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Right Superolateral Panorama of Midbrain, Cerebellum, Sella, Floor of Middle Cranial Fossa, and Trigeminal Nerve

Surgical Correlation

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Right superolateral panorama of midbrain, cerebellum, sella, floor of middle cranial fossa, and trigeminal nerve. The cerebrum has been dissected away and the brainstem preserved in situ in this specimen. 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. The oculomotor (CNIII) nerves can be seen leaving the ventral midbrain, passing through the interpeduncular fossa toward the lateral walls of the cavernous sinus. 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. They penetrate the dura between the anterior and posterior petroclinoid ligaments (the latter attach from a posterior clinoid process to its ipsilateral petrous apex and form the anteromedial free edge of the tentorial notch) lateral to and in front of the posterior clinoid process. 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. 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. 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. The middle cranial fossa is the lateral depression between the lesser wing of the sphenoid and petrous portion of the temporal bone. The dura mater has been stripped to reveal the trigeminal ganglion and 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 ganglion lies in Meckel's cave on the trigeminal depression anteromedial to the trigeminal prominence, an elevation on the petrous ridge. The greater superficial petrosal nerve can be seen leaving its hiatus on the anterior surface of the petrous bone. It passes deep to the mandibular nerve toward the foramen lacerum and pterygoid canal and unites with the deep petrosal nerve to form Vidian nerve. The middle meningeal artery can also be seen emerging through foramen spinosum. The tentorium has been incised to expose 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 transverse sinus is exposed in the posterior tentorium at the junction of the occipital bone and petrous ridge where it continues as the sigmoid sinus. It receives the superior petrosal sinus, contained in the tentorial attachment to the petrous ridge, draining the cavernous sinus. (Image courtesy of PA Rubino)

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