anatomy vasculature

1. ANGIOGRAPHIC ANATOMY
OF THE INTRACRANIAL AND
EXTRACRANIAL ARTERIES

5. Angiographic anatomy principles
 Variation is the rule  benign
variants, dangerous variants,
pathologic variants
 Hemodynamic balance
 Visible vs invisible  collateral
circulation, and anastomoses
 Time and space
 Image orientations
 Direction of flow – reflux

6. Phases
 Early arterial – CCA to carotid bifurcation
 Late arterial – distal intracranial vasculature
 Capillary – choroidal blush is a good marker, indistinct
capillary blush
 Early venous – emergence of intracranial cortical and deep
veins
 Late venous – emergence of venous sinuses
 Complete cycle – 4 seconds, 1-2 seconds from arterial to
venous phase
 Exact timing depends on cardiac output, lumen diameter, ICP
and blood pressure
 Different arteries require different contrast injection rates
Note choroidal blush somewhat overlapping
With the orbital rim

7. CTA vs Cerebral angiography
CTA Cerebral Cerebral angiography
Complications Access complications
Artery complications including stroke
Contrast complications
Contrast allergies and nephropathy
Spatial resolution Fair (down to 2mm) Good (<1mm) GOLD STANDARD
Anatomy Good (with volume 3D and orthogonal
reconstruction)
Fair – limited to bony landmarks
Dynamic imaging Limited – one pass, unless 4D-CTA is performed Good
Intramural imaging Some direct imaging possible Limited to luminal imaging
Collaterals Limited ability, due to lack of dynamic imaging Good, but may require selective catheterization
Radiation exposure Moderate, 4D-CTA may be higher than cerebral
angiography. Trivial operator risk
High, depending on procedural complexity ,less
exposure with biplane systems. Nontrivial lifetime
operator risks.
Artifacts May be significant, especially in proximity to bony
structures or calcification (Volume averaging)
Mostly due to overlapping views, can be resolved with
3D reconstruction or oblique views
Posterior circulation Moderate to good, but limited due to volume
averaging and bony artifacts
Good, but access to both vertebral arteries may
depend on operator skill and anatomy
Ease of set up and use Simple, and fast to perform Moderate
Repeatability Theoretically unrestricted, practically restricted to
contrast dosage (5ml/kg, max 300ml)
Multiple procedures increase procedural risk
Failure rates Trivial restrictions to procedure Nontrivial restrictions to procedure eg dissection,
inability to cannulate

8. Sensitivity vs Specificity

9. External Carotid Artery(ECA)

14. Internal Carotid Artery(ICA)

18. 4D- CTA
Tabuchi S, Nakajima S. Usefulness of 320-row area detector computed
tomography for the diagnosis of cystic falx meningioma. Case Rep Oncol.
2013;6(2):362-366. Published 2013 Jul 6. doi:10.1159/000353929

19. Collateral score – MCA infarct, ASINR

21. ICA branches
 Cervical – None
 Petrous – Caroticotympanic, Vidian artery (if not mandibular origin)
 Lacerum – None
 Cavernous – Meningohypophyseal, Inferolateral trunk, McConnell’s capsular
arteries (occasionally seen)
 Clinoidal – None
 Ophthalmic – Ophthalmic artery, Superior hypophyseal
 Communicating – Posterior communicating, anterior choroidal, bifurcation

24. Meningohypophyseal trunk
 Proximal cavernous segment origin
 Main trunks – Inferior hypophyseal,
marginal tentorial, lateral tentorial
artery
 Posteriorly orientation
 Usually barely/not visible
 Supplies pituitary and dura

25. Purple – Marginal tentorial artery
White – Pituitary blush
Red – Inferior hypophyseal artery
Blue – Inferolateral trunk
Enlarged marginal tentorial artery
Secondary to tentorial meningioma

26. Inferolateral Trunk
 Medial cavernous segment origin
 Network, collateralizes
 Supplies cranial nerves, dura
 Branches – CN6, SOF, Rotundum,
Ovale

28. ACA

31. MCA

33. Vertebral Artery(VA)

38. PICA

39. DIAMETERS OF ARTERIES

40. Collaterals
 Physiologic redundancy - The brain’s bailout system
 “The invisible roads”  unimaged in normal states
 ICA-ICA collaterals
 Anatomic collaterals – ACOM, PCOM
 Self-reconstitution
 Distal collaterals (watershed compensation)
 Leptomeningeal collaterals
 Capillary collaterals (White matter disease)
 ECA-ICA collaterals (Moyamoya, IMAX)
 Distant-ICA collaterals

42. Compensation via distal collaterals of infarcted MCA
Territory by ACA
Compensation via ILT branches of occluded distal
ICA

43. ICA occlusion with reconstitution by vasa vasorum, compensation by ILT,
MMA and occipital artery
Moyamoya syndrome in ICA occlusion

44. ACOM crossfilling from right ICA
Distal ACA branches backfilling occluded ipsilateral MCA

45. Post surgical EC-IC bypass

46. Variations
 May be congenital/developmental, secondary to pathology
 More the rule than exception
 Origin, constitution
 Size
 Number
 Branching
 Communication and balance

47. ACA variations
Modification of
Kayembe,
Sasahara, and
Hazam
Classification.
Krzyzewski et
al., 2015

48. BRANCHING – MCA
 MCA variation is the rule
 80% bifr, 10% tri, 10% nothing (Osborn)
 Accessory/Duplications
 Lenticulostriate patterns
 Lenght of M1

49. PERSISTENT FETAL ANASTOMOSES
 Persistence of fetal carotid-
vertebrobasilar anastomoses
 Apart from PCOM, others range
from rare to very rare
 May increase risk of aneurysm
formation
Incidence Comments
Fetal PCOM 20-25% of
population
, common
When PCOM is larger than
P1, or when P1 is not
opacified on vert run
Primitive trigeminal
artery
0.5% Connects cavernous ICA with
basilar
Persistent otic
artery
Very rare
?existence
Petrous ICA to basilar
Persistent
hypoglossal artery
0.1% Cervical ICA to basilar,
enlarges hypoglossal canal
Proatlantal
intersegmental
artery
Very rare Cervical ICA to basilar at
level of C1-2, may originate
from ECA or ICA, may take
over vertebral artery.
Arterial anastomoses
frequent same area.

50. Persistent trigeminal artery

51.  The trigeminal artery is the largest of the fetal carotid-basilar anastomotic
arteries, and it persists for the longest embryonic period.
 The artery usually involutes after the development of the posterior
communicating artery.
 PRIMITIVE trigeminal arteries appear in the 3-mm. human embryo, connecting
the internal carotid arteries with the paired longitudinal arteries which
eventually fuse to form the basilar artery
 After the formation of the posterior communicating arteries, at the 14-mm.
stage, the trigeminal arteries regress as a rule. Rarely, they persist in the
adult.

52.  There are 2 types of PTA:
• Saltzman type I: PTA supplies the distal vertebrobasilar arteries. The posterior communicating
posterior communicating artery is absent and the caudal basilar is absent or hypoplastic with
hypoplastic distal vertebral arteries.
• Saltzman type II: PTA supplies the superior cerebellar arteries with the posterior cerebral

53. • Persistent hypoglossal artery, note similarity on lateral view to proatlantal intersegmental variant.
• C: CTA demonstrating passage of artery through hypoglossal canal.

54. • Proatlantal intersegmental artery on ICA run
• Persistence of the proatlantal intersegmental arteries is a rare form of primitive
carotid-basilar anastomoses.
• The proatlantal artery usually involutes by the 7- to 12-mm embryonic stage.
• Persistence of these channels is a well-recognized anomaly

55.  The proatlantal artery is one of the persistent carotid-vertebrobasilar anastomoses, and can be
subdivided into two types depending on its origin:
• type I: (~55%)
• also known as the proatlantal intersegmental artery
• arises from the internal carotid artery
• corresponds to the first segmental artery
• type II: (~40%)
• corresponds to the second segmental artery
• arises from the external carotid artery
• rarely (~5%) it arises from the common carotid artery

56. Fetal PCOM
 A fetal (origin of the) posterior cerebral artery is
a common variant in the posterior cerebral
circulation, estimated to occur in 20-30% of
individuals.
 The posterior communicating artery (PCom) is
larger than the P1 segment of the posterior
cerebral artery (PCA) and supplies the bulk of the
blood to the PCA. If bilateral, the basilar artery is
significantly smaller than normal.
 The term is typically used to refer to the situation
where the PCom is larger than the P1. However,
variation in usage abounds.

57. • Supposed primitive otic artery (very rare and often of uncertain provenance)
– AB Patel et al 2003, AJNR

58.  The primitive otic artery is one of four transient carotid-basilar
anastomoses and usually the first to disappear during embryogenesis.
 The early disappearance of the artery is theorized to account for its extreme
rarity, as compared with the frequency of other persistent anastomoses

59. Sources
 Neuroangiography.org
 Osborn’s Diagnostic Cerebral Angiography 2nd Edition
 Vasculature of the Brain and Cranial Base 2nd Edition
 3D Angiographic Atlas of Neurovascular Anatomy and Pathology. 1st Edition
 Elijovich L, Goyal N, Mainali S, et al CTA collateral score predicts infarct volume and
clinical outcome after endovascular therapy for acute ischemic stroke: a retrospective
chart review Journal of NeuroInterventional Surgery 2016;8:559-562.
 Botz, B., Deng, F. Multiphase CT angiography collateral score in acute stroke. Reference
article, Radiopaedia.org. (accessed on 19 Feb 2022) https://doi.org/10.53347/rID-
62280
 Etc