Third Nerve Palsy
Pupil sparing 3rd nerve is rarely due to an aneurysm and more often ischemic injury - Andy Rogers MD
image by: Patrick J. Lynch, medical illustrator
HWN Suggests
Cranial Nerve Three Palsy
CT/CTA followed by MRI/MRA is our procedure of choice in that order for the evaluation for third nerve palsy, and make sure it's not an aneurysm.
If everything's negative then you're going to look for the usual suspects: ischemia would be the number one cause and vasculopathic age patients, giant cell arteritis has to be considered in every elderly patient who has new onset diplopia even if it looks like a third nerve palsy and then you could test for the infectious and inflammatory etiologies but the main point is making sure it's not an aneurysm.
Resources
Isolated binocular diplopia – is this cranial nerve 3 or not?
An acute CN3 palsy is an aneurysm or ruptured aneurysm until proven otherwise. If the patient has isolated diplopia, rule out CN3 involvement. CN4 or CN6 isolated palsies are typically less urgent.
Diplopia Evaluation and Management
The presence of 3rd nerve palsy, multiple concomitant palsies, evidence of papilledema, infection, trauma, or cavernous sinus thrombosis require urgent imaging in the ED.
Double Trouble II
Third nerve palsy results from damage to the oculomotor nerve anywhere along its route from the nucleus in the dorsal mesencephalon, its fascicles in the brainstem parenchyma, the nerve root in subarachnoid space, the cavernous sinus or the posterior orbit.
Oculomotor Nerve Palsy Secondary to Cavernous Internal Carotid Aneurysm
Oculomotor nerve palsy has been classically separated into pupil sparing and non-pupil sparing (i.e., pupils that react to light).
Self-Resolving Ischemic Third Nerve Palsy
Imaging practices for suspected ischemic pupil-sparing third nerve palsy are currently under debate. Some sources suggest obtaining a head CT or a CT angiogram, and only order a head MRI if the head CT or CT angiogram are not available or contraindicated. However, the most commonly used initial imaging modality is MRI.
Third Cranial Nerve Lesions
“down and out” – because of antagonism of the trochlear nerve (superior oblique) and abducens nerve (lateral rectus).
Third nerve palsy
The traditional teaching on III palsy categorises medical and surgical III palsy depending on pupil involvement and patient medical history. However, the pupil rule is only 90% true, so 10% of aneurysms can cause a ‘medical III palsy’ not involving the pupil. The current advice from leading neuro-ophthalmology experts is to investigate all III palsies thoroughly with a CT angiogram or MRA to rule out aneurysms before suggesting it is medical rather than surgical... if normal then MRI head and orbit is requested.
Cranial Nerve Three Palsy
... CT/CTA followed by MRI/MRA is our procedure of choice in that order for the evaluation for third nerve palsy, and make sure it's not an aneurysm. If everything's negative then you're going to look for the usual suspects: ischemia would be the number one cause and vasculopathic age patients, giant cell arteritis has to be considered in every elderly patient who has new onset diplopia even if it looks like a third nerve palsy and then you could test for the infectious and inflammatory etiologies but the main point is making sure it's not an aneurysm. CT/CTA followed by MRI/MRA is the preferred imaging for third nerve palsy.
5-Minute Emergency Consult
There are six muscles that control eye movement innervated by three cranial nerves (CN): CN III, or oculomotor nerve, innervates 4 of the 6 eye muscles and also innervates the lid and pupil...
BC Emergency Medicine Network
The absence of mydriasis (a.k.a “Rule of the Pupil”)is not a sensitive way to r/o a compressive aneurysm.
EyeWiki
Management depends on the presented scenarios. In a conscious patient presenting with ophthalmoplegia, ptosis and mydriasis a compressive etiology, as an intracranial aneurysm, must be ruled out. In the other hand if a patient presents with complete oculomotor nerve palsy without pupil involvement it is most likely to be related to ischemic process, but compression and inflammation should also be considered.
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