Background Carefully tailoring the transclival approach to the involved parts of the upper, middle, or lower clivus requires a precise understanding of the focal relationships of the clivus. Objective To develop an optimal classification of the upper, middle, and lower clivus and to define the extra and intracranial relationships of each clival level. Methods Ten cadaveric heads and 10 dry skulls were dissected using the surgical microscope and endoscope. Results The clivus is divided into upper, middle, and lower thirds by 2 endocranial landmarks: the dural pori of the abducens nerves and the dural meati of the glossopharyngeal nerves. Useful surgical landmarks exposed in the transnasal approach that aid in locating the junction of the clival divisions are the lower limit of the paraclival segment of the internal carotid artery, which is located 4.9 mm above the posterior opening of the vidian canal, and the pharyngeal tubercle. The upper, middle, and lower clival approaches provide access to the anterior midline parts of the previously described upper, middle, and lower neurovascular complexes in the posterior fossa. The nasal and nasopharyngeal relationships important in expanding the transnasal approach to the borders of the clivus are reviewed. Conclusion The transclival approach can be carefully tailored to expose focal lesions in the anterior part of the posterior fossa.
