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    Neuro-Ophthalmology/Orbit

    Tl-weighted, Cavernous Sinus.. CN IV is inferolateral to CN III, but cannot be delineated because of its small size, only 3400 axons. CN V-I lies below CN III. CN V-I divides into three branches in the most anterior part of the cavernous sinus, the largest of which is the frontal nerve. CN V-2 has already departed from the cavernous sinus and is seen as a separate structure below the cavernous sinus, in FR. The nerves cannot be labeled with certainty because of their shifting relationships within the cavernous sinus. Note the superomedial course of ON as it passes from the orbit into the brain. At this level, it is difficult to be certain whether all borders of ON are within the optic foramen, in which case ON is separated from the cavernous sinus contents by the optic strut of the sphenoid bone. Posterior to the point where the inferior border of ON exits the optic foramen, the superior border is covered by a layer of dura, the falciform fold. On Tl-weighted scans, the sphenoid bone, air in SS, and dura forming the falciform fold overlying the nerve all have a similar appearance. TT (or tubal elevation) is comprised of cartilage arising from the medial pterygoid process; it marks the nasopharyngeal opening of the auditory (eustachian) tube. CN III = Oculomotor Nerve, CN V•I = Trigeminal Nerve-1st Division, CN V•2 = Trigeminal Nerve-2nd Division, CN VI = Abducens Nerve, FR = Foramen Rotundum, ON = Optic Nerve, SS = Sphenoid Sinus, TT = Torus Tubarius