| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (DM) Class of 2024, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we are going to be talking about arterial dissections in neuro ophthalmology and the two that come to us are the carotid dissection and the vertebral dissection. So, a dissection is different from an aneurysm because not all three walls of the artery are disrupted. So, when we have a dissected segment it is a false lumen that occurs and inside that false lumen there will be stagnant blood. And so, most of the dissections are cervical in your neck and not in your head. So that is the first most important thing, but we are dealing with either a carotid or vertebral dissection we need to image both the head and the neck. So, we need MRI/MRA head and neck and in the emergency room we would do CT/CTA head and neck for dissections. So, this is the ER version of it (pointing to CT/CTA) but probably we are still going to need an MRI/MRA. What we are looking for in cross-section is the arterial flow void which is going to be dark on all sequences on MRI (because it is a void in the signal created by flow) will be surrounded by a crescent of hyper-intense signal intensity and that imaging sign is called the crescent sign. And we can see that both in the carotid and the vertebral, so in an axial section when we are in the posterior fossa, the vertebral dissections are going to be in the posterior fossa versus the carotid dissections, which are going to be in the middle cranial fossa. And, depending on which segment is involved, the crescent sign might be seen anteriorly, or it might be seen posteriorly. And the presentations of these two conditions to neuro-ophthalmology is slightly different. So, in the carotid dissection, because we have thrombus here that thrombus could become thromboembolic disease that could cause amaurosis fugax (transient monocular vision loss). And because the sympathetic plexus is running around the carotid, the combination of the Horner's syndrome plus transient monocular vision loss in the ipsilateral eye suggest that we have a carotid dissection. Especially if it is a young patient who has no other vascular path risk factors or if they have had trauma. So, the typical story is trauma, transient vision loss, headache and they may or may not have neck pain or headache. In the vertebral dissection the same problem with crescent sign and thromboembolic disease. But instead of monocular vision loss, because the vertebrals meet at the basilar end and then end in the posterior cerebral arteries, that is going to produce TIA (Transient Ischemic attack) in the posterior circulation, so the posterior cerebral artery distribution is the occipital lobe. That produces a transient bilateral, usually homonymous hemianopia or cortical vision loss. And if it is in the basilar distribution that can cause transient diplopia. So, the vertebral dissection comes to us with brainstem symptoms and signs. Those are the D's: diplopia dysarthria, difficulty walking, difficulty speaking, drop attacks. Carotid dissection is unilateral, ipsilateral vision loss amaurosis fugax. But both vertebral dissection and the carotid dissection had produced the Horner's syndrome. The carotid because of the carotid plexus, but the vertebral because the Horner's pathway, the ocular sympathetic pathway, the first order neuron travels down and posterior-laterally in the brainstem. So, vertebral artery disease can lead to basilar disease, that basilar disease are the little perforating arteries into the brainstem and that could produce Horner's, the prototype of course is the lateral medullary syndrome, the Wallenberg syndrome that often has a Horner's syndrome. So, when we are dealing with dissections in neuro-ophthalmology, you should be thinking about carotid and vertebral dissections in acute transient ischemic attacks or acute carotid or vertebral distribution ischemic infarction. Especially if it's a young person, especially if it is trauma like a motor vehicle accident. In the carotid circulation we are going be thinking about CT/CTA, MRI/MRA head and neck. And then the vertebral dissection, same thing and we are going to be looking for the crescent sign either in the anterior or the posterior circulation. It may or may not have neck pain, and because in the carotid distribution, that is innervated by the general visceral efferent, which is the trigeminal, that pain might be felt as pain in the eye, that is called referred pain. So even though the pain and the problem are in the neck, you might feel it in your eye. And so that combination of symptoms: face pain, neck pain, eye pain, Horner's syndrome, transient vision loss is also a symptom of carotid dissection in the neck even though it seems like the pain is in their eye. That is referred pain. In addition, you need to know about a strange symptom called dysgeusia. Dysgeusia is a funny taste in their mouth. That funny taste in the mouth is also a symptom that is associated with carotid dissections and usually that is from the chorda tympani. And that chorda tympani in the carotid occurs as we are making the bend in the internal carotid artery from the cervical portion to the petrous portion and then becoming the intracranial component and the inter-cavernous component of the internal carotid artery. So, we always ask patients about their taste sensation and that is a special afferent to the anterior two-thirds of the tongue carried on chorda tympani. So dysgeusia is a very unusual but specific symptom that you should be thinking about in carotid dissections. |
