A classification of juxta-dural ring aneurysms with reference to surgical anatomy.

We report a subgroup of internal carotid artery (ICA) aneurysms located near the carotid ring which we call juxtadural ring aneurysms. These aneurysms are classified into three types: paraclinoid intradural, carotid cave and infraclinoid extradural aneurysms. The paraclinoid intradural aneurysms arise from the ICA distal to the origin of the ophthalmic artery and are close to the dural ring, which may include some so-called carotid-ophthalmic aneurysms. The carotid cave aneurysms are located in the carotid cave which is seated in the infraclinoid carotid groove and proximal to the origin of the ophthalmic artery. They are located at the angiographical genu and in the intradural space anatomically. The infraclinoid extradural aneurysms are located close to the dural ring extradurally in the infraclinoid carotid groove sinus, a peripheral venous space of the cavernous sinus. The infraclinoid extradural aneurysms should be differentiated from aneurysms in the cavernous sinus, because they are located in the infraclinoid carotid groove sinus.