The paraclinoid carotid artery: anatomical aspects of a microneurosurgical approach.

The paraclinoid area is investigated anatomically for possible microneurosurgical approaches to the C3 segment of the internal carotid artery and to structures in the vicinity of the anterior siphon knee. Removal of the anterior clinoid process reveals a tight connective tissue ring that fixes the internal carotid artery to the surrounding osseous structures at the point of its transdural passage. Transection of this fibrous ring opens a microsurgical pathway to the carotid C3 segment. The artery is surrounded by a loose connective tissue layer that allows blunt preparation along the C3 segment, without compromising the cranial nerves and without damaging venous compartments of the cavernous sinus. This approach provides neurosurgical access to paraclinoidal aneurysms, to partly intracavernous aneurysms, and to carotid-ophthalmic aneurysms, allowing control of the proximal aneurysm neck and of the parent artery itself. In cases of tumors involving the medial sphenoid ridge, the apex of the orbit, or the cavernous sinus, the pericarotid connective tissue can serve as a guide layer for access along the internal carotid artery.