A 55-year-old woman with idiopathic intracranial hypertension and marked papilledema is found to have isolated weakness of the right lateral rectus. Imaging shows no mass lesion. This finding is best explained by which anatomical feature of the abducens nerve?

• A Its passage through the cavernous sinus adjacent to the carotid artery
• B Its exit from the brainstem between the basilar and vertebral arteries
• C Its very long intracranial course with sharp bends over the petrous apex ✓
• D Its crossing to the opposite side within the pons

Explanation

The abducens nerve has the longest intracranial course of any cranial nerve and is tethered where it bends over the petrous apex and pierces the dura to enter Dorello canal. Raised intracranial pressure stretches the nerve, producing unilateral or bilateral lateral rectus weakness that may be unrelated to the underlying pathology, hence the term false localizing sign. Its cavernous sinus segment lies free in the sinus, but that location explains cavernous sinus syndromes, not raised pressure palsies.

Reference: Gray's Anatomy for Students, 4th ed.

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