Distal dural ring

The distal dural ring (DDR) is part of the fold that extends from the outer layer of the lateral wall of the cavernous sinus to the superior aspect of the anterior clinoid process, planum sphenoidale, and the internal carotid artery. It delimits the border between the intra- and extradural compartment of the internal carotid artery

Unlike the proximal dural ring, the distal dural ring  forms a complete ring around and fuses with the adventitia of the internal carotid artery and is firmly adherent to the dorsolateral aspect of this vessel.