Background The medial wall (MW) of the cavernous sinus (CS) is often invaded by pituitary adenomas. Surgical mobilization and/or removal of the MW of the CS remain a surgical challenge. The surgical anatomy and nuances for removal and/or mobilization of the MW of the CS have not been previously described.
Methods Twenty human head specimens were used for endoscopic endonasal dissections. The configuration of the MW, its relation to the internal carotid artery (ICA), and the ligamentous connections in between them were investigated in 40 cavernous sinuses.
Results The MW was confirmed to be an intact single layer of meningeal dura that is distinct from the periosteal layer that forms the anterior wall of the CS. In 32.5%, the MW was indented by or well adhered to the cavernous ICA. We identified multiple ligamentous fibers that anchored the MW to other walls of the CS and/or to specific ICA segments. These cavernous sinus ligaments (CSLs) were classified into four groups: (1) caroticoclinoid ligament (CCL), which spanned from the middle clinoid toward the clinoidal ICA segment and anterior clinoid process (ACP); (2) superior CS ligament (SCSL), which connected the MW to the horizontal cavernous ICA and/or lateral wall of CS; (3) inferior CS ligament (ICSL), which bridged the MW to the anterior wall of CS or anterior surface of short vertical cavernous ICA segment; (4) posterior CS ligament (PCSL), which anchored the MW to the posterior wall of CS or posterior aspect of short vertical cavernous ICA segment. The CCL and ICSL were present in most cavernous sinuses (97.7 and 95%, respectively), while the SCSL and PCSL were identified in approximately half of them (57.5 and 45%, respectively). The CCL was the strongest and largest ligament, as it was typically assembled as a band of fibers with a fan-like arrangement that formed the roof of the cavernous sinus, and separated the clinoidal space from the CS. The ICSL was the first to be encountered after opening the anterior wall of the CS during an interdural transcavernous approach. The SCSL and PCSL were not only less frequent, but when present they were also less robust. The PCSL had the highest chance to attach to the inferior hypophyseal artery (83%, when present). Based on the arrangement of the CSLs, we propose three distinct patterns of MW anchoring: (1) independent anchoring (62%), in which the CSLs arise independently from different aspects of the MW (superior, inferior, posterior); (2) CCL anchoring (32%), where the fibers of the ICSL attach to the MW via the CCL; (3) common anchoring (6%), in which all CSLs are joined to form a strong common attachment to the MW.
Conclusion Here we introduce a classification of the CSLs and their role in anchoring the MW of the CS. These ligaments should be identified and transected to safely mobilize the MW away from the cavernous ICA during a transcavernous approach and for safe and complete resection of adenomas that selectively invade the MW.
