The Connective Tissue Architecture of the Cavernous Sinus: An Anatomical Study and Unifying Conceptualization

<black square> OBJECTIVE: The aim of this study was to synthesize existing knowledge regarding the anatomy of the cavernous sinus (CS), critically evaluate the current anatomical hypotheses concerning its walls, to conduct anatomical dissections, and develop a comprehensive understanding of the connective tissue structure of the CS. <black square> METHODS: We performed systematic dissections on 15 fresh adult cadavers. Specifically, 5 specimens were approached laterally, 5 were sectioned in the axial plane, and 5 were dissected using endoscopic endonasal techniques. <black square> RESULTS: Based on histological and embryological data, we formulated several anatomical concepts and examined them through dissection studies. 1) An uninterrupted periosteum envelops all surfaces of the skull and establishes a periosteal dural layer within the cranial cavity. 2) All structures of the neuraxis are encased by a meningeal layer of dura mater. 3) Cranial nerves (CNs) are ensheathed by 1 layer of meningeal layer as they pierce it. This meningeal layer invaginates along the course of the nerves to various lengths forming the corresponding CN cisterns before fusing with the nerve's perineurium. 4) Fibers of the periosteal layer that are strained between the nearby bony structures form a thin periosteal "ligamentous" layer. This layer is mostly attenuated but becomes more robust in named "ligaments". These ligaments covered by meningeal layer of dura form "dural folds" such as anterior and posterior petroclinoidal folds. Consequently, the lateral wall of the CS is composed of the following elements: 1) the meningeal layer associated with the mesial temporal lobe; 2) a thin periosteal "ligamentous" layer; and 3) the meningeal layers corresponding to CNs III, IV, and V1 originating from the posterior cranial fossa. The medial wall of the CS is constituted by a single layer of periosteal dura inferiorly and a meningeal layer superiorly. The superior wall of the CS is exclusively formed by the periosteal layer of the anterior clinoid process at the anterior aspect of the clinoidal triangle (referred to as the carotidooculomotor membrane). In contrast, the posterior aspect of the oculomotor triangle consists of both a meningeal layer and a thin "periosteal ligamentous layer" that extends between 3 more substantial periosteal condensations: the anterior and posterior petroclinoidal ligaments and the interclinoidal ligament. The posterior wall of the CS is comprised of the meningeal layer of the dura mater from the posterior cranial fossa, along with a periosteal layer that envelops the clivus and petrous apex, contributing to the formation of the posterior petroclinoidal and Gruber's ligaments. Finally, a single layer of periosteal dura delineates both the anterior and inferior walls of the CS. <black square> CONCLUSIONS: The dural anatomy of the CS involves an intricate interplay between the meningeal and periosteal dural layers, which is elucidated more effectively through the application of fundamental principles informed by embryological development.