Microsurgical and Endoscopic Characterization of the Anteroinferior Wall of the Cavernous Sinus: A Cadaveric Study at the Intersection of Anatomical Fossae.

Abstract

The cavernous sinus (CS) has traditionally been described as having 5 walls-roof, posterior, medial, lateral, and anterior. However, as inferolaterally expanded trans-cavernous approaches become more common, the anatomy of the transition zone between the anterior (AWCS) and lateral (LWCS) walls-located at the intersection of the middle cranial fossa, superior orbital fissure, and pterygopalatine fossa-remains inadequately defined. Five latex-injected cadaveric heads (10 sides) underwent expanded endoscopic endonasal dissection of the AWCS and its anterior extension. Complementary microsurgical dissections of the middle cranial fossa were performed in axial and coronal planes. Neuronavigation-assisted quantitative measurements were obtained for relevant anatomical structures. A distinct anteroinferior wall of the cavernous sinus (AIWCS) was consistently identified, bridging the AWCS and LWCS and confirming the presence of a sixth wall. Its junction with the AWCS, the annulus of Zinn-prelingual ligament (ZLL), defined the basis of an "enhanced anteromedial triangle." The AIWCS measured 82 ± 9 mm², and the ZLL averaged 14 ± 1 mm in length. The inner layer of the LWCS lacked a continuous periosteal dura. Novel three-dimensional renderings were produced to visualize these relationships. Comprehensive delineation of the AIWCS and adjacent structures refines the anatomical model of the CS and enhances spatial understanding of this complex region. These findings may facilitate safer and more targeted endoscopic endonasal approaches while minimizing iatrogenic risk during cavernous sinus surgery.