar system.

•  This occurs in approximately 20–30% of cases. •  Clinically, if we treat the ICA–PCoA aneurysm, we

should not occlude fetal PCA to avoid infarction of the PCA territory


Fetal posterior cerebral artery. Axial MRA shows the right fetal posterior cerebral artery (arrows). Left persistent primitive trigeminal artery is also noted (arrowheads)


Fetal posterior cerebral artery. (A) Axial CTA, (B) axial MRA, (C) lateral projection cerebral angiogram after injection of left common carotid artery, and (D) AP projection cerebral angiogram after injection of left common carotid artery. Dr. Emanuel R. Dantas

Fetal posterior cerebral artery. (A) Axial CTA, (B) axial MRA, (C) lateral projection cerebral angiogram after injection of left common carotid artery, and (D) AP projection cerebral angiogram after injection of left common carotid artery.


Hyperplastic anterior choroidal artery

•  The incidence of hyperplastic anterior choroidal artery is reported to be 1.1–2.3% .

•  In this case, it supplies the posterior cerebral artery branches, especially in the temporooccipital lobes


Supero-‐‑inferior (a) and lateral (b) partial maximum intensity projection MRA shows a hyperplastic anterior choroidal vessel (arrowhead) arising from the distal left internal carotid artery and supplying the left medial occipito-‐‑temporal lobe along with left posterior cerebral artery (arrow). The normal posterior communicating artery (small arrow) is seen separately


ADENDO LESÕES ARTERIAIS


Arteriovenous Malformation

•  These vascular malformations are defined by the presence of an enlarged feeding artery and draining vein and associated cluster of entangled vasculature called nidus.

•  They are identified as flow voids on magnetic resonance imaging.


Arteriovenous malformation. Patient 1A-‐‑F: (A) Axial CTA, (B) axial MRI T1W post gadolinium, (C) axial MRI FLAIR, (D) coronal CTA, (E) sagiaal CTA,


Arteriovenous malformation. Patient 1A-‐‑F: (A) Axial CTA, (B) axial MRI T1W post gadolinium, (C) axial MRI FLAIR, (D) coronal CTA, (E) sagiaal CTA, Dr. Emanuel R. Dantas

Capillary Telangiectasia •  Capillary telangiectasias are angiographically

occult and demonstrate typical “brush-like” enhancement.

•  They do not hemorrhage; thus, they are commonly identified incidentally.

•  They are characterized by normal neural tissue between clusters of abnormal capillaries.

•  Most commonly they are located in the pons and midbrain


Capillary Telangiectasia •  Because lesions do not bleed, there is no deposition

of blood breakdown products and thus no abnormal low signal on T2W images from hemosiderin deposition

•  They are associated with Osler-Weber-Rendu syndrome and rarely with developmental venous anomalies.


Capillary telangiectasia. (A) MRI of the brain axial T1W with gadolinium, (B) MRI of the brain axial T2W, (C) MRI of the brain coronal T1W with gadolinium, (D) MRI of the brain sagiaal T1W with gadolinium


Cavernous Malformation •  Cavernous malformations are hemorrhagic lesions. •  As they contain blood products with high protein

content, they present as high-density lesions on CT and may calcify.

•  They are angiographically occult but can enhance •  Characteristically, they demonstrate a complete

rim of hemosiderin. •  Hemosiderin deposition causes signal dropout in

magnetic resonance perfusion imaging due to paramagnetic effect.


Cavernous Malformation •  A “blooming” effect from blood product deposition

is seen on gradient echo (GRE) sequences. •  Histologically, we see vascular hamartomas with

associated immature blood vessels and hemorrhage and no interposed neural tissue (latter 2 characteristics used to differentiate from capillary telangiectasia)


Cavernous malformation. (A) MRI axial FLAIR, (B) MRI axial T2W, (C) MRI axial GRE, (D, E) CT axial unenhanced


Developmental Venous Anomaly

•  Developmental venous anomaly is an anatomical variant of normal venous drainage that presents as dilated or tortuous intramedullary veins.

•  They usually converge onto a larger vein that drains into the superficial or deep venous system.

•  The lesions are most often asymptomatic and may rarely hemorrhage.

•  They are visible with angiography and are associated with cavernous hemangiomas


Developmental venous anomaly. (A) MRI axial T1W with gadolinium, (B) MRI coronal T1W with gadolinium, (C) axial enhanced CT, (D) MRI axial T1W with gadolinium


anatomic variations of the cerebral arteries - avaliação por imagem

Education

left internal carotid

apericallosal artery

thecarotid artery

anteriorcerebral artery

single trunk azygos

fenestration of aca

opposite aca

smallfenestration of