Cavernous segment (C4)

The cavernous segment (C4) of the internal carotid artery is covered by avascular membrane lining the cavernous ssinus,.

After the foramen lacerum, the internal carotid artery asses anteriorly then supero-medially, bends posteriorly (medial loop of ICA), travels horizontally, and bends anteriorly (part of anterior loop of ICA) to anterior clinoid process.

The cavernous segment (C4) ends at the proximal dural ring (incompletely encircles ICA), which is formed by the medial and inferior periosteum of the anterior clinoid process. The cavernous segment is surrounded by the cavernous sinus.

In this part of its course, the artery is situated between the layers of the dura mater forming the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the posterior clinoid process, then passes forward by the side of the body of the sphenoid bone, and again curves upward on the medial side of the anterior clinoid process, and perforates the dura mater forming the roof of the sinus. The curve in the cavernous segment is called the carotid siphon. This portion of the artery is surrounded by filaments of the sympathetic trunk and on its lateral side is the abducent nerve, or cranial nerve VI.

The branches of the cavernous segment are:

• The meningohypophyseal artery

• The inferolateral trunk

• Variable small capsular arteries that supply the wall of the cavernous sinus.