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 two 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.
From: Focal Transnasal Approach to the Upper, Middle, and Lower Clivus by Rhoton et al.