Clivus

The clivus (Latin for “slope”) is a part of the cranium, a shallow depression behind the dorsum sellae that slopes obliquely backward. It forms a gradual sloping process at the anterior most portion of the basilar occipital bone at its junction with the sphenoid bone. On axial planes, it sits just posterior to the sphenoidal sinuses. Just lateral to the clivus bilaterally is the foramen lacerum (the internal carotid artery reaches the middle cranial fossa above the foramen lacerum), proximal to its anastamosis with the Circle of Willis. Posterior to the clivus is the basilar artery.

The pons sits on the clivus.

Clivus is also used as an abbreviated term for the clivus ocularis which is the sloping inner wall of the retina as it dips into the foveola in the macula of the eye.

Early in life an articulation exists between these two regions known as the sphenoid occipital synchondrosis; this articulation usually disappears by adulthood. Laterally, the clivus meets the petrous portion of the temporal bone at the petro-occipital fissure. Together, these three bones form the skull base and middle fossa floor. The entire region is lined with a double layer of dura consisting of the endosteal and periosteal layers. Between these two layers are found various venous sinuses and plexi.

Upper clivus

Clivus lesion

The clivus protects the brainstem and posterior cranial fossa. A thorough appreciation of the anatomy of these various areas allows for endoscopic endonasal approaches to the skull base ¹⁾.

Penetration of the clivus is required for surgical access of the brainstem.

The surgical corridor to the upper third of the clivus and ventral brainstem is hindered by critical neurovascular structures, such as the cavernous sinus, petrous apex, and tentorium.