Anatomy of the Intracranial Arteries The Internal Carotid Ar PDF

A n a t o m y o f th e I n t r a c r a n i a l Ar t e r i e s The Internal Carotid Artery Dylan N. Wolman, MDa, Adrienne M. Moraff, MDb, Jeremy J. Heit, MD, PhDa,* KEYWORDS  Artery  Intracranial  Cerebral  Internal carotid artery  Ophthalmic artery  Posterior communicating artery  Anterio...

A n a t o m y o f th e I n t r a c r a n i a l Ar t e r i e s The Internal Carotid Artery Dylan N. Wolman, MDa, Adrienne M. Moraff, MDb, Jeremy J. Heit, MD, PhDa,* KEYWORDS  Artery  Intracranial  Cerebral  Internal carotid artery  Ophthalmic artery  Posterior communicating artery  Anterior choroidal artery  Superior hypophyseal artery KEY POINTS  The internal carotid artery is defined segmentally by anatomic landmarks and branch vasculature into the cervical, petrous, cavernous, ophthalmic, superior hypophyseal, posterior communicating, anterior choroidal, and terminal segments.  The ophthalmic through terminal segments are together grouped under the supraclinoid segment of the internal carotid artery and are named for each eponymous segmental vessel origin.  The caroticotympanic and mandibulovidian arteries arise from the petrous segment, and the menin- gohypophyseal and inferolateral trunks arise from the cavernous segment and form a rich anasto- motic network through remnant fetal connections to the dura and the external carotid circulation. INTRODUCTION anastomotic pathways, and touch on portions of its embryologic development as they relate to The cerebral arteries provide blood flow to the persistent fetal anastomoses and arterial variants. brain through perhaps the most elegant vascular Cerebrovascular diseases are discussed as exam- anatomy bed in the body. The arterial supply to ples in this article, with a particular focus on char- the brain is separated into the anterior circulation, acteristic aneurysms of the internal carotid artery which is composed of arteries that arise from the but all are considered in the context of the under- bilateral internal carotid arteries, and the posterior lying anatomy. A discussion of the remainder of circulation, which is composed of arteries that the anterior circulation and of the posterior circula- arise from the paired vertebral arteries. A detailed tion follows in the subsequent article. understanding of normal and variant cerebral arte- rial anatomy is important to understanding com- mon cerebrovascular diseases, such as ischemic INTERNAL CAROTID ARTERY stroke, steno-occlusive disease, cerebral aneu- The internal carotid arteries provide the dominant rysms, cerebral arteriovenous malformations, and arterial supply to the right and left cerebral hemi- pial and dural arteriovenous fistulae. spheres, and they are generally the largest intra- In this article, we will discuss the internal carotid cranial arteries. Each internal carotid artery arises artery and its complex branch vasculature, from the bifurcation of the common carotid artery neuroimaging.theclinics.com a Department of Radiology, Department of Neuroimaging and Neurointervention, Stanford School of Medi- cine, Center for Academic Medicine, 453 Quarry Road, Palo Alto, CA 94304, USA; b Division of Neurosurgery, Howard University School of Medicine, 2041 Georgia Avenue Northwest, Suite 4000, Washington, DC 20060, USA * Corresponding author. Stanford School of Medicine, 453 Quarry Road, Palo Alto, CA 94304. E-mail address: [email protected] Twitter: @JeremyHeitMDPHD (J.J.H.) Neuroimag Clin N Am 32 (2022) 603–615 https://doi.org/10.1016/j.nic.2022.04.006 1052-5149/22/Ó 2022 Elsevier Inc. All rights reserved. Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 604 Wolman et al Fig. 1. Lateral angiographic view of a normal internal Fig. 2. Normal anteroposterior (AP) and lateral (Lat) carotid artery. Each segment of the internal carotid ar- angiographic views of the carotid bifurcation demon- tery is color labeled as follows: (1) Cervical segment in strating a normal course and caliber of the distal com- light blue; (2) petrous segment in light green; (3) mon carotid artery, the proximal external carotid cavernous segment in orange; (4) ophthalmic segment artery trunk, and the carotid bulb and cervical in light red; (5) superior hypophyseal segment in pur- segment of the internal carotid artery with a normal ple; (6) posterior communicating segment in yellow; posterolateral origin of the internal carotid artery. (7) anterior choroidal segment in dark green; and (8) Note slight dilation of the normal carotid bulb. the carotid terminus in crimson. The anterior choroidal artery (A-choroidal), posterior communi- definable branch vessels, and typical sites of path- cating artery (P-comm), ophthalmic artery (OA), and meningohypophyseal trunk (MHT) are labeled in ologic condition.5 The internal carotid artery may black and marked by arrows. be considered as having 8 separate segments1: the cervical segment, which includes the carotid bulb2; the petrous segment, which includes the or- into the external and internal carotid arteries. This igins of the caroticotympanic and mandibulovidian bifurcation is located in the cervical soft tissues, arteries3; the cavernous segment, which includes most commonly at the C3–C5 vertebral body the origins of the inferolateral trunk and the menin- levels, although it has been reported as high as gohypophyseal trunk4; the ophthalmic segment at the C1 or as low as the T2 vertebral level.1 There the origin of the ophthalmic artery5; the superior are multiple proposed systems of subdivision to hypophyseal segment from which the superior hy- classify the segments of the internal carotid artery pophyseal arteries arise6; the posterior communi- based on the embryologic origins of each segment cating segment from which the posterior as they arise from segmental regression and anas- communicating artery arises7; the anterior tomoses of the third fetal aortic arches and exten- choroidal segment from which the anterior sions of the dorsal aortae,2 or based on choroidal artery arises; and8 the carotid terminus anatomically distinct subdivisions of the internal (Fig. 1). In the following paragraphs, we briefly carotid artery from cadaveric dissections.3,4 How- discuss each segment and the relevant arteries ever, although anatomically accurate, the seg- that arise from each segment. ments defined by these systems can be difficult The origin of the cervical segment of the internal to apply to cross-sectional or angiographic im- carotid artery is termed the carotid bulb and is ages, which are used frequently in modern medi- often broad and bell-shaped before smoothly cal practice. Therefore, a descriptive and tapering into the true cervical segment, which typi- practical naming scheme is used here to account cally has no branches. Rare variant branches from for angiographically visible anatomic landmarks, the cervical segment may be encountered, which Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  Anatomy of the Intracranial Arteries 605 Fig. 3. Axial computed tomography image through the skull base demonstrating incidental bilateral aber- rant internal carotid arteries extending within the middle ear (red arrows), formed by reconstitution of the caroticotympanic artery as a continuation of the internal carotid artery in the setting of aplasia of the petrous segment. Hyperattenuating material within the anterior clivus is an unrelated shrapnel Fig. 4. Single AP magnified angiographic projection fragment from a prior injury. of the right internal carotid artery demonstrating a prominent mandibulovidian artery (red arrow) arising from the petrous segment. There is a prominent ar- includes the origins of the ascending pharyngeal, tery of the pterygoid canal/Vidian artery (blue arrow) occipital, or superior thyroidal arteries, or persis- extending superiorly and a pterygovaginal artery ex- tent carotico-basilar anastomotic arteries, such tending inferiorly (yellow arrow) with supply to the as the persistent hypoglossal or proatlantal fossa of Rosenmüller and the Eustachian tube. segmental arteries.1,2 The cervical internal carotid usually arises posterolateral relative to the origin of the external carotid artery at the common carotid The petrous segment of the internal carotid ar- bifurcation but approximately 15% of patients tery courses through the carotid canal within the demonstrate a reverse orientation.1,6 petrous bone and is anatomically defined by 3 Approximately 70% of the inflow from the com- separate segments: a vertical segment that as- mon carotid artery is drawn into the internal carotid cends into the bone from the carotid sheath within artery, and there are complex flow dynamics the neck, an anteromedial genu as the artery is within the bulb owing to the sharp divergence deflected along the course of the canal, and a from the common carotid. Slipstreams of laminar longer horizontal segment toward the petrous blood flow at the acute angle of the carotid artery apex. There are 2 normal branches that arise bifurcation and recirculatory eddies within the pos- from the petrous segment: the caroticotympanic terior bulb may result in temporary stagnation of artery and the mandibulovidian artery. flow within the posterior carotid bulb predisposing The caroticotympanic artery is often small and this segment to significant atherosclerotic plaque angiographically obscured by the skull base but formation, thrombus formation in the setting of ca- it may be enlarged in vascular tumors of the skull rotid webs, or significant tortuosity owing to pre- base or middle ear that derive blood supply from dominantly helical rather than laminar this vessel. A remnant of the embryologic hyoid ar- downstream flow dynamics in chronic hyperten- tery, the caroticotympanic artery arises from the sion or with age, including a predisposition to the posterior vertical petrous segment and courses development of cervical loops (Fig. 2).1,6 The cer- posterolaterally to the middle ear where it passes vical segment terminates at the skull base where through the stapes and anastomoses with the infe- the artery enters the bony petrous canal and rior tympanic branch of the ascending pharyngeal courses anteromedially. artery. This normal anastomosis forms the basis of Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 606 Wolman et al the pterygoid canal), which courses superiorly through the pterygoid canal and anastomoses with a posteriorly directed branch of the distal in- ternal maxillary artery (Fig. 4). Second, the ptery- govaginal artery, which courses inferiorly through foramen lacerum to anastomose with the superior pharyngeal branch of the ascending pharyngeal artery. Both of these arteries provide arterial blood flow to the Eustachian tube and the fossa of Rose- nmüller (see Fig. 4). The cavernous segment of the internal carotid artery begins as the artery exits the petrous bone, crosses the petrolingual ligament, which is the periosteal reflection of the sphenoid bone lin- gula and the petrous apex, before entering the cavernous sinus. The cavernous segment is located lateral to the sella turcica and formed by apposition of the dural leaflets of the middle cranial fossa and the endosteum of the sphenoid bone.9 The cavernous segment is often divided into 3 subsegments1: a posterior vertical segment,2 a horizontal segment, and3 an anterior vertical segment, which are separated by the character- istic posterior and anterior genua, respectively. Within the cavernous sinus, cranial nerves III, IV, and the first and second divisions of cranial nerve V are located lateral to the cavernous sinus, whereas cranial nerve VI is located medial to the cavernous sinus. Laterally directed aneurysms of the cavernous internal carotid artery classically Fig. 5. Single magnified oblique projection of the left result in a third cranial nerve palsy owing to mass internal carotid artery demonstrating a laterally and effect or a water hammer effect on the immediately inferiorly directed aneurysm (red arrow) of the adjacent nerve (Fig. 5). cavernous segment of the internal carotid artery. The anterior and posterior genua of the cavernous The relationship of the dura to the distal segment are seen as double densities in plane and cavernous segment is critical to understanding medial to the aneurysm dome. the risk of subarachnoid hemorrhage posed by an- eurysms that arise from this segment. The dural leaflets of the cavernous sinus and of the tentorium the course of the aberrant internal carotid artery, form 2 dural rings that envelop the cavernous ca- an uncommon variant in which there is regression rotid artery: a proximal and a distal dural rings or agenesis of the petrous segment of the internal that attach to the anterior clinoid process. The carotid artery, which subsequently reconstitutes distal dural ring, which is typically located at the through hypertrophy of the caroticotympanic level of the clinoid process, demarcates the transi- branch resulting in a sharply angulated and retro- tion between the extradural segment of the tympanic course of the petrous internal carotid ar- cavernous carotid artery. Aneurysms that arise tery through the middle ear. This aberrant internal distal to the dural ring incur a risk of subarachnoid carotid artery often demonstrates a focal stenosis hemorrhage, whereas aneurysms below this point as the vessel courses through the bony ostium of present a risk of direct carotid-cavernous fistula the inferior tympanic canaliculus (Fig. 3).7 but not subarachnoid hemorrhage in most cases. The mandibulovidian artery is a variable branch There is a potential space between the distal that arises from the anterior horizontal petrous cavernous carotid artery and the distal dural ring, segment and courses anteromedially toward the which is termed the carotid cave. The carotid pterygopalatine fossa. This artery is often hyper- cave is located immediately inferior to the distal trophied in vascular nasopharyngeal tumors, ring, and an aneurysm in this location may extend such as juvenile nasopharyngeal angiofibromas.8 superiorly into the intradural compartment, and the There are 2 common subdivisions of the mandibu- indentation of the dural ring may be visible on the lovidian artery. First, the Vidian artery (or artery of aneurysm wall at angiography (Fig. 6).10 Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  Anatomy of the Intracranial Arteries 607 Fig. 6. Anteroposterior and lateral magnified views of the right internal carotid artery demonstrating a laterally and superiorly oriented aneurysm (red arrows) arising from the distal cavernous segment of the internal carotid artery adjacent to the anterior genu at the expected location of the clinoid process. There is a linear indentation (blue arrowheads) on the aneurysm dome seen on the lateral projection due to impingement by the distal dural ring, therefore confirming location of the aneurysm within the carotid cave. There are 2 major visible branches that arise The inferolateral trunk originates from the from the cavernous segment of the carotid artery: anterolateral surface of the horizontal segment the meningohypophyseal trunk and the inferolat- just proximal to the anterior genu and courses eral trunk. There is an inconsistent third group of inferolaterally along the inferior aspect of the arteries that may be seldom observed on angiog- cavernous sinus, where it courses deep to the raphy, which represent the capsular arteries of sixth cranial nerve and provides vasa nervorum McConnell.6 These small arteries supply the supply to the third, fourth, and sixth nerves, adenohypophysis and extend medially from the and to the Gasserian ganglion of the fifth cranial horizontal cavernous segment before penetrating nerve and the dura of the cavernous sinus. There the diaphragma sellae and becoming intradural. are 3 significant anastomotic branches that arise Therefore, aneurysms that arise in this arterial from the inferolateral trunk1: the deep recurrent group may pose a risk of subarachnoid meningeal artery, which is a vestige of the prim- hemorrhage. itive dorsal ophthalmic artery. This artery passes The meningohypophyseal trunk originates from through the superior orbital fissure and provides the posteromedial surface of the posterior genu a potential anastomotic pathway to the of the cavernous segment and gives rise to the ophthalmic artery and vasa nervorum supply to inferior hypophyseal artery that supplies the the first division of the fifth cranial nerve2; the neurohypophysis. In addition, there are multiple tentorial branch, which provides dural supply dural branches that arise from the meningohypo- and may anastomose with the middle meningeal physeal trunk, such as the basal tentorial artery, artery at foramen spinosum and the accessory the dorsal and medial clival branches, and the meningeal artery; and3 the artery of the foramen marginal tentorial artery, which may be referred rotundum, which is a commonly seen persistent to as the artery of Bernasconi and Cassinari.6,11 anastomosis between the distal internal maxillary The marginal tentorial artery describes a posterior artery and the internal carotid artery; this vessel course and follows the medial tentorial incisura to- is often seen in cases of proximal arterial ward the midline posteriorly, and this vessel is steno-occlusive disease as a pathway of collat- often hypertrophied in dural arteriovenous fistulae eral reconstitution of the distal internal carotid or hypervascular tentorial tumors (Fig. 7). (Fig. 8). Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 608 Wolman et al Fig. 7. Lateral magnified view of the internal carotid Fig. 8. Coronal maximum intensity projection of an artery demonstrating a hypertrophied and tortuous unsubtracted 3 dimensional rotational angiogram of marginal tentorial artery of Bernasconi and Cassinari the left internal carotid artery demonstrating a hyper- (red arrows) arising from the MHT, which had previ- trophied inferolateral trunk (ILT) with a branch ex- ously provided arterial supply to a now treated dural tending through the superior orbital fissure with arteriovenous fistula. supply to the artery of the foramen rotundum (yellow arrow, with the bony foramen marked by a blue ar- row). Note the incidental caroticotympanic artery pseudoaneurysm medial to the foramen rotundum The persistent trigeminal artery is an additional on this projection, which was the result of a surgical uncommon variant that arises from the cavernous injury following resection of a hypervascular skull segment of the internal carotid artery, seen in only base tumor. 0.2% of patients. The persistent trigeminal artery is a remnant fetal carotico-basilar anastomosis derived from incomplete or absent regression of the superior cerebellar, anterior inferior, or poste- the fetal trigeminal artery. The persistent trigeminal rior inferior cerebellar arteries; Fig. 9).1,2 artery may be classified into 4 general subtypes The supraclinoid segment of the internal carotid defined by the degree of supply to the posterior artery begins just above the distal dural ring, and it circulation1: type 1: supplies the distal basilar ar- courses anteroposteriorly between the optic nerve tery and anastomoses to the basilar artery be- medially and the anterior clinoid process laterally. tween the superior cerebellar and anterior inferior This segment is often considered as a single cerebellar arteries2; type 2: supplies the ipsilateral segment until its terminal division into the anterior superior cerebellar artery territory and anastomo- cerebral and middle cerebral arteries just below ses distal to the superior cerebellar artery (seen the anterior perforating substance. However, the with an ipsilateral fetal posterior cerebral artery)3; supraclinoid segment may be practically subdi- type 3: similar to type 2, except with additional vided into the ophthalmic, hypophyseal, posterior supply to the contralateral posterior cerebral ar- communicating, choroidal, and terminal seg- tery; and4 a persistent trigeminal artery variant, a ments, and each segment is named for the arteries rare subtype in which the trigeminal artery does arising from each division. These segments are not join the basilar trunk and instead directly sup- also common sites of eponymous aneurysm for- plies one or multiple cerebellar arteries (such as mation (Fig. 10). Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  Anatomy of the Intracranial Arteries 609 Fig. 9. Left panel: Axial maximum intensity projection MRA demonstrating a persistent trigeminal artery (type 1; red arrow) arising from the cavernous segment of the right internal carotid artery to supply the distal basilar ar- tery. Right upper and lower panels: Lateral angiogram of the right internal carotid artery (upper panel) and sagittal maximum intensity projection MRA (lower panel) demonstrating a persistent trigeminal artery variant arising from the cavernous segment of the internal carotid artery with supply to a posterior fossa arteriovenous malformation (purple arrow). MRA, Magnetic resonance angiogram. The ophthalmic division is the first short horizon- ophthalmic artery originates at the anterior cere- tal intradural segment from which the normal bral artery and segmentally regresses and reanas- ventral ophthalmic artery arises, typically just infe- tomoses to its final position as the definitive rior and slightly medial to the internal carotid ar- ophthalmic artery at the superomedial aspect of tery. The embryology of the ophthalmic artery is the supraclinoid internal carotid artery. However, complex but in simplified form, a fetal orbital arte- variants of persistence of the dorsal ophthalmic ar- rial complex is formed between the primitive dor- tery, both dorsal and ventral ophthalmic arteries, sal ophthalmic artery (arising from the fetal or of a deep recurrent ophthalmic artery arising cavernous internal carotid artery), the primitive from the cavernous internal carotid artery owing ventral ophthalmic artery (arising from the fetal to persistent anastomosis between the definitive anterior cerebral artery), and the stapedial artery ophthalmic artery and the inferolateral trunk may (arising from the fetal hyoid artery), which provides be rarely identified (Figs. 14–16). an orbital branch through the superior orbital The normal ophthalmic artery has 3 defined seg- fissure and an extracranial segment to the middle ments1: the ocular segment, which usually cranial fossa dura. Through segmental regression courses below the optic nerve and provides the or- of the primitive dorsal ophthalmic artery and the igins of the central retinal and ciliary arteries imme- stapedial artery, the stapedial artery gives rise to diately before coursing laterally and superiorly to the definitive caroticotympanic artery and variable round the nerve within the orbit2; the orbital persistence of the extracranial segment leads to segment, which is the straight segment along the meningeal variants, such as a recurrent meningeal optic nerve that provides arterial supply to the artery that arises from the ophthalmic artery lacrimal gland, the extraocular muscles, and the (Fig. 11) or persistent meningolacrimal branches, site of origin of the recurrent meningeal artery (if which may provide an anastomotic pathway be- present); and3 the extraorbital segment, which tween the middle meningeal and ophthalmic ar- provides multiple anastomotic branches to the teries (Fig. 12). Variable ophthalmic artery distal facial artery, and is the origin of the regression may lead to additional variant origins ethmoidal and anterior falcine arteries. The ante- of the ophthalmic artery from the middle menin- rior and posterior ethmoidal branches may anasto- geal artery (Fig. 13). The primitive ventral mose with the sphenopalatine arteries of the Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 610 Wolman et al Fig. 10. Anteroposterior and lateral magnified oblique internal carotid angiograms demonstrating example su- perior hypophyseal (first row), paraophthalmic (second row), posterior communicating (third row), anterior choroidal (fourth row), and carotid terminus (fifth row) aneurysms, each respectively arranged by row with Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  Anatomy of the Intracranial Arteries 611 Fig. 11. Lateral magnified internal carotid angiogram demonstrating the course of a normal ophthalmic artery (yellow arrow) with origination of a robust recurrent meningeal artery (red arrow) from the midophthalmic artery. internal maxillary artery and provide a pathway of choroidal arteries originate (Fig. 18). The poste- collateral reconstitution of the internal carotid ar- rior communicating artery is a common but vari- tery (Fig. 17). The anterior falcine artery is a distal able branch that connects the internal carotid dural branch supplying the anterior cerebral falx, artery to the P1 segment of the posterior cerebral and it is frequently hypertrophied in frontal dural artery, and this vessel forms the basis of the circle arteriovenous fistulae (see Fig. 17). of Willis in concert with the anterior communi- The hypophyseal segment of the internal carotid cating artery. Arising from the posteroinferior sur- artery is a short segment distal to the ophthalmic face of the distal supraclinoid segment of the artery origin just superior and lateral to the sella internal carotid artery, the posterior communi- turcica, from which the grouped superior hypo- cating artery is typically medial to the cisternal physeal arteries arise. These arteries are typically segment of the third cranial nerve, and in its angiographically invisible and are variable in num- normal configuration is smaller than the posterior ber, and they course medially toward the pituitary cerebral artery to which it anastomoses. A fetal- infundibulum to supply the adenohypophysis. The type configuration of this vessel is seen when origin of the superior hypophyseal arteries may the posterior communicating artery is larger serve as a common site of inferomedially oriented than the ipsilateral P1 segment of the posterior aneurysms that arise from the internal carotid ar- cerebral artery, and a true fetal configuration is tery in this segment. seen with an aplastic ipsilateral P1 segment of The posterior communicating and choroidal the posterior cerebral artery, which indicates segments, respectively, refer to the short portions failed regression of the early fetal origin of the of the mid-to-distal supraclinoid segment from posterior cerebral artery from the embryonic in- which the posterior communicating and anterior ternal carotid artery (Fig. 19).6 = the aneurysm labeled with a red arrow. First row: Left internal carotid angiogram demonstrating a broad-based saccular inferomedially oriented superior hypophyseal aneurysm extending from the ventromedial internal ca- rotid artery surface. Second row: Right internal carotid angiogram demonstrating a broad-based superolaterally oriented paraophthalmic artery saccular aneurysm without the involvement of the origin of the ophthalmic ar- tery, with the aneurysm dome seen as a double density on the lateral projection. Third row: Left internal carotid angiogram demonstrating a narrow necked saccular aneurysm with involvement of the origin of a large fetal- type left posterior communicating artery at the aneurysm neck. Fourth row: Right internal carotid angiogram demonstrated a wide-necked, bilobed saccular and posteroinferiorly oriented aneurysm of the anterior choroidal artery with involvement of the anterior choroidal artery origin from the aneurysm neck. Fifth row: Right internal carotid angiogram demonstrating a wide-necked anterosuperiorly oriented saccular aneurysm of the carotid ter- minus at the bifurcation of the supraclinoid segment into the right middle and anterior cerebral arteries. Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 612 Wolman et al Fig. 12. Lateral magnified angiogram of the distal external carotid artery trunk demonstrating a robust meningolacrimal branch (MLB) arising from the fron- tal division of the middle meningeal artery, which takes a recurrent course through the Foramen of Hyrtl to enter the orbit, subsequently retrogradely opacify- Fig. 14. Lateral magnified angiogram of the internal ing the proximal OA trunk. Note flash reflux into the carotid artery demonstrates variant origin of the OA internal carotid artery that faintly opacifies the from the undersurface of the distal cavernous petrous through supraclinoid segments and clearly segment consistent with a persistent dorsal (persistent demonstrates the normal origin of the OA from the dorsal OA; yellow arrow), with an otherwise normal proximal supraclinoid internal carotid artery. course and caliber of the OA and normal origination of the central retinal arteries and ciliary arterial com- plex (red arrow and text). Throughout the embryologic development, the arterial supply between the anterior choroidal communicating artery and is divided into cisternal and posterior cerebral arteries remains in balance, and plexal segments. The cisternal segment and there is a rich anastomotic network through courses around the lateral aspect of the midbrain thalamic arterial supply that allows each artery to within the circumpeduncular cistern before share or trade their supplied territories. However, entering the choroidal fissure, with grouped perfo- in a normal configuration, the anterior choroidal ar- rator supply along this course to the optic tract, tery arises just distal to the origin of the posterior posterior lentiform nucleus, posterior limb of the Fig. 13. Lateral magnified angiogram of the distal external carotid artery trunk demonstrating the origin of the OA proper from the hypertrophied frontal division of the MMA. Selective angiography of the ipsilateral internal carotid artery (not shown) demonstrated no associated OA branch or anastomotic vessel. Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  Anatomy of the Intracranial Arteries 613 Fig. 15. Lateral magnified angiogram of the internal carotid artery in a patient with Moyamoya disease resulting in steno-occlusive disease of the supraclinoid segment of the internal carotid artery. Variant persistent of both the ventral and dorsal ophthalmic arteries (green and yellow arrows, respectively), with retinal and ciliary arterial supply arising from the distal ventral OA with the ethmoidal, supratrochlear, and anterior falcine arteries seem to arise from the dorsal OA. internal capsule (superior perforator group), the uncus, amygdala and hippocampus (lateral perfo- rator group), and the anterolateral midbrain and lateral geniculate nucleus (medial perforator group).9 The plexal segment of the anterior choroidal artery extends posteriorly and superiorly from the choroidal fissure to the atrium of the lateral ventricle and supplies a portion of the ipsi- lateral choroid plexus, where it anastomoses with the lateral posterior choroidal artery from the pos- terior cerebral artery. It is common to see infundib- ular origins of either the posterior communicating or anterior choroidal arteries, and these structures Fig. 17. Lateral magnified angiogram of the internal carotid artery demonstrating a normal ventral ophthalmic artery with robust anterior and posterior ethmoidal arteries (green arrows) and a tortuous hy- pertrophied anterior falcine artery arising from the distal ophthalmic artery, which provides arterial sup- ply to a Cognard grade I dural arteriovenous fistula of the anterior superior sagittal sinus (blue arrows). Fig. 16. Lateral magnified angiogram of the internal There are multiple hypertrophied deep recurrent carotid artery demonstrating origination of the and clival meningeal branches arising from the infero- ophthalmic artery from the proximal horizontal lateral trunk (ILT), which supply an incidental intraor- cavernous segment consistent with a deep recurrent bital vascular malformation (red arrow). A prominent (OA; yellow arrow). A prominent MHT and ILT are marginal tentorial artery of the meningohypophyseal additionally annotated in black text. trunk (MHT) is also present. Downloaded for Anonymous User (n/a) at Pontifical Catholic University of Chile from ClinicalKey.com by Elsevier on July 12, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 614 Wolman et al SUMMARY The internal carotid artery is an elegant and com- plex vessel that serves as the dominant pathway to the anterior circulation. An understanding of the underlying development and branch anatomy of the internal carotid artery is critical to the accu- rate diagnosis of anterior circulation cerebrovas- cular disease and for subsequent treatment. CLINICS CARE POINTS 1. Segmental anatomy of the internal carotid artery is anatomically defined by the course of the vessel through the skull base and in relationship to definable branch vessels. Fig. 18. Lateral magnified angiogram of the internal carotid artery demonstrating a normal origin of the 2. Defined branch vessels arising from the in- posterior communicating and anterior choroidal ar- ternal carotid artery provide pathways of teries from the distal embryologically termed collateral reconstitution, meningeal and cra- “ventral” but anatomically posterior surface of the nial nerve arterial supply, and additionally supraclinoid internal carotid artery. provide a framework for understanding common pathologic condition of the inter- nal carotid artery, such as aneurysm develop- ment and treatment. are seen angiographically as small focal triangular 3. Variant arterial anatomy is common and is dilations, leading into the proximal vessel trunk. frequently owing to remnant embryonic ar- The final segment of the internal carotid artery is teries or incomplete regression of fetal ar- the terminal segment extending to the origins of teries, which additionally form the basis of the anterior and middle cerebral arteries, an addi- a rich network of anastomotic pathways tional potential site of aneurysm formation (see among multiple circulations. Fig. 10). DISCLOSURE The authors have nothing to disclose. REFERENCES 1. Osborn AG, Jacobs JM. Diagnostic cerebral angi- ography. 2nd edition. Philadelphia: Lippincott Wil- liams & Wilkins; 1999. p. 1999. 2. Lasjaunias P, Berenstein A, ter Brugge KG. Surgical neuroangiography, 2001. New York: Spring-Verlag Berlin Heidelberg; 2001. p. 789. 3. Gibo H, Lenkey C, Rhoton AL Jr. Microsurgical anat- omy of the supraclinoid portion of the internal carotid Fig. 19. 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