Surgical Anatomy of the Medial Wall of the Cavernous Sinus and Technical Nuances for its Surgical Resection

Introduction: Pituitary adenomas often invade the medial wall of the CS. Complete removal of these lesions, including the medial wall, is imperative particularly for functioning adenomas. There is significant controversy about the anatomy of the medial wall of the CS, with previous studies identifying from none to 2 dural layers. Additionally, there is a lack of information on the ligaments that attach the medial wall of the CS and their relationship with the cavernous ICA. In this study we provide a detailed description of the medial wall of the CS, and the various adhesions and ligaments encountered within, propose an updated terminology especially from the endonasal perspective, and discuss the surgical implications of this complex anatomy.

Methods: Six formalin-fixed, colored silicone-injected anatomical specimens were dissected endoscopically. Another four similar specimens were used for a microscopic dissection of the parasellar region. Representative cases of pituitary adenomas were selected to describe the technical nuances of the surgical resection of the medial wall.

Results: The medial wall of the CS is formed by a single layer of meningeal dura surrounding the pituitary gland. The pituitary capsule is a distinct layer that belongs to the pituitary gland; it can be compared with the pia mater, and should not be mistaken with the meningeal dural layer that forms the medial wall of the CS. The main ligament that arises from the medial wall is the carotico-clinoidal ligament (CCL), commonly formed by a strong band of fibrous tissue that arises from the middle clinoid process (MCP), and in a fan-like fashion gives off a varying number of fiber bundles that suspend the medial cavernous sinus wall from anterior to posterior. These fiber bundles loop around the anterior genu of the ICA, attach to the cavernous ICA, and extend toward the undersurface of the anterior clinoid process. The branching fibers of the CCL vary depending on the morphology and tortuosity of the ICA but have stable attachment sites both on the posterior genu and at the venous confluence below the dorsum sellae. The CCL forms the ventral aspect of the proximal dural ring, thus represents the ventral roof of the cavernous sinus and the inferior limit of the clinoidal space from a ventral perspective. The interclinoid ligament (ICL), which extends from the posterior clinoid (PCP) to the anterior clinoid process (ACP), is located immediately posterior to the CCL. The CCL and ICL run laterally toward the ACP, but diverge medially as the ICL attaches to the PCP and the CCL attaches to the MCP. The CCL represents the junctional line between the medial wall and the ventral roof (clinoidal space) of the CS, while the ICL represents the junctional line between the dorsal roof (oculomotor triangle) and the sellar diaphragm. Transection of the CCL is a key step for safe and effective removal of the medial wall of the CS.

Conclusion: Here we describe the role of the interclinoid and caroticoclinoid ligaments in the suspension of the medial cavernous sinus wall, relevant for efficient and safe intracavernous surgery.

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