Wish you had a sixth sense to localize that sixth cranial nerve palsy?
Feeling six feet under when you see a sixth nerve deficit?
Here’s a cheat sheet to help you locate the lesion in a sixth cranial nerve palsy!
Just remember the Six Syndromes of the Sixth Cranial Nerve!
There are six syndromes of CN6—one for each of its five stops along the way to its destination in the orbit—and one that is idiopathic
1. Brainstem
🔸CN6 nucleus is at the facial colliculus—looks like a baby’s butt of the brainstem
🔸Many important structures here
🔸Rarely get an isolated palsy & uniquely can get associated MOTOR deficits
2. Subarachnoid space
🔸CN6 exits under the dad bod belly of the pons & enters Dorello canal
🔸Susceptible to changes in intracranial pressure—can get stretched!
🔸ICP changes can cause BILATERAL palsies here
3. Petrous apex
🔸Exits Dorello canal & travels under the petroclinoid ligament, like under a seat belt
🔸Many other nerves here
🔸Rarely get an isolated palsy & uniquely can get associated HEARING deficit
4. Cavernous sinus
🔸Many nerves in close proximity!
🔸Rare to get an isolated palsy
🔸Many pathologies can affect the cavernous sinus—so many differentials & many deficits!
5. Orbit
🔸Short orbital course—quick lateral turn after the superior orbital fissure to innervate the lateral rectus
🔸Rare to have isolated palsy
🔸Get a SOF syndrome or orbital apex syndrome
6. Idiopathic
🔸No other identifiable etiology
🔸Like transverse myelitis—likely microvascular or post-inflammatory
🔸1/4th of CN6 palsies are idiopathic
But you must exclude the other five first!
Now you know the Six Syndromes of the Sixth Cranial Nerve.
Hopefully now when you see a CN6 palsy, there will never be six degrees of separation between you & the etiology!