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Panoramic Superior View of Right Trigeminal Nerve and Cavernous Sinus, Inner and Middle Ear Structures, and Sellar Region

Surgical Correlation

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Panoramic superior view of right trigeminal nerve and cavernous sinus, inner and middle ear structures, and sellar region. The cerebrum has been dissected away to expose the brainstem and cerebellum in situ. The anterior petroclinoid ligament extends from the anterior clinoid process of the lesser wing of sphenoid to the petrous apex of the temporal bone and is part of the tentorium cerebelli. The remainder of the tentorium cerebelli is attached to the superior ridge of the petrous bone and to the transverse groove of the occipital bone. It divides the cranial cavity into supratentorial and infratentorial compartments. The tentorial notch or incisura is a U-shaped space that curves around the junction of the midbrain and pons to accommodate passage of the brainstem into the posterior fossa. The hyper-pigmented substantia nigra lies within the tegmentum of the midbrain posterior to the cerebral peduncles. Toward its dorsal surface in the midline is the narrow cerebral aqueduct that connects the third ventricle with the fourth ventricle. 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 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) nerves leave the ventral midbrain, pass through the interpeduncular fossa, and penetrate the dura between the anterior and posterior petroclinoid ligaments lateral to and in front of the posterior clinoid processes. In their course they pass caudal to the posterior cerebral artery, between this and the superior cerebellar artery, both branches of the midline basilar artery. The trochlear (CNIV) nerves are seen leaving the dorsal surface of the midbrain and curving around the cerebral peduncle to gain the lateral wall of the cavernous sinus. They also penetrate 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 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 middle meningeal artery is shown emerging through the foramen spinosum. Deep to the ophthalmic nerve is the abducens nerve. After leaving the pontomedullary sulcus, it ascends on the clivus, penetrates its dura, and passes across the petrous apex below the petrosphenoid ligament (Gruber's ligament; Dorello's canal) to enter the cavernous sinus. Here it courses on the lateral surface of the internal carotid artery before entering the orbit through the superior orbital fissure. Posterolateral to the trigeminal prominence, the roof of the internal auditory canal has been drilled to expose the facial and vestibulocochlear nerves. Distally within the canal the facial nerve ends at the geniculate ganglion, the sensory ganglion of this nerve. From here, the greater superficial petrosal nerve takes its origin. It leaves the anterior surface of the petrous bone through a hiatus 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 distal end of the auditory canal separates the cochlea, anteriorly, from the bony labyrinth, posteriorly. The semicircular canals have been drilled out as well as the tegmen tympani to expose the contents of the tympanic cavity. In the epitympanum, the head of the malleus articulates with the body of the incus. At the anterior wall of the tympanic cavity can be seen the Eustachian tube and the tensor tympani muscle. 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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