The carotidoclinoidal ligament (CCL) spans from the medial wall of the cavernous sinus (MWCS) to the internal carotid artery (ICA) and anterior clinoid process. In endoscopic endonasal transcavernous surgery, safe transection of the CCL requires not only knowledge of its typical anatomy, but also an understanding of its possible variations. The aim of this study was to analyze the anatomical variations of the CCL and the patterns of CCL invasion by pituitary adenomas (PAs).

This investigation comprised an anatomical and a clinical study. Endonasal dissections of 20 specimens (40 sides) were performed to investigate CCL variations. A retrospective analysis of 145 patients with PA invading the CS (160 CS sides) was conducted to report the incidence and patterns of CCL invasion.

The CCL was present in all investigated sides (n = 40). In the coronal plane, 1 CCL branch was found in 20 sides (50.0%) and ≥ 2 CCL branches were found in 20 sides (50.0%). The main CCL branch was defined as the medial continuation of the proximal dural ring, marking the transition from the cavernous to the paraclinoidal ICA segment. When additional accessory CCL branches were present, they attached to the paraclinoidal ICA (n = 17, 53.1%), the horizontal cavernous ICA segment (n = 10, 31.3%), and/or the anterior genu of the cavernous ICA (n = 5, 15.6%). The CCL most commonly attached to the upper (n = 29, 72.5%) and middle third (n = 26, 65.0%) of the MWCS. In the axial plane, the CCL was found to be a fenestrated membrane in 29 sides (72.5%) and an intact membrane in 11 sides (27.5%). All CCLs attached to at least the anterior third of the MWCS. Additionally, some CCLs attached to the middle third (n = 23, 57.5%) and/or the posterior third (n = 17, 42.5%). The CCL was connected to the inferior parasellar ligament in 14 sides (35.0%). Among all PAs invading the CS, the CCL was invaded in 36 cases (22.5%). Two patterns of CCL invasion were identified: 1) tumor adherent to and infiltrating the CCL fibers (n = 30, 83.3%), and 2) CCL thickened due to tumor growth within and along the fibers (n = 6, 16.7%).

This study represents a comprehensive analysis of the anatomical variations and patterns of invasion of the CCL, which is particularly relevant for the safe and effective resection of PA invading the CS.