Anatomical basis of endoscopic endonasal internal carotid artery transposition technique-freeing the limiting structures.

To investigate the relevant surgical anatomy of the endonasal endoscopic ICA transposition technique (EEITT). Six cadaveric heads were prepared for dissection. The trabeculae fibers in the cavernous sinus(CS), branches of cavernous segment ICA (csICA), dura rings and the bony structures around the ICA were meticulously dissected and photographed. The limiting structures around ICA consist of: the bony, dura structures and the tethering structures inside CS. The tethering structures in the CS could be summarized into four groups. The medial group includes the carotid clinoidal ligament (100%), the inferior hypophyseal artery (100%), the inferior parasellar ligament (91.7%) and the superior parasellar ligament (50%) The lateral group comprises the inferolateral trunk (100%), the sympathetic nerve plexus (100%), and the trabeculae fibers between internal carotid artery (ICA) and cranial nerves (CN)3 (50%), CN4 (41.7%), and CN6 (100%). The anterior group is defined by trabeculae fibers between the proximal dural ring and the anterior genu or the anterior ascending segment of the ICA (66.7%). The posterior group consists of the meningohypophyseal trunk (100%) and the trabeculae fibers (50%) between the posterior genu of the ICA and the posterior wall of the cavernous sinus. The EEITT was graded according to the detaching extent of the limiting structures: Grade 1 (disconnecting the tethering structures inside CS), Grade 2 (Grade 1 with the addition of dura ring opening), and Grade 3 (Grade 2 plus anterior clinoidectomy). The tethering structures around csICA could be classified into four groups: medial, lateral, anterior, and posterior. EEITT could be categorized into three grades according to the detaching extent of the limiting structures. This technique enlarges the working zone and increases the surgical freedom for complex lesions with parasellar extensions in endoscopic endonasl approaches.