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Sellar and Parasellar Anatomy

Surgical Correlation

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Sellar and parasellar anatomy. The cerebrum has been dissected away to expose the brainstem and cerebellum in situ. The tentorial notch or incisura (toward upper left corner of image) 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. 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 bone of the planum sphenoidale has been removed to expose the sphenoid sinus. 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 from the lateral surface of the sphenoid body and greater wing and a portion of the greater wing has been drilled. In this process, the lateral wall of the cavernous sinus has been exposed containing the oculomotor and trochlear nerves in its superior portion and the cavernous segment of the internal carotid artery. 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 right trochlear (CNIV) nerve is seen here leaving the dorsal surface of the midbrain and curving around the cerebral peduncle between the posterior cerebral and superior cerebellar arteries to gain the lateral wall of the cavernous sinus. Both nerves enter the orbit via 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. Posterolateral to the foramen ovale is the foramen spinosum. The middle meningeal artery can be seen emerging from it. Posterolateral to the trigeminal prominence, the roof of the internal auditory canal has been drilled. In this view, the geniculate ganglion is exposed at the distal end of the canal. Here, the facial nerve continues posteriorly in the facial canal along the medial wall of the tympanic cavity inferior to the lateral semicircular canal and the greater superficial petrosal nerve takes its origin anteriorly from the ganglion. The greater superficial petrosal nerve 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 bone covering the roof of the infratemporal fossa has been drilled to reveal the superior head of the lateral pterygoid muscle. Emerging from the foramen ovale is the smaller anterior division of the mandibular nerve and its larger posterior division. The superior petrosal sinus is exposed in the tentorial attachment to the petrous ridge. It drains the posterior part of the cavernous sinus to the transverse sinus.  (Image courtesy of PA Rubino)

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