Bilateral suspended optic nerve within the sphenoid sinus: a rare case report of a critical anatomical variant

Introduction: The intimate and variable relationship between the optic nerve (ON) and the sphenoid sinus poses a significant risk of iatrogenic injury during endoscopic sinus surgery. A Type 3 ON, which courses directly through the sinus cavity, is uncommon; however, a nerve completely suspended and free from the lateral wall represents an exceptionally rare and high-risk anatomical variant. Case Presentation: A 23-year-old female presented with chronic otological symptoms. A non-contrast computed tomography (CT) scan for cholesteatoma workup incidentally revealed extensive sphenoid sinus pneumatization. Crucially, both ONs were found to be coursing freely within the sinus cavities, completely separated from the lateral walls, with no associated ocular symptoms. Discussion: This bilateral presentation exemplifies the most extreme end of anatomical variability. Such a configuration drastically increases the risk of catastrophic visual loss during any sphenoid intervention, as standard landmarks are absent. The case underscores the critical importance of meticulous preoperative CT review to identify key risk indicators, such as anterior clinoid process pneumatization, and the radiologist's vital role in explicitly communicating these findings. It also highlights that these variations can be entirely asymptomatic and discovered incidentally. Conclusion: A free-lying ON within the sphenoid sinus is a critical surgical hazard. Prevention of iatrogenic injury is paramount and hinges upon detailed preoperative imaging analysis, heightened anatomical awareness, and disciplined surgical planning to avoid instrumentation in high-risk areas. This case serves as a potent reminder of these principles for ensuring patient safety in skull base surgery.