Introduction

Sphenoid sinus is housed within the body of the sphenoid bone . enclosed by a thin layer of bone which separates it from the nearby crucial structures like the internal carotid artery, cavernous sinus, optic nerve, optic chiasm and the pituitary gland. Occasionally, it extends into the lesser wings, the greater wings and pterygoid plates of the sphenoid bone, as well as to the clivus posteriorly.
The sphenoid sinus is normally made up of two asymmetrical cavities partitioned by one or more septae that are often asymmetric. It is highly variable in shape, size, and relationship to the Sella and adjacent neurovascular structures.
In Lang's classification there are four patterns of pneumatization; conchal, presellar, sellar and postsellar. Sphenoid sinus pneumatization can vary from being nonexistent to being substantial, which causes the bone that protects important structures including the internal carotid arteries, the optic nerves, maxillary nerves and the Vidian nerve to be thin or entirely missing.
Protrusion of the optic nerve in majority of studies was defined as a bulging of the optic canal into the sphenoid sinus cavity so as to cause the exposure of more than half the circumference of the nerve, with or without defects in the bony margins .
Delano et al. categorized the various relationships between the optic nerve and posterior PNS into four groups, as follows: type 1 optic nerve, type 2 optic nerve, type 3 optic nerve and type 4 optic nerve.