The Dural Architecture of the Cavernous Sinus' Anterior Roof and Clinoid Space: Microsurgical Anatomy and Technical Nuances for Intracavernous and Perisellar Endoscopic Surgery

Background The extension of endoscopic approaches beyond the sagittal plane requires an accurate understanding of the related microanatomy and the ICA, which must be transversed to expand laterally into the coronal plane. The dural architecture of the cavernous sinus and carotid collar is of particular interest in the treatment of invasive intracavernous adenomas and meningiomas, vascular pathologies such as hemangiomas, AV fistulae, or aneurysms arising from or requiring access to the carotid cave. In this study, we aim to provide a detailed description of this complex anatomy, propose an updated terminology especially from the endonasal perspective, and discuss some surgical implications.

Methods Twelve formalin-fixed, colored, silicone-injected anatomical specimens were dissected endoscopically, another seven similar specimens were used for comparative microscopic examination. Representative cases of endoscopic endonasal procedures, mainly invasive pituitary adenomas, were selected to illustrate the technical nuances.

Results The cavernous sinus' anterior roof consists of the dura mater of the clinoidal triangle, the proximal and distal rings (both merge posteriorly at the apex of the triangle), and the carotid collar. The posterior roof corresponds to the oculomotor triangle, which is bounded by the interclinoid fold anteromedially and the anterior and posterior petroclinoid folds. The cavernous sinus' roof is composed of two dural layers: the outer layer is in continuum with the roof of the pituitary fossa and the sellar diaphragm; it is consistently found to be complete. In contrast, the inner dural layer is largely incomplete and made up of a complex apparatus of firm, interconnected ligaments: the interclinoid ligament (ICL) connects the anterior and posterior clinoid process, respectively, and thereby forms the anteromedial limit of the oculomotor triangle. The carotico-clinoid ligament (CCL) arises from the middle clinoid, gives off a varying number of fiber bundles to suspend the medial wall of the cavernous sinus, and then loops around the anterior genu of the ICA to merge with the ICL and to insert at the undersurface of the anterior clinoid. The middle clinoid, although a variable landmark, marks the transition from cavernous to clinoidal ICA and covers the anteromedial portion of the roof of the cavernous sinus. Just in the same way the anterior clinoid covers the anterior roof of the cavernous sinus and its removal facilitates access in transcranial approaches, a middle clinoidectomy allows for gentle mobilization of the parasellar ICA and thereby increases access to the cavernous sinus, in particular to the superior and lateral compartments. The clinoid space is an interdural, extracavernous space which communicates both with the cavernous sinus and the carotid cave. The CCL/proximal dural ring represents the medial aspect of the cavernous sinus' roof and the inferior limit of the clinoid space.

Conclusion We provide a microanatomical description of the dural architecture of the cavernous sinus' anterior roof and clinoid space, as well as technical nuances for efficient and safe endoscopic surgery within the cavernous and the adjacent perisellar region.

Fig. 1