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VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION

Comprehensive exploration of arterial variations and anomalies in cerebral circulation, including origins, courses, and significance of anomalies. Detailed examination of internal carotid, anterior cerebral, and anterior communicating arteries.

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VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION

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  1. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIALCIRCULATION F. Maiuri Cattedra di Neurochirurgia, Scuola di Medicina Università Federico II, Napoli

  2. CLASSIFICATION OF THE ARTERIALVARIATIONSAND ANOMALIES A. VARIATIONS Variations of the level of origin Variations of course Variations of caliber Variations of the vascularterritory B. ANOMALIES Agenesis and aplasia Hypoplasia Multiplications(duplication, fenestration, triplication) Fusion Anomalies of origin (from othervessels) Persistence of anomalousarteries Accessoryarteries 1998, 342 pp.

  3. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION • Internal carotid artery • Anterior cerebral- anterior communicating artery complex: 2.1 Proximal anterior cerebral artery (A1) 2.2 Anterior communicating artery 2.3 Distal anterior cerebral artery (A2) • Middle cerebral artery • Posterior communicating artery • Ophthalmic artery • Anterior choroidal artery • Posterior cerebral artery • Persistent carotid-vertebral and carotid-basilar anastomoses • Significance of the arterial variants and anomalies • Anomalies of the venous sinuses TOPICS

  4. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 1.1 Variations and anomalies of origin: a. level of origin ( common carotid bifurcation) b. separate origin of ICA and ECA (exceptional) (aortic arch, anonymous trunk, subclavear artery) 1.2 Variations of the carotid syphon 1.3 Hypoplasia 1.4 Agenesis 1.5 Duplication and fenestration (few cases -exceptional) 1. INTERNALCAROTIDARTERY r. ICA agenesis with transsellar anastomosis ICA fenestration ICA duplication

  5. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 1. INTERNAL CAROTID ARTERY 1.1 Variations of the origin: above C4 31% at C4 48.5% below C4 20.5% Exceptional locations C1-C2 0.3% C5-C7 0.15% Lazorthes G, Gouazé A: Vascularisation et circulation de l'encéphale. Masson 1976 Krayenbühl H; YaşargilM G: Cerebral angiography. Lippincott 1968

  6. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION • INTERNAL CAROTID ARTERY 1.2 Variations of the carotid syphon: Lazorthes G, Gouazé A: Vascularisation et circulation de l'encéphale. Masson 1976

  7. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 1. INTERNAL CAROTID ARTERY 1.3 Hypoplasia : • incidence: 0.079 % • location: from 2 cm above the bifurcation to the cranial cavity (variable extension) • well defined, very thin vessel (caliber 1-2 mm) with patent lumen • smaller bony carotid canal on CT

  8. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 1. INTERNAL CAROTID ARTERY 1.4 Agenesis: • incidence: 0.01 % (bilateral exceptional) • whole ICA or one or more segments • no evident vessel (or fibrous remnant with no lumen) • absence of carotid canal on CT • associated aneurysm : 20% • Origin of the ophthalmicartery • terminal branch of ICA • MCA • PCoA • ECA • BA Right ICA agenesis Left ICA agenesis CT: absence of left carotid canal

  9. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION Types of ICA agenesis and pathways of collateral circulation

  10. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2. ANTERIORCEREBRAL – ANTERIORCOMMUNICATINGARTERYCOMPLEX 2.1 Proximal ACA (A1 segment) 2.2 Anterior communicating artery (ACoA) 2.3 Distal ACA (A2 segment)

  11. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1) SEGMENT • Variations • Hypoplasia and aplasia • Fenestration and supraoptic duplication • Infraoptic course and its variants • Accessory anterior cerebral artery

  12. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1 SEGMENT) A. Variations • length: 7.2 to 20 mm • caliber: 0.9-4mm(median 2.3 mm) • symmetric • asymmetric • location of the A1-ACoAjunction • ( depending on the length of A1segments and opticnerves) • above the chiasm 70% • anterior or posterior to the chiasm 30%

  13. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1) SEGMENT B. Hypoplasia and aplasia • Hypoplasia (<1mm) 7-10% • Aplasia: 1-2%

  14. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1) SEGMENT C. Fenestration and supraoptic duplication • Fenestration • incidence 0.1-7.2% • alwaysatitsdistalportion • 65% with an associatedaneurysm • Supraopticduplication(exceptional) • (complete duplication of the A1segmentabove the ON)

  15. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1 SEGMENT) D. Infraoptic course and its variants • Infraoptic course • Perioptic duplication • Triplication (infraoptic course + supraoptic duplication) Infraoptic course perioptic duplication

  16. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMMUNICATING ARTERY • Variations of caliber • Absence • Fenestration, duplication and triplication

  17. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMUNICATING ARTERY A. Variations of caliber • a. fetaltype: • large caliber (>3mm) similar to A1 • (oftengives rise to medialcallosalartery) • b. transitionaltype: • intermediate caliber < A1segment • c. adulttype: • caliber 1.5 to 3mm, lessthanhalf of A1segments • d. hypoplastic: • very small vessel (<1.5 mm) Fetal type ACoA Hypoplastic ACoA ACA-ACoA complex of fetal type 1-2: A2 segments; 3 HA Heubner artery; 4: left ACA fenestration

  18. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMMUNICATING ARTERY B. Absence • type 1: ACoAabsence with separatedACAs (0.2-0.5%) • type 2: ACAsfused on the midline (2.6%)

  19. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMUNICATING ARTERY C. Fenestration, duplication and triplication • fenestration(partialduplication) (at the A1-A2 angle level) • complete duplication (20%) : • twovessels of similarcaliber, bothprovidingperforators • Twovessels of differentcaliber, the mainprovidingperforators Fenestration • triplication: threevessels with onelargerprovidingperforators (5-6%) • plexiformtype: multiple very small channels Duplication

  20. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION • Unpaired, fused(azygos) ACA OnebihemisphericA2 (feeding the medialsurface of bothhemipheres) B. TwoA2 segments a. UnihemisphericA2(classictype) (eacharteryfeeding the homolateralhemisphere) b. Oneunihemispheric and onebihemisphericA2 (one A2 feedingbranchesalso to the controlateralhemisphere) • Three A2 segments(triplication, accessory ACA) • The third A2 distributedonly to onehemisphere (unihemisphericthird A2) • The thirdA2distributed to bothhemispheres (biemisphericthirdA2) 2.3 DISTAL(A2) ANTERIOR CEREBRAL ARTERY

  21. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL(A2) ANTERIOR CEREBRAL ARTERY Azygos ACA Incidence overall 0.3-5% in ACoAaneurysms4.5-8% In pericallosalaneurysms 8.6% Yasargil MG: Microneurosurgery Vol,2 1984

  22. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL(A2) ANTERIOR CEREBRAL ARTERY Two ACA A2 Segments Bihemisphericdistribution (dominant ACA) proximaltype: the dominant ACA continuesasbihemisphericarteryproximally, oftenproviding the homolateralcallosomarginalartery distaltype: the dominant ACA bifurcates more distally, and provides to the contralateralhemisphereonly the parietalbranches proximal type distal type

  23. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL(A2) ANTERIOR CEREBRAL ARTERY C. Triplication

  24. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL(A2) ANTERIOR CEREBRAL ARTERY C. Triplication of the distal ACA

  25. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.1 Level of the bifurcation 3.2 Types of the maindivision 3.3 Fenestration 3.4 Duplication 3.5 Accessory middle cerebralartery

  26. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRALARTERY 3.1 Level of the bifurcation false bifurcation a. earlybifurcation (1.4%): veryshort (4-5 mm) M1 segment(lateralperforatorsarising to the bifurcation) b. late bifurcation (1-2%): very long M1 segment (up to 4 cm) that bifurcates at the insular region (prefrontal and medial temporal branches arising from M1)

  27. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRALARTERY 3.2 Types of the maindivision type1 : single trunk with no bifurcation (6%) type2 : bifurcation (70-90%) with twobranches 2.1 : superior and inferiorsimilarbranches 2.2 : dominantsuperiorbranch 2.3 : dominantinferiorbranch type3 : trifurcation (6-29%) with threebranches : superior, middle, inferior type4 : quadrifurcation (< 1%) with fourbranches: onesuperior, two middle, oneinferior

  28. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRALARTERY 3.3 Fenestration • incidence : 0.2-0.3% • location : M1 segment proximally, between its origin and the medial striate arteries • associated aneurysms : 40 – 50%

  29. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRALARTERY 3.4 Duplication incidence: 0.3 – 1.5 % anatomicalarrangement: - anomalousarteryarising from distal ICA and coursinginferiorlyparallel to M1 segment - similarcaliber of the twovessels or mainsuperiortrunk - superiortrunkfeedingfrontal and parietalbranches, inferiortrunkfeedingtemporalbranches

  30. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRALARTERY 3.5 Accessory M.C.A. incidence: 0.3 – 2.5% definition: anomalousarteryarising from the ACA, coursinglaterallyabove the A1 segment and entering the silvianfissuremedially to the M1 segment. site of origin: from the proximalpart of A1(more frequent) from the distal part of A1 from the initialsegment of A2 vascularterritory: orbito-frontaland anteriorfrontalbranches

  31. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. VARIATION AND ANOMALIES OF THE POSTERIOR COMMUNICATING ARTERY 4.1. Variations of caliber 4.2. Infundibular origin 4.3. Anomalous origin from the anterior choroidal artery (exceptional) 4.4. Hypoplasia and absence 4.5. Duplication (exceptional)

  32. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. POSTERIORCOMMUNICATINGARTERY 4.1. Variation of caliber* onethird to half of P1 67.5%* similarto P1 8 % largerthan P1 (fetaltype) 24.5% * Yasargil MG : Microneurosurgery vol 1, 1984

  33. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. POSTERIORCOMMUNICATINGARTERY 4.2. Infundibular origin funnel-shapeddilatation of vessel origin with a diameter of no more than 3 mm Incidence : 2-4% in autopticstudies 5-7% in radiologicalseries

  34. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. POSTERIORCOMMUNICATINGARTERY • hypoplasia 22-30% • absence : unilateral 0.5 – 2% bilateral : exceptional 4.4 Hypoplasia and absence

  35. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 5. OPHTHALMICARTERY 5.1. Variations and anomalies of origin A. from the ICAsegment • supraclinoidICA 83% • ICAat exit of the C3 2-8% • cavernousICA 0.2% • petrousICA • ICAbifurcation • ACA B. from ECA segment • M.M. artery 1% • Accessory M.M. (exceptional) C. from ICA and ECA segments Cavernous ICA origin exceptional Origin of O.A. from M.M.A. Origin of M.M.A. from O.A.

  36. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 6.1 Variations and anomalies of origin 6.2 Absence 1.7% 6.3 Duplication 4% 6.4 Anomalies of the vascular territory 6. ANTERIORCHOROIDAL ARTERY

  37. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 6. ANTERIORCHOROIDALARTERY • from the internalcarotidartery(85-100%) (withinseveralmillimeters from PCoA and ICA bifurcation) • duplex origin • twodistinctvessels (duplication) 4% • from the PCoA(0.1-9%) • from the ICA bifurcation(0.3-3%) • from the middle cerebralartery(1-8%) • anomalousorigin of uncalartery - from ICA - from MCA 6.1. Variations and anomalies of origin

  38. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 6. ANTERIORCHOROIDALARTERY • anomalous feeding of the temporal and occipital territories from AChA (1-2%) (lesser development of the temporal branches of PCA) • anomalous extension of the choroidal territory of the AchA (8%) (absence of the posterolateral choroidal artery from PCA) 6.4. Anomalies of the vascularterritory inverse correlation and extension of temporal and choroidal territories of AChA and PCA Hyperplastic AChA supplying the calcarine artery

  39. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7.1. Variations and anomalies of origin 7.2. P1 segment • hypoplasia and absence (fetal type PCA) • duplication and fenestration 7.3. choroidal and cortical branches 7. POSTERIORCEREBRALARTERY Fenestration of right P1 Duplication of PCA

  40. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7. POSTERIORCEREBRALARTERY • prevalent from BA 72% • prevalent from ICA throughPComA 17% • prevalent from ICA throughAChA 2% • equivalent from ICA and BA 8% • exclusive from BA 0.5% • exclusive from ICA 0.5% * Hitterwallmer FV : Acta Anat 1955 7.1 Variations and anomalies of origin (anatomicalstudies*)

  41. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7. POSTERIORCEREBRALARTERY • Complete fetaltype: unilateral 4-26% bilateral 2-4% • PCA originatescompletely from ICA • P1 segmentabsent • ICA supplies the occipitallobes • BA hypoplastic in bilateralcases r..complete and l. partial fetal type 7.2 Fetalorigin (radiologicalstudies*) bilateral complete fetal type • Partial fetal PCA : unilateral 11-23% bilateral 1-9% • P1 segment is present but smaller than PComA • partial blood supply of occipital lobes from ICA *Shaban A et al. : Circle of Willis variants: fetal PCA. Stroke Res Treat 2013 left complete fetal type

  42. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION T: persistent trigeminal artery (PTA) O: persistent otic artery (POA) H: persistent hypoglossal artery (PHA) Pa1: proatlantal artery 1 Pa2: proatlantal artery 2 8. PERSISTENTCAROTIDVERTEBRAL AND CAROTIDBASILARANASTOMOSES

  43. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 8. PERSISTENT CAROTID VERTEBRO-BASILAR ANASTOMOSES

  44. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 8.1 PRIMITIVE TRIGEMINAL ARTERY Trigeminal artery with giant aneurysm MR angiography: PTA from the cavernous sinus ICA to the distal BA CT angiography: PTA: a. type 1 or intrasellar; b. type 2 or parasellar CT angiography: PTA: a. type 1 or intrasellar; b. type 2 or parasellar Lateral type PTA

  45. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 8.2 PERSISTENT HYPOGLOSSAL ARTERY 8.3 PERSISTENT PROATLANTAL INTERSEGMENTAL ARTERY

  46. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.1 Clinical 9.2 Neuroradiological 9.3 Preoperative planning for surgery and neurointerventional procedures 9. SIGNIFICANCE OF THE ARTERIALVARIANTS AND ANOMALIES

  47. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.1 CLINICAL SIGNIFICANCE • Usually incidental findings • Cranial nerve symptoms and signs: • trigeminal neuralgia in PTA and variants • glossopharingeal neuralgia in PHA • pulsatile tinnitus in PSA • Ischemic events ( ICA agenesis, PCA fetal type, ACA azygos, carotid-vertebral and carotid-basilar anastomoses)

  48. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.2 NEURORADIOLOGICAL SIGNIFICANCE • Identification of the anomalous vessel (MRangiography, digitalangiography) • Diagnosis of anatomicalvariant versus pathology • Hypoperfusion and delayedopacization in the territory of the anomalous vessel • D. Association with aneurysms and AVMs

  49. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.2 NEURORADIOLOGICAL SIGNIFICANCE Association with aneurysms • agenesis and hypoplasia of ICA 67% • aplasia A1 14% • azygos ACA 41% • fenestrations 7% • persistent trigeminal artery 14% • persistent hypoglossal artery 26% • proatlantal intersegmental artery 10% Literature review from Hakim A et al.: European Society of Radiology 2016

  50. VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.3 PREOPERATIVE PLANNING FOR SURGERY AND NEUROINTERVENTIONAL PROCEDURES • Riskof hemorrageduringsurgicalprocedures: • trans-sphenoidalsurgery in PTAcases • middle earoperations in PSAcases • pharingealand tonsillarregionoperations in cases of aberrantpharingealartery • Intraarterialnavigation for endovascularprocedures • Risk of brain ischemia duringendovascularocclusion of AVMs and aneurysms • Post-embolizationrecanalization of AVMs from anomalousvessels

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