The sphenoid lies in the base of the skull forming part of the floor of the middle cranial fossa. On its upper surface the bone carries a chamber for the pituitary gland. Anterior to the pituitary fossa the bone is hollowed out as the sphenoidal air sinus. Foramina in the bone transmit nerves and vessels. The superior orbital fissure transmits the ophthalmic division of the trigeminal nerve, the abducent, trochlear and oculomotor nerves. The foramen rotundum transmits the maxillary division of the trigeminal nerve. The pterygoid canal transmits the nerve of the pterygoid canal (sympathetic fibres plus the greater superficial petrosal branch of the facial nerve). The foramen ovale transmits the mandibular division of the trigeminal nerve. The optic foramen transmits the optic nerve and ophthalmic artery. The ophthalmic veins drain back to the cavernous sinus which lies on either side of the sella turcica. The cavernous sinus drains through the superior petrosal sinus to the transverse sinus, and through the inferior petrosal sinus to the jugular vein. The internal carotid artery lies for part of its course in the cavernous sinus. Running along the dura of the cavernous sinus are the ophthalmic, oculomotor and trochlear nerves. The abducent nerve runs through the sinus.
Although the sphenoid lies centrally it is still prone to fracture. The many neurovascular structures that traverse the sphenoid bone are vulnerable to injury. Sphenoidal fractures are frequently associated with vascular injuries such as traumatic pseudoaneurysm of the internal carotid artery, carotid-cavernous sinus fistula, bleeding from the middle meningeal artery, and nerve palsies due to damage to the optic, trigeminal, oculomotor, abducent and trochlear nerves.
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