Back of skull Anatomy

Anterior cranial fossa and body of the sphenoid.The greater portion of the anterior floor is convex and grooved by the frontal lobe gyri. This portion of the skull base consists of the orbital portion of the frontal bone. The ethmoid bone forms the central part of the floor, which is the deepest area of the anterior cranial fossa. In the center of this region is the cribriform plate, through which the olfactory tracts pass.Bony orbit, oblique view. The fovea ethmoidalis, or the roof of the ethmoid cavity, continues laterally from the cribriform plate. The cribriform plate may be more than 1 cm lower than the roof of the ethmoid cavity (fovea ethmoidalis), and it is made of extremely thin bone compared with the relatively thick bone of the lateral fovea ethmoidalis. During transethmoidal approaches to the anterior skull base, this relationship is extremely important to remember.

The foramen cecum sits between the frontal crest and the prominent crista galli and is a site of communication between the draining veins of the nasal cavity and the superior sagittal sinus. The crista galli, which projects up centrally between the cerebral hemispheres, serves as the site of attachment for the falx cerebri.

The optic chiasm, or chiasmatic sulcus, sits slightly posteriorly in the midline. The anterior clinoid processes form the posterolateral segment and help form the roof of the optic canal. In the medial aspect, the lesser wing of the sphenoid forms the anterior clinoid process, an important landmark for the optic nerve and supracavernous internal carotid artery (ICA).

Inferior relationships — extracranial aspects

The most important anatomic structures below the anterior cranial fossa are the orbits and the paranasal sinuses. A thorough description is beyond the scope of this article, but important anatomy and relationships are discussed.

The bony orbit is often a route for intracranial and extracranial spread of infection and tumors because of its direct proximity to the anterior fossa. The posterior wall is thin and adjacent to the superior sagittal sinus and frontal lobe dura.Meningeal arteries, intracranial view. The posterior aspect includes the optic canal, the superior orbital fissure (SOF), and the inferior orbital fissure (IOF). The SOF conveys the oculomotor, trochlear, abducens, and ophthalmic nerves (cranial nerves [CN] III, IV, VI, and V1, respectively), as well as the ophthalmic veins.

The IOF transmits the maxillary nerve (CN V2) and infraorbital vessels, and it communicates with the infratemporal and pterygomaxillary fossae. The lateral portion of the IOF is an important surgical landmark for positioning lateral orbital osteotomies during anterior skull base resections. The optic canal transmits the optic nerve (CN II) and the ophthalmic artery.

Contents of the infratemporal fossa. Cranial venous sinuses and the basilar plexus.

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