Which nerve is the classic false localizing sign in raised intracranial pressure, and why?
- A Abducens nerve, because its long intracranial course makes it vulnerable to stretching over the petrous temporal bone ✓
- B Trochlear nerve, because it decussates completely in the midbrain
- C Oculomotor nerve, because it passes close to the uncus of the temporal lobe
- D Optic nerve, because it is surrounded by meningeal sheaths continuous with the dura
Correct answer: A. Abducens nerve, because its long intracranial course makes it vulnerable to stretching over the petrous temporal bone
Explanation
The abducens nerve has the longest intracranial course of any cranial nerve. Raised intracranial pressure stretches it against the sharp ridge of the petrous temporal bone and the basilar plexus, producing unilateral or bilateral lateral rectus weakness that does not correspond to the site of the primary lesion, hence the term false localizing sign. The uncus relates to the oculomotor nerve in herniation, but that produces a true localizing sign of transtentorial coning.
Reference: Snell's Clinical Neuroanatomy, 8th ed.
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