A 6-year-old boy presents with intermittent headache and vomiting of two weeks duration. He has bilateral papilloedema and a right abducens nerve palsy. Brain MRI and MR venography are the appropriate next step primarily because the abducens palsy here may represent:
- A Ischaemia of the abducens nucleus from a basilar infarct
- B Direct compression of the nerve by an orbital apex mass
- C A false localizing sign of raised intracranial pressure ✓
- D Congenital absence of the abducens nerve
Correct answer: C. A false localizing sign of raised intracranial pressure
Explanation
The abducens nerve has the longest intracranial course of any cranial nerve and runs upward along the clivus, so raised intracranial pressure stretches it against the petrous apex and tentorial edge. C unilateral or bilateral sixth nerve palsy with papilloedema is therefore a classic false localizing sign and does not indicate a lesion at the nerve itself. Imaging is mandatory to identify the cause of the raised pressure, such as a posterior fossa tumour or venous sinus thrombosis.
Reference: Parsons' Diseases of the Eye, 23rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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