Anatomosurigical Classification of the Ventral Clivus and Endoscopic Endonasal Transclival Approaches

Introduction: Recent introduction of the endonasal endoscopic approach is facilitating the transgression of conventional anatomical and surgical frontiers, with great implications for the treatment of lesions in the clival region. Consequently, novel anatomical studies are needed to ascertain the limitations of this approach. The objective of this study is to describe an endosurgical, anatomically based classification of the clivus to aid in understanding the surgical landmarks, neurovascular structures at risk, anatomical boundaries, and areas of exposure during the performance of an endoscopic endonasal transclival approach.

Methods: Ten fresh latex-injected anatomical specimens were dissected using rod lens endoscopes attached to a high-definition camera. Superior, middle, and inferior endonasal transclival approaches were completed in a stepwise manner. Selected surgical cases were used to illustrate the anatomical findings.

Results: The superior clivus is formed by the dorsum sellae and posterior clinoids, and it has a trapezoid shape with superior base. It is limited inferiorly by the sellar floor and laterally by the parasellar and clinoidal ICA. The extradural or intradural (with pituitary transposition) superior transclival approach provides access to the interpeduncular cistern and its contents, including the basilar artery bifurcation, mammillary bodies, and floor of the third ventricle. The lateral limits of the exposure are the third nerves and posterior communicating arteries, and the superior limits are the suprasellar cistern and the infrachiasmatic and tuberoinfundibular region. Lateral extension of the exposure can be accomplished by adding a transsellar-transcavernous approach, and superior extension can be accomplished by adding a transtubercular-transplanum approach. Approach through the superior clivus is ideal for retroinfundibular (type III) craniopharyngiomas, and upper extension of petroclival meningiomas, chondrosarcomas, and chordomas.

The middle clivus is formed by the clival bone between the sellar floor and the lower face of the sphenoid sinus, right at the level of the pharyngeal tubercle where the basopharyngeal fascia inserts in the midline. It has a rectangular shape. It is limited laterally by the paraclival ICA and inferolaterally by the vidian nerve and lacerum segment of the ICA. A middle transclival approach gives access to the prepontine cistern and its contents, including the basilar trunk and AICA. The lateral limits of the exposure are the sixth nerves at the interdural segment. Lateral extension of the exposure can be obtained by adding medial petrous apex and Meckel's cave approaches. This approach is deal for clival chordoma, chondrosarcoma, and petroclival meningioma.

The inferior clivus runs from pharyngeal tubercle to the foramen magnum. It has a trapezoid shape with superior base. It is limited laterosuperiorly by the lacerum segment of the ICA and lateroinferiorly by the occipital condyles. The inferior transclival approach exposes the premedullary cistern and its contents, vertebral arteries, vertebrobasilar junction, and PICA. The lateral margin of the exposure is marked by the hypoglossal nerve. Lateral extension of the exposure can be achieved by adding transcondylar and transjugular tubercle approaches, and inferior extension by adding and odontoidectomy. This approach is deal for anterior foramen magnum meningiomas and inferior extension of chordomas.

Conclusion: The classification described allows for a more precise analysis of the expected anatomic relationships and provides the basis for selection of a combination of approaches.