2026 Proffered Presentations
S121: CROSSING PATHWAYS: SURGICAL ANATOMY OF THE FOURTH NERVE FROM THE CAVERNOUS SINUS TO THE ORBIT
Luciano Leonel, PhD; Florian Moser, MD; Rosaria Abbritti, MD; Alexander Yohan, MD; Sandhya Palit, MD; Maria Peris-Celda, MD, PhD; Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, USA
Introduction: The trochlear nerve (CN IV) presents an intrinsic relationship with neurovascular structures when crossing the orbital apex from the cavernous sinus to the orbit of essential importance during anterolateral transcranial approaches requiring anterior clinoidectomy and exposure of the roof of the orbit and orbital apex.
Objective: To describe the anatomical relationship of the trochlear nerve within the anterior part of the cavernous sinus, orbit and orbital apex and its surgical relevance during transcranial procedures to the anterolateral skull base.
Material and Method: Eight sides of four formalin-fixed specimens with colored latex injection were utilized for dissections. An axial section was performed, the calvaria and brain removed exposing the anterior cranial fossa (ACF) and intracranial cavity. The dura of the ACF was dissected and the orbital plate of the frontal bone drilled exposing the periorbita. The periorbita of the superior aspect of the orbital cavity was incised, the orbital fat body removed to study CN IV and orbital content. The configuration and anatomical relationships of CN IV were then evaluated and described. Measurements were taken using a millimeter scale ruler taken into account anatomical landmarks related to CN IV (Table 1).
Results: A quantitative analysis was performed for each measurement in Table 1 and Figure 1. CN IV stablishes an intrinsic relationship with CN III when entering the cavernous sinus located inferiorly in the posterior aspect, and lateral in the anterior aspect. At the level of the meningo-orbital band (MOB) and annulus of Zinn, CN IV crosses medially and superiorly CN III into the orbital apex to offer innervation to the superior oblique muscle. Considering its anatomical relationship within the orbital apex, CN IV becomes the most superficial anatomical structure in the orbit deep to the periorbita at the level of the MOB and base of the anterior clinoid process, along with the frontal nerve. Such anatomical landmarks present surgical relevance during anterior clinoidectomy and open procedures to treat lesions within the orbital cavity and cavernous sinus.
Conclusion: The MOB is a reliable reference to be used as a surgical landmark when performing anterolateral approaches to the skull base in order to avoid iatrogenic procedures damaging CN IV as it becomes superficial crossing the orbital apex from the cavernous sinus.
