| Identifier |
incomplete_third_nerve_palsy_approach_lee |
| Title |
Incomplete Third Nerve Palsy Approach |
| Creator |
Andrew G. Lee, MD; Nicole Weber |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (NW) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Subject |
Third Nerve Palsy; Ptosis; Extraocular Muscles; Cranial Nerves |
| Description |
Summary: • A complete third nerve palsy manifests as a complete or near complete ptosis and involvement of all the extraocular muscles (EOM) innervated by CN III o Reminder: this does NOT include the superior oblique muscle (innervated by CN IV) or the lateral rectus muscle (innervated by CN VI) • Pupil involvement helps dictate likelihood of aneurysm o Pupil involved -> assume posterior communicating artery aneurysm until proven otherwise o Pupil not involved but complete palsy in vasculopathic patient -> likely to be small vessel ischemia • Third nerve palsy may be considered "partial" when: o There are any signs of an abnormal pupil including slightly larger pupil, lack of pupil reaction and recent surgery (i.e. for cataracts) o Divisional muscle involvement such as incomplete ptosis or incomplete involvement of all of the EOM innervated by CN III > ALL partial palsies must be worked up for aneurysm • Standard work-up for aneurysm in a partial third nerve palsy o Non-contrast CT scan > followed by contrast CTA (to look for aneurysm) o Also obtain a contrast MRI (for non-aneurysmal causes). |
| Transcript |
So, we've talked about in the past third nerve palsy and today I just want to tell you a little bit about an incomplete third nerve palsy. So, just to remind you, a complete third nerve palsy means: the lid is down, a complete ptosis or an almost complete ptosis, and involvement of all the extraocular muscles innervated by cranial nerve III. Which is basically all of them except for the superior oblique muscle, which is of course cranial nerve IV, and the lateral rectus muscle, which is cranial nerve VI. So if you have all the muscles involved and you have a complete or near complete ptosis that is what we call a complete third nerve palsy. Then, the pupil becomes the important thing at that point. And if you have pupil-sparing or pupil involvement, that is going to help dictate whether this person has a higher or lower likelihood of an aneurysm. So, anybody who has a pupil-involved palsy, regardless of whether it's complete or incomplete, should be assumed to have a posterior communicating artery aneurysm until proven otherwise. That's the rule of the pupil. And, if it's a negative pupil, a totally normal pupil, but it's a complete palsy and in isolation in a vasculopathic patient-- that's extremely likely to be small vessel ischemia. So, today we're talking about the dangerous one, which is the partial third nerve palsy. And there's two ways that this can be partial as opposed to complete. The partial palsy can be partial because the pupil is slightly bigger or the pupil is slightly less reactive, or the pupil has had surgery on it for cataract surgery, or ten million other reasons why your pupil could be not completely normal. And then, we have partial palsies. Partial palsies could be either the lid is not involved, or the lid is not involved all the way, or it's a divisional palsy, or just the superior rectus and the lid is involved but not the inferior or not the medial rectus. And these partial palsies all have to be worked up for aneurysm. So, the rule for the pupil only applies if you have a complete palsy and only if you have pupil sparing or pupil involvement-- then use the rule of the pupil. But if it's a partial palsy or a partial pupil, that could still be aneurysm and normally we're going to start with a non-contrast CT scan for subarachnoid hemorrhage, followed by a contrast CTA to look for the aneurysm, and you still need to have a contrast MRI even after a negative CT and a negative CTA because the MRI is better for non-aneurysmal causes of third nerve palsy, like tumors and ten million other causes that have nothing to do with an aneurysm. So, we really need to have all three imaging studies if we have a partial palsy or a partial pupil. The only person that you can get away with not imaging is pupil-spared, complete third in a vasculopath who's getting better. If it's pupil involved then you're back over here: CT, non-con, CTA, MRI. So, in summary, partial palsy-- very, very dangerous. That could still be an aneurysm. Do not apply the rule of the pupil for partial palsies. And my standard work up: non-contrast CT of head, followed by contrast CTA in the same sitting, followed by contrast MRI head or with gadolinium if the CT/CTA is negative for all partial palsies and all partial pupils. |
| Date |
2021-04 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s6m1030p |
| Setname |
ehsl_novel_lee |
| ID |
1680607 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s6m1030p |
