Classification of the clival region; endonasal approach. The upper or sellar clivus is formed by the dorsum sellae and posterior clinoids, and it is limited inferiorly by the sella floor. A superior transclival approach provides access to the cerebral peduncle, and interpeduncular cistern with the basilar artery bifurcation an mammillary bodies, and floor of the third ventricle. The oculomotor nerves run in the lateral recess of the interpeduncular cistern and, along with the PCoA, they form the lateral limit of this approach. The middle or sphenoidal clivus is located between the sella floor and the floor of the sphenoid sinus or choana. A middle transclival approach provides access to the pons, prepontine cistern and basilar trunk. The lateral limit of this approach is the interdural and cisternal segment of the abducens nerve. The lower or nasopharyngeal clivus is located between the choana and the foramen magnum. An inferior transclival approach reaches the premedullary cistern and vertebral arteries. The lateral limits of this approach are the hypoglossal nerves. (Image courtesy of JC Fernandez-Miranda)