The Clinoid Space: Surgical Anatomy and Relevance for Endoscopic Approaches

Objective: A carotid injury is a major complication in endoscopic endonasal surgery and the clinoid segment is the most susceptible area. This segment is delimited by the distal and proximal dural rings and is well described from traditional open approaches but is less understood from an endoscopic endonasal perspective. The objective of this study was to provide a detailed investigation of the surgical anatomy and anatomical relationships of this segment from an endonasal and open perspective.

Methods: 6 fresh human silicon-injected heads underwent an endonasal transsellar approach. 12 clinoid segments were dissected to expose the dural rings and their relationship with the pituitary gland, surrounding bone structure and associated ligaments. The clinoid segments were measured and the anatomical variation was recorded ([Figs. 1] and [2]).

Results: we show that the clinoid segment is delimited superiorly by the distal dural ring and inferiorly by proximal dural ring. From a transcranial perspective, the proximal ring is formed by carotidoculomotor membrane, lateral to the carotid artery, and carotidoclinoidal ligament (CCL) medially. Endoscopically, CCL attaches the medial wall of the cavernous sinus (CS) to the anterior clinoid process ([Fig. 3]). We identified several anatomical variations of the clinoid space: (1) Continuous and thick CCL; (2) fenestrated CCL with direct communication between the clinoid space and the CS; (3) CCL continuous with the inferior parasellar ligament in the CS; and (4) multiple bands of CCL extending and attaching in a vertical orientation to the medial wall of the CS. The morphology of the CCL and dimension of the clinoid space were correlated with the presence and size of the middle clinoid. The caroticoclinoid ligament is the boundary between the clinoid space and the roof of the cavernous sinus, endoscopically. From a transcranial perspective this limit correspond a carotidoculomotor membrane ([Fig. 4]).

Conclusion: This study provides an important anatomic comprehension of the clinoid space in the endonasal perspective that may facilitate its safe exposure for removal of lesions, minimizing the risk of injury to the internal carotid artery.

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