Cavernous Sinus Compartments from an Endoscopic Endonasal Approach: Proposed Anatomical Compartments and Surgical Relevance

Introduction: Lesions involving cavernous sinus (CS) are surgically challenging because of the risk of neurovascular injury. Conventional anatomical classification is based on open approaches. We aimed to redefine this anatomy from an endonasal perspective and evaluate surgical results in relation to CS invasion by pituitary adenomas.

Methods: A total of 20 fresh and 5 formalin-fixed colored silicon-injected cadaveric specimens were dissected using an endoscopic endonasal approach and Dolenc approach. Pre- and postoperative MRI scans were reviewed for 138 patients with at least unilateral CS invasion and 1-year follow-up after surgery.

Results: Anatomical, Four distinct CS compartments are identified in relation to the intracavernous internal carotid artery: superior (posterior and superior to the anterior genu and horizontal segment respectively with cranial nerve [CN] III in its lateral wall protected proximally by a dural envelope; commonly called the “medial CS”); posterior (posterior to the ascending segment and anterior to the clival dura with CN VI present inferiorly); inferior (inferior to horizontal and anterior genu segments with CN VI present laterally) and the lateral compartment (anterolateral to the anterior genu and horizontal segments; contains CN III, IV, V1, and VI). Clinical, A total of 138 patients underwent 142 endoscopic endonasal surgeries. Mean age was 55.5 years. In 142 surgical procedures, 284 CS sides were examined: invasion was noted in 50, 22.2, 33.8, and 29.9% of the superior, posterior, lateral, and inferior compartments, respectively. The corresponding complete resection rates were 78.9, 65.1, 56.5, and 41.7% for the superior, posterior, lateral, and inferior compartments, respectively.

Conclusion: Appreciation of endoscopic CS compartments allows evaluation of surgical difficulty and facilitates safe maximal removal of lesions from the superior compartment with the highest invasion rates. In the lateral wall of the superior compartment proximally, CN III (beyond the cisternal segment) is relatively protected by a dural envelope and as such, this segment can be considered to be interdural. Aggressive resection in the inferior and lateral compartments is limited because of proximity of the involved neural structures. Evaluation of preoperative imaging using this classification scheme rather than the conventional Knosp grade may allow a better determination of the preoperative strategy in terms of addressing tumors invading the CS.