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

CLASSIFICATION OF THE ARTERIAL VARIATIONS AND ANOMALIES A. VARIATIONS Variations of the level of origin Variations of course Variations of caliber Variations of the vascular territory B. ANOMALIES Agenesis and aplasia Hypoplasia Multiplications (duplication, fenestration, triplication) Fusion Anomalies of origin (from other vessels) Persistence of anomalous arteries Accessory arteries 1998, 342 pp.

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION TOPICS 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

1. INTERNAL CAROTID ARTERY VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 1. INTERNAL CAROTID ARTERY 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) r. ICA agenesis with transsellar anastomosis ICA fenestration ICA duplication

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; Yaşargil M G: Cerebral angiography. Lippincott 1968

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

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

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 ophthalmic artery terminal branch of ICA MCA PCoA ECA BA Right ICA agenesis Left ICA agenesis CT: absence of left carotid canal

Types of ICA agenesis and pathways of collateral circulation VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION Types of ICA agenesis and pathways of collateral circulation ICA segment Agenesic embryonal artery Revascularized ICA segment Pathways of collateral circulation 1. cervical inferior proximal aortic sac, 3rd aortic arch cervical distal persistent cervical intersegmental artery 2. cervical inferior and superior intrapetrous tympanic branch of the ascending pharyngeal artery, carotid-tympanic artery 3. cervical and ascending intrapetrous dorsal aorta between 2nd and 1st aortic arch distal intrapetrous vidian artery, acoustic artery 4. cervical and whole intrapetrous dorsal aorta between 1st arch and primitive maxillary artery intracavernous intercarotid transsellar anastomosis, primitive trigeminal artery 5. cervical, intrapetrous, intracavernous dorsal aorta from the maxillary artery to the dorsal ophthalmicartery supraclinoid ophthalmic artery through the meningeal recurrent artery 6. complete (all segments) dorsal aorta between the dorsal and ventral ophthalmic arteries no visible segment circle of willis, anastomoses between maxillary and ophthalmic arteries

2. ANTERIOR CEREBRAL – ANTERIOR COMMUNICATING ARTERY COMPLEX VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2. ANTERIOR CEREBRAL – ANTERIOR COMMUNICATING ARTERY COMPLEX 2.1 Proximal ACA (A1 segment) 2.2 Anterior communicating artery (ACoA) 2.3 Distal ACA (A2 segment)

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

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-ACoA junction ( depending on the length of A1 segments and optic nerves) above the chiasm 70% anterior or posterior to the chiasm 30%

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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.1 PROXIMAL ACA (A1) SEGMENT C. Fenestration and supraoptic duplication Fenestration incidence 0.1-7.2% always at its distal portion 65% with an associated aneurysm Supraoptic duplication (exceptional) (complete duplication of the A1 segment above the ON)

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

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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMUNICATING ARTERY A. Variations of caliber a. fetal type: large caliber (>3mm) similar to A1 (often gives rise to medial callosal artery) b. transitional type: intermediate caliber < A1 segment c. adult type: caliber 1.5 to 3mm, less than half of A1 segments 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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMMUNICATING ARTERY B. Absence type 1: ACoA absence with separated ACAs (0.2-0.5%) type 2: ACAs fused on the midline (2.6%)

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.2 ANTERIOR COMUNICATING ARTERY C. Fenestration, duplication and triplication fenestration (partial duplication) (at the A1-A2 angle level) complete duplication (20%) : two vessels of similar caliber, both providing perforators Two vessels of different caliber, the main providing perforators Fenestration triplication: three vessels with one larger providing perforators (5-6%) plexiform type: multiple very small channels Duplication

2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY Unpaired, fused (azygos) ACA One bihemispheric A2 (feeding the medial surface of both hemipheres) B. Two A2 segments a. Unihemispheric A2 (classic type) (each artery feeding the homolateral hemisphere) b. One unihemispheric and one bihemispheric A2 (one A2 feeding branches also to the controlateral hemisphere) Three A2 segments (triplication, accessory ACA) The third A2 distributed only to one hemisphere (unihemispheric third A2) The third A2 distributed to both hemispheres (biemispheric third A2)

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY Azygos ACA Incidence overall 0.3-5% in ACoA aneurysms 4.5-8% In pericallosal aneurysms 8.6% Yasargil MG: Microneurosurgery Vol,2 1984

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY Two ACA A2 Segments Bihemispheric distribution (dominant ACA) proximal type: the dominant ACA continues as bihemispheric artery proximally, often providing the homolateral callosomarginal artery distal type: the dominant ACA bifurcates more distally, and provides to the contralateral hemisphere only the parietal branches proximal type distal type

2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 2.3 DISTAL (A2) ANTERIOR CEREBRAL ARTERY C. Triplication Type Medial callosal artery caliber course territory Pericallosal arteries 1. Short smaller than the pericallosal arteries up to the anterior third of CC anterior third of CC, septum pellucidum well developed, normal territory 2. Middle almost similar to the pericallosal arteries up to the middle third of CC bihemispheric distribution of pericallosal and parietal cortex less developed (frontal regions) 3. Large larger than the pericallosal arteries up to the posterior third of CC of frontal and parietal regions hypoplastic (only frontopolar branches)

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

3. MIDDLE CEREBRAL ARTERY VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.1 Level of the bifurcation 3.2 Types of the main division 3.3 Fenestration 3.4 Duplication 3.5 Accessory middle cerebral artery

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.1 Level of the bifurcation a. early bifurcation (1.4%): very short (4-5 mm) M1 segment (lateral perforators arising to the bifurcation) false 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)

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.2 Types of the main division type 1 : single trunk with no bifurcation (6%) type 2 : bifurcation (70-90%) with two branches 2.1 : superior and inferior similar branches 2.2 : dominant superior branch 2.3 : dominant inferior branch type 3 : trifurcation (6-29%) with three branches : superior, middle, inferior type 4 : quadrifurcation (< 1%) with four branches: one superior, two middle, one inferior

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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.4 Duplication incidence : 0.3 – 1.5 % anatomical arrangement: - anomalous artery arising from distal ICA and coursing inferiorly parallel to M1 segment - similar caliber of the two vessels or main superior trunk - superior trunk feeding frontal and parietal branches, inferior trunk feeding temporal branches

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 3. MIDDLE CEREBRAL ARTERY 3.5 Accessory M.C.A. incidence : 0.3 – 2.5% definition : anomalous artery arising from the ACA, coursing laterally above the A1 segment and entering the silvian fissure medially to the M1 segment. site of origin: from the proximal part of A1 (more frequent) from the distal part of A1 from the initial segment of A2 vascular territory: orbito-frontal and anterior frontal branches

4. VARIATION AND ANOMALIES OF THE POSTERIOR COMMUNICATING ARTERY 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)

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. POSTERIOR COMMUNICATING ARTERY 4.1. Variation of caliber* one third to half of P1 67.5%* similar to P1 8 % larger than P1 (fetal type) 24.5% * Yasargil MG : Microneurosurgery vol 1, 1984

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 4. POSTERIOR COMMUNICATING ARTERY 4.2. Infundibular origin funnel-shaped dilatation of vessel origin with a diameter of no more than 3 mm Incidence : 2-4% in autoptic studies 5-7% in radiological series

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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 5. OPHTHALMIC ARTERY 5.1. Variations and anomalies of origin A. from the ICA segment supraclinoid ICA 83% ICA at exit of the C3 2-8% cavernous ICA 0.2% petrous ICA ICA bifurcation 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.

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

6.1. Variations and anomalies of origin VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 6. ANTERIOR CHOROIDAL ARTERY 6.1. Variations and anomalies of origin from the internal carotid artery (85-100%) (within several millimeters from PCoA and ICA bifurcation) duplex origin two distinct vessels (duplication) 4% from the PCoA (0.1-9%) from the ICA bifurcation (0.3-3%) from the middle cerebral artery (1-8%) anomalous origin of uncal artery - from ICA - from MCA

6.4. Anomalies of the vascular territory VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 6. ANTERIOR CHOROIDAL ARTERY 6.4. Anomalies of the vascular territory 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) inverse correlation and extension of temporal and choroidal territories of AChA and PCA Hyperplastic AChA supplying the calcarine artery

7. POSTERIOR CEREBRAL ARTERY VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7. POSTERIOR CEREBRAL ARTERY 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 Fenestration of right P1 Duplication of PCA

7.1 Variations and anomalies of origin (anatomical studies*) VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7. POSTERIOR CEREBRAL ARTERY 7.1 Variations and anomalies of origin (anatomical studies*) prevalent from BA 72% prevalent from ICA through PComA 17% prevalent from ICA through AChA 2% equivalent from ICA and BA 8% exclusive from BA 0.5% exclusive from ICA 0.5% * Hitterwallmer FV : Acta Anat 1955

7.2 Fetal origin (radiological studies*) VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 7. POSTERIOR CEREBRAL ARTERY 7.2 Fetal origin (radiological studies*) Complete fetal type: unilateral 4-26% bilateral 2-4% PCA originates completely from ICA P1 segment absent ICA supplies the occipital lobes BA hypoplastic in bilateral cases r..complete and l. partial fetal type 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

8. PERSISTENT CAROTID VERTEBRAL AND CAROTID BASILAR ANASTOMOSES VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 8. PERSISTENT CAROTID VERTEBRAL AND CAROTID BASILAR ANASTOMOSES T: persistent trigeminal artery (PTA) O: persistent otic artery (POA) H: persistent hypoglossal artery (PHA) Pa1: proatlantal artery 1 Pa2: proatlantal artery 2

8. PERSISTENT CAROTID VERTEBRO-BASILAR ANASTOMOSES VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 8. PERSISTENT CAROTID VERTEBRO-BASILAR ANASTOMOSES Anomalous artery Incidence Origin Connection pathway Persistent trigeminal artery 0.1-0.2 % cavernous ICA distal BA intrasellar or parasellar Otic artery exceptional petrous ICA proximal BA internal auditory canal Hypoglossal artery 0.03-0.26 % cervical ICA hypoglossal canal Proatlantal intersegmental artery cervical ECA VA above C1 through C1

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

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

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

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)

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.2 NEURORADIOLOGICAL SIGNIFICANCE Identification of the anomalous vessel (MR angiography, digital angiography) Diagnosis of anatomical variant versus pathology Hypoperfusion and delayed opacization in the territory of the anomalous vessel D. Association with aneurysms and AVMs

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

VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 9.3 PREOPERATIVE PLANNING FOR SURGERY AND NEUROINTERVENTIONAL PROCEDURES Risk of hemorrage during surgical procedures: trans-sphenoidal surgery in PTA cases middle ear operations in PSA cases pharingeal and tonsillar region operations in cases of aberrant pharingeal artery Intraarterial navigation for endovascular procedures Risk of brain ischemia during endovascular occlusion of AVMs and aneurysms Post-embolization recanalization of AVMs from anomalous vessels

10. ANOMALIES OF THE VENOUS SINUSES VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 10. ANOMALIES OF THE VENOUS SINUSES Type A: confluence and almost equal trasverse sinuses Type B: confluence and one dominant trasverse sinus Type C: unilateral trasverse sinus only Maiuri F. et al. The Management of the Venous Sinuses During Surgery for Posterior Fossa Meningiomas. World Neurosurgery 2019

10. ANOMALIES OF THE VENOUS SINUSES VARIATIONS AND ANOMALIES OF THE SUPRATENTORIAL CIRCULATION 10. ANOMALIES OF THE VENOUS SINUSES Preoperative Postoperative Maiuri F. et al. Meningioma of the transverse-sigmoid sinus junction area. Br. J. Neurosurg 2011

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