Clinical Anatomy

Fig. 2.1

Foramina of the osseous skull base specifying the pervading neurovascular structures

Fig. 2.2

Overview of the anterior-middle fossa junction and components: 1 planum sphenoidale, 2 limbus sphenoidale, 3 prechiasmatic sulcus, 4 tuberculum sellae, 5 falciform ligament, 6 anterior clinoid process, 7 internal carotid artery (supraclinoid segment), 8 middle cerebral artery (M1 segment), 9 anterior cerebral artery (A1 segment)

2.1.2 Foramina and Their Contents

The lamina cribrosa (cribriform plate of the ethmoid bone) possesses multiple openings for the filia olfactoria of the olfactory nerve (CN I). The anterior meningeal artery, a branch of the anterior ethmoidal artery, runs intracranially through the lamina cribrosa. The anterior ethmoidal nerve, a branch of the nasociliary nerve (from the ophthalmic nerve [V1]), initially goes through the cribriform plate intracranially, and from there peters out extracranially to the nasal mucosa. The optic nerve (CN II) and the ophthalmic artery reach the inferior part of the orbital cavity through the optic canal (◘ Figs. 2.1, 2.2, 2.3, and 2.4).

Fig. 2.3

Osseous skull base, inferior view, with foramina

Fig. 2.4

Schematic drawing of the most important neurovascular structures of the skull base

The oculomotor nerve originates from the anterior aspect of the midbrain. It runs anteriorly, passing below the posterior cerebral artery and above the superior cerebellar artery . The nerve pierces the dura mater and enters the lateral aspect of the cavernous sinus at the oculomotor triangle. This triangle consists of three ligaments as shown in ◘ Fig. 2.5: anterior petroclinoid ligament, posterior petroclinoid ligament, and interclinoid ligament. Opening and cutting these ligaments is necessary in different approaches to the cavernous sinus.

Fig. 2.5

Overview of the cavernous sinus, oculomotor triangle, and their correlations. a Bony structures, b anatomical structures: pay attention to the ophthalmic artery origin from the internal carotid artery at the left side and its correlation to the optic nerve

The ophthalmic artery is a branch of the supraclinoid portion of the internal carotid artery in most cases. This vessel follows the optic nerve into the optic canal and orbit and is responsible for the supply of the orbital structures. The origin of the ophthalmic artery is usually medial to the anterior clinoid process and below the optic nerve. At the level of the optic canal, this artery has passed to a position lateral to the nerve. This anatomical fact must be kept in mind during the opening of the falciform ligament to avoid an iatrogenic lesion of this artery (◘ Fig. 2.5b).

2.2 Middle Cranial Fossa, Sellar Region, and Temporal Base

2.2.1 Osseous Components

The middle cranial fossa is formed in its anterior portion by the greater and lesser wings of the sphenoid bone , whereby the lesser wing represents the border between middle and anterior cranial fossa. The temporal bone (os temporale) forms the major portion of the middle cranial fossa. The tip of the petrous part of the temporal bone represents the boundary to the posterior cranial fossa (◘ Fig. 2.1).

The sella turcica is completely formed by the medial portions of the sphenoid bone. Important landmarks here are the anterior, middle, and posterior clinoid processes (◘ Figs. 2.2, 2.5, and 2.6) [4, 9, 17].

Fig. 2.6

Intracranial a and transnasal endoscopic b view of the middle clinoid process. 1 prechiasmatic sulcus, 2 anterior clinoid process, 3 middle clinoid process, 4 carotidoclinoid ring, 5 posterior clinoid process, 6 optic nerve, 7 lateral opticocarotid recess, 8 internal carotid artery (supraclinoid segment), 9 sella turcica, 10 clivus recess

The middle clinoid process is an osseous prominence that arises from the body of the sphenoid bone at the anterolateral margin of the sella turcica. It is identifiable in 60% of the normal population (bilateral in 35%). Recognition of this structure, especially when there is a caroticoclinoid ring , is very important in the surgical planning of endoscopic endonasal surgeries in the perisellar region (◘ Fig. 2.6) [7].

The prechiasmatic sulcus is a groove on the upper surface of the sphenoid bone running transversely between the optic canals bounded anteriorly by the sphenoidal limbus and posteriorly by the tuberculum sellae ; the optic chiasm is located just above the prechiasmatic sulcus (◘ Figs. 2.2 and 2.6) [2].

2.2.2 Foramina and Their Contents

Numerous structures permeate the superior orbital fissure (◘ Figs. 2.1 and 2.4):

Oculomotor nerve (CN III)
Trochlear nerve (CN IV)
Abducens nerve (CN VI)
Nasociliary nerve (branch from CN V₁)
Lacrimal nerve (branch from CN V₁)
Frontal nerve (branch from CN V₁)
Superior ophthalmic vein

The cranial nerves III, IV, and VI control the oculomotor system, while cranial nerve III also controls the pupillomotor system. The branches from the ophthalmic nerve (V₁) have sensory fibers from the cornea and upper facial area. The lacrimal nerve additionally has attached sympathetic and parasympathetic fibers for the lacrimal gland.

The inferior orbital fissure contains:

Infraorbital nerve (branch from V₂)
Zygomatic nerve ( branch from V₂)
Infraorbital artery
Parasympathetic fibers from the pterygopalatine ganglion

Both nerve branches from V₂ are the sensory provision for the middle facial region. The zygomatic nerve receives parasympathetic fibers at the pterygopalatine ganglion for the lacrimal gland, which it passes on to the lacrimal nerve.

The maxillary nerve (V₂) and mandibular nerve (V₃) each possess their own foramina in the middle cranial fossa — foramen rotundum and foramen ovale (◘ Figs. 2.1, 2.3, and 2.4).

The maxillary nerve is the sensory provision for the middle third of the face, as well as the gums and teeth of the upper jaw.

The mandibular nerve is the sensory provision for the lower facial region and tongue, as well the motor provision for the masticatory muscles, portions of the muscles in the base of the mouth, the tensor tympani muscle, and the tensor veli palatini muscle [5, 10, 13].

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