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Superior View of Cranial Nerves in Right Middle Cranial Fossa

Surgical Correlation

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Superior view of cranial nerves in right middle cranial fossa. The cerebrum has been dissected away to expose the brainstem and cerebellum in situ. The dura mater of the middle cranial fossa has been stripped away to reveal the trigeminal nerve and ganglion, the cavernous sinus, and associated nerves. The oculomotor (CNIII) nerve leaves the ventral midbrain, passes through the interpeduncular fossa, and penetrates the dura between the anterior and posterior petroclinoid ligaments lateral to and in front of the posterior clinoid process. In its course it passes caudal to the posterior cerebral artery, between this and the superior cerebellar artery, both branches of the midline basilar artery. The right trochlear (CNIV) nerve is seen leaving the dorsal surface of the midbrain and curving around the cerebral peduncle to gain the lateral wall of the cavernous sinus. It also passes between these two arteries and penetrates the dura between the free and attached edges of the tentorium cerebelli. Both nerves are located in the superior portion of the lateral sinus wall before passing to the orbit through the superior orbital fissure. The middle cranial fossa is the lateral depression between the lesser wing of the sphenoid and petrous portion of the temporal bone. The trigeminal nerve leaves the lateral surface of the pons and crosses the apex of the petrous bone where it then expands as the trigeminal ganglion. The ganglion lies in Meckel's cave on the trigeminal depression anteromedial to the trigeminal prominence, an elevation on the petrous ridge.  From this sensory ganglion arise its three divisions: ophthalmic (CNV1), maxillary (CNV2), and mandibular (CNV3) coursing toward their openings of exit; superior orbital fissure, foramen rotundum, and foramen ovale, respectively. The roof of the internal auditory canal has been drilled just posterior to the trigeminal prominence to expose the facial nerve, geniculate ganglion, and the greater superficial petrosal nerve. The latter leaves its hiatus on the anterior surface of the petrous bone and passes deep to the mandibular nerve toward the foramen lacerum and pterygoid canal to unite with the deep petrosal nerve to form Vidian nerve. The vestibulocochlear nerve is also visible in the internal auditory canal. The middle meningeal artery is shown emerging through the foramen spinosum. Ventral to the midbrain is the body of the sphenoid featuring the sella turcica, the midline depression containing the pituitary gland and distal pituitary stalk through the opening of the diaphragma sellae. The sella is bounded anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae and its posterior clinoid processes. In this view, medial to the anterior clinoid processes are the optic nerves (CNII) emerging from the optic canals and the supraclinoid internal carotid arteries. The tentorium has been incised to expose part of the rostral cerebellum. This surface is supplied by the medial and lateral branches of the superior cerebellar arteries that course posteriorly in the pontomesencephalic sulcus above the superior cerebellar peduncles before ramifying. The superior petrosal sinus has been exposed in the tentorial attachment to the petrous ridge and drains the cavernous sinus to the transverse sinus. (Image courtesy of PA Rubino)

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