1	Completing The Circle- Evaluating the Circle of Willis. Common and Uncommon Variants: What Your Interventionalist and Neurosurgeon Want To Know Darren Fitzpatrick, MD Rona Woldenberg, MD Karen Black, MD Avi Setton, MD North Shore University Hospital, Manhasset, NY
2	"NO DISCLOSURES" NO DISCLOSURES
3	Objectives Describe clinically relevant anomalies and variants of the circle of Willis Describe how variants of the circle of Willis affect the diagnosis and management of cerebrovascular disease on both angiography and noninvasive imaging
4	Internal Carotid Artery Intracranial Portions Petrous (1) Cavernous (2) Ophthalmic (3) Communicating Segment (4)
5	Cavernous Carotid Artery Located within cavernous sinus medial to Meckel’s cave Anomaly Persistent trigeminal artery
6	Persistent Trigeminal Artery Connects fetal carotid artery to paired longitudinal neural arteries, precursors of the vertebrobasilar system Occurs in 0.02-0.6% of population Most common intracranial persistent fetal vessel encountered Associated with vascular steal, ocular palsies, aneurysm formation, vascular rupture, subarachnoid hemorrhage, trigeminal neuralgia, and arteriovenous fistula
7	Persistent Trigeminal Artery Aneurysm
8	Ophthalmic Carotid Artery Branches: Ophthalmic artery Superior hypophyseal artery Variations: Cavernous origin Origin from middle meningeal artery
9	Cavernous Origin of Ophthalmic Artery
10	Communicating Carotid Segment Passes between CN II and CN III Branches: Posterior communicating artery Anterior choroidal artery Anterior Choroidal Artery Courses posteromedial Supplies zone between corpus striatum and thalamus
11	Anterior Communicating Artery Connects the two A1 segments and provides collateral flow to the contralateral hemisphere Best visualized in an oblique projection Variations: Single in 60% of cases Plexiform (multiple vascular channels) Duplication Absent (5%)
12	Duplicated Anterior Communicating Artery
13	Absent Anterior Communicating Artery
14	Posterior Communicating Artery Unites anterior and posterior circulations Bilateral Varies greatly in size Variations: Absent vessel Infundibulum Fetal origin- supplies ipsilateral posterior cerebral artery territory
15	Posterior Communicating Artery Infundibulum
16	Posterior Communicating Artery Aneurysm
17	Posterior Communicating Artery
18	Anterior Cerebral Artery Distal ACA: Courses above corpus callosum, splenium, callosomarginal artery, parietal branches Supplies anterior 2/3 of medial hemisphere and body of corpus callosum Variations: A1 segments vary in size- may be hypoplastic or even absent Duplicated segments Azygos A2 segment Proximal ACA: Perforators for medial lenticulostriate and corpus callosum Orbital and frontal branches Supplies head of caudate, anterior-medial basal ganglia, inferior-medial internal capsule, olfactory bulb, gyrus rectus and ventromedial frontal lobe
19	Asymmetric A1 Segments
20	Absent A1
21	Absent A1 Segment
22	Duplicated A1 Segment
23	Azygos Anterior Cerebral Artery
24	Azygos Anterior Cerebral Artery
25	Middle Cerebral Artery M1 segment bifurcates or trifurcates M2 segment divides into 6-8 stem arteries M2 segments loop within roof of Sylvian fissure to demarcate the insula
26	Middle Cerebral Artery Proximal Branches Perforating lenticulostriate arteries Anterior temporal cortical branch Territory: Caudate Internal capsule Basal ganglia Anterior pole of temporal lobe
27	Accessory Middle Cerebral Artery
28	Accessory Middle Cerebral Artery
29	Early Middle Cerebral Artery Bifurcation
30	Posterior Cerebral Artery Proximal P1 segment: Territory: Posterior thalamus Hypothalamus Posterior limb internal capsule Midbrain (CN III & IV nuclei) Choroidal branches Inferior-lateral surface of temporal lobe Variants: Differ in size and position
31	Posterior Cerebral Artery Distal Segment Medial division: Posterior 1/3 interhemispheric fissure Parietal lobe Occipital lobe Lateral division: Temporal lobe
32	Absent P1 Segment
33	Hypoplastic P1 Segment
34	Fetal Origin of Posterior Cerebral Artery in Basilar Occlusion
35	Persistent Hypoglossal Artery
36	Basilar Artery Branches: Pontine perforators Anterior inferior cerebellar artery (AICA) Superior cerebellar artery Territory: Brainstem Upper-mid cerebellum and vermis Occipital and temporal lobes Thalamus Posterior limb internal capsule Variations: Fenestration Dolichoectasia Hypoplasia
37	Fenestrated Basilar
38	Fenestrated Basilar Artery with Aneurysm
39	Dolichoectatic Vertebrobasilar System
40	Dolichoectatic Vertebrobasilar System
41	Hypoplastic Posterior Circulation
42	Vertebral Arteries Extracranial branches: Cervical and meningeal branches Intracranial branches Posterior inferior cerebellar artery (PICA) Spinal arteries Vascular territory: Lateral medulla Upper cord Cerebellar tonsils Inferior cerebellar hemispheres and vermis
43	Vertebral Artery Variants: Duplication Size (left dominant in majority of cases) Direct origin from the aortic arch Common AICA-PICA trunk Vessel terminating in PICA
44	Duplicated Vertebral Artery
45	Vertebral Artery Terminating in PICA
46	Hypoplastic Vertebral Artery
47	Common AICA/PICA Trunk
48	Importance of Common AICA/PICA Trunk
49	Conclusion There are a wide variety of variants of the circle of Willis which are important in the management of cerebrovascular disease These lesions may mimic disease, may predispose patients to aneurysm formation or may alter invasive therapy Reporting the presence of these variants is helpful to guide referring physicians, particularly when endovascular or surgical therapy is being considered
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