Ascending pharyngeal artery

The ascending pharyngeal artery, the smallest branch of the external carotid artery, usually arises from the proximal portion of the external carotid artery. It has an ascending vertical course, along the posterolateral wall of pharynx, anterior to the longus capitis muscle, and medial to the styloglossus and stylopharyngeus muscles (Fig. 2-8A, B). This initial segment of the artery can be seen, in the lateral angiogram, in front of the vertebral column, and medial to the main external carotid trunk on the anteroposterior view.

FIGURE 2-8 A, Lateral view of the left parapharyngeal space and the ascending pharyngeal artery origin and course. The ascending pharyngeal artery makes a sharp anterior turn at the base of the skull, running downward and forward, following the upper border of the superior pharyngeal constrictor muscle to supply the pharynx and auditory tube. B, The segment of the internal carotid artery below the carotid canal has been removed and the stump retracted posteriorly to expose the anterior and posterior divisions of the ascending pharyngeal artery. The anterior division gives off the pharyngeal rami and the posterior, or neuromeningeal division, sends branches to the posterior fossa dura. The ascending ramus of the anterior branch, also called Eustachian branch, supplies the Eustachian tube and gives off a carotid branch, which accompanies the internal carotid artery within the carotid canal, supplying the periosteum, the sympathetic network around the vessel, and the arterial walls. The jugular branches of the ascending pharyngeal and occipital arteries send branches to cranial nerves IX, X, and XI. C, Intracranial view of the left jugular foramen. The jugular branch descends below the jugular foramen. D, Lateral view of a left mastoidectomy. The mastoid air cells have been removed to expose the superior, posterior, and lateral semicircular canals, facial nerve, sigmoid sinus, and jugular bulb. The lateral division of the jugular branch of the ascending pharyngeal artery ascends along the anterior edge of the sigmoid sinus and anastomoses medially with the meningeal branches of the internal carotid artery, superiorly with the subarcuate artery, and laterally with the mastoid branches of the occipital artery. E, Posterior view of the left lower cranial nerves. The cerebellum and accessory nerve have been elevated to expose the hypoglossal nerve. The hypoglossal branch of the ascending pharyngeal artery passes through the hypoglossal canal with the hypoglossal nerve and enters the dura. F, Posterior view of a hypoglossal canal that has been opened to expose the hypoglossal nerve and the hypoglossal branch of the ascending pharyngeal artery. The hypoglossal branch supplies the dura of the lateral portion of the foramen magnum and inferolateral cerebellar fossa. The posterior inferior cerebellar artery arises from the extradural segment of the vertebral artery. G, The right cerebellar tonsil has been elevated to expose a meningeal artery that arises from intradural vertebral artery and supplies the dura on the lateral edge of the lateral foramen magnum. A., artery; Ant., anterior; Asc., ascending; Br., branch; Cap., capitis; Car., carotid; CN, cranial nerve; Constr., constrictor; Div., division; Ext., external; For., foramen; Hypogl., hypoglossal; Int., internal; Jug., jugular; Lat., lateral; Long., longus; M., muscle; Men., meningeal; Occip., occipital; P.I.C.A., Posterior inferior cerebellar artery; Palat., palatini; Pharyng., pharyngeal; Post., posterior; Proc., process; Semicirc., semicircular; Sig., sigmoid; Sup., superior; Tens., tensor; Vert., vertebral.

The meningeal contribution of the ascending pharyngeal artery is via three branches: hypoglossal, jugular, and carotid (see Fig. 2-8A). The hypoglossal and jugular branches, the more constant, originate from the posterior division,¹⁰ and the carotid branch from the anterior division (Fig. 2-8C–G). The hypoglossal branch accompanies the hypoglossal nerve and enters the skull through the hypoglossal (anterior condylar) canal, to be distributed to the dura surrounding the foramen magnum and clivus, where it anastomoses with the branches arising from the ipsilateral cavernous carotid and vertebral arteries, and its mate from the opposite side. The hypoglossal artery may also arise from the vertebral artery (see Fig. 2-8G). The area of supply of the hypoglossal branch (see Figs. 2-1, 2-6, and 2-7) may extend to the dura of the lateral portion of the cerebellar fossae, where it borders and has a reciprocal relationship with the territory supplied by the mastoid branch of the occipital artery and the posterior meningeal artery of the vertebral artery. In the clival area it may anastomose superiorly with the medial clival branch of the inferior hypophyseal artery and the dorsal meningeal artery and inferiorly with the anterior meningeal artery of the vertebral artery.^9,10

The jugular branch enters the jugular foramen with cranial nerves IX, X, and XI, where it divides into medial and lateral branches. The lateral branch courses along the dural wall of the sigmoid sinus (see Fig. 2-8D), where it anastomoses with the jugular branch of the occipital artery (Fig. 2-9). The medial branch courses along and supplies the dura bordering the inferior petrosal sinus. Its territory (see Figs. 2-1, 2-6, and 2-7) borders the area supplied by the dorsal meningeal artery and medial clival artery from the cavernous carotid. Superiorly, it anastomoses with the subarcuate artery and the petrosquamosal branch of the middle meningeal artery and laterally with the mastoid branches of the occipital artery. The jugular branch distal to the jugular foramen supplies the dura facing the inferior part of the cerebellopontine angle^9,10 (see Fig. 2-6). The hypoglossal and jugular branches also supply of the adjacent segments of cranial nerves IX through XII.^10,19,20 On lateral angiograms, the posterior division of the ascending pharyngeal artery ascends besides and overlaps the foramen magnum. On anteroposterior views, the hypoglossal is the most medial of the terminal branches of the posterior division.

FIGURE 2-9 A, Lateral view of a left occipital artery in the area below the mastoid process. The occipital artery originates from the posterior surface of the external carotid artery, courses posteriorly and upward, and passes deep to the posterior belly of digastric muscle in the occipital groove of the temporal bone. B, Posterior view of the retroauricular area. The occipital artery passes between the longissimus capitis and semispinalis capitis muscle and gives rise to a mastoid branch that passes through the mastoid foramen to reach the dura in the area of the junction of sigmoid and transverse sinus. C, A descending branch of the occipital artery arises as the artery passes above the superior oblique muscle and gives rise to deep rami that anastomose with the vertebral artery. D, Enlarged view of C. The mastoid branch of occipital artery enters the cranium, by passing through the mastoid foramina and anastomoses over the junction of sigmoid and transverse sinus with the branches of the middle meningeal artery. E and F, Left (E) and right (F) retromastoid areas. E, When the occipital artery’s course is low, no occipital groove is present and the artery passes superficial to the longissimus capitis muscle. F, If the artery courses below the skull base in an occipital groove it passes deep to the longissimus capitis muscle. G, Posterior view of the left occipitomastoid area. The mastoid foramen transmits the mastoid emissary vein and the mastoid branch of the occipital artery. H, A meningeal branch of this segment courses toward the midline and passes through the parietal foramen. I, Posterior view of the sagittal and lambdoid sutures. The parietal foramen, which transmits an emissary vein and a meningeal branch of the terminal segment of the occipital artery, is located near the midline, 3–5 cm above the lambda. J, Lateral view. The stylomastoid artery arises from the posterior surface of the external carotid artery and passes through the stylomastoid foramen to reach the facial canal, where it supplies the mastoid portion of the facial nerve and walls of the tympanic cavity. K, The posterior belly of digastric has been removed to expose the jugular branch of the occipital artery, which ascends behind the carotid sheath to supply the dura around the jugular foramen and cranial nerves IX, X, and XI. A., artery; Br., branch; Brs., branches; Cap., capitis; Car., carotid; CN, cranial nerve; Desc., descending; Digast., digastric; Ext., external; For., foramen; Gr., greater; Inf., inferior; Int., internal; Jug., jugular; Longiss., longissimus; M., muscle; Men., meningeal; Mid., middle; N., nerve; Obl., oblique; Occip., occipital; Occipitomast., Occipitomastoid; Par., parietal; Petrosquam., petrosquamosal; Post., posterior; Proc., process; Sag., sagittal; Sup., superior; Superf., superficial; Temp., temporal; Transv., transverse; V., vein; Vert., vertebral.

The carotid ramus originates from the anterior branch of the ascending pharyngeal artery. It courses in the periosteal lining of the carotid canal and anastomoses, at the level of the foramen lacerum, with branches arising from the carotid siphon^9,10 to form the recurrent artery of the foramen lacerum. This recurrent artery also anastomoses at the lower edge of the trigeminal ganglion with the posterior branch of the inferolateral trunk and the cavernous branch of the middle meningeal artery. The carotid branch usually does not extend to the dura of clivus and cerebellopontine angle as do the other dural branches of the ascending pharyngeal artery.^9,10 The recurrent artery of foramen lacerum may be involved in the supply of angiomas, lymphoid tumors, angiofibromas of the nasopharynx, and tumors of the cavernous sinus and caroticocavernous fistulas.^9,10

Occipital artery

The occipital artery originates from the posterior surface of the external carotid artery, at the level of the angle of the mandible, and courses posteriorly and upward, being crossed superficially by the hypoglossal nerve. It passes deep to the posterior belly of the digastric muscle and lateral to the internal jugular vein, vagus nerve, internal carotid artery, and accessory nerve (see Fig. 2-9A). At the level of a vertical plane crossing the posterior border of the external auditory canal, the occipital artery can be found in a tunnel formed above by the occipital groove of the temporal bone—a prominent sulcus on the undersurface of the temporal bone, medial to the digastric groove—medially by the attachment of the superior oblique muscle on the transverse process of atlas, and laterally by the cranial insertion of the posterior belly of the digastric muscle in the digastric groove (see Fig. 2-9B–F). The presence of the occipital groove is dependent on whether the artery courses superficial or deep the longissimus capitis muscle. The groove is present if the artery courses deep to the longissimus capitis muscle along the lower surface of the skull base and is absent if the artery courses inferior to the skull base or lateral to the longissimus capitis muscle (see Fig. 2-9E–G).¹²

The occipital artery at the level of the posterior border of the upper insertion of the longissimus capitis muscle courses in the upper part of the space between the occipital bone and C1 and lateral to the rectus capitis posterior major and semispinalis capitis muscle. It is covered by a deeper layer formed by the splenius capitis muscle and a more superficial layer formed, from lateral to medial, by the sternocleidomastoid and trapezius. The occipital artery pierces the fascia between the trapezius and sternocleidomastoid, near the superior nuchal line and ascends in the superficial fascia of the scalp, where it is accompanied by the greater occipital nerve (see Fig. 2-9H).

The occipital artery gives rise to the auricular branch, which anastomoses with the posterior auricular artery behind the ear; the stylomastoid artery, muscular branches to the sternocleidomastoid, digastric, stylohyoid, splenius, and longissimus capitis muscles; and meningeal branches to the posterior fossa that enter the skull through the jugular foramen and condylar canal and to inconstant branches that runs through the mastoid foramen (see Fig. 2-9B, D, G).

The occipital artery is divided into three portions: (1) ascending cervical, (2) cervico-occipital or horizontal, and (3) ascending occipital²¹ (see Fig. 2-9A). The meningeal branches most frequently originate from the second and third arterial segments.

The mastoid branch, present in about one half of specimens²¹ (see Fig. 2-9B, D, G), also called the transmastoid branch or the artery of the mastoid foramen,^3,9,10 originates from the second segment of occipital artery, at the level of the insertion of the semispinalis capitis muscle, midway between the inferior and superior nuchal lines. From its origin, the mastoid branch courses between the splenius capitis muscle and the junction of the mastoid and occipital bones. It enters the cranial cavity at the level of the superior nuchal line, by passing through the mastoid foramen. Intracranially, the superior nuchal line corresponds to the level of the transverse sinus. The mastoid branch emerges intracranially at the posterior border of the upper end of the sigmoid sinus and divides into three groups of branches: descending, ascending, and posteromedial.²¹ The descending branches are directed toward the jugular foramen and border the dural territory supplied by the jugular branch of the ascending pharyngeal artery (see Fig. 2-8D). The posteromedial branches anastomose with the petrosquamous branch of the middle meningeal artery and constitute the main supply to the lateral part of the cerebellar fossae that borders the territory of the hypoglossal branch of the ascending pharyngeal artery or the posterior meningeal branch of the vertebral artery, or both. The ascending branches, which are directed to the dura covering the superior part of the posterior surface of the temporal bone that faces the cerebellopontine angle, anastomoses with the subarcuate branch of the anterior inferior cerebellar artery (see Figs. 2-1 and 2-6), and can supply acoustic neurinomas, meningiomas, and arteriovenous fistulas. The mastoid branches also supply the endolymphatic duct and sac.²²

The third or ascending occipital portion gives rise to the terminal branches of the occipital artery, which supply the musculocutaneous structures of the posterior portion of the cranial vault, and anastomoses with the branches of the superficial temporal artery (see Fig. 2-9H). The parietal foramen (see Fig. 2-9J), which is an inconstant opening located near the sagittal suture, about 3 to 5 cm in front of the lambda,³ transmits a meningeal branch of the ascending occipital segment and a small emissary vein.²¹

Variations of the stylomastoid artery and the mastoid branch include their origin from the ascending pharyngeal artery or from the posterior auricular artery. Alternatively, other meningeal arteries that commonly have other sites of origin, like the posterior meningeal and the branch to the falx cerebelli from the posterior meningeal artery, may also arise from the occipital artery.

Maxillary artery

The maxillary artery, through its middle meningeal and accessory meningeal arteries (Figs. 2-10 and 2-11), provides almost all of the supply to the dura over the convexity and important contributions to the supply of the basal dura (see Figs. 2-1,2-3, and 2-4).

FIGURE 2-10 A, Lateral view of the left mandible and infratemporal area. The superficial temporal artery arises from the external carotid artery and courses behind the condylar process of the mandible and the temporomandibular joint. B, The maxillary artery is divided into mandibular, pterygoid, and pterygopalatine segments. The mandibular segment courses deep to the neck of the mandible. The pterygoid segment courses between the temporalis and pterygoid muscles and gives rise to the deep temporal and pterygoid arteries. The pterygopalatine segment passes through the pterygomaxillary fissure to enter the pterygopalatine fossa. The deep temporal arteries and nerves enter the deep surface of the temporalis muscle. C, The middle meningeal veins accompany the divisions of the artery and communicate above with the superior sagittal sinus through the venous lacunae. D, Middle meningeal artery, which arises from the mandibular segment of the maxillary artery, passes upward between the roots of the auriculotemporal nerve and the foramen spinosum to reach the middle fossa dura. E, Enlarged view. The pterygoid venous plexus has been removed to expose the middle meningeal artery arising from the maxillary artery and coursing between the roots of the auriculotemporal nerve. F, The dura has been elevated from the floor of the left middle fossa to expose the bifurcation of the middle meningeal artery into anterior and posterior divisions lateral to the foramen spinosum. The medial branch of the anterior division courses near the sphenoid ridge and anastomoses with the meningolacrimal or sphenoidal branches of the ophthalmic system, or both. The lateral branch ascends toward the superior sagittal sinus. G, The middle meningeal artery gives rise to cavernous and petrous branches before splitting into anterior and posterior divisions just anterior and lateral to the foramen spinosum. H, Enlarged view of G. Immediately after entering the cranial cavity, the middle meningeal artery gives off a short vessel, which divides into the petrosal artery laterally and a cavernous branch to the trigeminal ganglion medially. The cavernous branch anastomoses with the posterior branch of the inferolateral trunk. The petrosquamosal branch arises from the posterior trunk at the junction of the skull base and convexity; supplies the insertion of the tentorium to the petrous ridge, the dura of the torcula, and the junction of the sigmoid, transverse, and superior petrosal sinuses; and extends to the dura of the posterior fossa bordering the area supplied by the external carotid branches. I, Lateral view of the anterior division of the left middle meningeal artery in another specimen. A branch of the anterior division ascends grooving the parietal bone approximately 1.5 cm behind the coronal suture. In this case, the segment encased in a bony canal was removed in elevating the bone. The petrosquamosal branch, described in H, arises from the middle meningeal artery at the junction of the skull base and convexity. J, Posterolateral view of the dura over the right transverse sinus and torcula. The petrosquamosal branch of the middle meningeal artery supplies the insertion of the tentorium; the dura of the torcula; and the junction of the sigmoid, transverse, and superior petrosal sinus and extends to the dura of the posterior fossa bordering the area supplied by the external carotid branches. K, Superior view of the convexity dura. The middle meningeal arteries give rise to a rich anastomotic layer of vessels referred to as the primary anastomotic arteries. These arteries change little in diameter as they course and anastomose over the dural surface. They cross the superior sagittal sinus, connecting the dura over the paired cerebral hemispheres into a single vascular unit. L, Enlarged view of the area of the superior sagittal sinus. Each middle meningeal artery forms a paramedian arcade just lateral to the superior sagittal sinus. The arcades anastomose across the midline connecting the dural arterial network in a single vascular unit. M, Enlarged view of the sagittal sinus. The middle meningeal branches reach and participate in the supply of the walls of the superior sagittal sinus, where they give off descending branches to the adjacent falx cerebri and anastomoses with the other falcine arteries. N, The superior sagittal sinus has been opened and its walls hold laterally with pins to expose the branching pattern of the middle meningeal arteries along the sinus walls. A., artery; Alv., alveolar; Ant., anterior; Auriculotemp., auriculotemporal; Br., branch; Car., carotid; Clin., clinoid; CN, cranial nerve; Div., division; Ext., external; Fiss., fissure; For., foramen; Gr., greater; Inf., inferior; Int., internal; Lat., lateral; M., muscle; Mandib., mandibular; Med., medial; Men., meningeal; Mid., middle; N., nerve; Parieto-Occip., parieto-occipital; Palat., palatini; Pet., petrosal; Petrosquam., petrosquamosal; Plex., plexus; Post., posterior; Proc., process; Pteryg., pterygoid; Pterygomax., pterygomaxillary; Sag., sagittal; Sup., superior; Superf., superficial; Temp., temporal, temporalis; Tens., tensor; Transv., transverse; Tymp., tympani; V., vein; Ven., venous; Zygo., zygomatic.

FIGURE 2-11 A, Inferolateral view of the right foramina ovale and spinosum and the middle and accessory meningeal arteries passing through the skull base. The accessory middle meningeal artery arises from the maxillary artery, and passes through the foramen ovale in this case. B, Anterior view of the right foramen ovale exposing the sharp lateral curve of the middle meningeal artery above foramen spinosum. The intracranial territory of the accessory meningeal artery includes the gasserian ganglion and adjacent middle fossa dura, where it anastomoses with the meningeal branches from the ophthalmic and middle meningeal arteries and the carotid siphon. C, Endocranial surface of the sella and middle fossa. The sphenoidal emissary foramen is present in approximately 40% of the skulls. It is located medial to the foramen ovale. D, The deep temporal nerves and arteries pierce the deep surface of the temporalis muscle. The middle meningeal artery arises from the mandibular segment of the maxillary artery and gives rise to the accessory meningeal artery. E, Enlarged view of D. In this specimen, the accessory meningeal artery ascends superficial to lingual and inferior alveolar nerves. F, The upper segment of the ascending pharyngeal artery makes a sharp anterior turn, superficial to constrictor pharynx muscle and gives rise to a well developed carotid branch that follows the carotid artery into the carotid canal. A., artery; Access., accessory; Alv., alveolar; Ant., anterior; Asc., ascending; Auriculotemp., auriculotemporal; Br., branch; Cap., capitis; Car., carotid, Clin., clinoid; CN, cranial nerve; Emiss., emissary; For., foramen; Inf., inferior; Int., internal; Jug., jugular; Long., longus; M., muscle; Men., meningeal; Mid., middle; N., nerve; Occip., occipital; Pharyng., pharyngeal; Post., posterior; Sphen., sphenoidal; Temp., temporal; Superf., superficial; V., vein.

Middle meningeal artery

The middle meningeal artery normally arises from the first or mandibular segment of the maxillary artery, just behind the condylar process of the mandible, and enters the skull through the foramen spinosum (see Fig. 2-10A–H). After passing through the foramen spinosum, the main stem courses laterally, grooving the greater sphenoid wing, where it divides in its anterior and posterior divisions, which supply the dura of frontal, temporal, and parietal convexity; the upper surface of the temporal bone; and the adjacent walls of the transverse and sigmoid sinus as well as the middle fossa dura adjacent to the cavernous sinus (see Fig. 2-10F–N). In its path between the anterosuperior angle of the greater sphenoid wing and the sphenoid angle of the parietal bone, the anterior division, and sometimes the sphenoparietal sinus, can be encased in a bony canal that varies in extension from 1 to greater than 30 mm.²³ The anterior division is usually single but may be composed of two branches (duplicated) in 0.8%, or absent in 0.7% of cases, while the posterior division is duplicated in 8.1%.²³ At the level of the superior sagittal sinus the middle meningeal artery anastomoses with the anterior falcine branch of the ophthalmic artery to supply the dural layers of the falx (see Fig. 2-5).

The middle meningeal artery, and the osseous groove in which it courses, begins at the foramen spinosum and divide into anterior and posterior divisions 15 to 30 mm anterolateral to foramen spinosum (see Fig. 2-10F–I). The anterior division and its groove divide behind the lateral part of the greater wing into a lateral branch, which passes across the pterion to reach the dura of the lateral convexity, and a medial branch, which courses medially along the lower surface of the sphenoid ridge where it anastomoses with the recurrent branch of the lacrimal artery. In 9 out of 10 orbits dissected, Liu and Rhoton²⁴ reported the presence of anastomotic connections between the recurrent meningeal branch of the lacrimal artery and the medial branch of the anterior division of the middle meningeal artery. Occasionally, the recurrent meningeal branch of the lacrimal artery gives rise to the anterior segment of the middle meningeal artery or more rarely, the ophthalmic artery can give rise to the main stem of the middle meningeal artery itself. In these cases, with an ophthalmic or lacrimal origin of the middle meningeal artery, the grooves marking the course of the main stem of the middle meningeal artery will originate at the lateral edge of the superior orbital fissure²⁵ and the foramen spinosum will be hypoplastic or absent.²⁶ Another, less frequent, site of origin of the middle meningeal artery is from the petrous portion of the internal carotid artery, referred to as a stapedial-middle meningeal artery, an anomaly that results from failure of the embryonic stapedial branch of the internal carotid artery to regress and allow the middle meningeal artery to become connected to the external carotid artery.²⁶

Angiographically, in the anterior view, the middle meningeal artery is easily recognized by a sharp turn along the floor of the middle fossa after passing through the foramen spinosum. Its course along the inner table is characterized by smooth curves, in contrast with the sinuous course of the overlapping superficial temporal artery. This initial intracranial portion of the middle meningeal artery can be elevated and stretched by lesions arising at the skull base (see Fig. 2-5B). Radiographically, the grooves for the meningeal branches can become tortuous and the foramen spinosum can enlarge in meningiomas and vascular malformations.^27,28

Immediately adjacent to the foramen spinosum the middle meningeal artery gives off a short branch, which divides into the petrosal artery laterally and a branch to the trigeminal ganglion medially (see Fig. 2-10G, H). The trigeminal branch has been referred to as the cavernous branch of the middle meningeal artery. The petrosal branch runs with the greater petrosal nerve and penetrates the temporal bone by passing through the facial hiatus and supplies the facial nerve and walls of the tympanic cavity.^29,30 Damage to the petrosal branch occurring as the dura is elevated in a subtemporal extradural approach to the trigeminal nerve, cavernous sinus, or internal acoustic meatus may result in a facial nerve deficit. Bleeding at this site should be controlled by a method other than coagulation in order to avoid damaging the facial nerve, which may be exposed in the floor of the middle fossa at the level of the hiatus fallopii.^25,30

The posterior branch of the middle meningeal artery gives rise to the petrosquamosal branch at the junction of the skull base and convexity (see Fig. 2-10I, J). It supplies the insertion of the tentorium along the petrous ridge and groove for the transverse sinus; the dura of the torcular; and the junction of the sigmoid, transverse, and superior petrosal sinuses, and extends to the dura of the posterior fossa bordering the area supplied by the other branches of the external carotid artery³¹ (see Fig. 2-7). The petrosquamosal artery may infrequently supply almost all the posterior fossa dura, including the cerebellar fossa and tentorium cerebelli.³¹ The parieto-occipital branch of the middle meningeal artery supplies the dura over the posterior convexity (see Fig. 2-10J).

The middle meningeal artery in the middle fossa has anastomotic connections with the ophthalmic system and the meningeal branches of the cavernous carotid artery (see Fig. 2-1). The middle meningeal artery may contribute to the supply of the second and third trigeminal divisions in addition to the facial nerve.¹⁹ It may supply most of the tentorium when giving rise to a medial tentorial branch. The medial tentorial artery may arise from either the main divisions of the middle meningeal artery or from the accessory meningeal artery,³¹ described in the next section.

The middle meningeal artery anastomoses over the upper clivus and adjacent posterior surface of the temporal bone with the dorsal meningeal artery and the subarcuate artery. The distal part of the petrosquamosal branch anastomoses, at the level of the junction of the sigmoid, transverse, and superior petrosal sinuses, with the branches of the occipital artery that passes through the mastoid foramen and the meningeal branches of the ascending pharyngeal and vertebral arteries.

The middle meningeal artery may also anastomose with a branch of the basilar artery.^32,33

Accessory meningeal artery

The accessory meningeal artery, also called the lesser or small meningeal artery^34,35 (see Table 2-1), may arise from either the maxillary or middle meningeal artery depending on the relationship of the maxillary artery to the pterygoid muscles.^10,34 It arises from the maxillary artery if the maxillary artery courses deep to the pterygoid muscles and from the middle meningeal artery if the maxillary artery passes superficial to the pterygoid muscle. In the cases in which the middle meningeal artery arises from the ophthalmic, internal carotid or basilar artery, the accessory meningeal artery will arise directly from the trunk of the maxillary artery.³⁶ The caliber of the accessory middle meningeal artery is about one third to one half of the middle meningeal artery (see Fig. 2-11A, B, D–F) and in 30% to 45% of the cases it is formed by of multiple small arteries,^34,35 especially if it arises from the maxillary artery.³⁴

From its origin, the accessory meningeal artery courses toward the angle between the posterosuperior edge of the lateral pterygoid plate and the infratemporal surface of the sphenoid bone. It usually passes posterior to the inferior alveolar and lingual nerves³⁴ (see Fig. 2-11A, E). In 78% of the cases, the accessory meningeal artery enters the cranium through the foramen ovale. In the remaining 22%, it passes through the emissary sphenoid foramen (foramen of Vesalius), an opening occasionally found 2 to 3 mm medial to the anterior edge of foramen ovale that also transmits an emissary vein linking the pterygoid plexus and the cavernous sinus^34,36 (see Fig. 2-11C).

The extracranial segment of the accessory meningeal artery has anastomoses with the ascending pharyngeal artery and pterygopalatine arteries^9,10,36 (see Fig. 2-11A, F). It supplies the membranous portion of the Eustachian tube and external acoustic meatus, the lateral pharyngeal wall and medial pterygoid muscle, the mandibular nerve below the foramen ovale, and sphenoid periosteum. It has been suggested that it be called the pterygomeningeal artery because the extracranial structures receive the predominance of its flow while the intracranial branch receives only 10%.³⁶

The intracranial territory of the accessory meningeal artery includes the gasserian ganglion and adjacent middle fossa dura, where it anastomoses with the meningeal branches from the ophthalmic and middle meningeal arteries and the carotid siphon. The accessory meningeal artery has a reciprocal relationship with the inferolateral trunk of the internal carotid artery in the supply of the mandibular nerve and the dura adjacent to the cavernous sinus. It has prominent anastomoses with the posterolateral branch of the inferolateral trunk (see Fig. 2-1). Lasjaunias and Theron³⁶ found that the accessory meningeal artery was small in 25% of the cases that it anastomoses with the inferolateral trunk of the cavernous carotid artery, had a size similar to the inferolateral trunk in 59%, and that it was the only supply to the cavernous sinus area in 16%. In the latter case, the diameter of this accessory meningeal artery approaches that of the middle meningeal artery.^9,36 Occlusion of this artery during endovascular procedures may result in cranial nerve deficits because of its supply to the oculomotor, trochlear, trigeminal, abducens and facial nerves.^10,36

Dilenge and Geraud³⁵ found that the artery could be identified in lateral angiograms throughout its extracranial course in 60% of 100 selective angiographies, but was recognizable intracranially in only six cases because of its small size. It was more easily identified when it was part of an anastomotic network between the carotid siphon and the internal maxillary artery. On the anteroposterior angiographic view, the accessory meningeal artery slants medially, above the skull base, toward the cavernous sinus at the point of arborization of the inferolateral trunk. It may contribute to the vascular pedicle of meningiomas and schwannomas of the gasserian ganglion,³⁵ and can be involved in paracavernous arteriovenous malformations.

Cavernous segment

The cavernous portion of the internal carotid artery gives rise to branches that supply the walls and enclosed structures of sella, cavernous sinus, and the tentorium (see Figs. 2-3 and 2-4). The branches can be divided based on the direction of their course into a medial group that includes the inferior hypophyseal, medial clival, and capsular arteries; a lateral group that includes the inferolateral trunk, also called artery of the inferior cavernous sinus, and its branches and the lateral tentorial artery; and a posterior group that includes the dorsal meningeal artery and medial tentorial artery (Fig. 2-12A–L). The medial branches, including the inferior hypophyseal and medial clival artery, derive from the primitive maxillary artery, while the dorsal meningeal artery is the adult remnant of the primitive trigeminal artery. When these two embryonic vessels originate in a single trunk, the meningeal, hypophyseal, and neural branches will arise from a single source, referred to as the meningohypophyseal trunk.^9,10

FIGURE 2-12 A, Superior view of the sella and roof of the cavernous sinus. The right anterior clinoid has been removed. The medial clival artery, usually a branch of the inferior hypophyseal artery and less commonly of the cavernous carotid artery, runs in the dura of the sinus roof and is distributed to the dura over the posterior clinoid and upper dorsum. B, Superolateral view of the left cavernous sinus. The meningohypophyseal trunk gives origin to the dorsal meningeal, medial clival, and tentorial arteries. C, Superolateral view after opening the lateral sinus wall. The first division of the trigeminal nerve has been retracted laterally to expose the inferolateral trunk, which arises from the lateral side of the midportion of the horizontal segment of the cavernous carotid, passes above the abducens nerve, and deep to the first trigeminal segment, supplies the dura of the inferolateral wall of the cavernous sinus and adjacent middle fossa, and anastomoses with the recurrent artery of the foramen lacerum. The dorsal meningeal artery passes posteriorly with the abducens nerve and is distributed to the dura over the dorsum sellae and clivus and anastomoses with its mate from the opposite side. Its territory has a reciprocal relationship with that of the medial clival artery. The medial clival artery arises from the meningohypophyseal trunk in this specimen. Its initial course is anterior to the posterior clinoid, but it also reaches to the dura over the posterior surface of dorsum sellae. The tentorial arteries pass laterally to reach the tentorium. D, Lateral view. The medial edge of the petrolingual ligament marks the beginning of the intracavernous segment of the carotid. E, Enlarged view of D. The meningohypophyseal trunk arises near the apex of the posterior bend of the intracavernous carotid on the medial side of the trochlear nerve. The tentorial artery arises as a branch of the meningohypophyseal trunk and divides into the medial and lateral tentorial arteries at the level of the petrous ridge. The medial tentorial artery supplies the medial edge and medial one third of the tentorium, reaching the area around the straight sinus and posterior attachment of falx. The lateral tentorial artery supplies the lateral two thirds of the tentorium and the attachment of the tentorium to the petrous ridge and anastomoses with the petrosal and petrosquamosal branches of the middle meningeal artery, the lateral branch of the dorsal meningeal artery, and the mastoid branch of the occipital artery. The dorsal meningeal artery runs posteriorly and passes through Dorello’s canal located below the petrosphenoidal ligament. F, The posterior bend of the intracavernous carotid artery has been retracted laterally to expose the inferior hypophyseal artery passing medially across the cavernous sinus to reach the lateral surface of the posterior lobe and capsule of the pituitary gland.G, Lateral view of the posterior part of a right cavernous sinus. The tentorial, inferior hypophyseal, and dorsal meningeal arteries arise from the meningohypophyseal trunk. The petrosphenoidal ligament has been excised to expose the passage of the dorsal meningeal artery to the clival dura. The inferior hypophyseal artery passes to the posterior lobe of pituitary gland and sellar floor. H, Posterior view after removal of the dorsum sellae in another specimen. The tentorial, inferior hypophyseal, and dorsal meningeal arteries arise directly from the cavernous carotid artery. The paired inferior hypophyseal arteries anastomose on the posterior surface of the posterior lobe to form an arterial circle that reaches the dura over the floor and posterior wall of sellae. Dorello’s canal has been unroofed on the right. The dorsal meningeal artery divides into medial and lateral branches. The lateral branch supplies the abducens nerve and the dura around Dorello’s canal and the medial branch supplies the dura over dorsum and upper clivus. The territory supplied by the medial branch of the dorsal meningeal artery has a reciprocal relationship with the territory of the medial clival artery. I, Enlarged view of the right cavernous sinus shown in H. The tentorial, dorsal meningeal, and inferior hypophyseal arteries arise separately from the posterior bend of cavernous carotid artery. J, Lateral view of the left cavernous sinus. The tentorial and the meningohypophyseal arteries arise from the posterior bend of the carotid. The meningohypophyseal trunk gives rise to the inferior hypophyseal, medial clival, and dorsal meningeal arteries. K, Lateral view. The medial tentorial artery runs parallel to the trochlear nerve in the upper portion of Parkinson’s triangle located between the trochlear nerve and first trigeminal division. The anterolateral branch of the inferolateral trunk courses between V1 and V2 and toward the foramen rotundum. L, Superior view of the specimen shown in K. The inferolateral trunk arises from the lateral side of the midportion of the horizontal segment of the intracavernous carotid and passes between the abducens nerve and the first trigeminal division to supply the dura over the inferolateral wall of the cavernous sinus and adjacent middle fossa. The anterior division of the inferolateral trunk gives rise to anterolateral and anteromedial branches. The anteromedial branch passes forward and supplies the oculomotor, trochlear, and abducens nerves and enters the orbit through the superior orbital fissure. The medial tentorial artery has been removed. M, Superior view of the right cavernous sinus. The roof has been opened and the oculomotor, trochlear, and ophthalmic nerves have been retracted laterally to expose the dorsal ophthalmic artery, the segment of the deep recurrent ophthalmic artery that courses inside the cavernous sinus. The deep recurrent ophthalmic artery arises from the initial intraorbital part of the ophthalmic artery and courses backward through the annulus of Zinn and medial portion of the superior orbital fissure to cross the anterior venous space of the cavernous sinus. The deep recurrent ophthalmic artery anastomoses with the anterolateral branch of the inferolateral trunk. N, Anterior view. A right capsular artery arises from the horizontal segment of the intracavernous carotid and runs medially to supply the dura over the floor of the sella. O, Lateral view. The inferolateral trunk arises medial to the first trigeminal division, but its branches can be seen between the trigeminal divisions. The anterolateral branch of the anterior division courses toward and gives a branch to the foramen rotundum. The posterior division is exposed between the second and third trigeminal divisions. P, Posterior–superior. The posterior division of the inferolateral trunk courses above the motor root of the trigeminal ganglion and supplies the gasserian ganglion and adjacent dura. Q, The trigeminal nerve has been removed to expose the inferolateral trunk and its divisions. In this specimen, the superior division of the inferolateral trunk gives rise to the medial tentorial artery, which supplies the medial third of tentorium and posterior attachment of falx cerebri. The anterior division supplies the segment of the oculomotor, trochlear, and abducens nerves near the superior orbital fissure. The posterior division reaches the gasserian ganglion, mandibular nerve, and adjacent dura and anastomoses with the recurrent artery of foramen lacerum. The dorsal meningeal artery arises from the posterior carotid bend and supplies the abducens nerve in the region of Dorello’s canal. A., artery; Ant., anterior; Br., branch; Caps., capsular; Car., carotid; Cav., cavernous; Clin., clinoid, clinoidal; Cliv., clival; CN, cranial nerve; Diaph., diaphragma; Div., division; Dors., dorsal; For., foramen; Gr., greater; Hyp., hypophyseal; Inf., inferior, infero; Int., internal; Lat., lateral; Lig., ligament; Med., medial; Men., meningeal; Meningohyp., meningohypophyseal; N., nerve; Ophth., ophthalmic, P.C.A., posterior cerebral artery; Pet., petrosal, petrous; Petroling., petrolingual; Petrosphen., petrosphenoid; Pit., pituitary; Post., posterior; Rec., recurrent; Seg., segment; Sup., superior; Tent., tentorial; Tr., trunk.

The meningohypophyseal trunk and the inferolateral trunk are the most consistent branches of the cavernous segment of the internal carotid artery. They arise from a single trunk in 6% of the cavernous sinus.³⁷ These vessels anastomose with their mates of the opposite side and with the meningeal branches of the external carotid, ophthalmic, and vertebral arteries¹³ (see Figs. 2-1 and 2-4). The communication between the external carotid and internal carotid through the cavernous branches is of significance in the management of carotid cavernous fistulae, which must be based on evaluation of all these communicating channels. Increase in opacification of the cavernous carotid branches may occur with alteration of cerebral dynamics associated with increased intracranial pressure, a distant intracranial lesion, and in cerebrovascular disease in which the cavernous branches act as the rete mirabili.¹³

Meningohypophyseal trunk

The meningohypophyseal trunk is the largest intracavernous branch of the internal carotid artery.^38–40 It arises lateral to the dorsum sellae at or just proximal to the apex of the first curve of the intracavernous carotid (see Fig. 2-6). It is approximately the same size as the ophthalmic artery.³⁸ In its most complete form it gives rise to the tentorial, inferior hypophyseal, and dorsal meningeal arteries (see Fig. 2-12B–G, I, J). However, these branches can arise separately from the internal carotid artery or in different combinations,^9,36,37 and the origin of some secondary arteries directly from the meningohypophyseal trunk can give the appearance of more than the usual number of branches (see Fig. 2-12H). The posterior bend of the internal carotid artery and the origin of the meningohypohyseal trunk can be exposed through Parkinson’s triangle, located in the lateral view between the trochlear and ophthalmic nerves, except when the carotid is elongated and tortuous, causing the posterior bend to rise above the trochlear nerve^11,12 (see Fig. 2-12D–F). The oculomotor and trochlear nerves enter the dural roof of the cavernous sinus just above or slightly behind the trifurcation of the meningohypophyseal trunk. According to Harris and Rhoton,¹¹ the meningohypophyseal trunk provides a branch to the tentorium in 100% of 50 cavernous sinuses examined, making the tentorial artery the most constant branch leaving this trunk.

Tentorial arteries

The tentorium has two sources of supply: the medial tentorial and the lateral tentorial arteries. The medial tentorial artery usually arises from the meningohypophyseal trunk, but may also arise from the inferolateral trunk, middle meningeal, accessory meningeal, ophthalmic, and lacrimal arteries (see Fig. 2-12E, F, K, Q). It ascends to the roof of the cavernous sinus and then posterolaterally, along the free edge of the tentorium, to contribute to the supply of the transdural segment of the oculomotor and trochlear nerves, the walls of the cavernous sinus, and the medial third of the tentorium.^12,41,42 It departs from the cavernous sinus just beneath the entrance of the trochlear nerve and initially courses posteriorly about 5 mm from the free margin of the tentorium (see Fig. 2-12D, E). As it approaches the region of the straight sinus, it curves laterally, ramifying within tentorium and anastomosing along the base of the falx with branches from its mate from the opposite side^12,38,41 (see Figs. 2-3 and 2-5). It may also anastomose with the meningeal branches of the ophthalmic artery. Although usually described as a branch of the tentorial division of the meningohypophyseal trunk,³⁷ the medial tentorial artery may also arise directly from the posterior vertical or from the horizontal segment of the cavernous carotid (as a branch of the inferolateral trunk), the accessory meningeal, intraorbital ophthalmic, lacrimal, or middle meningeal arteries.^18,42

The term Bernasconi’s artery is used as a synonym for the medial tentorial artery^11,12,42 (see Table 2-1). Bernasconi and Cassinari (1956) were the first to describe an arterial vessel involved in the supply of the tentorium and its lesions. At that time, they thought the vessel originated from the external carotid artery^39,41,43,44 but its true origin from the internal carotid artery later became apparent.^38,41,44

When visible during normal angiography, the medial tentorial artery ranges in length from 5 to 35 mm. A pathologic lesion has been considered a possibility if the tentorial artery can be followed, in the angiogram, for a distance longer than 40 mm.^12,39 Other aspects such as increased diameter, undulating course, and multiple branching also suggest the presence of a lesion.¹³ Its presence on angiograms is not diagnostic of a tentorial meningioma as first suggested, because it can be seen in arteriovenous malformations, gliomas with tentorial invasion, trigeminal neuromas, and even in normal patients.^12,41,43,45

The lateral tentorial artery commonly arises as a single trunk with the medial tentorial artery (see Fig. 2-12D, E). From its origin, it passed backward, upward, and slightly laterally to enter the tentorium along its attachment to the petrous ridge, and continued backward to supply the tentorial area lateral to that supplied by the medial tentorial artery.^28,42,45 The lateral tentorial artery anastomoses with the petrosal and petrosquamosal branches of the middle meningeal artery and the lateral branch of the dorsal meningeal artery (see Figs. 2-3 and 2-6).

Dorsal meningeal artery

The dorsal meningeal artery, also called lateral clival artery, is the adult remnant of the trigeminal artery.^31,36 It arises from the meningohypophyseal trunk in most cases and passes posteriorly through the cavernous sinus, to supply the dura of the dorsum sellae and clivus and anastomose with its mate from the opposite side across midline (see Fig. 2-12B–E, G–J). It arose from the meningohypophyseal trunk in 90% of the 50 cavernous sinus studied by Rhoton and Harris.¹¹ In 6% of cases, it arises directly from the lateral surface of the posterior ascending portion of the cavernous carotid, just below the meningohypophyseal trunk.^11,12,46

The dorsal meningeal artery divides into medial and lateral branches (see Fig. 2-12H, I). The medial branch passes below the petrosphenoid ligament, which roofs Dorello’s canal, to accompany and supply the abducens nerve into the canal^31,36,38 and anastomoses with the clival ramus of the jugular branch of the ascending pharyngeal artery (see Figs. 2-1 and 2-6). The medial branch of the dorsal meningeal artery has a reciprocal relationship with the medial clival artery, which arises as a direct or as a secondary branch of the internal carotid artery from the inferior hypophyseal artery. The medial clival arteries initial course is anterior to the posterior clinoid process, but it also distributes to the dura over the posterior surface of dorsum sellae, where it anastomoses, across the midline, with its counterpart from the opposite side and also with the medial branch of the dorsal meningeal artery (see Fig. 2-12A–C). If no medial clival artery is found, a branch arises directly from the dorsal meningeal artery or its medial branch and courses medially and superiorly, on the posterior aspect to the posterior clinoid process and dorsum sellae, supplying part of the territory of the medial clival artery (see Fig. 2-12H, I).

The lateral branch of the dorsal meningeal artery passes above the trigeminal cistern (Meckel’s cave) and accompanies the superior petrosal sinus along the petrous ridge, thus participating in the basal arterial arcade of the tentorium cerebelli (see Fig. 2-3). This branch anastomoses, lateral to the trigeminal ganglion, with the lateral tentorial artery and branches of the middle meningeal artery running over the superior surface of the temporal bone.

Inferior hypophyseal artery

The inferior hypophyseal artery arises most frequently from the meningohypophyseal trunk (see Fig. 2-12F, G) or directly from the medial surface of the posterior ascending segment of the cavernous carotid artery (see Fig. 2-12H–J, N).^11,31,36 It passes medially across the cavernous sinus to reach the lateral surface of the posterior lobe and capsule of pituitary gland. The artery divides into superior and inferior branches that anastomose with their mates of the opposite side, forming an arterial circle anterior to the dorsum sellae (see Fig. 2-12H). The inferior branch of this arterial circle, along with the more anteriorly located capsular arteries, may supply the dura on the sellar floor.^11,13,40,46 The capsular arteries usually arise directly from the medial surface of the horizontal cavernous carotid (see Fig. 2-12N), but may also be branches of the inferior hypophyseal artery.³⁸ The dura of the posterior clinoid and cavernous sinus can also be supplied by the inferior hypophyseal branch, through the medial clival artery, which can also arise directly from the cavernous carotid.^36,42

Luschka, in 1860^38,40 first identified the inferior hypophyseal artery in man. This artery is the adult remnant of the primitive maxillary artery. In the lateral angiogram, the inferior hypophyseal artery is superimposed on the carotid siphon and is therefore impossible to identify even after subtraction studies.^36,40

Inferolateral trunk

The inferolateral trunk, also called the lateral main stem³⁹ or the artery of the inferior cavernous sinus,³⁸ arises from the lateral side of the midportion of the horizontal segment of the intracavernous carotid, approximately 5 to 8 mm distal to the origin of the meningohypophyseal trunk^11,46 (see Fig. 2-12K, L). It arises directly from the carotid artery in 84% of the cavernous sinuses and from the meningohypophyseal trunk in another 6%.¹¹

The inferolateral trunk passes above (96%) or below (4%) the abducens nerve⁴⁷ and descends, through or lateral to the ophthalmic nerve, and supplies the dura of the inferolateral wall of the cavernous sinus and adjacent middle fossa up to the gasserian ganglion (see Figs. 2-1,2-4, and 2-12K–P). The branches of the inferolateral trunk anastomose with the middle and accessory meningeal arteries.⁴⁶ The branches to the gasserian ganglion may run in the dura lateral to the ganglion or pass superior to the motor root to reach the dura on the medial side of the ganglion (see Fig. 2-12P).

In its most complete form, the inferolateral trunk gives rise to superior, anterior, and posterior branches^9,48 (see Fig. 2-12Q). The superior branch supplies the roof of the cavernous sinus. It gives rise to a medial tentorial branch in approximately 40% of cases⁴⁸ (see Fig. 2-12K, Q). The anterior and the posterior divisions divide into a medial and a lateral branch. The medial branch of the anterior division passes forward and supplies the oculomotor, trochlear, and abducens nerves; enters the orbit through the superior orbital fissure; and terminates as the deep recurrent ophthalmic artery (see Fig. 2-12K–M). The lateral branch passes toward the foramen rotundum and supplies the dura of the adjacent temporal fossa and maxillary nerve (see Fig. 2-12K, O, Q). The medial branch of the posterior division is distributed to the abducens nerve, medial third of the gasserian ganglion, and the mandibular nerve (see Fig. 2-12P). The lateral branch of the posterior division supplies the middle and lateral thirds of the gasserian ganglion and adjacent dura⁴⁸ (see Fig. 2-12Q). Because of its reciprocal relationship with the cavernous branch of the middle meningeal artery, the posterior division may also reach the hiatus fallopi to supply the facial nerve.^9,19 The posterior division of the inferolateral trunk anastomoses with the recurrent artery of foramen lacerum (see Fig. 2-4).

McConnell’s capsular arteries

The term McConnell’s capsular arteries refers to the anterior and inferior capsular arteries, tiny branches that arise distal to the origin of the inferolateral trunk. The inferior capsular artery is the more proximal of the capsular arteries. It arises from the inferomedial surface of the horizontal segment of the cavernous carotid, distal to the origin of the inferolateral trunk, or as a secondary branch of the inferior hypophyseal artery. It runs medially in the dural covering of the inferior surface of the anterior lobe, giving branches to the dura of the floor of the sella turcica (see Fig. 2-12N). The anterior capsular artery arises from the medial aspect of the internal carotid artery just before it pierces the roof of the cavernous sinus and runs medially in the dura of the anterior margin and roof of the sella turcica, anastomosing with its mate of the opposite side.

McConnell’s capsular arteries are frequently absent,^11,38,40,46 being found in 8% to 50% of cavernous sinuses.^37,38,40,46 This variability may be due to difficulty in injecting these arteries⁴⁰ or its origin as a branch of the inferior hypophyseal artery.⁴⁶ The capsular arteries have been visualized angiographically in patients with sphenoid sinus carcinoma, craniopharyngioma, and parasellar meningiomas.¹³

Recurrent artery of foramen lacerum

This tiny artery originates from the posterior ascending portion of the carotid siphon and descends into the foramen lacerum, supplying the pericarotid autonomic nervous plexus and the arterial wall^9,48 (see Figs. 2-11F and 2-12C, Q). This artery cannot be seen angiographically after internal carotid artery injections, because of the density of the parent carotid, but is visible after ascending pharyngeal injection because of its anastomoses with the carotid branch of the ascending pharyngeal artery. The recurrent artery of the foramen lacerum also anastomoses along the inferior surface of the trigeminal ganglion with the posterior branch of the inferolateral trunk (see Figs. 2-1 and 2-4).

Ophthalmic artery

Contributions from the ophthalmic artery to the dura derive mainly from its ethmoidal, recurrent ophthalmic and lacrimal branches (Figs. 2-13 to 2-15).

FIGURE 2-13 Superior view. A, The anterior and posterior ethmoidal arteries arise from the ophthalmic artery, and the anterior and posterior ethmoidal nerves arise from the nasociliary nerves and both the arteries and nerves course medially, passing above the optic nerve and between the superior oblique and medial rectus muscles to enter the ethmoidal canals. B, The lacrimal artery arises from the initial segment of the ophthalmic artery, courses laterally, and anastomoses through its recurrent meningeal or the meningolacrimal branch with the middle meningeal artery. C, Superior view of the dura around the cribriform plate after removal of the olfactory bulbs. The anterior ethmoidal arteries emerge from the ethmoidal canal at the lateral edge of the cribriform plate. The anterior ethmoidal arteries runs anterior and medially to reach and ascend in the falx, where they continue as the anterior falcine arteries The anterior falcine artery provides the major supply to the anterior third of falx. D, Superior view. The anterior ethmoidal artery reaches the anterior fossa at the anterolateral edge of the cribriform plate, and the inferior attachment of the falx to the crista galli. E, Superior view of the same specimen. The anterior falcine artery ascends within the falx and anastomoses with the middle meningeal branches that reach the sagittal sinus and descend on the falx and with the falcine branches of pericallosal branch of the anterior cerebral artery. A., artery; Ant., anterior; CN, cranial nerve; Crib., cribriform; Eth., ethmoidal; Front., frontal; Lac., lacrimal; Med., medial; M., muscle; N., nerve; Nasocil., nasociliary; Obl., oblique; Olf., olfactory; Ophth., ophthalmic; Post., posterior; Sup., superior.

FIGURE 2-14 A, Osseous relationships. Anterior view of the right orbit. The recurrent meningeal (sphenoidal) branch of the lacrimal artery courses through the lateral portion of the superior orbital fissure, to anastomose with branches of the middle meningeal arteries. This accessory anastomotic branch between the lacrimal and middle meningeal artery, called the meningolacrimal artery, courses through the lacrimal foramen located just below the lesser sphenoidal wing lateral to the superior orbital fissure. B, Enlarged view of the right orbit. The lacrimal foramen occupies a variable position relative to the superior orbital fissure. It can be located lateral to the superior orbital fissure, confluent with its lateral end or occupy any intermediate position between these extremes. C, Intracranial view of the superior orbital fissure. The surface of the anterior clinoid process exhibits the opening of a tiny bony tunnel that starts inside the optic canal and gives passage to the superficial recurrent ophthalmic artery, which supplies the roof of cavernous sinus and may continue posteriorly along the tentorium as the medial tentorial artery. The lateral portion of the superior orbital fissure is enlarged (arrow) for the passage of the recurrent meningeal (sphenoidal) artery, which anastomoses with the anterior branch of the middle meningeal artery. D, Intracranial view of the right superior orbital fissure and sphenoid ridge. E, Superior view of the right sphenoid ridge. The anterior division of the middle meningeal artery may be encased in a 1- to 30-mm canal, like that shown, in its course along the sphenoidal ridge. After reaching the upper or distal end of the canal, the branches of the artery ascend in bony grooves on the inner table of the skull. F, View of the medial wall of the orbit. The ethmoidal arteries and nerves course through the ethmoidal canals, located in the suture between the orbital plates of the frontal and ethmoid bones. A., artery; Ant., anterior; Br., branch; Clin., clinoid; Eth., ethmoidal; Fiss., fissure; For., foramen; Front., frontal; Gr., greater; Inf., inferior; Infraorb., infraorbital; Lac., lacrimal; Less., lesser; Max., maxillary; Med., medial; Men., meningeal; Mid., middle; Ophth., ophthalmic; Orb., orbital; Post., posterior; Rec., recurrent; Sphen., sphenoidal; Sup., superior; Supraorb., supraorbital.

FIGURE 2-15 Superolateral view. A, Part of the roof and lateral wall of the left orbit have been removed and the intraorbital structures exposed to demonstrate the anastomotic pathways between lacrimal and middle meningeal arteries. The anterior division of the middle meningeal artery gives off a medial branch, which runs medially along the sphenoid ridge and anastomoses with the lacrimal branch of the ophthalmic system. In this specimen, there is a dual connection between the middle meningeal and lacrimal arteries. The most lateral artery is the meningolacrimal branch, a recurrent meningeal branch that pierces the sphenoid wing by passing through the lacrimal foramen. Another vessel, called the recurrent meningeal artery or sphenoid artery (shown in B), courses through the superior orbital fissure to create a second anastomosis between the anterior division of the middle meningeal and the ophthalmic system. B, Enlarged view of A. The meningolacrimal artery has been depressed to expose the tortuous course of the recurrent meningeal artery, also called the sphenoidal artery, which courses through the lateral edge of the superior orbital fissure to reach the dura of the middle fossa and parasellar area. C, Lateral view of the left frontal dura. A frontal branch that arises from the ophthalmic artery passes through the orbital roof to supply the frontal dura, reaching forward to the dura that covers the frontal pole. A., artery; Ant., anterior; Br., branch; CN, cranial nerve; Div., division; Front., frontal; Lac., lacrimal; Lat., lateral; M., muscle; Men., meningeal, meningo; Mid., middle; Ophth., ophthalmic; Orb., orbital; Post., posterior; Sphen., sphenoidal.

Ethmoidal arteries

The anterior and posterior ethmoidal arteries arise from the ophthalmic artery in the medial third of the orbit (see Fig. 2-13A, B) and range in diameter between 0.5 and 1 mm in diameter.⁴⁹ These arteries enter the anterior and posterior ethmoidal canals with their corresponding ethmoidal nerves and leave the canals to enter the anterior cranial fossa at the anterior and posterior ends of the lateral edge of the cribriform plate (see Fig. 2-13A–D). The orbital opening of the ethmoidal canals are located at the junction of the roof and medial wall of the orbit, along the frontoethmoid suture formed by the medial edge of the orbital plate of the frontal bone above and the perpendicular plate of the ethmoid below (see Fig. 2-14F). Intracranially, the ethmoidal canals open on the suture between the orbital part of the frontal bone and the cribriform plate. Before reaching the intracranial cavity, the ethmoidal arteries send branches to the ethmoid sinuses and nasal cavity and septum. The ethmoidal arteries are prominently enlarged in vascular tumors or dural arteriovenous malformations of the anterior fossa.

Intracranially, the anterior ethmoidal artery has been also called the anterior meningeal artery, especially when its territory extends to the dura of the frontal convexity⁵⁰ (see Fig. 2-2). It gives origin to the artery of the falx cerebri, also called the anterior falcine artery,^50–52 which enters the falx at the cribriform plate and supplies the anterior portion of the falx cerebri and adjacent dura covering the frontal pole that borders with the dural territory of the middle meningeal artery (see Fig. 2-13C–E). The anterior falcine artery may be present on both sides but either the right or left may predominate.⁵² It artery is frequently seen, on normal carotid angiograms, ascending in the falx near its attachment to the convexity dura.⁵² It may enlarge in falx meningiomas and occlusive cerebrovascular diseases.⁵¹ The anterior meningeal branches of the ethmoidal arteries often supplies meningiomas from the olfactory groove and may be seen on angiography to be displaced in arch along the surface of the tumor.²⁸ The anterior falcine artery is not shifted laterally by intracranial masses because it courses within the rigid falx.⁵²

The posterior ethmoidal artery passes through the posterior ethmoidal canal and enters the dura at the posterior margin of the cribriform plate and supplies the dura of the medial third of the floor of the anterior cranial fossa, including the planum sphenoidale, anterior clinoid process, and chiasmatic groove (see Fig. 2-1). It anastomoses posteriorly with the branches of the internal carotid artery, laterally with branches of the middle meningeal artery, and anteriorly with the meningeal branches of the anterior ethmoidal artery (see Figs. 2-1 and 2,4).

Recurrent ophthalmic arteries

The ophthalmic arteries may give rise to two recurrent ophthalmic arteries, one superficial and one deep that supply the dura. The superficial recurrent ophthalmic artery generally arises at a sharp angle, from the proximal portion of the ophthalmic artery in the optic canal, and passes backwards, to supply the dura over the anterior clinoid, adjacent lesser sphenoid wing, and the anterior and medial parts of the middle fossa⁵⁰ (see Fig. 2-14C) and anastomoses with branches of the middle meningeal artery and posterior ethmoidal artery (see Figs. 2-1 and 2-4). It supplies the dural roof of the cavernous region and may continue as the medial tentorial artery (see Table 2-1). In the lateral angiographic view it projects above the C4 portion of the carotid siphon crossing the C3 portion under or on the anterior clinoid process somewhat more cephalad than the deep recurrent ophthalmic artery.⁵³

The deep recurrent ophthalmic artery arises from the initial intraorbital part of the ophthalmic artery, courses laterally, through the annulus of Zinn and the medial portion of the superior orbital fissure, crossing the anterior venous space in the cavernous sinus to supply the dura adjacent to the wall of cavernous sinus, bordering the territory of the inferolateral trunk (see Fig. 2-12M). The presence of the deep recurrent ophthalmic artery is closely related to the embryological process that results in the adult form of the ophthalmic artery. Initially the primitive ophthalmic artery arises from two sources, the anterior cerebral artery and the intracavernous carotid artery. The ophthalmic artery, arising from the anterior cerebral artery, undergoes a process of migration to arise from the paraclinoid internal carotid artery. The ophthalmic artery, arising from the cavernous carotid, also undergoes regression to become the deep recurrent ophthalmic artery.⁴⁸ A cavernous origin of the ophthalmic artery, either with or without an ophthalmic artery arising in the usual intradural location, has been reported in 6% to 8% of the cases,¹¹ a finding explained by the persistence of the dorsal primitive ophthalmic artery. When there are two ophthalmic arteries, one passing through the optic canal and one through the superior orbital fissure either may be dominant.

Lacrimal branch

The most important collateral blood supply to the orbit is the middle meningeal artery⁵⁴ and, in reverse fashion, the ophthalmic arterial system can provide flow to the territory of the middle meningeal artery and its branches through the anastomoses between the anterior branch of the middle meningeal artery and the lacrimal branch of the ophthalmic artery (see Fig. 2-15). The presence of arterial connections between the ophthalmic arterial system and the middle meningeal artery has its origin in the embryonic development of the stapedial artery⁵⁵ and involves persistence of anastomoses that are normal at one stage of the development but later regress.^24,56 In a 20-mm embryo the stapedial artery (a branch of the hyoid artery) divides into maxillomandibular and supraorbital divisions. The maxillo-mandibular division penetrates the foramen spinosum and is eventually annexed by the external carotid artery, to form the maxillary artery and extracranial segment of the middle meningeal artery. The supraorbital division, arises in the middle fossa and reaches the superior orbital fissure, providing retro- and intraorbital branches that will, in the adult, become the site for the anastomose of the lacrimal with the middle meningeal artery. The supraorbital division of the primitive stapedial artery is thus responsible for formation of the intracranial segment of the middle meningeal artery and the extraocular ophthalmic artery.^56,57 The supraorbital division also gives off a branch near the superior orbital fissure that courses medially along the posterior edge of the lesser wing of the sphenoid to be distributed to the anterior clinoid process and roof of the cavernous sinus, participating in the supply of the oculomotor and trochlear nerves and sometimes coursing posteriorly as the marginal artery of the tentorium. This arterial branch provides the link between the intraorbital vessels (lacrimal or ophthalmic) and the posterior branches of the carotid siphon.^42,48 In the adult, this artery possibly corresponds to the superficial recurrent ophthalmic artery.

Partial or complete persistence of intraorbital and retro-orbital branches of the supraorbital artery explains both the dependence of the orbital vascularizarion on the middle meningeal artery and the variable participation of the ophthalmic artery in vascularization of the convexity dura^56,58 (see Fig. 2-15C). If the proximal portion of the ophthalmic artery regresses, the adult ophthalmic artery originates, not from the internal carotid artery, but from the middle meningeal artery.^24,54 Unilateral middle meningeal artery origin of the ophthalmic artery was seen in 2 of 170 anatomic specimens and 3 of 3500 cerebral angiograms. Demonstration of this anomaly bilaterally is extremely rare; only 4 cases have been reported.⁵⁹ Ophthalmic origin of the middle meningeal artery can be detected in skulls by the absence or reduced size of the foramen spinosum and/or absence, attenuation or interruption of the osseous sulcus for the middle meningeal artery along the floor of the middle fossa, and has been found in 10% of specimens.^44,54,60 Elevating the dura from the greater and lesser wings of the sphenoid, removing the sphenoid ridge, or embolization procedures involving the external carotid artery risk blindness in patients with a middle meningeal origin of the ophthalmic artery.^24,56,59 If the supraorbital stapedial branch persists, but its embryonic anastomoses with the primitive ophthalmic artery regresses, the resultant anomaly includes an ophthalmic artery that supplies only the globe and remains separated from intraorbital extraocular branches (muscular and lacrimal branches), which are then supplied by the middle meningeal artery.

The ophthalmic artery complex can supply the dura of the convexity and related lesions by three different anomalous meningeal vessels. The commonest found, in 0.5% of angiograms, is the middle meningeal artery that originates from the ophthalmic artery. This results from failure of the proximal intraorbital stapedial branches to involute in association with the involution of the maxillomandibular division of the stapedial artery. The ophthalmic artery may also supply dural lesions through the anterior branch of the middle meningeal, as occurs if there is a partial involution of retro-orbital stapedial branches. The accessory meningeal artery can also arise from the ophthalmic artery. The anatomico–radiologic features of anomalous meningeal branches arising from the ophthalmic artery are typical. These vessels usually arise at the point that the ophthalmic artery passes above the intraorbital optic nerve near the origin of the posterior ethmoidal artery, and pass upward through the superior orbital fissure to reach the cranial dura. Meningeal vessels of ophthalmic origin and related lesions are opacified exclusively by internal carotid artery injection whereas external carotid artery injection fails to visualize them. The anterior branch of the middle meningeal artery and the accessory meningeal artery of ophthalmic origin may be distinguished on angiograms from the anterior meningeal artery or artery of the falx, because this later branch courses near the midline in anteroposterior view and a few millimeters inside the frontal convexity in the lateral view, while the anterior branch of the middle meningeal artery and the accessory meningeal artery of ophthalmic origin have a more lateral course, away from the midline in the AP view and posterior to the frontal convexity in the lateral view.⁵⁶

In 30% of the cases^48,53 in which the orbital branch of the supraorbital artery divides proximally, within the middle cranial fossa, the sphenoid bone, which ossifies later, will allow more than one transosseous route for these vessels. The anastomotic ramus between the lacrimal and the middle meningeal artery usually enter the orbit through the superior orbital fissure; however, in as much as 50% of dissected specimens an additional foramen can be seen in the greater wing of the sphenoid⁶⁰ (see Fig. 2-14A–C). This foramen has been given several names including the lacrimal, Hyrtl, meningorbital, cranio-orbital, sinus canal, or sphenofrontal foramen.^54,60

The lacrimal foramen is composed of multiple openings in 5% to 15% of the cases and occupies a variable position relative to the superior orbital fissure.^54,60 The lacrimal foramen can be located lateral to the superior orbital fissure or confluent with its lateral end⁵⁴ (see Fig. 2-14A–C). Two middle meningeal branches can coexist: one penetrating the orbit through the superior orbital fissure and the other, the lacrimal foramen. The branch that passes through the lacrimal foramen is referred to as the meningolacrimal artery, and the one entering the orbit through the superior orbital fissure is called sphenoidal artery or recurrent meningeal artery or orbital branch of the middle meningeal artery (see Fig. 2-15A, B).

Sometimes the meningolacrimal artery is intact distally but fails to anastomose proximally with the middle meningeal artery and instead breaks up into a fine anastomotic plexus within the dura.⁵⁴ The recurrent meningeal artery runs in the sphenoparietal sulcus, on the lower edge of the sphenoid ridge, with the sphenoparietal sinus. This artery is long and tortuous while the meningolacrimal has a short, straight path to the orbit and to its anastomosis with the lacrimal artery (see Fig. 2-15A, B). The recurrent meningeal artery may be associated with a laterally expanded superior orbital fissure (see Fig. 2-14C). The meningeal branches of the ophthalmic artery, because of this variable distribution, should be carefully studied in sphenoid ridge, frontobasal, and anterior falcine tumors. A common angiographic finding in these lesions is enlargement of the ophthalmic artery.⁵⁰

Anterior cerebral artery

Dural branches can arise at two levels along the anterior cerebral artery.⁹ The olfactory branches from the anterior cerebral artery, which course on the olfactory bulb may anastomose with the olfactory branches from the ethmoidal arteries in the region of the cribriform plate; and the pericallosal artery can send branches to the free margin of falx, anastomosing anteriorly with the anterior falcine branch of the ophthalmic artery and posteriorly with the dural branches from the posterior cerebral artery⁹ (see Figs. 2-1 and 2-4).

Vertebral artery branches

The anterior and posterior meningeal arteries arise from the extracranial segment of the vertebral artery to supply a portion of the posterior fossa dura (Fig. 2-16).

FIGURE 2-16 A, Posterior view. The anterior meningeal artery arises from the anteromedial surface of the extracranial vertebral artery, between the C2 and C3 transverse processes. The anterior meningeal artery anastomoses with the hypoglossal and jugular branches of the ascending pharyngeal artery to supply the dura of the lateral portion of foramen magnum. The second, third, and fourth segments of the vertebral artery are labeled. B, Posterior view. The posterior meningeal artery arising from the third segment of the vertebral artery, which courses in a bony sulcus on the upper edge of C1. C, Enlarged view of B after a suboccipital craniotomy. The third segment of the vertebral artery is located between the transverse process of atlas and the dural entrance and gives rise to the posterior meningeal artery near the dura entrance than the transverse process of C1. A lateral branch of the posterior meningeal artery runs toward the occipital condyle. The posterior condylar vein passes through the condylar canal. D, The posterior meningeal artery ascends, nearly parallel to the internal occipital crest, to reach the dura over the medial cerebellar fossae and falx cerebelli and above the torcula to reach the dura of the falx cerebri. E, Posterior view of the torcula area. The posterior meningeal artery anastomoses with the meningeal branches of the ascending pharyngeal artery and mastoid branch of the occipital artery at the level of the foramen magnum and over the cerebellar fossae. Above the torcula, the posterior meningeal artery anastomoses with the petrosquamosal and parieto-occipital branches of the middle meningeal arteries. F, Posterior view. The left posterior meningeal artery has an anomalous origin from posterior inferior cerebellar artery. At the level of the cisterna magna, the caudal loop of the posterior inferior cerebellar artery gives rise to a meningeal branch, which pierces the arachnoid to supply the territory of the posterior meningeal artery. G, Posterior view of the right cerebellopontine angle. The anterior inferior cerebellar artery gives off the subarcuate and labyrinthine arteries. H, Posterior view of the right petrous bone adjacent to the subarcuate fossa. A., artery; A.I.C.A., anterior inferior cerebellar artery; Ant., anterior; Asc., ascending; Atl., atlas, atlantal; Br., branch, C1, first cervical nerve; C2, second cervical nerve; C3, third cervical nerve; CN, cranial nerve; Cap., capitis; Cond., condylar; Dors., dorsal; Endolimph., endolymphatic; Flocc., flocculus; For., foramen; Gang., ganglion; Int., internal; Intermed., intermedius; Jug., jugular; Labyr., labyrinthine; Lat., lateralis; M., muscle; Maj., major; Men., meningeal; Mid., middle; Min., minor; N., nerve, nervous; Occip., occipital; Pet., petrosal; Pharyng., pharyngeal; P.I.C.A., posterior inferior cerebellar artery; Post., posterior; Subarc., subarcuate; Suboccip., suboccipital; Sup., superior; Transv., transverse; V., vein; V.A.2, vertebral artery second segment; V.A.3, vertebral artery third segment; V.A.4, vertebral artery fourth segment.

Anterior meningeal artery

The anterior meningeal artery arises from the vertebral artery at the level of the C2, passes medially through the C2–C3 foramen in front of the C3 root, and courses upward near the midline, sending several twigs to the anterior dura along its course (see Fig. 2-16A). These paired arteries join to form an arch in the dura at the level of the apex of the dens, which gives off multiple fine rami to the dura in the atlanto-occipital space.^16,60–62 Intracranially, the anterior meningeal artery anastomoses with the hypoglossal branch of the ascending pharyngeal artery^16,61,63,64 (see Figs. 2-1 and 2-6).

The anterior meningeal artery can be identified in approximately 50% of subtraction angiograms.⁶⁰ Its small size, results in only the first 1 to 1.5 cm of its course being seen angiographically.^17,61 In the frontal angiogram, it is seen to arise from the medial aspect of vertebral artery and courses upward toward the foramen magnum. In the lateral angiogram, its initial segment is projected behind the vertebral artery, but it is subsequently seen into the anterior portion of the spinal canal, immediately posterior to the vertebral bodies, and anterior to the anterior spinal artery.^16,61,65

Posterior meningeal artery

The posterior meningeal artery usually arises from the segment of the vertebral artery that runs in the groove for the vertebral artery on the upper edge of the posterior arch of atlas (V3 segment) (see Fig. 2-16B–D). Its origin is usually closer to the dural entrance than to the transverse foramen of the atlas. Its initial course is along the upper posterior aspect of the extradural vertebral artery toward the posterolateral edge of foramen magnum, where it enters the intracranial dura (see Fig. 2-16B). It ascends posterosuperiorly, nearly parallel to the internal occipital crest, to reach the attachment of the cerebellar falx. Around the level of the external occipital protuberance, the artery bifurcates and anastomoses with the meningeal branches of the occipital and middle meningeal arteries⁶ (see Figs. 2-7 and 2-14D).

The posterior meningeal artery can be divided into an extracranial and an intracranial portion. The extracranial portion is tortuous, probably as a response to the motility of the neck¹⁶ and extends from origin to the atlanto-occipital space. The intracranial portion shows a relatively straight configuration¹⁷ (see Fig. 2-14B–D). This pattern, on angiography, facilitates differentiation of the posterior meningeal artery from the branches of the posterior inferior cerebellar artery. The posterior meningeal artery, seen on 30% to 40% of angiograms, is easier to identify on lateral films.^16,17

The posterior meningeal artery may also originate from the occipital artery, the hypoglossal branch of the ascending pharyngeal artery, the cervical internal carotid artery,⁶⁶ and the posterior inferior cerebellar artery.⁶ Its origin from an artery supplying the brain parenchyma can result from the persistence of the preexisting anastomotic channels between the primitive cerebral and meningeal vessels, and regression of the proximal stem of the posterior meningeal artery (see Fig. 2-14F).

Anterior inferior cerebellar artery

The subarcuate artery usually originates from the lateral pontine segment of the anterior inferior cerebellar artery (AICA), medial to the porus, penetrates the dura covering the subarcuate fossa, and enters the subarcuate canal (see Fig. 2-14G). It may arise as a branch of the labyrinthine artery, which also arises from AICA or as a single trunk from a cerebellar branch of AICA (cerebellosubarcuate artery). In the few cases in which the artery arises inside the internal acoustic canal, it reaches the subarcuate canal after a short recurrent segment or by piercing the meatal roof.¹² The subarcuate artery anastomoses with the branches of the stylomastoid artery within the petrous bone, the branches of the middle meningeal artery running over the superior surface of the petrous bone and the mastoid branches of the occipital artery. It supplies the dura of the internal acoustic meatus and adjacent posterior surface of the petrous bone as well as the bone in the region of the semicircular canals. Although not seen angiographically, the subarcute artery is involved in the formation of the dural collateral circulation that joins the leptomeningeal collaterals in cases of anterior inferior cerebellar artery occlusion.^48,58

Posterior cerebral artery

The posterior part of the falx cerebri and the adjacent medial part of tentorium may be supplied in part by a meningeal branch of the posterior cerebral artery. Wollschlaeger and Wollschlaeger⁶⁷ first described this meningeal branch during anatomical dissections and named it the artery of Davidoff and Schechter, in honor of their mentors (see Figs. 2-3 and 2-5). This artery originates from the peduncular or ambient segment of the posterior cerebral artery, courses around the brainstem to the midline and makes a sharp angulated upward turn to pierce the tentorium and supplies the tentorium and adjacent falx cerebri along the falcotentorial angle. An enlarged meningeal branch of the posterior cerebral artery has been identified angiographically in vascular tumors and arteriovenous malformations involving the falcotentorial junction.⁶⁸ A meningeal branch of the posterior cerebral artery could not be identified in this study or in a prior study from this laboratory.⁶⁹ However the senior author (ALR) has noted the presence of this variation in studies related to other areas.