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: Anatomic dissections were performed in 33 cadaveric specimens (bilateral). Anatomic correlations were analyzed.

Results: Based on anatomic correlations, the ICA may be described as 6 distinct segments: (1) parapharyngeal (common carotid bifurcation to ICA foramen); (2) petrous (carotid canal to posterolateral 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, the fossa of Rosenmüller, 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.

Conclusions: The proposed endoscopic classification outlines key anatomic reference points independent of the vessel's geometry or the sinonasal pneumatization, thus serving as (1) a practical guide to navigate the ventral cranial base while avoiding injury to the ICA and (2) further foundation for a modular access system.