A patient with raised intracranial pressure develops a unilateral lateral rectus palsy without any other focal neurological deficit, and imaging shows no mass lesion compressing the nerve locally. This false localizing sign is best explained by which feature of the abducens nerve?
- A It pierces the dura mater at the clivus within a rigid dural tunnel
- B It decussates completely within the brainstem
- C It has the longest intracranial course among the cranial nerves ✓
- D Its nucleus lies in the midbrain tectum
Correct answer: C. It has the longest intracranial course among the cranial nerves
Explanation
The abducens nerve has the longest intracranial course of any cranial nerve, ascending on the clivus from the pontomedullary junction before entering the cavernous sinus and superior orbital fissure. Raised intracranial pressure stretches it against the petrous apex and the rigid dural entry point, producing a sixth nerve palsy that does not localize the site of the pressure. Complete decussation is the feature of the trochlear nerve.
Reference: Gray's Anatomy for Students, 4th ed.
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