Clivus | pacs

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The clivus (of Blumenbach) is the sloping midline surface of the skull base anterior to the foramen magnum and posterior to the dorsum sellae . Specifically, it is formed by the sphenoid body and the basiocciput, which join at the spheno-occipital synchondrosis. At the clivus, the occipital bone has articulations with the petrous part of temporal bone at the petroclival fissure.

Inferiorly, the clivus is flanked by the rounded prominences of the jugular tubercles, which represents the fusion of the basiocciput with the lateral jugular parts of the occipital bone.

At the level of the jugular tubercles, the clivus is occupied by the medulla .

Above the jugular tubercles, the clivus is wider and occupied by the pons.

Anatomically it is also closely related to the basilar venous plexus and pontine cistern.

Variant anatomy

There are multiple variant defects or channels through the clivus :

fossa navicularis magna
canalis basilaris medianus
foveola pharyngica (pharyngeal fossa)
craniopharyngeal canal
basilar transverse fissure (Sauser fissure)

There are several occipital vertebrae variants in which bony protuberances arise from the clivus at the anterior margin of the foramen magnum :

processus basilares (basilar processes): small bumps, possibly bilateral
condylus tertius (third condyle): oval facet that may articulate with the dens or anterior arch of atlas)
arcus praebasioccipitalis (prebasioccipital arch): horseshoe-shaped bony mass, functionally representing a combination of bilateral processus basilares and a condylus tertius