Читать книгу Anterior Skull Base Tumors - Группа авторов - Страница 13

On both sides, the lateral segment of the ASB is the orbital roof, which is formed by the orbital plate of the frontal bone anteriorly and the lesser wing of the sphenoid posteriorly (Fig. 1, 13). The periorbit and dura mater line the inferior and superior surfaces of the orbital roof, respectively, and merge at the superior orbital fissure forming the meningo-orbital fold.

Fig. 13. Lateral sagittal section of a specimen (right side, seen from lateral to medial). The lateral portion of the ASB is formed by the orbital plate of the frontal bone (OPFB) and lesser wing of the sphenoid bone (LWSB) and separates the intracranial structures from the frontal sinus (FS) and orbital content. V3, mandibular nerve; ET, eustachian tube; Ey, eyeball; GWSB, greater wing of the sphenoid bone; ICA, internal carotid artery; LOG, lateral orbital gyrus; LPM, lateral pterygoid muscle; MCA, middle cerebral artery; MS, maxillary sinus; ON, optic nerve; SRM, superior rectus muscle; TL, temporal lobe.

On the orbital side, the orbital roof is adjacent to several neurovascular and muscular structures. From medial to lateral, the trochlear (IV cranial nerve), frontal, and lacrimal nerves run within the extraconal fat just beneath the periorbit. The trochlear nerve reaches the posterior portion of the superior oblique muscle, which lies from the Zinn annulus (the common origin of the four rectus muscles, superior oblique muscle, and levator palpebrae superioris muscle surrounding the optic nerve at its entrance at the apex of the orbit) to the trochlea (a cartilaginous ring lying at the superior-medial-anterior corner of the orbital cavity and serving as the anchor point for the superior oblique muscle). The frontal nerve, coming from the ophthalmic branch of the trigeminal nerve, forms the supratrochlear nerve (medial) and supraorbital nerve (lateral), and both provide the sensitive nerve supply of the forehead. The lacrimal nerve (branch of the ophthalmic nerve) goes towards the lacrimal gland, whose orbital portion is located in the superolateral angle of the orbital rim. The superior ophthalmic vein usually reaches the superior orbital fissure in an area between the frontal and lacrimal nerves. The proximal tract of the intraorbital ophthalmic artery, its main branches, and other orbital nerves are not adjacent to the skull base as they run caudally to the levator palpebrae superioris and superior rectus muscle. After entering the orbit from the inferior portion of the optic canal, the ophthalmic artery usually turns lateral and above the optic nerve (below the superior rectus muscle), and gives rise to the anterior, middle (when present), and posterior ethmoidal arteries. The anatomy of the ophthalmic artery is considerably variable: in particular, it can arise from other portions of the internal carotid artery, thus changing its relationships with neighboring structures (especially with the optic apparatus) [12, 13]. The nasociliary nerve (branch of the ophthalmic nerve) runs within the annulus of Zinn and then close to the orbital beak, parallel to the ophthalmic artery and inferomedial to the superior oblique muscle.

On the intracranial side, the orbital roofs are in contact with the inferior surface of the frontal lobes. The anterior, posterior, and lateral orbital gyri overlie the orbital roof and are supplied by the lateral orbitofrontal artery, which comes from the middle cerebral artery. These circumvolutions are separated by the orbital sulci, which has an “H” shape. The olfactory vein (posterior-lateral), fronto-orbital vein (posteromedial), and prefrontal veins provide the venous drainage of this area. The dura of the orbital roof is vascularized by the lateral branches of the anterior meningeal arteries and variably by branches of the middle meningeal artery. The frontal division of the middle meningeal artery usually gives rise to some branches for the far lateral dura of the orbital roof and a large branch that runs towards the superior orbital fissure. This branch can reach the ophthalmic artery (meningo-ophthalmic artery) or the lacrimal artery (meningo-lacrimal artery), passing through either the superior orbital fissure or an isolate lateral foramen (Hyrtl’s foramen), reported in <20% of cases (Fig. 1). After entering the orbit, the meningo-ophthalmic or meningo-lacrimal artery gives rise to a small branch that recurs through the superior orbital fissure or Hyrtl’s foramen to provide the blood supply of the dura of the lesser wing of the sphenoid bone. Furthermore, additional meningo-orbital foramina can be found along the lateral portion of the orbital roof, serving as routes for branches of the lacrimal artery for the blood supply of the dura of the anterior cranial fossa. Rarely, the paraclinoid internal carotid artery gives rise to some small branches that perforate the anterior clinoid process and vascularize the surrounding dura [1].