||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX; Professor of Ophthalmology, Weill Cornell Medicine; Kayla Walter, McGovern Medical School Class of 2021
||So today we will be talking about the superior orbital fissure and differentiating it from cavernous sinus lesions and orbital apex lesions. And they're very similar because they're very close together, and so you need to know a little bit about the anatomy of these structures before we can make any kind of decision on localization. So as you know, the cavernous sinus in this example in coronal section has a dural wall and the internal carotid artery is inside the cavernous sinus. In the wall are cranial nerves III, IV, and V1 in the anterior portion of the cavernous sinus. In the posterior portion of the cavernous sinus we have V2. The V3 does not go into the cavernous sinus and exits out the foramen ovale. The sixth nerve is in the substance of the cavernous sinus, not in the wall. And that means cavernous sinus lesions can present with just the sixth nerve palsy and that's why that's particularly dangerous. So any lesion in the cavernous sinus can produce any combination of cranial nerves III, IV, V1, V2, and VI. In addition, the sympathetics travel for a short course on the sixth nerve before traveling on the V1 to pass through the superior orbital fissure. And so we might have a concomitant Horner syndrome in patients who have a cavernous sinus syndrome. The superior orbital fissure connects the cavernous sinus with the orbital apex. And so, once you have the orbital apex you're going to add in the cranial neuropathy of optic nerve. That's a II (cranial nerve II). (Cranial nerve) II does not live in the cavernous sinus. So if we have an RAPD (relative afferent pupillary defect), loss of acuity, loss of field, or a swollen or pale nerve: that's a II. And if we have a combination of III, IV, V1, VI, plus II, that's going to place this into the orbital apex. The superior orbital fissure is going to be very difficult to differentiate from cavernous sinus, because it's the same cranial nerves. You should know, however, that the pattern of involvement of the superior orbital fissure involves the branches of the trigeminal as well as the individual divisions of the third cranial nerve. So that's going to be the lacrimal nerve, the frontal (nerve), the trochlear (nerve), the superior division of cranial nerve III, the nasociliary nerve, the inferior branch of cranial nerve III, and the abducens nucleus. So in the superior orbital fissure we have branches of the trigeminal, the branches of cranial nerves III, IV, and VI, and that's going to represent the general orientation of the nerves inside the superior orbital fissure. So, when you're dealing with patients who have a multiple cranial neuropathy you should be thinking about cavernous sinus - if all the cranial nerves are on the same side with or without the Horner's syndrome. If you have the multiple cranial neuropathy, proptosis, orbital signs, and an optic neuropathy, that's going to put us in the orbital apex. The superior orbital fissure and the cavernous sinus are going to be quite similar but because of the divisional nature you can get divisional palsies in the superior orbital fissure. That's much harder to do in the cavernous sinus, but in general superior orbital fissure and cavernous sinus have very similar presentations. So, you know you need to know a little bit about the anatomy because it only tells you where the lesion is, it doesn't tell you what it is - whether it's cavernous sinus meningioma, or intra-cavernous aneurysm, or thrombosis, or tumor. You cannot tell. You just need to know where the lesion is first, and then you can figure out why the lesion is, and you're going to direct the imaging towards the locations that we see.