Background: The cavernous sinus (CS) has been extensively studied to refine surgical approaches and indications. We recently proposed a classification of the CS from the endonasal perspective in four different compartments: superior, inferior, posterior, and lateral. Among them, the posterior compartment has received little attention. In this study, we investigated the posterior compartment of the cavernous sinus to translate microscopic anatomy to endoscopic view, define surgical landmarks, and discuss relevant surgical nuances.
Material and Methods: Thirteen anatomical specimens with colored-latex injection were used for endoscopic (10) and microscopic (3) dissection.
Results: The posterior compartment of the CS includes the posterior wall (PW) and floor of the CS. The PW of CS has a trapezoid shape defined by dorsum sellae and posterior clinoid medially, posterior petroclinoid dural fold superiorly, trigeminal porus laterally, and the petrous process of the sphenoid bone inferiorly. The PW itself carries no contents of surgical interest, but is surrounded by relevant structures: basilar plexus, inferior and superior petrosal sinuses on its medial, inferior and lateral borders respectively; cranial nerves (CN) III and IV running on its superior border, CN V laterally, and CN VI on the lateral portion of its inferior border. We suggest using the PW as a surgical landmark for locating the venous sinuses and CNs, as well as a safe entry point (or potential tumor spreading route) into the paratrigeminal (inferiorly) and parapeduncular (superiorly) spaces.
We propose the term floor of CS and define it as an area limited by the lingual process of sphenoid and petrolingual ligament anterolaterally, petrous apex posterolaterally, petrous process of sphenoid posteromedially, and carotid sulcus—between petrous process and lingual process of the sphenoid—anteromedially. The floor can be divided into three compartments, from anterior to posterior: (1) carotid compartment, or carotid canal; (2) osseous compartment, or petrous process/petroclival fissure; and (3) venous compartment, or opening of the inferior petrosal sinus. The CN VI entered the floor of CS vertically through the lateral edge of the venous compartment in 80% of cases, while in 20% it ran more medially. CN VI is separated from ICA by the osseous compartment; then, it turns anteriorly over the osseous compartment and runs lateral and tangential to the ICA. The dura over the petrous process of sphenoid and adjacent petroclival fissure is usually thickened and recognizable from a ventral perspective, which we named petroclival dural fold (PCDF). We suggest using the petrous process of the sphenoid and the PCDF, particularly in cases of bone erosion by tumors, as reliable landmarks to find the entrance of CN VI into the CS during surgery.
Conclusion: We define and describe the PW and floor of the CS, as well as their relevant anatomy. The PW can be used as the central landmark for surgery at the posterior compartment of the CS, while the petrous process of sphenoid and the PCDF at the floor of CS can serve as critical landmarks to identify the petrous and proximal cavernous segments of CN VI intraoperatively.
