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Vascular Anatomy and Variants
MRI/CT Course ASN Annual Meeting 2014
John A. Bertelson, MD
Assistant Professor of Neurology, UT-Southwestern Clinical Assistant Professor of Psychology, UT-Austin
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DISCLOSURES
• None
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Outline
• Arterial Anatomy and Variants – Intracranial – Extracranial – Watershed
• Venous Anatomy and Variants
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Arterial Anatomy
• Intracranial
– Circle of Willis
– Anterior Circulation
– Posterior Circulation
– Watershed
– Other
• Extracranial
– Cervical
– Intra-Thoracic
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Intracranial arterial structures
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Intra-Cranial Arterial Anatomy
Circle of Willis
1. L. ICA 2. L. ACA (A1) 3. Ant. COM 4. R. Post. COM 5. R. PCA (P1) 6. Basilar Art. 7. MCA 8. Vertebral Art. 9. Optic Chiasm 10.L PCA (P2) 11. ACA (A2) Note: Many variations exist
Diagnostic Radiology, p. 126
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Circle of Willis- Common Variants
Neuroradiology, p. 87
• ACOM – Variants 10-15%
• PCOM – Hypoplastic or Absent 25-33%
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Anterior Cerebral Artery (ACA)
• A1 – Horizontal segment – Hypoplastic in 5-18% – Branch:
• Medial lenticulostriate
• A2
– Branch: • Recurrent artery of
Heubner, from distal A1 or proximal A2
• A3 – Pericallosal branch – Callosomarginal branch
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Anterior and Posterior Cerebral Arteries
Neuroanatomy, p. 29
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ACA- Vascular Territory
Views: A. Lateral
B. Medial
C. Superior
D. Base
Diagnostic Radiology, p. 135
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Anterior Cerebral Artery- Variants
Vasculature of the Brain and Cranial Base, p. 116-7
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38 yo female with headache and vertigo
Azygous (or azygos) ACA
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ACA Variants- Third A2 Segment
• 3T MRA
– Time of flight (TOF)
– Left carotid sequence
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Middle Cerebral Artery
• M1 (Horizontal) – Lateral Lenticulostriates
• Lateral putamen
• Caudate nucleus
• External capsule
• M2 (Insular)
• M3 (Opercular)
• M4 (Cortical)
Osborn’s Brain, p. 176
.
↑
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Middle Cerebral Artery
• MRA
– Submentovertex view
– M1 • Genu/Bifurcation
– M2
– M3
Osborn’s Brain, p. 176
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MCA- Distal Branches
Neuroanatomy p. 19
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MCA- Vascular Territory
Views: A. Lateral
B. Medial
C. Superior
D. Base
Diagnostic Radiology, p. 136-8
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Vascular Neuro-Anatomy- Posterior Fossa
• Vertebral – Branches:
• Anterior spinal • PICA • ± AICA
– Variants: • Embryonic carotid-vertebral
fenestrations • Terminates at PICA (1%)
• Basilar
– Branches: • AICA • SCA • Perforating arteries
– Variants: • Hypoplasia • Fenestrations
Diagnostic Radiology, p. 143-5
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PCA Branches • P1
– Peduncular segment – Branches:
• Thalamo-perforating
• Medial posterior choroidal
• P2 – Ambient segment – Branches:
• Lateral posterior choroidal
• P3 – Quadrigeminal
segment
• Variant: – Fetal PCA: from the
ICA rather than basilar artery, seen in 15-20%
Diagnostic Radiology, p. 139-41
Neuroanatomy, p. 21
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“Fetal PCA”: Dominant Left PCOM, Hypoplastic Left P1
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PCA- Vascular Territory
Views:
• A. Lateral
• B. Medial
• C. Superior
• D. Base
Diagnostic Radiology, p. 139-41
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Vertebrobasilar Variants and Anomalies
• Asymmetry common – Right dominant in 25%
• Shared AICA-PICA trunk
• Vertebral terminates at PICA
• Extradural origin of PICA
(5-18%)
• Duplicated PICA (2%)
• Conjoined origin of P1 and SCA
• Anomalous origin (5-6%) – Usually from aortic arch
• PICA anomalous origin
– May be from ICA, associated with increased incidence of aneurysms
• Duplicated vertebral (<1%)
– Two origins
• Fenestrated vertebral (<1%)
– One origin – Associated with other
malformations, including aneurysms and AVMs
Diagnostic Cerebral Angiography, p. 180-4
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Vertebrobasilar Variants
• A: hypoplastic right vert. ends in PICA
• B: absent right vert. (rare)
• C: hypoplastic right vert.
• D: hypoplastic left vert.
Vasculature of the Brain and Cranial Base, p. 169
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Vertebrobasilar Variants
Diagnostic Cerebral Angiography, p. 191,3
Vertebral angiogram, AP view Vertebral angiogram, oblique view
Double SCA
Fenestrated basilar artery
Basilar tip aneurysm
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66 yo female with headache
Fenestration
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Vascular Neuro-Anatomy:
• Watershed territory – Cerebral volume in-
between multiple major vascular territories
– Potentially at risk to ischemia with hypotension, especially with comorbid, critical, large vessel stenosis
– Common location for metastatic lesions
Diagnostic Radiology, p. 137
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Watershed Territory
Neuroanatomy, p. 17
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Watershed Ischemia
• Left MCA/ACA watershed ischemic stroke secondary to high grade, left ICA stenosis
##############
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52 year old male with dementia
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Persistent Trigeminal Artery
Diagnostic Cerebral Angiography, p. 92
Lateral View, ICA angiogram
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Persistent Trigeminal Artery
• Aka “Primitive trigeminal artery”
• Embryonic carotid-basilar anastamosis
• Connects cavernous ICA with dorsal longitudinal neural arteries (precursor to the vertebro-basilar arteries)
• Normally completely regresses
• Most common persistent embryonic carotid-basilar anastamosis – Seen in 0.02%-0.6% of cerebral angiograms
Diagnostic Cerebral Angiography, p. 91
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Carotid-Basilar Anastamoses
1
2
3
4
5
Diagnostic Cerebral Angiography, p. 65, 69
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Aortic Arch and Great Vessels: Embyrologic Development
Diagnostic Cerebral Angiography, p. 7-11
4 weeks 5 weeks 6 weeks 7 weeks
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Persistent Trigeminal Artery Clinical Significance
• Usually none, except…
– Associated with increased incidence of other vascular abnormalities (up to 25%) and up to 15% of PTA cases have coexistant aneurysms
Diagnostic Cerebral Angiography, p. 94
Lateral View, ICA angiogram
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Internal Carotid Artery (ICA)
• Bouthillier nomenclature:
• C1- cervical – Bulb and ascending segment
• C2- petrosal
• C3- lacerum
• C4- cavernous
• C5- clinoid
• C6- ophthalmic
• C7- communicating
Diagnostic Cerebral Angiography, p. 58
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Location Branches
Bulb (C1) Extra-cranial None
Cervical (C1) Extra-cranial Rare
Petrous (C2) Intra-osseous - Tympanic
- Vidian
- Caroticotympanic
Cavernous
(C4)
Cavernous - Meningohypophyseal
Supraclinoid
(C6-7)
Intracranial -Ophthalmic
-PCOM
-Ant. Choroidal
Vascular Neuro-Anatomy:
Internal Carotid Artery Segments
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17 yo female with migraine
• Bovine variant:
– Origin of left CCA from brachiocephalic trunk
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Aortic Arch and Great Vessels
• Brachiocephalic trunk – Aka “Innominate” art.
– Branches: • Right subclavian art.
– Right vertebral
• Right common carotid
• Left common carotid
• Left subclavian – Branches:
• Left vertebral
• Other
Atlas of Neuroanatomy,p.113
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Aortic Arch: “Bovine origin”
Aortic Arch: Standard Anatomy
“Bovine” Variant A “Bovine” Variant B
Layton 2006
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True Bovine Anatomy
Layton 2006
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Aortic Arch- Normal Variants
• A: normal
• Most common variants – B-C: “bovine” variant
– H: Left vert. off arch
– K: Seen in Downs synd.
Practical Neuroangiography, p. 100
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Venous Anatomy and Variants
Normal anatomy Venous territories
Variants Other
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Central Venous System
• Sinuses:
– Superior Sagittal Sinus – Inferior Sagittal Sinus – Straight Sinus – Transverse Sinus
• Veins:
– Great cerebral vein (of Galen) – Basal vein, of Rosenthal – Internal Cerebral Vein
Neuroanatomy, p. 29
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Vein of Galen
Vasculature of the Brain and Cranial Base, p. 196
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Superficial Veins
Vein of Trolard- to SSS
Vein of Labbé- to Trans. Sinus
Insert Haines 19 b
Neuroanatomy, p. 19
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Venous Territories
• Cortex (Green) – Cortical Veins
– Superior Sagital Sinus
• Perisylvian region (Purple) – Sphenoparietal sinus
– Cavernous sinus
• Deep structures (Red) – Internal Cerebral Vein
– Vein of Galen
• Cortex (Yellow) – Vein of Labbe
– Transverse sinuses
Osborn’s Brain, p. 221
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Sinus Thrombosis?
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Arachnoid Granulation (AG)
• Common variants
– 8.3% M
– 12.2% F
• Subarachnoid protrusion into sinus
• Function: CSF reabsorption
• Small AG usually demonstrate imaging features similar to CSF
Osborn, p. 216
Br. J. Rad, 1999
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Arachnoid Granulation- Characteristics
Location 1,2 % of Total
Sigmoid Sinus 2
Transverse Sinus 80-85
Confluence of Sinuses 5-6
Straight Sinus 1-2
Superior Sagittal Sinus 1-4
1. AJNR, 1996,
2. Br. J. Rad, 1999
3. AJNR, 2010
Size (mm) 2,3 % of Total
< 2 9.7
2-4 37.3
4-6 31.3
6-8 14.9
> 8 6.7
> 1cm (Giant)
Probably rare
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Giant Arachnoid Granulation
CT T2W
AJNR, 2010
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Arachnoid Granulation vs. Other T1W FLAIR T2W
???
???
Br. J. Rad, 1999
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Arachnoid Granulation vs. Other T1W FLAIR T2W
Arachnoid
Granulation
Epidermoid
Br. J. Rad, 1999
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DDx Venous Sinus Lesion
• Thrombus
• Arachnoid Granulation
• Sinus hypoplasia
• Variant bifurcation
• Intrasinus variants
– Septa
– Fenestrations
– Duplications
• Other
– Subdural Hematoma
– Tumor
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Venous Sinus Lesions
Osborn, p. 230
• Thrombus
• Arachnoid Granulation
• Sinus hypoplasia
• Variant bifurcation
• Intrasinus variants
– Septa
– Fenestrations
– Duplications
• Other
– Subdural Hematoma
– Tumor
T2
GRE
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Venous Sinus Lesions
Osborn, p. 235
• Thrombus
• Arachnoid Granulation
• Sinus hypoplasia
• Variant bifurcation
• Intrasinus variants
– Septa
– Fenestrations
– Duplications
• Other
– Subdural Hematoma
– Tumor T1 C+
MP RAGE
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Venous Sinus Lesions
Osborn’s Brain, p. 236
CT Venogram, Coronal
CT Venogram, Axial
• Thrombus
• Arachnoid Granulation
• Sinus hypoplasia
• Variant bifurcation
• Intrasinus variants
– Septa
– Fenestrations
– Duplications
• Other
– Subdural Hematoma
– Tumor
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Venous Sinus Lesions
• Thrombus
• Arachnoid Granulation
• Sinus hypoplasia
• Variant bifurcation
• Intrasinus variants
– Septa
– Fenestrations
– Duplications
• Other
– Subdural Hematoma
– Tumor Osborn’s Brain, p. 235
CT Axial
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Conclusions
• Vascular lesions are commonly seen in the routine practice of neuroimaging: – Symptomatic
– Incidental
– Normal variant
• Always look for the second lesion
• Thank you
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References
• Practical Neuroangiography. Baltimore, Williams and Wilkins, 1997. • Magnetic Resonance Angiography: Techniques, Indications, and Practical Applications. Milan,
Springer, 2005 • Diagnostic Cerebral Angiography 2nd Ed. Philadelphia, Lippincott Williams & Wilkins, 1999. • Vasculature of the Brain and Cranial Base: Variations in Clinical Anatomy. New York, Thieme.
1999. • Diagnostic Radiology. Mosby, 1994. • Atlas of Neuroanatomy. Boston. Butterworth- Heinemann, 1999. • Curtin JC and Kelly MA “Subarachnoid Hemorrhage” In: Atlas of Cerebrovascular Disease.
Philadelphia, Current Medicine, 1996. • Diagnostic Imaging: Brain. Amirsys, 2004. • Comi AM. “Pathophysiology of Sturge-Weber Syndrome.” Journal of Child Neurology 2003;
18(8):509-16. • Taylor DC. “Tolosa-Hunt Syndrome.” http://emedicine.medscape.com/article/1146714-
overview . Downloaded 1/13/2012. • Layton KF et al. “Bovine Aortic Arch in Humans: Clarification of a Common Misnomer.” AJNR
27: 1541-2. 2006. • Osborn’s Brain. Amirsys, 2013. • Neuroradiology: The Requisites, 2nd Edition. Mosby, 2003. • Neuroantomy: An Atlas of Structures, Sections, and Systems, 6th Ed. Lippincott Williams &
Wilkins 2004.