A road map to the internal carotid artery in expanded endoscopic endonasal approaches to the ventral cranial base

BACKGROUND: Injuring the internal carotid artery (ICA) is a feared complication of endoscopic endonasal approaches. OBJECTIVE: To introduce a comprehensive ICA classification scheme pertinent to safe endoscopic endonasal cranial base surgery. METHODS: Anatomical dissections were performed in thirty-three cadaveric specimens (bilateral). Anatomical correlations were analyzed. RESULTS: Based on anatomical correlations, the ICA may be described as six distinct segments: 1) parapharyngeal (common carotid bifurcation to ICA foramen); 2) petrous (carotid canal to posterlateral aspect of foramen lacerum); 3) paraclival (posterolateral foramen lacerum to the superomedial aspect of the petrous apex); 4) parasellar (superomedial petrous apex to the proximal dural ring); 5) paraclinoid (from the proximal to the distal dural rings); and 6) intradural (distal ring to ICA bifurcation). Corresponding surgical landmarks included: the Eustachian tube, Rosenmüller\u27s fossa, and levator veli palatini, for the parapharyngeal segment; the vidian canal and V3 for the petrous segment; the fibrocartilage of foramen lacerum, foramen rotundum, maxillary strut, lingular process of the sphenoid bone, and paraclival protuberance for the paraclival segment; the sellar floor and petrous apex for the parasellar segment; and the medial and lateral opticocarotid and lateral tubercular recesses, as well as the distal osseous arch of the carotid sulcus for the paraclinoid segment. CONCLUSION: The proposed endoscopic classification outlines key anatomical reference points independent of the vessel\u27s geometry or the sinonasal pneumatization; thus, serving as: 1) a practical guide to navigate the ventral skull base while avoiding injury to the ICA, and 2) further foundation for a modular access system