Stepwise dissection showing the structures that form the lateral limit of the transnasal route to the clivus. A, The entire clivus is located above the level of the hard palate and, in most cases, can be accessed through the nasal cavity and nasopharynx. The nasal turbinates and meati and the eustachian tubes are in the lateral margin of the exposure. B, A portion of the superior, middle, and inferior turbinates has been removed and the area between the sphenoid pterygoid process and the posterior wall of the maxilla has been opened to expose the pterygopalatine fossa in the lateral wall of the nasal cavity. The ostia of the maxillary and frontal sinuses opens into the middle meatus located below the middle turbinate. The nasolacrimal duct opens below the lower turbinate into the inferior meatus. The eustachian tube, located in front the foramen magnum and lower edge of the clivus, opens into the nasopharynx at the posterior edge of the pterygoid process. Accessing the clivus plus the atlas and axis requires an approach that can be directed above and below the level of the palate. Rosenmüller’s fossa is located behind the eustachian tube. C, The medial wall of the maxillary sinus has been opened to expose the infraorbital nerve, which arises in the pterygopalatine fossa and passes forward in the sinus roof. The maxillary nerve passes through the foramen rotundum to enter the pterygopalatine. The upper cervical carotid and eustachian tube form the lateral limit of the exposure of the lower clivus and the junction of the petrous and cavernous carotid limits the lateral exposure of the upper clivus. D, Enlarged view. The bone and dura covering the optic canal in the superolateral part of the sphenoid sinus has been opened to expose the optic nerve and ophthalmic artery in the optic canal. The junction of the petrous and cavernous carotid limits the exposure below the level of the sella. The maxillary nerve exits the foramen rotundum and enters through the pterygopalatine fossa where it gives rise to the infraorbital, zygomatic, and greater palatine nerves, plus communicating rami to the pterygopalatine ganglion. Terminal branches of the maxillary artery intermingle with the neural structures in the pterygopalatine fossa. (Images courtesy of AL Rhoton, Jr.)