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Superior View of Right Orbit, Middle Fossa, and Brainstem

Surgical Correlation


Superior view of right orbit, middle fossa, and brainstem. The roof of the right orbit has been removed and the periorbita is shown enclosing the orbital contents. The optic nerve and ophthalmic artery course to the orbit within the optic canal. The oculomotor, trochlear, and ophthalmic nerves course within the lateral wall of the cavernous sinus before entering the orbit via the superior orbital fissure. The abducens nerve also uses that fissure to the orbit after first passing through the cavernous sinus on the lateral surface of the internal carotid artery. Medial to the orbit are the ethmoid air cells that drain into meati of the nasal cavity. Behind the posterior most ethmoid air cell is the sphenoid sinus. The nasal cavity is roofed by the crista galli and cribriform plate of the ethmoid that contains the olfactory fossae for the olfactory bulbs. These receive the neurofilaments of the olfactory nerve and convey sensory information of smell to the olfactory cortex via the olfactory tracts. Behind the optic chiasma is the pituitary stalk connecting to the pituitary gland through an opening in the diaphragma sellae. Dura and bone have been removed in the middle cranial fossa to reveal the trigeminal or Gasserian ganglion at the petrous apex. From this sensory ganglion arise the ophthalmic, maxillary, and mandibular nerves that pass through, respectively, the superior orbital fissure, foramen rotundum, and foramen ovale. Posterior to the ganglion the roof of the internal auditory canal has been drilled to show the facial and vestibulocochlear nerves. Distally this canal lies posterior to the cochlea and anterior to the semicircular canals. Within the canal, the facial nerve ends at the geniculate ganglion. From here arises the greater superficial petrosal nerve that passes deep to the mandibular nerve to enter the pterygoid canal where it delivers its preganglionic parasympathetic fibers to the pterygopalatine ganglion within the pterygopalatine fossa. The roof of the tympanic cavity has been opened to reveal the three ossicles: malleus, incus, stapes. In the posterior fossa, the mesencephalon is shown in transverse section with its pigmented substantia nigra. Ventral to this can be seen the basilar artery giving rise to its superior cerebellar and terminal posterior cerebral arteries. (Image courtesy of PA Rubino)