| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (GZ) Class of 2024, Baylor College of Medicine, Houston, Texas |
| Description |
Summary: • Notochord general overview: o Present in organisms in the phylum Chordata o Humans fall under this category o In humans, the notochord eventually becomes the nucleus pulposus • Potential problems arising from the notochord o Can get stuck at either the clivus or the sacrum o Clival lesion can occur at the clivus • Chordoma and chondrosarcoma o Chordoma and chondrosarcoma are both masses that can develop in the clivus that affect sixth cranial nerve o Both are difficult to treat, but chondrosarcoma has the better prognosis o Chordoma is benign and doesn't metastasize but can recur, requiring surgery and post-operative radiation therapy o No way to differentiate between these two, thus requiring a biopsy • Sixth nerve palsy o When presented with a sixth nerve palsy, you need to look at the clivus o Clival lesions may also resolve spontaneously. |
| Transcript |
So today we're going to be talking about chordoma - and it's chord with a C-H not C-O-R-D - and even though it's related to the spinal cord, it's not really that kind of cord. The cord we're talking about is the notochord, and if you remember from embryology and studying kingdom, phyla, family, genus, species, etc., you know that we live inside the kingdom animalia, but our phylum is Chordata. And if you live in the Chordata phylum, you have to have had a notochord at some point in your life cycle and for human beings that means we still have the notochord remnant inside of us because we live in the phylum Chordata. In Chordata you can be vertebrate or invertebrate but we're just going to be talking about human beings now, the notochord. So, the notochord is a rigid rod that embryologically, and in the past, as in the evolutionary Tree, provided a rigid construct to allow the dorsal hollow cord to have some structure. Over time, this gets surrounded by bone and became vertebra and that is what we are: vertebrates. However, we still have the notochord even though we are vertebrates and this notochord becomes the nucleus pulposus in human beings. So it has evolved in its purpose; once it causes the local differentiation and migration of tissue in the development of the embryo, it becomes the nucleus pulposus. And the reason it's important to know this is it can show up later in life; it usually gets stuck either upstairs at the clivus or downstairs at the sacrum although it can be anywhere in between. And so the one that comes to me is the clival lesion. So as you know, the clivus is in the skull base, it means slope, and so it's right at the boundary zone with the pons - so the sixth nerve is the normal nerve that we see as the problem - so this is cranial nerve number six, it exits the root exit zone from the pons, rides up the slope, and the name of that slope is the clivus. And so chordoma and chondrosarcoma - similar sounding words - but both chordoma and chondrosarcoma, the chondro- is the cartilaginous tumor, can get a mass in the clivus and present to me as a sixth nerve palsy, either unilaterally or bilaterally. You need to know that the chordoma and the chondrosarcoma are difficult to treat but the chondrosarcoma, even though it sounds worse, is actually a better prognosis. The chordoma is technically benign, it doesn't metastasize, but it has a tendency for local aggressive recurrence and so it needs surgery and then usually post-operative radiation therapy afterwards to treat this chordoma lesion. And so when we're presented with a sixth nerve palsy, one of the places you need to look and be careful of is in this clivus because the cranial nerve six is the only nerve on the clivus, it can be the presenting or only symptom. The other thing that's weird about the clival lesions, because it's pulling and stretching the nerve, it can resolve. The sixth might resolve spontaneously and so resolution of sixth nerve palsy does not pretty prove that it's not a skull-based lesion. So if you have a mass in the clivus and if you're thinking about both chondrosarcoma and chordoma, there's no way to differentiate these, clinically, radiographically, they all look the same. You need a piece of tissue, that means a biopsy, to prove it's chordoma; if it's chordoma, it's a remnant of the primitive notochord which is becoming the nucleus pulposus in vertebrates and you have one because you're in Chordata, and if you're in the phylum Chordata you have had to have the notochord a nerve cord and gill slits at some point in your life cycle so you need to know a little bit about the notochord. |
