Question:medium
A patient presents with unilateral proptosis and bilateral abducent (sixth) nerve palsy. This could be from a lesion of the?
A patient presents with unilateral proptosis and bilateral abducent (sixth) nerve palsy. This could be from a lesion of the?
Show Hint
Only one structure carries the sixth nerve and connects both sides, explaining a bilateral palsy with proptosis.
Updated On: Jun 23, 2026
- Cavernous sinus
- Orbital cellulitis
- Orbital pseudotumor
- Orbital lymphoma
Show Solution
The Correct Option is A
Solution and Explanation
Localise-then-pick strategy. The decisive clue is bilateral sixth nerve palsy. A purely orbital problem affects one orbit, so it can never paralyse the abducent nerve on both sides. That single observation eliminates orbital cellulitis, pseudotumor and lymphoma at once.
What structure can hit both sixth nerves and also cause proptosis? The cavernous sinus. The abducent nerve travels inside the cavernous sinus, and the two cavernous sinuses are joined across the midline by intercavernous channels. So a cavernous sinus thrombosis spreads to the opposite side and knocks out both abducent nerves, while venous back-pressure pushes the eye forward, first on one side, then often both.
That neat fit of unilateral proptosis plus bilateral abducens palsy points squarely to the cavernous sinus. Ref: Parson's Diseases of the Eye, 22e, p. 497.
What structure can hit both sixth nerves and also cause proptosis? The cavernous sinus. The abducent nerve travels inside the cavernous sinus, and the two cavernous sinuses are joined across the midline by intercavernous channels. So a cavernous sinus thrombosis spreads to the opposite side and knocks out both abducent nerves, while venous back-pressure pushes the eye forward, first on one side, then often both.
That neat fit of unilateral proptosis plus bilateral abducens palsy points squarely to the cavernous sinus. Ref: Parson's Diseases of the Eye, 22e, p. 497.
Was this answer helpful?
0
